Long-term increase in rainfall decreases soil organic phosphorus decomposition in tropical forests

Increased rainfall may affect soil phosphorus (P) cycling in tropical forest ecosystems, yet the key biotic and abiotic factors that govern soil organic P transformations remain unclear. In this study, we conducted a long-term (7 years) rainfall manipulation experiment in the field to examine the effects of increased rainfall (+25%) in the wet season on soil P dynamics in a tropical forest. We found that an increase in rainfall in the wet season enhanced the maximum P adsorption capacity of forest soil as a result of a greater availability of soil organic matter and organic iron (Fe)/aluminum (Al) oxides. Newly formed stable ternary complexes between soil organic matter, metals (Mn, Mg and Ca) and P increased the surface adsorption of soil organic P. Moreover, the alkaline phosphomonoesterase (ALP) activity was reduced under our experimental treatment owing to a decrease in the abundance of both ALP-producing bacteria (Bradyrhizobium and Methylobacterium being the dominant genera) and bacterivores (Rhabditis and Acrobeloides). Our findings demonstrated an overall negative impact of elevated rainfall in wet season on soil organic P decomposition in tropical forests through the enhancement of soil P adsorption capacity and the inhibition of soil ALP activities. Our results implied that a long-term rainfall increase in the wet season could increase soil organic P accumulation, which in turn further reduce soil P availability for plant uptake in the tropical forests.