Warming and increased precipitation individually influence soil carbon sequestration of Inner Mongolian grasslands, China

The impact of climate change (i.e. warming and changes in precipitation patterns) on carbon (C) sequestration in the continental steppe is currently disputed and uncertain. We conducted a six-year field experiment in the temperate grassland ecosystem in Inner Mongolia, China. We found that C storage in the 0-30 cm soil layer significantly decreased by 129.3 g C m(-2) under warming (W) but significantly increased by 145.9 g C m(-2) with increased precipitation (P), with no apparent interaction of W x P. The effects of W and P on soil C sequestration varied in different soil fractions (labile vs. recalcitrant soil organic matter) and layers (topsoil vs. subsoil), which complicated the prediction of the short- and long-term effects of soil C sequestration in climate change scenarios. Furthermore, C:nitrogen (N) ratios in soils with increasing C and N were asynchronous under W, P, and W + P treatments, suggesting that the limiting effect of N on soil C sequestration would be intensified under W with P conditions. Our findings suggest that, without an increase in precipitation or concurrent P and W, the semiarid Inner Mongolian grasslands may potentially act as a net C source in the future. (C) 2012 Elsevier B.V. All rights reserved.