| Summary: | 2013 Summer. Includes bibliographical references. Cold, wet conditions limit microbial activity in many parts of the Arctic tundra, resulting in slow decomposition of soil organic matter, low nitrogen (N) mineralization rates and the accumulation of massive amounts of soil organic carbon (SOC). Climate change is currently reducing these physical environmental constraints, allowing for Arctic SOC to become vulnerable to decomposition. However, historically low decomposition rates due to climatic inhibition have resulted in soils with extremely poor nutrient availability in the active soil layer for much of the year further inhibiting ecosystem productivity and limiting microbial decomposition. N limitation of both primary productivity and microbial activity, in addition to extremely low soil N availability throughout much of the active season, make many Arctic tundra ecosystems among the most N limited in the world. Changing climatic conditions can potentially allow for increased annual N mineralization resulting in greater soil N availability. Enduring increases in soil N availability would alter microbial driven biogeochemical cycles with cascading long-term effects on Arctic tundra ecosystems. Despite previous experimental findings of N limitation of microbial decomposition in Arctic tundra, seasonal variability in soil N availability in conjunction with the influences of other soil factors indicate that N may not be the primary control of microbial activity in these soils during the entirety of the Arctic active season. The tight coupling of biogeochemical cycles suggests that labile carbon (C) may be co-limiting for portions of the active season when there is greater soil N available. Furthermore, most observations of N stimulation of microbial activities have originated from relatively few research sites due to the inaccessibility of much of the Arctic, but N limitation of decomposition may be site dependent and vary across small geographic areas. Questions of inter-annual and intersite variability of ...
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