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The sign and magnitude of permafrost carbon (C)-climate feedback are highly uncertain due to the limited understanding of the decomposability of thawing permafrost and relevant mechanistic controls over C release. Here, by combining aerobic incubation with biomarker analysis and a three-pool model, we reveal that C quality (represented by a higher amount of fast cycling C but a lower amount of recalcitrant C compounds) and normalized CO2–C release in permafrost deposits were similar or even higher than those in the active layer, demonstrating a high vulnerability of C in Tibetan upland permafrost. We also illustrate that C quality exerts the most control over CO2–C release from the active layer, whereas soil microbial abundance is more directly associated with CO2–C release after permafrost thaw. Taken together, our findings highlight the importance of incorporating microbial properties into Earth System Models when predicting permafrost C dynamics under a changing environment.
Permafrost, defined as sub-surface earth materials that remain below 0 °C for at least two consecutive years1, is the single largest component of the terrestrial carbon (C) pool2. A fraction of this huge soil organic carbon (SOC) stock has been exposed to microbial decomposition due to substantial permafrost thaw under continuous climate warming3. In situ thawing experiments reveal that C release from thawing permafrost has already become a substantial component of C fluxes, potentially triggering a strong positive C-climate feedback3,4. By incorporating incubation data and post-thaw soil processes, recent modelling studies have demonstrated that the future C balance across permafrost regions largely depends on the vulnerability of deeper permafrost C (refs 5, 6, 7). These in situ experiments and model predictions collectively highlight the importance of understanding the decomposability of thawing permafrost and relevant mechanistic controls over C release5,8.
Permafrost C decomposition is a process involving complex interactions of multiple factors and mechanisms9. SOC quality10,11, microbial properties12 and environmental drivers13,14 are three sets of interacting factors that primarily regulate the decomposition of SOC. Despite all the work conducted so far, our understanding of the determinants of permafrost CO2–C release is still limited by the following three aspects. First, despite the widely applied C quality in C decomposition models, empirical evidence from permafrost deposits is still limited9,10,15. Using pyrolysis gas chromatography/mass spectrometry (Py-GC/MS), the incubation of peatland permafrost revealed that CO2–C release was best predicted by the relative abundance of polysaccharides and proteins in SOC (ref. 11). However, the labile compounds highlighted in the study were assumed to possess short mean residence time (MRT) and could be rapidly depleted after permafrost thawing9,10. Instead, slowly degrading C fractions could become more important for the long-term permafrost CO2–C release after thaw16. The variation in these slowly degrading C fractions and the long-term CO2–C release from permafrost soils were further demonstrated to depend on SOC quality16. Nevertheless, SOC quality was indirectly represented by C:N with little chemical information on the slowly degrading C fractions. Organic matter biomarker analysis is a molecular level method that can provide unparalleled insight into SOC quality, especially for recalcitrant compounds17, and is thus instrumental in understanding the characterization of SOC degradation18.
Second, it remains unknown whether the factors controlling CO2–C release in the active layer and permafrost deposits differ. In permafrost regions, the existence of an active layer (seasonally unfrozen surface layer)5 leads to a separation between seasonally thawed and perennially frozen soils and further results in substantial differences in their physicochemical and biological properties19. For example, most SOC in the active layer is derived from vegetation inputs with relatively short MRT, whereas the lability in permafrost C likely varies according to the rates and timing of C burial20,21. It has been suggested that high SOC quality could occur in permafrost deposits in which relatively undecomposed organic matter is preserved through cryoturbation (mixing of soils by the freeze–thaw process)22,23 and syngenetic permafrost growth with ongoing sedimentation11,13. By contrast, substrates such as epigenetic permafrost deposits that are subjected to repeated freeze/thaw cycles and cryochemical precipitation are likely to be more recalcitrant11,20,21. Additionally, due to sub-zero temperatures, the abundance and activity of microbial communities were significantly lower in permafrost deposits24, which may limit the subsequent response after permafrost thaw15. Despite all of these considerations, the factors controlling the CO2–C release from the active layer and permafrost deposits remain poorly understood, but such information is a prerequisite for accurately projecting permafrost C release under climate change.
Third, current studies about the controls on soil CO2–C release have been primarily conducted at high latitudes; our understanding of the magnitude and determinants of CO2–C release in alpine permafrost remains obscured. The Tibetan Plateau is the largest alpine permafrost region around the world, accounting for approximately three quarters of the total area of alpine permafrost in the Northern Hemisphere25. During the past 50 years, significant increases in the temperature26 have caused a 20% decline in the permafrost in this region27. In contrast to the large amounts of visible ice contained in high-latitude permafrost deposits1, the Tibetan permafrost, especially the upland permafrost, is characterized as being ice-poor as a result of a dry climate with strong solar radiation, wind and high evaporation27. Moreover, the Tibetan permafrost has a scarce organic layer28, which could increase the thermal conduction from air to the deep permafrost1,29,30. The lack of an insulation effect provided by the organic layer was considered the main reason for the larger degree of permafrost degradation on the Tibetan Plateau compared with high-latitude permafrost in recent years28. Collectively, the distinct climatic and environmental conditions are therefore expected to cause high vulnerability in the C of this permafrost region in response to climate warming. However, a comprehensive understanding of potential C release from Tibetan permafrost remains unavailable.
In this study, we quantified the magnitude and determinants of CO2–C release between the active layer and permafrost deposits using data obtained from five representative sites on the Tibetan Plateau (Supplementary Fig. 1). The main objectives of this study were to identify C quality differences between the active layer and permafrost deposits, and determine the controlling factors of CO2–C release for both the active layer and permafrost deposits after thaw. Our results demonstrate that the C quality in permafrost deposits is similar to or even higher than that in active layer soils, which contributes to the high vulnerability of permafrost C on the Tibetan Plateau. The CO2–C release from the active layer is primarily controlled by SOC quality (for example, the abundance of suberin-derived compounds), whereas CO2–C release from permafrost deposits is more associated with microbial abundance (for example, the abundance of fungal phospholipid fatty acid (PLFAs)).
Soil C quality
Three types of proxies (soil C:N ratio, relative abundance of soil organic matter (SOM) components derived from the biomarker analysis and the pool sizes of the C fractions derived from a three-pool model) were used to describe the C quality of soil samples from five typical sites (Supplementary Fig. 2, Supplementary Tables 1 and 2). Of these proxies, both soil C:N ratio and the relative abundance of SOM components were determined by experimental measurements. In comparison to the traditional proxy C:N ratio, the relative abundance of SOM chemical components is a more direct proxy of SOC quality17. In addition to the empirical proxies, parameter estimates (that is, pool sizes of C fractions) derived from a C decomposition model were also used as another proxy to quantify SOC quality16,31. Considering these three types proxies simultaneously is therefore expected to provide more comprehensive information on SOC quality.
Soil chemical compositions as determined by SOM biomarkers differed in certain respects between the active layer and permafrost deposits. The abundance of major lignin-derived phenols (vanillyls, cinnamyls and syringyls) was significantly lower in permafrost deposits than in the active layer except for samples from the town of Changmahe, Maqin County (hereafter, CMH) (P<0.05, Table 1). Surprisingly, both ratios of vanillic acid to vanillin (Ad/Alv) and syringic acid to syringaldehyde (Ad/Als), which are commonly used lignin oxidation parameters, were significantly lower in permafrost deposits (P<0.05), suggesting that the observed low abundance of lignin-derived compounds in permafrost deposits did not primarily result from a higher extent of lignin oxidation but might be due to fewer fresh inputs from plants compared with the active layer. Moreover, cutin-derived and suberin-derived compounds, which originate from the aboveground waxy coating of leaves and belowground roots, respectively, were significantly higher in the active layer compared with the permafrost deposits at Youyun, Maqin County (hereafter, YY), Huashixia, Maduo County (hereafter, HSX) and Wenquan, Xinghai County (hereafter, WQ) (P<0.05), but there was no difference in suberin-derived compounds between the two layers at CMH or Kunlunshankou, Geermu (hereafter, KLSK) (Table 1).
The chemistry of the aqueous soil extracts also differed between the two soil layers. Dissolved organic C (DOC) yield (mg C kg−1 OC) was greater from permafrost soils compared with the active layer at YY and CMH, whereas a contrasting pattern was observed at HSX and KLSK, in which the DOC yield was higher in the active layer (P<0.05, Supplementary Table 3). Despite the different depth effects on DOC yield among the five sites, SUVA254, an index for DOC aromaticity, showed consistent variation between depths. SUVA254 was significantly higher in extracts from the active layer soils than those from permafrost deposits (depth effect, P<0.05) and no site × depth interaction was observed (Supplementary Table 3), indicating that the permafrost DOC was more biodegradable than that released from the active layer soil.
The differences in C chemistry between two depths was further confirmed by the C fraction pool sizes estimated from the three-pool model (Fig. 1). The fast C pool size was significantly larger in permafrost deposits than in active layer soils at YY, CMH, HSX and WQ (P<0.05, Fig. 1a–e). The permafrost deposits also had larger slow C pool sizes but significantly smaller sizes of the passive C pool at YY, HSX and WQ (P<0.001, Fig. 1f–o). There were no significant differences in three C pool sizes between the active layer and permafrost deposits at KLSK.
Soil microbial abundance and composition
Soil microbial properties differed in certain aspects between the active layer and the permafrost deposits. The normalized abundances of all microbial groups, including bacterial PLFAs, fungal PLFAs and actinomycic PLFAs, were higher in permafrost deposits than those in the active layer at WQ, whereas a contrasting pattern was found at CMH and KLSK (P<0.05, Table 2). Despite the different effects of depth on microbial abundances among the five sites, the fungal–bacterial ratio (F/B), a surrogate for microbial community structure, showed relatively similar patterns across depths, except for CMH samples. F/B was significantly higher in permafrost deposits than in the active layer (depth effect, P<0.05, Table 2) and there was no site × depth interaction (P=0.63).
CO2–C release
The incubation temperature had a significant positive effect on CO2–C release, indicating that C release was highly temperature dependent (P<0.01) (Supplementary Table 4). No significant interactions between temperature and soil layer were found (P=0.21), demonstrating that the temperature limitation for CO2–C release was independent of soil depth.
Significant interactions between soil layers and sites (P<0.001) (Supplementary Table 4) indicated that the depth effects on CO2–C release varied among the five sites. Specifically, the normalized CO2–C release was significantly higher in permafrost deposits compared with the active layer at YY, HSX and WQ (Fig. 2). The largest difference between depths was observed in WQ samples, in which CO2–C release from the permafrost deposits was five times higher than that from the active layer (Fig. 2d). Surprisingly, although the CO2–C release rate decreased significantly with incubation time, the higher CO2–C release from permafrost deposits compared with the active layer at these sites lasted over the entire incubation duration (Fig. 2).
CO2–C release from both the active layer and permafrost deposits was significantly associated with environmental variables, microbial abundance and C quality (Fig. 3). CO2–C release declined with soil moisture (Fig. 3a) but increased with soil pH (Fig. 3b). Both fungi PLFAs (Fig. 3c) and actinomycete PLFAs (Fig. 3d) were positively correlated with CO2–C release over the 80-day incubation period at 5 °C. Moreover, CO2–C release was also dependent on C quality, which was described by a matrix of C:N, lignin-, cutin-, suberin-derived compounds and different C fraction pool sizes. CO2–C release exhibited a significant decrease with C:N ratio (Fig. 3e) and lignin- (Fig. 3f), cutin- (Fig. 3g) and suberin-derived compounds (Fig. 3h). Conversely, CO2–C release was positively correlated with both fast (Fig. 3i) and slow C pool size (Fig. 3j).
To quantify the relative importance of the different controls on CO2–C release, we constructed two structural equation models (SEMs) based on the known relationships between CO2–C release and their key drivers in the active layer and permafrost deposits (Supplementary Fig. 3). Our model explained 96% of the variance in CO2–C release for the active layer (Fig. 4a). Soil microbial abundance had direct positive effects on CO2–C release, whereas pH and C recalcitrance had direct negative effects on CO2–C release in the active layer. Moreover, soil moisture exerted strong indirect effects on CO2–C release through its positive correlation with C recalcitrance and its negative correlation with soil pH, which can subsequently lead to lower CO2–C release. Similarly, pH had an indirect effect on CO2–C release by positively affecting soil microbial abundance. Taken together, C quality and soil moisture were the most important direct and indirect predictors of CO2–C release for the active layer soils, respectively (Fig. 5a,b).
The model for permafrost deposits explained 91% of the variance in CO2–C release (Fig. 4b). Soil microbial abundance and C recalcitrance were the only two direct controls on C release for permafrost deposits. Compared with the standardized path coefficients for the active layer, the direct effect of C recalcitrance decreased from −0.97 to −0.35, whereas the direct effect of microbial abundance increased from 0.33 to 0.65 in the permafrost deposits (Fig. 5a). Instead of having bidirectional effects on CO2–C release, soil pH only exhibited indirect effects on CO2–C release for the permafrost deposits. Nevertheless, the strong indirect impact of soil moisture on CO2–C release was still observed in the permafrost deposits (Fig. 5b).
