摘要：The microbial respiration of ancient permafrost carbon represents a positive feedback to climate warming. However, warming-induced shrub expansion in circumpolar latitudes may partly offset these emissions, due to greater biomass and litter inputs than that of primary tundra vegetation. Quantifying this carbon sink is challenging as the simultaneous mineralization of ancient carbon renders the attribution of changes in soil carbon stocks uncertain. We measured the contribution of shrubs to the terrestrial carbon reservoir in a Low-Arctic region where ancient carbon stocks are among the lowest in the Arctic. The study site near the eastern shore of Hudson Bay is experiencing rapid Betula glandulosa Michx. expansion throughout lichen tundra. We find that the terrestrial carbon stocks(i.e. soil and vegetation) under a cover of low to medium-size shrubs is increased by 3.9 ± 1.3 kg m−2 , regardless of shrub cover age. Along water tracks, taller shrubs and the transition to moss understories provide an even greater increase in terrestrial carbon (6.5 ± 3.5 kg m−2 ). Using published maps of vegetation change from 1994 to 2010, we estimate that the carbon sink associated to shrub expansion in our study area (5.228 km2 ) has been 2.4 ± 0.8 Gg or 29 ± 9gm−2 yr−1 . Extrapolating this result to the Arctic requires additional studies in representative environments.
