Controls over carbon storage and turnover in high-latitude soils

Despite the importance of Arctic and boreal regions in the present carbon c ycle, estimates of annual high-latitude carbon fluxes vary in sign and magn itude. Without accurate estimates of current carbon fluxes from Arctic and boreal ecosystems, predicting the response of these systems to global chang e is daunting. A number of factors control carbon turnover in high-latitude soils, but because they are unique to northern systems, they are mostly ig nored by biogeochemical models used to predict the response of these system s to global change. Here, we review those factors. First, many northern sys tems are dominated by mosses, whose extremely slow decomposition is not pre dicted by commonly used indices of litter quality. Second, cold temperature , permafrost, waterlogging and substrate quality interact to stabilize soil organic matter, but the relative importance of these factors, and how they respond to climate change, is unknown. Third, recent evidence suggests tha t biological activity occurring over winter can contribute significantly to annual soil carbon fluxes. However, the controls over this winter activity remain poorly understood. Finally, processes at the landscape stale, such as fire, permafrost dynamics, and drainage, control regional carbon fluxes, complicating the extrapolation of site-level measurements to regional scal es.