Our study illustrates that the arithmetic means of the CO2–C release rates from the active layer and permafrost deposits at these five sites on the Tibetan Plateau were ∼116±27 μg CO2–C g−1 SOC d−1 and 223±44 μg CO2–C g−1 OC d−1 for the 80-day laboratory incubation, respectively. The C release rate for the Tibetan permafrost generally fell at the high end of the range of, or even higher than that measured across Artic and boreal permafrost zones at a similar incubation temperature and duration (4–182 μg CO2–C g−1 OC d−1)11,31,32,33. The higher CO2–C release rate observed in this study suggested that the vulnerability of C in the Tibetan upland permafrost was potentially higher than in the circumpolar region. It has been estimated that the soil organic carbon (SOC) pool within Tibetan permafrost (250–300 cm) is ∼1.29 Pg C (ref. 34). It has also been suggested that permafrost could decline by between 19–25% (RCP4.5) and 48–63% (RCP8.5) from the current extent by 2100 (ref. 35). By combining these values with an average aerobic CO2–C release of 45.4% over the same timeframe (assuming soils would be thawed for only 4 months per year for the next 85 years till 2100 and stay at a constant temperature of 5 °C)16, we generated a rough warming risk assessment for the Tibetan permafrost. Within the next 85 years, either 111–146 Tg C (RCP4.5) or 281–369 Tg C (RCP8.5) could be released to the atmosphere as CO2 from the Tibetan permafrost35. Therefore, our understanding of permafrost C-climate feedback is incomplete without considering what is occurring across the Tibetan permafrost.
The higher C vulnerability in the Tibetan upland permafrost may be attributed to the following two aspects. First, the difference could result from vegetation type, a good predictor of the lability of organic matter36. The dominant vegetation type across our study area is alpine grassland, in which graminoids and sedges are the main functional types (Supplementary Table 1). By contrast, high-latitude regions are dominated by mosses, dwarf shrubs and coniferous trees8,37. The higher C quality of herbaceous litter in comparison to shrub and moss litter could then result in the higher CO2–C release across the Tibetan permafrost. Moreover, a different decomposition stage of permafrost deposits could also lead to the difference between regions11,38. In Tibetan permafrost, undecomposed plant roots and stems were found near our sampling sites39. However, we could not compare the degree of decomposition of different permafrost regions due to scant data (but see refs 11, 38). Further studies should focus on the degree of decomposition in relation to permafrost C quality. Second, the difference could also result from the ice content of the permafrost. The high ice content contained in high-latitude permafrost usually results in near field capacity moisture during incubation33. By contrast, our permafrost deposits are ice-poor (Supplementary Table 2) and the moisture for incubation was set at 60% field capacity, the optimal water content for microbial activity40,41. Consequently, the low ice content associated with high oxygen availability after permafrost thaw may also contribute to the higher CO2–C release observed in the Tibetan upland permafrost.
The C vulnerability in Tibetan permafrost was as high as, or even higher than, that of active layer soils. To be specific, a higher C quality (Table 1) contributed to the higher CO2–C release from permafrost deposits at YY, HSX and WQ (Fig. 2). The observed high C lability of permafrost deposits could be attributed to syngenetic permafrost formation through aeolian, alluvial and colluvial sedimentation13,33,39 and cryoturbation1,22,23. This explanation was further confirmed by relict periglacial phenomena and the vertical permafrost distribution pattern near these sampling sites39. In addition to these differences in C quality, a higher soil pH in the permafrost deposits at the three sites (Supplementary Table 2) was positively correlated with the abundance of fungi and actinomycetes, which were assumed to accelerate the subsequent recalcitrant C decomposition15,42. By contrast, the similar C vulnerability between the soil layers at CMH and KLSK could be explained by similarities in C quality induced by climatic changes associated with the glacial/interglacial cycle20. Two buried permafrost tables separated by a talik were found in a borehole near the CMH site, suggesting that significant decaying of the permafrost deposits may have occurred during the Holocene Thermal maximum20,39. Moreover, the deeper permafrost deposits are presumed to be more protected against degradation by the association of SOC with minerals in organomineral associations43. Consistent with this assumption, higher clay and silt contents (Supplementary Table 2) and SOC concentration (Supplementary Fig. 4) in the permafrost deposits compared with the active layer were observed for these two sites.
Our study presents direct evidence of different controlling factors mediating CO2–C release from the active layer and permafrost deposits. As shown by SEM analysis, CO2–C release from the active layer was primarily directly determined by C recalcitrance. The determinant role of C recalcitrance observed in this study, together with previous findings in arctic and boreal regions16, jointly suggest the vital role of more slowly degrading C in governing SOC turnover in the active layer. Interestingly, short turnover times for the fast C pool were observed in both the active layer and the permafrost deposits, with an average turnover time of 0.34 years (Supplementary Table 5). The estimated short turnover time for the fast C pool was supported by previous results in high-latitude regions16,31. This small C pool (<1% of total C) (Fig. 1) having a short turnover time indicates that long-term permafrost C degradation will be dominated by more slowly degrading C (refs 16, 32). To further reveal the role of the more slowly decomposing C on total C release, we analysed the contribution of different C pools to total C release. The results indicated that, during the entire 80-day incubation, ∼29.0% and 64.9% of the C released as CO2 originated from the fast and slow C pools, respectively, whereas only 6.1% of CO2–C release originated from the passive C pool (Supplementary Table 6). However, when projected to a 10,200-day incubation period (∼85 years in situ until the year 2100), the contribution of the fast C pool substantially dropped to 2.4%, whereas the contribution of the slow and passive C pools increased to 73.6% and 24.0%, respectively (Supplementary Table 6). Taken together, these results demonstrated a crucial role of more slowly degrading C in long-term permafrost C degradation.
In contrast to previous studies16, our study showed the negative role of recalcitrant compounds (that is, lignin, suberin- and cutin-derived compounds) in affecting C release (Fig. 3f–h). Interestingly, among all of the more slowly degrading C compounds examined in this study, suberin-derived compounds, which originate from belowground roots, were the best predictor of CO2–C release in the active layer (r2=0.94, P<0.01). The predictive role of suberin for C release observed in our study may be attributed to the high proportion of root biomass in Tibetan grasslands44. Consistent with this deduction, suberin was the major recalcitrant compound in our soils, being two times more abundant than cutin (Table 1). Notably, the negative association between CO2–C release and soil C:N observed in our study (Fig. 3e) contrasted with the recent finding that soils with higher C:N in circumpolar regions tend to have higher C vulnerability16. Such contradictory patterns may be attributed to the different ranges of soil C:N in these two regions. Compared with the northern circumpolar permafrost region, lower SOC concentrations were observed across the Tibetan permafrost as a result of higher temperatures, better drainage conditions and a thicker active layer34. This low SOC concentration further resulted in a relatively low C:N in this region, which fell at the low end of the range measured in circumpolar regions (5.4–72.6)16.
In contrast to its critical role in the active layer, the importance of SOC quality decreased with depth, whereas microbial abundance became the most important direct control over CO2–C release in permafrost deposits (Fig. 5a). Surprisingly, among all microbial groups examined here, the abundance of fungal PLFAs was the strongest predictor of CO2–C release in permafrost deposits (r2=0.84, P<0.01). It is commonly recognized that fungi play a relatively weak role in permafrost C turnover due to their low abundance in comparison to bacteria and archaea in frozen soils24,45. Indeed, in our study, the relative abundance of fungal PLFAs was also significantly lower than that of bacterial and actinomycete PLFAs (Table 2). However, the highest predictive role of fungal PLFAs in predicting CO2–C release revealed their unexpected role in permafrost turnover when temperatures rise above 0 °C, which could be explained by their rapid reactivation after permafrost thawing. Sub-zero temperatures and limited unfrozen water substantially reduce the activity of all microbial communities in permafrost soils. The recovery of microbial function immediately following thaw could determine their role in permafrost C decomposition46. Among all microbial groups, a substantial increase in basidiomycete and ascomycete fungi after permafrost thaw has been reported, whereas the abundance of bacteria remained constant15,47. The rapid increase in fungal abundance could be due to their enzymatic potential to decompose recalcitrant SOC as labile substrates are depleted42. This assumption was demonstrated by a laboratory incubation study15 in which the activity of peroxidase involved in the degradation of lignin that was produced by fungi increase 2.5-fold after permafrost thaw in an Alaska peatland. Thus, fungi could act as an important group of decomposers in permafrost C turnover after permafrost thawing.
Although our study provides the evidence of the magnitude and determinants of CO2–C release in the Tibetan permafrost, some uncertainties still exist. First, limited samples mainly collected from the upland permafrost may induce uncertainty in the projection of CO2–C release for entire Tibetan permafrost. Although Tibetan permafrost mainly occurs in upland areas with good drainage48, flooding has also occurred in some lowland areas49. The poor drainage conditions in those lowland regions can significantly decrease the CO2–C release rate31,32,33,50. Consequently, long-term CO2–C release generated in this study may be overestimated, but it does indicate the high C vulnerability of Tibetan permafrost to climate warming. Second, the limited upland samples may also induce uncertainty in exploring controlling factors that regulate the CO2–C release. It has been suggested that the variations of anaerobic CO2–C release in lowland regions was mostly explained by the environmental controls (for example, relative water table position)51. Hence, the controls over the CO2–C released reported in this study mainly applies to Tibetan upland permafrost, which cannot be simply generalized to lowland permafrost. Further studies with large sample size should be conducted to explore the magnitude and determinants of permafrost CO2–C release across the entire Tibetan Plateau. Third, these results were determined in laboratory incubation, which represent a controlled environment (that is, 5 °C and 60% of water holding capacity (WHC)) that provides the best conditions to test mechanistic questions such as those in our study11,15,32,52. However, the results obtained through this laboratory incubation method may not be able to accurately represent a complete and realistic condition in permafrost zone in situ. Thus, in addition to effects of C quality and microbial abundance highlighted in our laboratory observations, other environmental controls could also have impacts on permafrost C release. For example, surface conditions such as organic layer thickness, which insulates the deep soil from variations in air temperature29,30, largely controls the stability of permafrost. This insulation effect of organic layer thickness was suggested as one of the most important factors with respect to thaw-depth variability in a continuous permafrost zone53.
In conclusion, based on the SOM biomarkers, the pool sizes of C fractions and the quality of leachable DOC, our results revealed that permafrost C was at least as labile as the C in the active layer in Tibetan permafrost. This labile C contributed to the high C vulnerability across the Tibetan permafrost, which together with the large C pool size (15.31 Pg C stored in the top 3 m)34 suggests a risk of C emissions and positive C-climate feedback across the Tibetan upland permafrost. On the basis of SEM, our results further demonstrated that the determinants of CO2–C release from the active layer and permafrost deposits in the Tibetan permafrost were different, as C quality was most crucial for the active layer soils, whereas soil microbial abundance was more important in permafrost C emissions after thawing. The highest direct explanatory power of the relative abundance of suberin-derived compounds and fungal PLFAs for CO2–C release from the active layer and permafrost deposits, respectively, suggests that these two variables could be used to predict C release across upland permafrost zones under a warming scenario. The microbial role in controlling C release from permafrost deposits after thawing implies the importance of incorporating microbial properties into Earth System Models when predicting permafrost C dynamics under a changing environment.
Soil sampling and preparation
The typical continuous permafrost of the Tibetan Plateau is distributed in southern Qinghai and northern Tibet54,55. In this typical permafrost region, the Xidatan-Amdo transect and the Gonghe-Qingshuihe transect were selected for long-term permafrost monitoring by geocryologists and permafrost engineers due to their typical permafrost characteristics and easy access39,55. In this study, five typical upland permafrost sites along these two typical transects, including two swamp meadows (YY and CMH), two alpine meadows (HSX and WQ) and one alpine steppe (KLSK), were sampled between July and August 2013 (Supplementary Fig. 1). The SOC concentration in these sites ranged from 2.2 to 79.9 g kg−1, with the highest SOC in swamp meadows (CMH and YY), followed by alpine meadow (WQ, HSX) and alpine steppe (KLSK) (Supplementary Table 2). The SOC concentration of each ecosystem type was consistent with previous studies on the Tibetan Plateau34. We collected three replicate cores per site within a 100 m2 plot. Boreholes were drilled at depths of 0–10, 10–20, 20–30, 30–50, 50–70, 70–100, 100–150, 150–200, 200–250 and 250–300 cm at each site. Frozen cores were transported to the Institute of Botany, Chinese Academy of Sciences and were stored at −20 °C until analysis. Based on the active layer thickness (Supplementary Table 1), we selected two segments from each sediment core to represent active layer (20–30 cm) and the surface permafrost deposits (Supplementary Table 2). The sub-surface soil in the active layer was selected to avoid the surface soil, which consisted of a large amount of live plant material, and to prevent the analysis of any sloughed material or soil contaminated during drilling14,15. The surface permafrost was selected because the deposits at this depth are expected to thaw first under global warming3. The selected segments were then cut lengthwise into at least 12 wedges to ensure uniform substrate characteristics and to minimize depth effects within replicates.
Incubation experiment
