Rain-induced changes in soil CO₂ flux and microbial community composition in a tropical forest of China

Rain-induced soil CO₂ pulse, a rapid excitation in soil CO₂ flux after rain, is ubiquitously observed in terrestrial ecosystems, yet the underlying mechanisms in tropical forests are still not clear. We conducted a rain simulation experiment to quantify rain-induced changes in soil CO₂ flux and microbial community composition in a tropical forest. Soil CO₂ flux rapidly increased by ~83% after rains, accompanied by increases in both bacterial (~51%) and fungal (~58%) Phospholipid Fatty Acids (PLFA) biomass. However, soil CO₂ flux and microbial community in the plots without litters showed limited response to rains. Direct releases of CO₂ from litter layer only accounted for ~19% increases in soil CO₂ flux, suggesting that the leaching of dissolved organic carbon (DOC) from litter layer to the topsoil is the major cause of rain-induced soil CO₂ pulse. In addition, rain-induced changes in soil CO₂ flux and microbial PLFA biomass decreased with increasing rain sizes, but they were positively correlated with litter-leached DOC concentration rather than total DOC flux. Our findings reveal an important role of litter-leached DOC input in regulating rain-induced soil CO₂ pulses and microbial community composition, and may have significant implications for CO₂ losses from tropical forest soils under future rainfall changes.