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 C hina. Soil inorganic N concentrations and rates of N mineralization, nitrification, nitrous oxide ( N 2 O ) 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 N 2 O 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 N 2 O 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.