Aboveground net primary productivity mediates the responses of soil respiration to nutrient additions in two tropical montane rainforests

Abstract

Tropical forests play a dominant role in mediating carbon (C) dioxide exchange between the terrestrial biosphere and the atmosphere. Plant production and microbial decomposition in tropical ecosystems are generally considered to be limited by soil nutrients, especially soil phosphorus (P), but the impact of nutrient inputs on soil respiration is little reported. We measured soil respiration rate (Rs) and its autotrophic (Ra) and heterotrophic components (Rh) during 2012–2017 in the nutrient addition experiments conducted in a primary and secondary tropical montane forest in Mt. Jianfengling, South China. Nutrient addition did not affect Rh, but promoted Ra and Rs in these two forests. The actual nutrient responsible for Ra and Rs increases differed between the forests, with a significantly positive P effect in the primary forest and a significantly positive nitrogen (N) effect in the secondary forest. The Ra and Rs increases induced by nutrient additions were likely attributed to the stimulation of aboveground net primary productivity (ANPP) rather than other factors. These results suggested that the ANPP induced increases in both Ra and Rs varied with forest successional stages and nutrient types. Our findings provide compelling evidence that N and P inputs may promote soil respiration in tropical montane forests, which has an important implication for predicting soil C efflux in tropical forests under increasing atmospheric N and P depositions.