We quantified the magnitude of CO2–C release from active layer (20–30 cm) and permafrost deposits (variable depths among sites) over an 80-day incubation period in Institute of Botany, Chinese Academy of Sciences as follows: three replicate microcosms were constructed by placing 15–30 g (varied according to soil moisture) fresh soil from each horizon into 250 ml amber jars with airtight lids. Sixty microcosms (5 sites × 2 soil layers × 2 temperatures × 3 replicates) were constructed in total. The amber jars were flushed periodically with synthetic air (20% O2 and 80% N2) when the headspace CO2 concentrations reached over 1,000 ppm to minimize the buildup of CO2 and to prevent formation of an anaerobic environment33. Samples were incubated at two different temperatures (−5 and 5 °C) using two incubators (BPS-250CA, Yiheng, China). The temperature inside the incubators was precisely maintained at ±0.5 °C from the set point. Given that good drainage and aeration occurs in most upland sampling sites, we focused on aerobic C release as the CO2–C in this study. It has been reported that 60% of WHC is the optimal water content for microbial activity in permafrost40,41. Soil moisture was thus adjusted to 60% of WHC and was maintained by deionized water addition. All samples were thawed at 5 °C for 24 h, and were then brought to incubation temperature for 7 days before measurements to reduce the possibility of measuring gas trapped in the permafrost14,32.
Flux measurements were calculated on the basis of the changes in headspace CO2 concentration over time. Before each measurement, the samples were flushed with CO2-free air for 10 min to homogenize the initial state of the concentration in the jars. A 10 ml headspace sample was then extracted by syringe to determine the initial CO2 concentration. To avoid the potential effects caused by negative pressure, 10 ml of CO2-free air was injected into the jar immediately after the extraction of the headspace sample. All jars were then placed at their respective incubation temperatures for 48 h, and another 10 ml headspace sample was extracted to determine the changes in CO2 concentration over this period. The changes in headspace CO2 concentration were measured every 2 days up to day 7, and thereafter every 5–8 days up to 80 days of incubation using a GC (Agilent 7890A, Palo Alto, CA, USA). An Agilent 7890A GC coupled to a flame ionization detector was used to quantify CO2 concentrations. The data were acquired and processed with the GC ChemStation (Rev. B.04.03) software. It should be acknowledged that an 80-day incubation period represents short-term incubation. Nevertheless, this short duration of laboratory incubation has been widely used to explore the potential mechanisms of C decompositions following the thawing of permafrost11,15,56. Therefore, an 80-day duration is reasonable for this study, which is aimed at determining the controls of CO2–C release for both the active layer and permafrost deposits after thawing but not at quantifying long-term CO2–C release and projecting future C fluxes from thawing permafrost landscapes13,31.
Soil chemical and physical analysis
SOC concentrations were determined by the potassium dichromate oxidation method57. Total nitrogen (N) concentrations were measured for a ground subsample of each soil replicate after air drying using an elemental analyser (Vario EL Ш, Elementar, Germany). The soil C:N ratio was then calculated as the quotient of SOC and the total nitrogen concentration. DOC and total dissolved nitrogen were measured from soil water extracts. Soil extracts of 15 g fresh sample in 150 ml ultrapure water were shaken for 24 h at 15 °C and were filtered with prebaked 0.7 μm glass fibre filters (GF/F, Whatman, UK). The soil extracts were analysed on an Elementar TOC analyser (Liqui TOC II, Germany). DOC composition was characterized by ultraviolet absorbance at 254 nm (SUVA254), a photometric measure of DOC aromaticity58. Ultraviolet absorbance was measured on a Lambda 35 ultraviolet–vis spectrometer using a 1.0 cm quartz cell, and SUVA254 was calculated by dividing ultraviolet absorbance by DOC concentration. Soil NH4+–N and NO3−–N concentrations were determined from 2 mol l−1 KCl extracts by autoanalyser (SEAL-AA3, Germany). Soil pH was determined in a 1:2.5 soil-to-deionized water mixture and analysed using a pH electrode (PB-10, Sartorius, Germany). A 10 g subsample of fresh soil was oven-dried at 105 °C for 24 h to determine soil moisture. WHC was measured gravimetrically for each soil using a sample that was oven-dried at 105 °C for 24 h, and then rewetted until no more water could be absorbed11. Soil texture was determined using a particle size analyser (Malvern Masterizer 2000, UK) after the removal of organic matter and carbonates by hydrogen peroxide and hydrochloric acid, respectively.
Identification of soil C quality
We used three types of proxies (soil C:N ratio, relative abundance of SOM components derived from biomarker analysis and pool sizes for C fractions derived from the model) to examine the difference in SOC quality between soil layers (Supplementary Fig. 2). To be specific, soil C:N ratio is a traditional but indirect proxy for SOC quality16; by contrast, biomarker analysis is a molecular level method that provides unparalleled insight into SOC chemical composition, being one of the most direct methods to examine SOC quality17. In biomarker analysis, the relative abundance of the recalcitrant compounds was used as one direct proxy for SOC quality. In addition, the pool sizes for C fractions with different turnover times (ranging from less than one year to hundreds or thousands of years) estimated from the soil C decomposition model were also interpreted as another proxy for SOC quality16,31. Taken together, the elemental analysis, SOM biomarker analysis and three-pool model data were jointly used to obtain three types of proxies for SOC quality.
SOM biomarker analysis
The detailed biomarker analyses followed the procedures59, in which sequential chemical extractions (solvent extraction, base hydrolysis and CuO oxidation) were conducted to separate solvent-extractable compounds, hydrolysable lipids and lignin-derived phenols, respectively. To be specific, ∼5–10 g of the soil samples were extracted by ultrasonication three times, each with 20 ml dichloromethane:methanol (1:1 v/v) for 15 min. The combined extracts were then concentrated by rotary evaporation and dried by N2 gas. The air-dry soil residues after the solvent extraction were further divided into two subsamples to extract hydrolysable lipids and lignin-derived phenols.
For the hydrolysable lipid extraction, we added 15 ml of 1 M methanolic KOH and 20 μg 5α-cholestane to one subsample of soil residues and heated it at 100 °C for 3 h in Teflon-lined bombs. The extracts were then acidified to pH 1 with 6 M HCl. The bound lipids were recovered from the water phase by liquid–liquid extraction with 20 ml ethyl acetate three times. After the addition of anhydrous Na2SO4 to remove water, the ethyl acetate extracts were then concentrated by rotary evaporation and methylated with diazomethane at 70 °C for 90 min. The hydrolysable lipids were mixed with 1 ml ultrapure water and then extracted with 2 ml hexane three times. The combined organic phases were dried by N2 gas.
For the lignin-derived phenol analysis, one subsample of soil residues, 1 g CuO and 100 mg ammonium iron (II) sulfate hexahydrate were added to a Teflon bomb with 15 ml of 2 M NaOH, which was then heated at 170 °C for 2.5 h. The extracts were acidified to pH 1 with 6 M HCl and kept at room temperature for 1 h. After centrifugation at 3,000 rpm for 10 min, the supernatant was transferred to a funnel and recovered from the water phase by liquid–liquid extraction with 20 ml ethyl acetate three times. The ethyl acetate extracts were then added to anhydrous Na2SO4 to remove water, were concentrated by rotary evaporation and were then dried under N2 gas.
All biomarkers from the solvent extracts, base hydrolysis and CuO oxidation were converted to trimethylsilyl derivatives by reaction with 100 μl N,O-bis-(trimethylsilyl) trifluoroacetamide and 50 μl pyridine at 60 °C for 2 h. After cooling, dichloromethane was added to dilute the solution to 1 ml for solvent extracts, and ethyl acetate was added to dilute the solution to 1 ml for base hydrolysis and lignin-derived phenol extraction. The biomarkers were identified by GC–MS (Agilent 7890A-5973N). An Agilent 7890A GC coupled to an flame ionization detector was used for the quantification of biomarkers. The data were acquired and processed with the GC ChemStation (Rev. B.04.02) software. The concentration of individual compounds was normalized to the sample SOC concentration.
Soil C decomposition model
We developed a C decomposition model and compared the performance of two-pool and three-pool C decomposition models using data from our 80-day incubation procedure. Our analysis showed that the three-pool and two-pool models had similar Akaike information criterion values (−57.9 versus −55.6 for the three-pool and two-pool models, respectively, Supplementary Fig. 5), indicating that overfitting did not occur in the three-pool model. By contrast, the three-pool model displayed much better performance in estimating the C flux rate for our data (r2=0.83 versus 0.65; RMSE=0.05 versus 0.08 for the three-pool and two-pool models, respectively, Supplementary Fig. 5). Thus, to most accurately describe C dynamics, we chose to use the three-pool model to estimate the pool sizes of C fractions with different turnover times60, which was then used as another proxy for SOC quality. In the three-pool (that is, fast, slow and passive) model, SOC was conceptually grouped into a fast decomposable fraction that turns over within a few days to a few months, a slower decomposing C pool that has an MRT of a few years and a highly passive soil C fraction that has been described to have a turnover times of a few years to thousands of years16,60. We applied the three-pool model to each of the 30 soil samples separately at a given incubation temperature as follows:
where R(t) is the CO2–C emission rate at time t (mg C g−1 SOC d−1), Ctot is the initial soil SOC content (that is, 1,000 mg C g−1 SOC), f1 and f2 are the fractions of the fast and slow pools and k1, k2, and k3 are the decay rates of fast, slow and passive pools, respectively. In this soil C decomposition model, Ctot and R(t) are measured quantities. The five parameters (that is, f1, f2, k1, k2 and k3) were determined by a Markov Chain Monte Carlo (MCMC) approach16,60,61.
Briefly, the approach was based on Bayes's theorem:
where the posterior probability density function P(θ|Z) was obtained from the prior uniform probability density function P(θ) and the likelihood function P(Z|θ). It was assumed that the observed and modelled values followed a multivariate Gaussian distribution with a zero mean:
where Zi(t) and Xi(t) are the observed and modelled CO2–C emission rates, and σi(t) is the s.d. of the measurements. A MCMC technique, the Metropolis–Hastings (M–H) algorithm, was used to construct the P(θ|Z) of parameters62,63.
Before applying MCMC to each sample, the prior parameter range (Supplementary Table 7) was set as widely as possible in the initial model so as to cover the possibility for all the soil samples16. It should be noted that the prior range was adjusted a little bit depending on site conditions. For example, owing to the low C emission rate at CMH site, we chose a longer turnover time for the slow and passive C pool (upper limit in Supplementary Table 7) for these soils. Maximum likelihood estimates were quantified for all the well-constrained parameters, the mean values were calculated when parameters were not constrained16. The final estimated parameters (Supplementary Table 8) were then used to make short-term (80-day) and long-term (10,200-day, ∼85 years in situ until the year 2100) projection of CO2–C release for each of the 30 soil samples separately by using the following equation:
where Ccum is the cumulative CO2–C release at time t (mg C g−1 SOC).
To further validate the precision of the estimates of the C pools and decay rates derived from our short-term incubation, we used a long-term incubation dataset (390 days) from Yedoma soils collected in northeastern Siberia13 to test our C decomposition model on the Tibetan Plateau (Supplementary Table 9). Due to the different C inputs from plant production and different C outputs from microbial decomposition between these two regions34, the SOC concentration of the permafrost deposits in this dataset was higher than that on the Tibetan Plateau. To increase data comparability, only data from 5 °C incubation and similar sampling depth were used. The comparison of the mean estimated parameters indicated that the duration of incubation time minimally affected the parameters for the fast C pool (that is, k1 and f1) but had some influences on the estimated parameters associated with the slow and passive C pools. These differences did not affect the estimated C release from short-term incubation (that is, 80 days), whereas they could lead to a certain degree of uncertainty for the long-term projection (Supplementary Table 9).
Microbial communities
Soil microbial abundance and composition in each sample was assessed using PLFA analysis. Phospholipids are essential membrane components of all living microbes that decomposes rapidly upon cell death, so the total of PLFA biomarkers in a sample represent all living cells64. Moreover, different microbial groups produce specific or signature types of PLFA biomarkers allowing the quantification of important microbial groups and providing direct information about the structure of the active microbial community64. PLFAs were extracted from the soil following the protocol64. Qualitative and quantitative fatty acid analyses were performed with an Agilent 6890 GC (Agilent Technologies) and the MIDI Sherlock Microbial Identification System (MIDI Inc., Newark, DE, USA). Fatty acids were quantified by calibration against standard solutions of FAME 19:0 (Matreya Inc., State College, PA, USA). PLFAs specific to bacteria (i14:0, a15:0, i15:0, i16:0, 16:1w7c, a17:0, cy17:0, i17:0, 18:1 w7c, cy19:0), fungi (18:2 w6,9c) and actinomycetes (16:0 Me, 17:0 Me, 18:0 Me) were quantified65. The microbial community structure was assessed using the F/B ratio.
Data analysis
We used mixed effects modelling to investigate the differences in all soil physical, chemical and microbial properties and C pool sizes among sites (YY, CMH, HSX, WQ and KLSK) and depths (active layer versus permafrost deposits), in which site and depth were treated as fixed factor and depth nested in core was treated as a random factor. Similarly, we performed another mixed effects modelling analysis to test for differences in CO2–C release among temperature, soil layer and sampling sites (R package: nlme). The data were normalized using log transformation when necessary before analysis of variance analyses.
We conducted an ordinary least squares regression to evaluate the relationships between CO2–C release and soil physical/chemical/microbial properties across the five sites. The model r2 was used to indicate the explanatory power of the variables. To facilitate our analysis and interpretations, we classified all soil variables into three groups, including environmental variables (soil moisture and soil pH), C quality (C:N, cutin-derived compounds, suberin-derived compounds, lignin-derived phenols, fast C pool size, slow C pool size and passive C pool size), and microbial abundance and composition (total PLFAs, fungal PLFAs, actinomycete PLFAs and F/B). All of these statistical analyses were performed using R statistical software v3.2.4 (R Development Core Team, 2016).
