Phosphorus addition affects soil nitrogen dynamics in a nitrogen-saturated and two nitrogen-limited forests

Phosphorus (P) availability can affect nitrogen (N) dynamics in forest soil, and this effect might depend largely on the soil N status of forest ecosystems. So far, however, this view has not been well tested among forests with contrasting N status. Here, we used a 6-year experiment with additions of N and P to evaluate the effects of P availability and its interaction with N availability on soil N dynamics in one N-saturated and two N-limited tropical forests in southern China. Soil inorganic N concentrations and rates of N mineralization, nitrification, nitrous oxide (N2O) emission and nitrate leaching were measured. Our results showed that addition of P alone changed soil N dynamics in the N-saturated forest only; it accelerated rates of soil N transformation and decreased rates of N2O emission and nitrate leaching, but had no significant effects on N dynamics in the two N-limited forests. Furthermore, compared with the addition of N alone, addition of both N and P caused significant increases in the rates of net N mineralization and nitrification and a significant decrease in N2O emission in the two N-limited forests. Our results suggest that P availability stimulates soil N dynamics only when the ecosystem is saturated with N or there is considerable N deposition. Highlights We compared the effects of P addition on soil N dynamics among forests with different N status. Addition of P alone changed N dynamics in the N-saturated forest, but not in N-limited forests. Combined N and P additions had a larger effect on N dynamics than N addition alone. Phosphorus addition affects N dynamics only when an ecosystem has considerable N status.