Potential effects of warming on soil respiration and carbon sequestration in a subtropical forest

Subtropical ecosystems are receiving unprecedented changes in temperature as a consequence of anthropogenic activities, which potentially affects soil respiration (R (s)) and carbon (C) sequestration. Due to the large amounts of C store and cycle in subtropical forests, investigations about how R (s) and C sequestration respond to warming will be critical for our understanding of future global-scale climate and biogeochemical cycling. In this study, we transferred soil samples and plant seedlings collected from a mixed forest to the growth chambers in two sites (300 m and 30 m a.s.l.), which induced an artificial warming of ca. 1 A degrees C between the two corresponding forest mesocosms. We tested whether the modification of abiotic factors induced by the downward translocation could alter R (s) and soil C sequestration. We also investigated the effects on the biotic factors by including root biomass and soil microbial biomass. Our results showed that R (s) was greater in the warm site than in the control site, which were related to the higher aboveground biomass, litterfall and root biomass. R (s) showed a significantly positive exponential relationship with soil temperature. The downward translocation tended to decrease soil C sequestration, which was attributed to the decreased C use efficiency of soil microorganisms and increased root growth under downward translocation. R (s) responded strongly to downward translocation, suggesting that climate warming exacerbated R (s) and tended to reduce soil C sequestration. The ability of subtropical forests to act as CO2 sink may be reduced under climate warming.