Effects of nutrient additions on litter decomposition regulated by phosphorus-induced changes in litter chemistry in a subtropical forest, China

Nutrient additions directly alter exogenous nutrient availability in soil, and then affect endogenous nutrient concentration in litter (i.e., litter chemistry), modifying litter decomposition. However, how nutrient-induced changes in litter chemistry interacting with altered soil nutrients affect litter decomposition remain unclear. In this study, three field experiments with reciprocal transplants using litter bags were conducted in a phosphorous (P) limiting subtropical forest with control, nitrogen addition (+N), P addition (+P), and +NP treatments to examine effects of exogenous and endogenous nutrient availability on litter decomposition. Our results showed that, in Experiment I, decomposition of litter collected from the control plots was significantly inhibited by 16% under both +P and +NP treatments and reversed to become net P accumulation from P release compared to that in the control. In Experiment II, since litter collected from +P and +NP plots had higher litter P, lower C/P and N/P, its decomposition was significantly faster in the control plots by 9% and 26%, respectively, with the faster release of N and P in the litter. The in situ Experiment III found that +P and +NP treatments reduced litter decomposition by 6% and 14%, respectively, but +N did not affect it compared to the control. Our results indicate that effects of P addition on litter decomposition were mediated by P-induced changes in litter chemistry, which need to be incorporated into land surface models for predicting effects of nutrient deposition on ecosystem C cycling and assessing the climate-biosphere feedbacks. Main finding Effects of nutrient additions on litter decomposition were regulated by P-induced changes in litter chemistry.