We performed SEM to determine the relative importance of environmental variables, C recalcitrance and microbial properties in CO2–C release for the different layers (Supplementary Fig. 3). SEM is a multivariate statistical technique that has emerged as a synthesis of path analysis, factor analysis and maximum-likelihood analysis66,67. It can test the plausibility of a hypothetical model, which is based on a priori information regarding the relationships among particular variables68. Moreover, this technique goes beyond traditional multivariate techniques that relate predictors directly to the response variable, ignoring the overall effects derived from the interactions among variables. Conversely, SEM can partition direct and indirect effects that one variable may have on another, and estimate the strengths of these multiple effects66,67. Thus, it is useful for exploring the complex networks of relationships found in natural ecosystems.
We conducted the following data processing before the SEM analysis. Considering the nonlinear relationship between CO2–C release and soil moisture, we used the log-transformed soil moisture data to construct the SEM. Additionally, because the variables of both C recalcitrance and microbial community group were closely correlated, we conducted principal components analysis (PCA) to create a multivariate functional index to represent each group65. Within each group, only variables with significant correlations with cumulative CO2–C release were included in the PCA. The first component (PC1), which explained 68–94% of the total variance, was then introduced as a new variable into the subsequent SEM analysis (Supplementary Table 10). The fit of the final model was evaluated using the model χ2 test and the r.m.s. error of approximation. SEM analyses were conducted using AMOS 21.0 (Amos Development Corporation, Chicago, IL, USA).
Data availability
All relevant data are available from the corresponding author upon request.
Additional information
How to cite this article: Chen, L. et al. Determinants of carbon release from the active layer and permafrost deposits on the Tibetan Plateau. Nat. Commun. 7, 13046 doi: 10.1038/ncomms13046 (2016).
- 1.
Schuur, E. A. G. et al. Vulnerability of permafrost carbon to climate change: implications for the global carbon cycle. BioScience 58, 701–714 (2008).
- 2.
Hugelius, G. et al. Estimated stocks of circumpolar permafrost carbon with quantified uncertainty ranges and identified data gaps. Biogeosciences 11, 6573–6593 (2014).
- 3.
Schuur, E. A. G. et al. Climate change and the permafrost carbon feedback. Nature 520, 171–179 (2015).
- 4.
Schuur, E. A. G. et al. The effect of permafrost thaw on old carbon release and net carbon exchange from tundra. Nature 459, 556–559 (2009).
- 5.
Koven, C. D., Lawrence, D. M. & Riley, W. J. Permafrost carbon-climate feedback is sensitive to deep soil carbon decomposability but not deep soil nitrogen dynamics. Proc. Natl Acad. Sci. USA 112, 3752–3757 (2015).
- 6.
Koven, C. D. et al. A simplified, data-constrained approach to estimate the permafrost carbon-climate feedback. Philos. Trans. R. Soc. A 373, 20140423 (2015).
- 7.
Schneider von Deimling, T. et al. Observation-based modelling of permafrost carbon fluxes with accounting for deep carbon deposits and thermokarst activity. Biogeosciences 12, 3469–3488 (2015).
- 8.
Hobbie, S. E., Schimel, J. P., Trumbore, S. E. & Randerson, J. R. Controls over carbon storage and turnover in high-latitude soils. Glob. Chang. Biol. 6, 196–210 (2000).
- 9.
Moni, C. et al. Temperature response of soil organic matter mineralisation in arctic soil profiles. Soil Biol. Biochem. 88, 236–246 (2015).
- 10.
Dungait, J. A. J., Hopkins, D. W., Gregory, A. S. & Whitmore, A. P. Soil organic matter turnover is governed by accessibility not recalcitrance. Glob. Chang. Biol. 18, 1781–1796 (2012).
- 11.
Treat, C. C. et al. Temperature and peat type control CO2 and CH4 production in Alaskan permafrost peats. Glob. Chang. Biol. 20, 2674–2686 (2014).
- 12.
Xue, K. et al. Tundra soil carbon is vulnerable to rapid microbial decomposition under climate warming. Nat. Clim. Chang. 6, 595–600 (2016).
- 13.
Dutta, K., Schuur, E. A. G., Neff, J. C. & Zimov, S. A. Potential carbon release from permafrost soils of Northeastern Siberia. Glob. Chang. Biol. 12, 2336–2351 (2006).
- 14.
Roy Chowdhury, T. et al. Stoichiometry and temperature sensitivity of methanogenesis and CO2 production from saturated polygonal tundra in Barrow, Alaska. Glob. Chang. Biol. 21, 722–737 (2015).
- 15.
Waldrop, M. P. et al. Molecular investigations into a globally important carbon pool: permafrost-protected carbon in Alaskan soils. Glob. Chang. Biol. 16, 2543–2554 (2010).
- 16.
Schädel, C. et al. Circumpolar assessment of permafrost C quality and its vulnerability over time using long-term incubation data. Glob. Chang. Biol. 20, 641–652 (2014).
- 17.
Feng, X. & Simpson, M. J. Molecular-level methods for monitoring soil organic matter responses to global climate change. J. Environ. Monit. 13, 1246–1254 (2011).
- 18.
Strauss, J. et al. Organic matter quality of deep permafrost carbon–a study from Arctic Siberia. Biogeosciences 12, 2227–2245 (2015).
- 19.
Billings, S. A., Tiemann, L. K., Ballantyne, F. IV, Lehmeier, C. A. & Min, K. Investigating microbial transformations of soil organic matter: synthesizing knowledge from disparate fields to guide new experimentation. Soil 1, 313–330 (2015).
- 20.
Grosse, G. et al. Vulnerability of high-latitude soil organic carbon in North America to disturbance. J. Geophys. Res.: Biogeosci. 116, 130–137 (2011).
- 21.
Ping, C. L., Jastrow, J. D., Jorgenson, M. T., Michaelson, G. J. & Shur, Y. L. Permafrost soils and carbon cycling. Soil 1, 147–171 (2015).
- 22.
Ping, C. L. et al. Cryogenesis and soil formation along a bioclimate gradient in Arctic North America. J. Geophys. Res.: Biogeosci. 113, 65–75 (2008).
- 23.
Repo, M. E. et al. Large N2O emissions from cryoturbated peat soil in tundra. Nat. Geosci. 2, 189–192 (2009).
- 24.
Gittel, A. et al. Site- and horizon-specific patterns of microbial community structure and enzyme activities in permafrost-affected soils of Greenland. Front. Microbiol. 5, 541 (2014).
- 25.
Wang, B. L. & French, H. M. Permafrost on the Tibet Plateau, China. Quat. Sci. Rev. 14, 255–274 (1995).
- 26.
Wang, B., Bao, Q., Hoskins, B., Wu, G. X. & Liu, Y. M. Tibetan plateau warming and precipitation changes in East Asia. Geophys. Res. Lett. 35, 63–72 (2008).
- 27.
Yang, M., Nelson, F. E., Shiklomanov, N. I., Guo, D. & Wan, G. Permafrost degradation and its environmental effects on the Tibetan Plateau: a review of recent research. Earth-Sci. Rev. 103, 31–44 (2010).
- 28.
Wu, Q. & Zhang, T. Changes in active layer thickness over the Qinghai-Tibetan Plateau from 1995 to 2007. J. Geophys. Res.: Atmos. 115, 736–744 (2010).
- 29.
Johnson, K. D. et al. Permafrost and organic layer interactions over a climate gradient in a discontinuous permafrost zone. Environ. Res. Lett. 8, 1402–1416 (2013).
- 30.
Tarnocai, C., Mark Nixon, F. & Kutny, L. Circumpolar-Active-Layer-Monitoring(CALM) sites in the Mackenzie Valley, northwestern Canada. Permafr. Periglac. Process. 15, 141–153 (2004).
- 31.
Knoblauch, C., Beer, C., Sosnin, A., Wagner, D. & Pfeiffer, E. M. Predicting long-term carbon mineralization and trace gas production from thawing permafrost of Northeast Siberia. Glob. Chang. Biol. 19, 1160–1172 (2013).
- 32.
Elberling, B. et al. Long-term CO2 production following permafrost thaw. Nat. Clim. Chang. 3, 890–894 (2013).
- 33.
Lee, H., Schuur, E. A. G., Inglett, K. S., Lavoie, M. & Chanton, J. P. The rate of permafrost carbon release under aerobic and anaerobic conditions and its potential effects on climate. Glob. Chang. Biol. 18, 515–527 (2012).
- 34.
Ding, J. et al. The permafrost carbon inventory on the Tibetan Plateau: a new evaluation using deep sediment cores. Glob. Chang. Biol. 22, 2688–2701 (2016).
- 35.
Schuur, E. A. G. et al. Expert assessment of vulnerability of permafrost carbon to climate change. Clim. Chang. 119, 359–374 (2013).
- 36.
Jenkins, M. & Adams, M. A. Vegetation type determines heterotrophic respiration in subalpine Australian ecosystems. Glob. Chang. Biol. 16, 209–219 (2010).
- 37.
Walker, D. A. et al. The circumpolar Arctic vegetation map. J. Veg. Sci. 16, 267–282 (2005).
- 38.
Treat, C. C. et al. Effects of permafrost aggradation on peat properties as determined from a pan-Arctic synthesis of plant macrofossils. J. Geophys. Res.: Biogeosci. 121, 78–94 (2016).
- 39.
Jin, H. J., Chang, X. L. & Wang, S. L. Evolution of permafrost on the Qinghai-Xizang (Tibet) Plateau since the end of the late Pleistocene. J. Geophys. Res.: Atmos. 112, 261–263 (2007).
- 40.
Rodionow, A., Flessa, H., Kazansky, O. & Guggenberger, G. Organic matter composition and potential trace gas production of permafrost soils in the forest tundra in northern Siberia. Geoderma 135, 49–62 (2006).
- 41.
Wang, X. W. et al. Potential carbon mineralization of permafrost peatlands in Great Hing'an Mountains, China. Wetlands 30, 747–756 (2010).
- 42.
Högberg, M., Högberg, P. & Myrold, D. Is microbial community composition in boreal forest soils determined by pH, C-to-N ratio, the trees, or all three? Oecologia 150, 590–601 (2007).
- 43.
Doetterl, S. et al. Soil carbon storage controlled by interactions between geochemistry and climate. Nat. Geosci. 8, 780–783 (2015).
- 44.
Yang, Y., Fang, J., Ma, W., Guo, D. & Mohammat, A. Large-scale pattern of biomass partitioning across China's grasslands. Glob. Ecol. Biogeogr. 19, 268–277 (2010).
- 45.
Hultman, J. et al. Multi-omics of permafrost, active layer and thermokarst bog soil microbiomes. Nature 521, 208–212 (2015).
- 46.
Ernakovich, J. G. & Wallenstein, M. D. Permafrost microbial community traits and functional diversity indicate low activity at in situ thaw temperatures. Soil Biol. Biochem. 87, 78–89 (2015).
- 47.
Coolen, M. J. L., van de Giessen, J., Zhu, E. Y. & Wuchter, C. Bioavailability of soil organic matter and microbial community dynamics upon permafrost thaw. Environ. Microbiol. 13, 2299–2314 (2011).
- 48.
Natali, S. M. et al. Permafrost thaw and soil moisture driving CO2 and CH4 release from upland tundra. J. Geophys. Res.: Biogeosci. 120, 525–537 (2015).
- 49.
Cotrufo, M. F., Wallenstein, M. D., Boot, C. M., Denef, K. & Paul, E. The Microbial Efficiency-Matrix Stabilization (MEMS) framework integrates plant litter decomposition with soil organic matter stabilization: do labile plant inputs form stable soil organic matter? Glob. Chang. Biol. 19, 988–995 (2013).
- 50.
Schädel, C. et al. Potential carbon emissions dominated by carbon dioxide from thawed permafrost soils. Nat. Clim. Chang doi:10.1038/nclimate3054 (2016).
- 51.
Treat, C. C. et al. A pan-Arctic synthesis of CH4 and CO2 production from anoxic soil incubations. Glob. Chang. Biol. 21, 2787–2803 (2015).
- 52.
Hagerty, S. B. et al. Accelerated microbial turnover but constant growth efficiency with warming in soil. Nat. Clim. Chang. 4, 903–906 (2014).
- 53.
Mazhitova, G., Malkova, G., Chestnykh, O. & Zamolodchikov, D. Active-layer spatial and temporal variability at European Russian Circumpolar-Active-Layer-Monitoring (CALM) sites. Permafr. Periglac. Process. 15, 123–139 (2004).
- 54.
Zhou, Y., Guo, D., Qin, G., Cheng, G. D. & Li, S. Geocryology in China Science Press (2000).
- 55.
Jin, H., Luo, D., Wang, S., Lü, L. & Wu, J. Spatiotemporal variability of permafrost degradation on the Qinghai-Tibet Plateau. Sci. Cold Arid Reg. 3, 0281–0305 (2011).
- 56.
Wagner, D. et al. Methanogenic activity and biomass in Holocene permafrost deposits of the Lena Delta, Siberian Arctic and its implication for the global methane budge. Glob. Chang. Biol. 13, 1089–1099 (2007).
- 57.
Nelson, D. W. & Sommers, L. E. in Methods of Soil Analysis II (ed. Agronomy, A. S. O.) (1982).
- 58.
Weishaar, J. L. et al. Evaluation of specific ultraviolet absorbance as an indicator of the chemical composition and reactivity of dissolved organic carbon. Environ. Sci. Technol. 37, 4702–4708 (2003).
- 59.
Zhao, L., Wu, W., Xu, X. & Xu, Y. Soil organic matter dynamics under different land use in grasslands in Inner Mongolia (northern China). Biogeosciences 11, 5103–5113 (2014).
- 60.
Liang, J. et al. Methods for estimating temperature sensitivity of soil organic matter based on incubation data: a comparative evaluation. Soil Biol. Biochem. 80, 127–135 (2015).
- 61.
Schädel, C., Luo, Y. Q., Evans, R. D., Fei, S. F. & Schaeffer, S. M. Separating soil CO2 efflux into C-pool-specific decay rates via inverse analysis of soil incubation data. Oecologia 171, 721–732 (2013).
- 62.
Metropolis, N., Rosenbluth, A. W., Rosenbluth, M. N., Teller, A. H. & Teller, E. Equation of state calculations by fast computing machines. J. Chem. Phys. 21, 1087–1092 (1953).
- 63.
Hastings, W. K. Monte-Carlo sampling methods using Markov chains and their applications. Biometrika 57, 97–109 (1970).
- 64.
Bossio, D. A. & Scow, K. M. Impacts of carbon and flooding on soil microbial communities: phospholipid fatty acid profiles and substrate utilization patterns. Microb. Ecol. 35, 265–278 (1998).
- 65.
Chen, D. et al. Evidence that acidification-induced declines in plant diversity and productivity are mediated by changes in below-ground communities and soil properties in a semi-arid steppe. J. Ecol. 101, 1322–1334 (2013).
- 66.
Shipley, B. Cause and Correlation in Biology Cambridge University Press (2000).
- 67.
Grace, J. B. Structural Equation Modeling and Natural Systems Cambridge University Press (2006).
- 68.
Delgado-Baquerizo, M. et al. Decoupling of soil nutrient cycles as a function of aridity in global drylands. Nature 502, 672–676 (2013).
We appreciate the assistance in biomarker analysis provided by Yinghui Wang and Xinyu Zhang at Peking University and thank Daijiang Li at the University of Wisconsin-Madison and Liyin Liang at the University of Waikato for their assistance in data analysis. This work was supported by the National Basic Research Program of China on Global Change (2014CB954001 and 2015CB954201), the National Natural Science Foundation of China (31322011, 41371213 and 31400364), the Chinese Academy of Sciences-Peking University Pioneer Collaboration Team and the Thousand Young Talents Program.
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September 7, 14, 21, & 28
Conflict and animosity seem to have reached unprecedented levels in the current election season. The most disturbing aspect of this phenomenon, however may not be its shocking proportions, but on the contrary, its increasing inability to shock us. We are no longer surprised. Verbal attacks, corruption, negative integration: these "scandals" now seem routine, if not banal. Behind any compromise or agreement, we tend to assume not so much goodwill as an affinity of interests. Is it sensible to be so jaded? What is the end of politics anyway? How much or what kind of unity is necessary in a pluralistic society to be able to pursue a truly common good? Is there hope for politics, or is that just another self-serving slogan?
Faculty facilitators and students come together to explore these perennial questions by the sifting salient, classical responses to them. We consider brief selections from the great conversations of Plato, Aristotle, Augustine, Marx, Machiavelli, Rousseau, Winthrop, and Aquinas, none of whom were of one mind, and discuss them for our own sakes and, perhaps, for the sake of the polis.
Beauty and the Good Life
Module II: Fall 2015
October 12, 19, & 26
Beauty is in everything that surrounds us. We see it in art, the human body, and nature, and we hear it in music of all sorts of cadences and melodies. Where does this beauty come from? Even though much of the beauty we are aware of comes to us through our senses, there is also a beauty that comes to us through the intangible–the beauty of the intellect, of the virtues, and of the good. What is the good, and how can it help us come to a vision of this seemingly inaccessible form of beauty? How must we alter our conduct of life in order to live a good life, and essentially, to see true beauty?
Join us as we explore these perennial questions through examining brief selections from works by Plato, Plontinus, Schiller, Maritain, von Balthasar, and Hart.


