Plant growth in terrestrial ecosystems is commonly limited by nitrogen (N) or phosphorus (P). At high latitudes, temperature is low, soil N mineralization is also low, and plant growth is often limited by available N. In tropical forests on old soils, available soil P is low, and plant growth is often limited by P.

In recent years, co-limitation of ecosystem productivity by N and P is gaining increasing recognition, but this conclusion is mainly based on the response of plant biomass, and how co-limitation through N and P interactions differs among other growth-related variables (eg. plant N or P concentration) or different terrestrial ecosystems remains unclear. 

JIANG Jun, a postdoctoral researcher from South China Botanical Garden of the Chinese Academy of Sciences, 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 showed that 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. 

This study 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. 

This study entitled "Interactive effects of nitrogen and phosphorus additions on plant growth vary with ecosystem type" was published online recently in Plant and Soil.

This study was supported by the National Science Fund for Distinguished Young Scholars. 

Figure. Structural equation model (SEM) analysis of multivariate relationships among nutrient addition, response ratio (RR) of growth-related variables, MAT, MAP and experimental duration in terrestrial ecosystems. (Image by SBG)