Tropical forests play an important role in global carbon (C) cycling due to high primary productivity and rapid litter and soil organic C decomposition. However, it is still unclear how changing rainfall will influence soil CO2 losses (i.e. via soil respiration) in tropical forests. Here, we conducted a rainfall manipulation experiment in a tropical forest to study the effects of changing rainfall amount, frequency and intensity on soil respiration. We hypothesized that the responses of soil respiration to rainfall changes were regulated, at least partly, by rain-induced litter dissolved organic carbon (DOC) inputs. To test this hypothesis, we added litter treatments (including “litter intact” and “litter removal”) nested within the rainfall treatments.
Results showed that a 50% increase in rainfall frequency (no change in total rainfall amount) enhanced inputs of DOC by 28%, total dissolved nitrogen (TDN) by 17%, and total dissolved phosphorus (TDP) by 34 % through leaching from litter layer to soil surface, and stimulated soil respiration by ~17% (about 1.16 t C ha-1 yr-1). A 50% reduction in total rainfall (no change in rainfall frequency) did not change litter-leached DOC and nutrients fluxes, or annual mean soil respiration rates. Soil respiration also rapidly increased by ~83% after rains, but it in the plots without litters showed limited response to rains. In addition, rain-induced changes in soil respiration 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 soil respiration variations, and may have significant implications for CO2 losses from tropical forest soils under future rainfall changes.