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Happy Friday, everybody – the weekend is almost here and it's time to forget about work and follow your heart! It's felt like a very long week here and I'm glad it's finally Friday – I can follow my heart and find some stamping time. My project today is a CAS (clean and simple) card using the Follow Your Heart sentiment from the Bookmarks and Sentiments plate, along with a few other bits and pieces from Art Neko.
The little heart-shaped tins come in packs of two (currently at $1.00 for the two tins) and are so easy to decorate and alter. I didn't include a photo of the unaltered tin, as you can see that on the website. In the past I've used alcohol inks applied with a felt pad, and I know that this works very well on a tin surface. But I wanted this heart to be uniformly matt and a solid colour, so I used a Sharpie. The photo shows it after one coat – by the time I added a second coat it had a beautiful satin finish which I hope you can see in the final photo.
After allowing drying time between each coat, I decorated round the window aperture with some Liquid Pearls, and added a sparkly heart sticker to finish it off. I filled mine with some little resin hearts for a calorie-free treat, but of course you could use candy – or even some small jewellery as a gift for a special friend. The tins are also suitable for storing small embellishments, because of the window in the lid.
Thanks for coming by to check the blog this week. I hope that you find something to do this weekend which will make your heart happy!


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The August 12 issue of Britain's Spectator carries an interesting interview with former Israeli Prime Minister Benjamin Netanyahu by Allister Heath: "Bush won't allow Iran to go nuclear." Here is Netanyahu and Iran and Ahmadinejad:
[T]he conversation again turned to Iran and its president, Mahmoud Ahmadinejad, who has repeatedly called for Israel to be wiped off the map. 'While denying the Holocaust, he's openly preparing the next one,' Netanyahu said. 'Ahmadinejad is behaving exactly like an Islamist Hitler. He is using the same tactics of signalling in advance the act of destruction. That the same thing is happening is one thing, but that the West is reacting in the same way is unacceptable. What is history for?'
By now, Netanyahu was shouting angrily, shaking his fist as he explained the similarities he sees between the 1930s and today. 'Yes, there are differences, it is not a perfect analogy. Yes, Germany didn't have a billion Germans to infect. Yes, Germany had race and not creed as its prime goal. Nazism started its attacks on the Jews and spread to the rest of the world in their mad militancy, and that is exactly what is happening now.'
For Netanyahu, Israel is a latter-day Czechoslovakia, which deluded and desperately anti-war European powers, led by Neville Chamberlain, sacrificed to the Nazis in 1938 because of the German-speaking minority in Sudetenland, whom he compares with today's Palestinians. 'And, yes, there was apologetics and, yes, there was appeasement and, yes, there was pressure on a small resistant democracy in the face of this German onslaught. It was called Czechoslovakia at the time. And, yes, there were articles in the British press condemning Czechoslovakia for inciting a German response because of the denial of the rights of the Sudeten Germans. Do you want to go on with this?'
Netanyahu rejects the comparison between radical Islamic terrorists and communists. The main difference, he argues, is that the communists were rational when it came to foreign policy, putting their survival first and always backing down at the last moment, as shown in the Cuban missile crisis. This was not true of the Iranian regime, he said, arguing that they were trying to prompt the return of the Hidden Imam, an event which Shiites believe would be accompanied by an apocalypse. 'Is it possible in the 21st century to have a resurrection of the religious wars that we thought had ended in the 17th century? Yes, it's possible. This is what is going on.'


