Regulation of carbon allocation and turnover on the responses of soil carbon storage to drought and irrigation
Global climate models project that future precipitation regimes will largely alter across the globe due to the intensification of the hydrological cycle, which may induce considerable impacts on terrestrial carbon (C) cycle. Although substantial manipulative experiments had been conducted to probe the responses of ecosystem C processes to altered precipitation, how soil C storage responds to both drought and irrigation is still unclear across biomes and the globe. In this study, a meta-analysis of 179 published studies was carried out to examine responses of soil C storage and associated fluxes to drought and irrigation.
Our results show that drought and irrigation similarly induced minor increases in soil C pool (SCP) by 1.45% and 1.27%, respectively, despite of the opposite effects on both C fluxes and plant C pools. The drought-induced increase in root: shoot ratio, decreases in heterotrophic respiration (Rh) and lower soil-C turnover resulted in minor increase in SCP, while the similar increase in SCP by irrigation may be attributed to increase in newly fixed C inputs in soil. In addition, the relative changes in precipitation were positively correlated with response ratios of plant C pool, net primary production, microbial biomass C, ecosystem and soil respiration, and Rh. These results indicate that more attention should be paid to the responses of C allocation between aboveground and belowground to drought and irrigation, which should be incorporated into land surface models to better project effects of precipitation change on C turnover and risk in terrestrial ecosystems.