Interactive effects of nitrogen and phosphorus additions on plant growth vary with ecosystem type

Aims Co-limitation of ecosystem productivity by nitrogen (N) and phosphorus (P) is gaining increasing recognition, but how co-limitation through N and P interactions differs among different terrestrial ecosystems remains unclear. Methods We performed a meta-analysis of 133 independent studies conducted in four natural terrestrial ecosystems to examine the interactive effects of N and P additions on ten plant growth-related variables. Results Adding N and P individually or in combination significantly increased aboveground biomass (AGB), and the interactions were uniformly synergistic for AGB, and additive for belowground biomass (BGB), but variable for other eight growth-related variables among four different ecosystems. The interaction was synergistic for leaf P and soil NO3-N only in tropical forests, and antagonistic for soil available P (AP) in tropical forests, leaf N in grasslands, root P in wetlands, and leaf P and soil NH4-N in tundra. The interaction for leaf N: P ratios was additive only in tropical forests, and synergistic in the other three ecosystems. Conclusions Our results highlighted the interactions of N and P additions can promote uptake of both nutrients by plants, and plants tend to maintain the optimal nutrient balance for growth and reproduction through regulating biomass production and tissue nutrient concentrations.