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- Double victory for the Italians2017-08-01 00:38:43
- Still amazed2017-07-28 20:15:32
- Once an athlete, always an athlete2017-07-26 21:14:19
- Gyor is a beautiful city2017-07-24 21:18:19
- Fantastic vibes2017-07-24 20:57:47
- The Dutch team withdraws from the competition2017-07-24 12:08:55
- Volleyball (boys and girls)2017-06-28 14:53:16
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Mayor's Welcome
Dear Sports Friends,
Dear Visitor,
It is with great pleasure to welcome you on the official website of the European Youth Olympic Festival 2017 in Győr.
It has been a great honour for Hungary and the City of Győr to obtain the rights to host the 2017 European Youth Olympic Festival.
City of Győr


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Australian rapper Iggy Azalea was issued with a warning by police for unsafe driving while out and about in Beverly Hills, California on Monday (20Jul15).
The Fancy hitmaker, real name Amethyst Kelly, was photographed in her black SUV talking to an officer after she reportedly took an "unsafe left turn".
Editors at TMZ.com report that Azalea was let off with a warning because she accepted her error.


text: Wonderful 195m2 corner apartment with 4 bedrooms +1 Gym, in the complex "Marazul" near Callao Salvaje. The apartment is in a block of only 2 floors and has 3 bedrooms + 1 bedroom with own terrace and walk-in closet + 1 as gym room, 2 bathrooms, 15m2 kitchen with dining area, lounge with terrace and private heated pool. Parking with 15m2 included. The community has 2 swimming pools, tropical gardens, 3 tennis courts and a reception in the main building. Community fees are €1,000/quarter. The resort is situated on the sea front and close to the "Abama" Hotel with 18 hole golf course and near Callao Salvaje and Playa San Juan with shops, restaurants, bars and beaches.


