Autotrophic and heterotrophic soil respiration responds asymmetrically to drought in a subtropical forest in the Southeast China

Both increasing frequency of drought and drought duration are expected for many terrestrial ecosystems under on-going climate change. However, our understanding of the drought effect on soil respiration (R-s), which comprises the second largest carbon (C) flux of the global C cycle, remains limited. To explore the effects of reduced precipitation on Rs and its components, we conducted an experiment of throughfall rainfall exclusion during two consecutive growing seasons in a subtropical forest in the Southeast China. Following throughfall exclusion R-s declined rapidly, and did not recover until three to four months following rewetting, in both 2014 and 2015. During the experiment, throughfall exclusion significantly reduced autotrophic soil respiration (R-a); however, heterotrophic soil respiration (R-h) was unaffected, resulting in a reduced contribution (R-a/R-s) from 33 +/- 1% for the control to 16 +/- 3% under throughfall exclusion. Experimental drought significantly reduced soil microbial C and fine root biomass, and subsequent to rewetting, soil microbial C recovered quickly, but fine root biomass relapsed slowly. Our results suggested that prolonged drought decreases R-s through modifications in soil microbial activities and fine root metabolic capacity, which are induced by reduced soil water availability. Moreover, our results imply that drought-induced reductions in R-s originate primarily from R-a. Our results highlight the need to account for asymmetric responses to drought between R-a, and R-h when predicting the reaction of the ecosystem C balance in response to future drought events.