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Spatial variability in carbon dioxide exchange processes within wet sedge meadows in the Canadian High Arctic

Wet sedge meadows are the most productive plant communities in the High Arctic. However, the controls on carbon dioxide (CO2) exchange processes within wet sedge communities – and the scale at which they operate – are poorly understood. Here, the factors controlling CO2 exchange of wet sedge meadows experiencing different moisture regimes are examined. Environmental data are used to create predictive models of CO2 exchange on multiple temporal scales. Automated chamber systems recorded CO2 fluxes at 30-minute intervals at wet sedge sites in the Canadian High Arctic from June to August in 2014 and 2015. Static chambers were also deployed over a larger spatial extent in 2014. Our results show that wet sedge communities were strong CO2 sinks during the growing season (−7.67 to −44.36 g C·m). CO2 exchange rates in wetter and drier areas within wet sedge meadows differed significantly (Wilcoxon, p<0.001), suggesting that soil moisture regimes within vegetation types influence net CO2 balance. Random Forest models explained a significant amount of the variability in CO2 flux rates over time (R=0.46 to 0.90). The models showed that the drivers of CO2 exchange in these communities vary temporally. Variable moisture regimes indirectly influenced CO2 fluxes given that they exhibit different vegetation and temperature-response characteristics. We suggest that the response of a single vegetation type to environmental changes may vary depending on microenvironment variability within that community.