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Looking Glass Blue 91 KatSilk Saran Doll Hair
Looking Glass Blue(91)Katsilk Saran Doll Hair. This color is a dark inky blue with purple tones.
With each order you receive two skeins of saran.
Three size choices:
Standard: Two 18" inch skeins and weigh .5 oz each. (Enough to reroot a Barbie Doll)
Large: Two 21" inch skeins and weigh 1 oz each.
XL Extra Large: Two 31" inch skeins and weigh 1.5 ounces each.
Posted by Onaca on 5th Jul 2016
Incredibly dark blue, but the color is really rich in the right lighting. Exactly what I wanted.
Posted by Dirili on 23rd May 2015
Unless you have it in very bright light, this blue is so dark that it looks pretty much black. It's great for creating certain effects.


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', 'nextnewcars.com'); ga('send', 'pageview');
Regardless that the 2017 Porsche 911 R series is still on hot rumors discussion – it seems that Porsche will tend to build this car for the release date in the first semester of 2017. Curious people should be happy because in the 2016 Geneva International Auto Show – this car will arrive as its first public announcement chance. In the meantime, this time, we will discuss the details based on the rendering with some speculative specs. However, we cannot cover all the toys that this car will bring to us bluntly because this car still on the initial conception after all. According to some rumors, this vehicle will use the similar power plan that the GT3's series will have but it will not copy all the specs – it is only for role model based.
Before we jumping into the details of this future series – we need to know that the long span career that the 911 variant has always been a prestigious name in the Porsche production. The modification that this future series will have consist of revised on the front bumper, and the lightweight wheels for both front and rear section. Unlike some of the previous edition that use rear wing – this future production will not put that as the requirement. Besides this series – Porsche will produce the upcoming 2016 Porsche Macan Turbo series as the menu to serve the compact luxury crossover market. This series will have powertrain from the newest 3.0 liters with V6 Engine that produce 340 HP and 339 lb-ft of torque. That numbers might be a good numbers in its class, and so does the future 911 variant where the estimation of the output power is around 500 HP.
To start with estimation idea makes the starting price that the 2017 Porsche 911 R will have around $120,000 as the estimation price. This car will have one rival in the same year release date, and that is the Chevrolet Corvette Stingray. However, this Chevy will only have 460 HP so the future production for the 911 will win over it. Speaking of the Porsche plan production, this brand will produce the 2018 Porsche Cayenne that will receive promising engine options.
[Photos: TopSpeed]
[…] i knew whether i will get one, so let's wait and see, and keep the fingers crossed! stay tuned! http://nextnewcars.com/2017-porsche-…ease-date.html googletag.cmd.push(function() { googletag.display('div-gpt-ad-14'); […]


text: Because we value making space in our lives to embrace God's love for all people, we will intentionally meet in a variety of contexts. We will share life with those who identify with our faith community, and those who identify with the greater community at large. All are welcome at our Services at the Worthington Resource Pantry and in our Life Together Groups!


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Home » Windows » Audio and Video » Editors and Convertors » Avidemux 2.6.19
Not rated yet
The main feature of this software - you can Avidemux free download! It has a great set of features for working with video files, and can make cuts, coding tasks, or filtering. Avidemux works with such files as MKV, MPEG, AVI, MP4, DVD and ASF, and also has a solid set of filters and codecs. Download Avidemux, and you can automate your tasks and create projects.
In particular, the program includes:
Title: Avidemux 2.6.19
File Name: avidemux_2.6.19_win32.exe
File Size: 25.18MB (26,399,439 bytes)
Requirements: Windows XP / Vista / Windows7 / Windows8 / Windows 10
Languages: Multiple languages
Date Added: March 30, 2017
Author: Mean
Home Page: http://fixounet.free.fr/avidemux
Program Page: http://www.avidemux.org
MD5 Hash: A35865FB3F0634443B47F96BFFFAEB07


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One Patient's Story
Athletes endure tremendous strains to the mind and body, and rise to the challenge in sacrifice to achieve their goals. However, there is nothing "glorious" in being diagnosed with cancer and coping with the outcome.
I am an athlete that has been affected by skin cancer. At the time of my diagnosis I was training to challenge a National Tennis Singles title. My life was completely thrown upside down with emotions ranging from frustration to fear of the unknown.
I was blessed to meet and work with Dr. Robert Behar, a brilliant and world renown cancer specialist at North Cypress Medical Center, who emphasized the importance of maintaining my movement and flexibility before, during and post treatment. Due to the location and size of my cancer, I was told radiation treatment was my only hope.
It has now been almost three years since treatment and I am proud to announce that, after having two suspect areas treated in simple form, I have remained cancer-free. Although I had overcome the challenge of conquering my cancer, I was soon faced with another…now what? How do I return to what I used to call "the norm"?
Months after my treatment ended I attempted to get back into tennis. Dr. Behar not only saved my life, but he also protected the flexibility of my arm and shoulder, which granted me the opportunity for future athletic endeavors. Unfortunately, I was faced with a kidney stone following treatment and affects from the drugs and so much time off from sports prevented my ability to return to tennis.
Since competing in tennis for so many years, answering the common question of "Now What?" among cancer survivors became especially challenging. After treatment the feelings of helplessness, the need for such a tremendous amount of physical and mental support from others, and the final "enormity" of the entire situation became immensely overwhelming.
During this rough period in my life, my body and mind seemed to stand still. I would not allow myself to admit these feelings of helplessness because I did not want to appear weak to others. I remained in a state of "limbo" which left me hopeless, and unable to cry or find joy. Once I realized I could no longer go on living this way, I decided to seek help. Admitting the realization that I needed help was a major milestone for me in returning to a normal lifestyle.
The impressive support network at North Cypress Medical Center is never-ending. The North Cypress Oncology Social Worker understood my struggle and immediately offered me guidance. I explained my feelings and symptoms and was quickly reassured these feelings were normal affects after treatment. She explained how North Cypress offers options that could help me cope.
The best option for me at that time was to seek individual counseling from a therapist at the hospital. The counselor I had the pleasure of working with was able to immediately identify solutions to the physical and mental affects I was experiencing. I directly owe my full mental and emotional recovery to these counseling sessions and directions from which I was sent away with. I currently, a year later, still utilize the counselor's suggestions to better manage all that life has to offer.
These counseling sessions allowed me to begin living my life again and helped me return to the person I once was. Since I was now unable to play tennis, I decided to turn to something that had always been a passion of mine—Powerlifting. After only a six month venture in this sport I have proudly won 3 World titles, a second World record and been honored as a "Best Lifter" at three different meets (including World meets).
From a personal and athletic perspective, this experience has been humbling, humiliating, embarrassing and a learning process. It does not just take courage and stamina to survive, but the necessity for full support is imperative. My loving husband, family, coach and friends provided more than I could ever have asked and strengthened me during my journey. I continue to take nothing for granted, embrace the moment and strive to make a difference in the world.
I strongly wish someone would have given me advice before my cancer treatment and am honored to share my advice with those struggling to find their place after treatment. For those that are about begin their battle with cancer, acknowledge to yourself and everyone around you that you will need support throughout your journey. Don't be afraid to ask for whatever type of help you may need. Although it may seem impossible at times, try to focus on the positives of each situation you may encounter. During your journey, stay true to yourself, your spouse, family, doctors, and close friends. The people in your life need to know how you feel and you need to allow them to help. Accept the fact that there may be changes to your overall being. Whatever these changes may be, face them with love and remain willing to adapt to these changes as needed. Lastly, utilize all tools of support offered to you from North Cypress Medical Center. This gracious support can help you through this extremely difficult experience.
I am certain I was placed in this situation for a reason and can only hope I do what was intended. The Lance Armstrong Foundation has allowed me to volunteer for the LIVESTRONG Global Cancer Initiative, and I plan on speaking and writing as much as I can to promote early skin screening and evaluation. I will make that difference in the world and uphold the spirit of LIVESTRONG by protecting myself and informing others.


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A woman was killed on Saturday morning 20th in Caruaru. The victim, Aulilândia Gomes was 25 years old. According to the coroner she died from strangulation, and was killed elsewhere, and then dumped in the street.
Hélio José, said he woke up around 2am and found her missing, he also said she liked to drink and may of left the house for this purpose.
The coroner, Dr. Theophilus Ribeiro.


