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[Responses of non-structural carbohydrates content in leaves of different plant species in Pinus tabuliformis plantation to nitrogen addition].

Through its impact on plant physiological processes, global nitrogen deposition could alter the structure and composition of forest ecosystems. However, we are not clear about the effects of N deposition on leaves' non-structural carbohydrate (NSC) content of different plants. In this study, we compared the responses of NSC contents in seven different plant species to four nitrogen addition levels (0, 3, 6, and 9 g N·m-2·a-1, referred to as N0, N3, N6, N9, respectively), including Pinus tabuliformis, Quercus liaotungensis, Lonicera japonica, Spiraea salicifolia, Rosa xanthina, Rubia cordifolia, and Carex lanceolata in an artificial Pinus tabuliformis forest located in the hilly area of the Loess Plateau. The contents of soluble sugar and starch varied greatly in plant species, with the highest variability in R. xanthina and the lowest in S. salicifolia and C. lanceolata. There were significant differences in the responses of soluble sugar and starch contents to nitrogen addition among different species. Under N6 treatment, the variability of soluble sugar and starch in R. cordifolia came the first while S. salicifolia exceeded all other species under N3 and N9 treatments on that rating. The specific species with the lowest variability of soluble sugar and starch contents differed with nitrogen addition levels. With the increases of nitrogen addition rate, the soluble sugar content of P. tabuliformis and C. lanceolata exhibited a continuous rising trend, an opposite trend of S. salicifolia, while that of Q. liaotungensis, L. japonica, and R. xanthina decreased first and then increased, reaching its minimum at N6 treatment. The response of R. cordifolia to nitrogen addition was complex. With respect to starch content, P. tabuliformis, L. japonica and C. lanceolata showed a continuous increase trend with nitrogen addition whereas S. salicifolia decreased first and then increased, troughing at N3 treatment. R. xanthina and R. cordifolia responded complicatedly yet Q. liaotungensis appeared less responsive. Under N addition treatments, there was no explicit correlation between NSC content and soil physical and chemical properties including pH, organic carbon, total nitrogen and phosphorus. There was a significant influence of those soil properties on the soluble sugar/starch ratio under N0 or N3 treatment. Our results indicate that different species have obviously different responses of NSC to nitrogen addition. Future research concerning the impacts of global nitrogen deposition on forest ecosystems should take into account the target species, especially to pay attention to the responses of vegetation with different life forms.