Effects of nitrogen deposition and increased precipitation on soil phosphorus dynamics in a temperate forest

Nitrogen (N) deposition has increased dramatically since the industrial revolution due to anthropogenic activities. Meanwhile, global mean precipitation was predicted to rise. Although these two global change factors are co-occurring naturally, rare studies were contributed to understand how N deposition and increased precipitation interactively affect soil phosphorus (P) dynamics. In the present study, we conducted a novel canopy N and water addition experiment to investigate the effects of N deposition, increased precipitation, and their interactions on soil P dynamics in a temperate forest. We found that soil primary mineral P was significantly reduced after six years of canopy N deposition mainly due to N-induced soil acidification. Along with the reduction of primary mineral P, soil secondary mineral P was increased with N deposition due to increased exchangeable Al and Fe. Soil organic P associated with Al and Fe, microbial biomass P and phosphatase activity were also increased by N deposition. Our results also revealed that soil primary mineral P was reduced, and secondary mineral P was increased by increased precipitation. Increasing precipitation also significantly prompted soil microbial biomass P, which could explain the increase of soil secondary mineral organic P. In addition, we also found there were interactive effects between N deposition and precipitation on soil primary mineral P and secondary mineral organic P. The effect of N on these properties was strengthened by precipitation increase. Collectively, our results suggest that N deposition and increased precipitation can shift the composition of soil P fractions and drive the depletion of the primary mineral P. Thus, these two global change factors could synergistically affect soil P dynamics.