Independent and interactive effects of N and P additions on foliar P fractions in evergreen forests of southern China

Fertilization or atmospheric deposition of nitrogen (N) and phosphorus (P) to terrestrial ecosystems can alter soil N (P) availability and the nature of nutrient limitation for plant growth. Changing the allocation of leaf P fractions is potentially an adaptive strategy for plants to cope with soil N (P) availability and nutrient-limiting conditions. However, the impact of the interactions between imbalanced anthropogenic N and P inputs on the concentrations and allocation proportions of leaf P fractions in forest woody plants remains elusive. We conducted a meta-analysis of data about the concentrations and allocation proportions of leaf P fractions, specifically associated with individual and combined additions of N and P in evergreen forests, the dominant vegetation type in southern China where the primary productivity is usually considered limited by P. This assessment allowed us to quantitatively evaluate the effects of N and P additions alone and interactively on leaf P allocation and use strategies. Nitrogen addition (exacerbating P limitation) reduced the concentrations of leaf total P and different leaf P fractions. Nitrogen addition reduced the allocation to leaf metabolic P but increased the allocation to other fractions, while P addition showed opposite trends. The simultaneous additions of N and P showed an antagonistic (mutual suppression) effect on the concentrations of leaf P fractions, but an additive (summary) effect on the allocation proportions of leaf P fractions. These results highlight the importance of strategies of leaf P fraction allocation in forest plants under changes in environmental nutrient availability. Importantly, our study identified critical interactions associated with combined N and P inputs that affect leaf P fractions, thus aiding in predicting plant acclimation strategies in the context of intensifying and imbalanced anthropogenic nutrient inputs.