Soil organic carbon (C) in deep soils is relatively recalcitrant and old with turnover times of hundreds to thousands of years, and constitutes the largest near-surface reservoir of terrestrial C. Thus, a long-term positive feedback to the climate would occur if global warming causes a continuous transfer of old C from terrestrial soils to the atmosphere. However, the influence of warming on the stability of old soil organic C has received little attention. In this study, we determined the warming effect on old, recalcitrant organic C decomposition by combining long-term (9 yr) in-situ field and short-term (9 wk) laboratory incubations.
Results/Conclusions
After in-situ incubation for 9 yr, warming of approximately 2°C significantly facilitated the loss of C with several thousand years old in the deep soil layer. Results from the 9 wk laboratory incubation showed that microbial communities associated with warming were more active, resulting in larger C losses. Coupled stable isotope probing and meta-genomic analysis indicated that warming-induced old C decomposition was closely related to changes in the functional structure of active microbial communities. Detailed examination on functional communities that are responsible for C degradation showed that warming increased the abundance of genes involved in C degradation among active populations of microbial communities, but had less effect on the overall microbial communities. Our findings suggest that warming may significantly reduce the size of the vast pool of old C in global soils and thus reinforce the positive feedback between the C cycle and climate through altering the functioning of active populations of soil microbial communities.