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|Message view
|« Date » · « Thread »
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|Chris Anderson <jch...@apache.org>
|[ann] Relaxville, test suite reporter
|Wed, 14 Oct 2009 07:26:37 GMT
Devs, You may have noticed by the commit storm that I'm working on a new feature to store test suite reports from Futon in a local database. The Futon test suite now stores runtime, success and failure information, along with a timestamp and some browser / platform information, into the local database test_suite_reports. The test reports are completely private and remain on the localhost for convenient browsing by developers. However, replication makes it easy to share reports. I'm also working on a CouchApp to make browsing and replicating reports easy. I've only got it to rudimentary functionality, but I'm a firm believer in releasing things before I go to sleep for the night. Hopefully those in other timezones can enjoy it before I wake up. The source code is here: http://github.com/jchris/relaxville to install just git clone it and then run couchapp push . test_suite_reports then you can browse tests on your local machine. * Participate The best thing you can do is replicate your test_suite_reports db to the new database that's been set up at: http://couchdb.couchdb.org/test_suite_reports It should be available for writes (please don't abuse) -- also if anyone else wants a db on this server for community purposes, just holler. Eventually we should have a wiki and other CouchApps here. * Browse You can also just see Relaxville running on the CouchDB server here: http://couchdb.couchdb.org/test_suite_reports/_design/relaxville/index.html It will be updated as new people replicate their test_suite_reports to it. * Patches I'd like to add a Toast chat room to different entities in the UI. It could use some more views. Those should be easy to add. It also might be nice to start using sammy.js, if anyone feels like a more ambitious patch. Feedback and patches welcome! Chris -- Chris Anderson http://jchrisa.net http://couch.io
|View raw message


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For lower income households it's a different story. Millions of the working poor are helped by Social Security's progressive benefits. At the same time, though, a work- and earnings-based pension system doesn't do much to help people without a lot of work and earnings. And these days, poverty in retirement is often a function, not of a long career at low wages, but simply of sporadic attachment to the labor force. Those with short work histories will receive lower Social Security benefits and, sometimes, don't qualify for benefits at all. In the bottom fifth of the population, about 20 percent don't even qualify for Social Security benefits at retirement. And of Americans who do qualify, about one-third receive a benefit that's below the poverty line.So overall, we're displacing a lot of private savings and charging higher taxes than we have to for a program that's not helping the truly poor as much as it could. About 10 percent of older Americans currently live in poverty, despite spending roughly $700 billion on Social Security retirement benefits. We could provide a poverty-level Social Security benefit to every retiree for about half of what the current program costs.And that's basically what I propose, to gradually shift from our earnings-based Social Security model to something similar to the retirement programs in New Zealand and the new program in the United Kingdom, with some similarities to the programs in Canada and Australia as well. Over time, Social Security would transition to paying a universal, flat dollar benefit to every long-term US resident. The benefit would be set at the single, over-65 poverty threshold, which is currently about $850 per month. No one would get below this amount, and the over 65 poverty rate would almost immediately go from about 10 percent to something close to zero percent. This flat benefit would increase benefits for about the bottom third of Social Security beneficiaries. The benefit level would be indexed to wage growth, so it would maintain poverty protections relative to the living standards of the day.Yet while no one would receive a benefit below the poverty line, no one would get a benefit above the poverty threshold either. Once phased in, everyone would receive that same benefit. So while the bottom third would receive benefit increases, the top two third would receive benefit cuts, at least relative to what Social Security has promised. Cuts would be modest for people at the middle of the earnings distribution, but substantial for people with very high earnings.Those middle and higher income households would need to save more on their own, and we would implement policies to facilitate that saving. For instance, all employers offering 401(k) plans should automatically enroll their employees, a step that can dramatically increase participation. Likewise, small businesses should be allowed to band together to run 401(k)s, a step that would lower the fixed costs and regulatory burdens that cause many small employers not to offer retirement plans.While I'm not outright opposed to supplemental retirement savings plans being proposed by state governments in California, Illinois and other states, these are a second-best solution: these so-called "Secure Choice" plans have low contribution limits and no employer match, so the typical savings each year would be less than half what the typical 401(k) participant puts away. Plus, to be frank, I don't totally trust state governments that have made such a hash out of their own public employee retirement plans.As I said, these benefits changes would be made gradually, not overnight. And here I was guided by a simple and fair concept: to not reduce the Social Security benefits that Americans have already earned. Pension law governing the private sector says that an employer can alter the rate at which employees earn future benefits, but the benefits employees have already earned must be paid. A similar principle should govern with Social Security. It's one thing to say that we must change the rate at which we earn future benefits. People understand that the system isn't financially sustainable and that we either must increase tax rates or change the rates at which we pay benefits in the future. But Americans resist the idea that a benefit that they've already earned will be taken away from them. So I calibrated the phase-in of the transition to the flat benefit in such a way that, at least to a decent approximation, Americans will not have Social Security benefits they've already earned taken away from them.This flat benefit approach would effectively eliminate poverty in retirement, at least for long-term US residents. Immigrants would receive a guaranteed benefit pro-rated to the time they've lived in the country, using the same scale that Canada employs for its own minimum retirement benefit. But higher earners would have to save more and I'm confident they would save more. Overall, this approach would bring Social Security back to sustainable solvency without massive tax increases, while strengthening the safety net and leaving room in the budget for health care, welfare programs and other priorities.Andrew Biggs is a resident scholar at the American Enterprise Institute. He works on retirement policy, public sector pay and other issues.(c)2016, Andrew Biggs Used by permission. This column originally appeared in Forbes magazine.Opinions expressed are those of the author, and do not necessarily reflect the views of ASPPA or its members.
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Norcross, Georgia (PRWEB) September 19, 2016
EB Medicine will showcase its new risk reduction CME resource, ED CLEAR™ (Clinical Learning to Eliminate Avoidable Risk), October 16-19 at the ACEP Scientific Assembly 2016 in Las Vegas. The program employs data and evidence-based learning materials that prompt critical thinking and limit liability, resulting in improved resource utilization, fewer missed diagnoses, and reduced claims and malpractice costs.
"We are proud to add risk reduction to the spectrum of practical, evidence-based CME we offer to emergency clinicians," says EB Medicine CEO Stephanie Williford. "Our goal is to produce educational resources that empower physicians to provide the best possible care and improve patient outcomes, and in so doing we are also promoting the health of the field of emergency medicine at large."
ED CLEAR's blended learning modules include three key components:
1. A video featuring John Bedolla, MD, a practicing emergency physician who specializes in risk management: Dr. Bedolla monitors and researches all major malpractice cases involving EDs nationwide to determine high-impact topics. He interviews experts about how to diagnose, treat, and document high-risk conditions such as TIAs, testicular torsion, and appendicitis, with an emphasis on clinical decision-making methods proven in practice.
2. An evidence-based journal article to further inform and reinforce the video content: Each article is subject to peer review and the same rigorous quality standards upheld by EB Medicine, publisher of Emergency Medicine Practice and Pediatric Emergency Medicine Practice.
3. A CME test: Each article, in combination with the corresponding video segment, qualifies for 4.5 CME credits upon passing the test. The six-module annual series carries 27 CME credits.
ED CLEAR is designed for implementation across a group or within a hospital or health system to ensure the consistency of practice that can establish a culture of patient safety and yield measurable results. "Our participation in ED CLEAR education and protocols has undoubtedly reduced our medical malpractice exposure," says Todd Nash, MD, Medical Director, Emergency Department, Seton Northwest Hospital, Austin, TX. "Safer practice environments benefit doctors and patients and payors. ED CLEAR is clinical, well-researched, broadly applicable, and proven."
Another benefit of ED CLEAR is that the program instructs clinicians on how to optimize resource utilization. "As doctors, we are better at 'yes' and 'no' than 'maybe'," says Dr. Bedolla. "The strategies we cover in ED CLEAR clarify the gray areas and bring enlightenment to clinical decision-making so we can order the right tests and labs, in the right order, at the right time."
Dr. Bedolla and other ED CLEAR representatives will be available for comment and/or to demonstrate the features of ED CLEAR in Booth S1913 in the exhibit hall at the ACEP Scientific Assembly. To schedule a meeting or product demonstration, contact Susan Woodard (susan(at)ebmedicine.net; 678-366-7933, ext. 104). For more information on ED CLEAR™, visit http://www.ebmedicine.net/EDC.
About EB Medicine
EB Medicine is the premier provider of evidence-based clinical content and CME resources for emergency medicine practitioners. Delivered in print, digital, and mobile formats, publications and programs include ED CLEAR, Emergency Medicine Practice, Pediatric Emergency Medicine Practice, the Lifelong Learning and Self-Assessment Study Guide, Emergency Trauma Care, and Emergency Stroke Care: Advances and Controversies. EB Medicine's resources address real challenges in diagnosis and treatment and give actionable recommendations based upon the latest research and best available evidence. These resources provide ongoing education and guidance to physicians, residents, physician assistants, and nurse practitioners. For more information, visit http://www.ebmedicine.net.
EB Medicine is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for clinicians.
Susan Woodard
Director of Business Development
EB Medicine
(676) 366-7933


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*This is a sponsored post brought to you by G5 games – The Secret Society and Sverve.com
I have said it before and I will say it again, I have always been a gamer. I also married a gamer and yes, my kids are quickly becoming gamers too. I don't think that there is anything wrong with gaming, as long as it is done in moderation and it doesn't take over. I also think it's fantastic when games can bring family members together and foster team work like The Secret Society – Hidden Mystery did for us.
At first, it was just going to be me that tested and played this awesome hidden object game. However, almost instantly after I turned it on, the graphics and sounds caught my kids attention! They watched me play at first and then, they wanted to play more and more.
After playing through the game for a bit and determining that it was, indeed, family friendly, I decided to let me kids have a go at it.
My son loves all of the puzzle box games and my daughter loves collecting coins when she finds objects!
Here is the best part:
They will work together to complete rooms without fighting! I love when a game is family safe, fosters teamwork and truly offers some mental stimulation and focus.
I have also said in the past, "The family that plays together, has fun forever!".
The Secret Society – Hidden Mystery is free to download and free to play. There is no pressure to buy anything. It is also very easy to install and begin playing. The instructions are very straight forward and laid out for you from the beginning, so I think this is a game that truly anyone can get into!


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Kathryn Jean Lopez is editor-at-large of National Review Online and a nationally syndicated columnist.
I would also like to encourage parents to pray for vocations to come from within their own families: I read about a town in Italy called Lu, in which a number of mothers got together to pray for vocations, and they got quite a lot of them. This is a variation of the prayer they said:
O God, grant that one of my children may become a priest or religious!
I myself want to live as a good Christian
and want to guide my children always to do what is right,
so that I may receive the grace, O God, to be allowed to give you a holy priest or religious! Amen"
We have prayer ministries for vocations at our parish: one meets monthly to do prayer and adoration for the priests of our diocese, and another involves having one family take a 'vocation cross' for the week, and praying daily that week for an increase in vocations. They then return it to the church (at a side altar) for the next family to pick up.
Funny story - I remember some years ago that there was no one praying for vocations for a particular week, so I thought I'd silently do the prayers (I didn't know what they were, so I just said something simple, I don't even remember what), and well, long story short, one of my sons is now a first year seminarian at Mt. St. Mary's in Emmitsburg...
(That was not how I'd planned things to come out - I thought it would be someone *else's* vocation somewhere else!)
Looks interesting. I may buy this & put it away for a few years til my 3 yr old is a little bigger