Changes in net ecosystem exchange of CO_(2)in Arctic and their relationships with climate change during 2002-2017

Arctic wanning leads to permafrost degradation,which can increase ecosystem respiration and release more greenhouse gas into the at-mosphere.Meanwhile,climate warming also promotes the plant growth and increases carbon assimilation.Presently,it is largely unknown about the carbon budget and their responses to climate change in the Arctic regions.In this study,to investigate the seasonal and annual net ecosystem carbon exchange(NEE),we collected 71 observation stations for net ecosystem exchange(NEE)of CO_(2)in the high latitude permafrost regions during 2002-2017.The results showed that the annual NEE was-8.2±4.1 g CO_(2)m^(-2)d^(-1)for forest,-3.3±2.6 g CO_(2)m^(-2)d^(-1)for shrub,-4.8±4.1 g CO_(2)m^(-2)d^(-1)for grassland,-3.6±3.0 g CO_(2)m^(-2)d^(-1)for wetland and 0.02±0.62 g CO_(2)m^(-2)d^(-1)for tundra,respectively.From 2002 to 2017,the CO_(2)emissions of grassland(carbon source)showed a decreasing trend,and the CO_(2)assimilation of shrub and forest(carbon sink)has been increased.The wetland and tundra are shifting from carbon sources to sinks.There were great variations in temperature sen-sitivities(Q10)of NEE in different seasons,with larger values in winter and lower values in summer.These findings indicate that the Arctic terrestrial ecosystem presently acts as a carbon sink,while there is a possibility that future warming,especially the warming in winter,may decrease the carbon sink of the Arctic terrestrial ecosystem.