Drought-induced turnover of soil microbial biomass increases nutrient subsidies for the reproduction of tropical forest

Abstract

El Niño-induced drought, which is intensified by climate change, can have huge impacts on soil microbial biomass and plant productivity in tropical forests. We tested whether drought-induced turnover of soil microbial biomass can be a potential source of phosphorus (P), the limiting nutrient, for the reproduction of tropical forest trees (mast fruiting). We measured the seasonal variations in soil microbial biomass P and soil solution P concentrations including the periods before and after drought in a dipterocarp forest in Indonesia. Drought resulted in a decrease in soil microbial biomass C, N, and P, followed by a recovery after re-wetting. There was a sharp peak of soil solution P concentrations during the drought. The significant difference between soil microbial biomass P before and after drought amounted to 2.0 kg P ha−1. The potential P release from microbial turnover is not negligible compared to the additional P demand for fruit production (1.0 kg P ha−1) as well as the annual demand for litter production (2.5 kg P ha−1 year−1). In addition to the accumulation of nutrients for several non-fruiting years and their re-distribution in tree biomass, drought-induced microbial turnover can be nutrient subsidies for dipterocarp reproduction in highly-weathered soils.