Enhanced water-use efficiency mediates the synergistic effects of nitrogen and phosphorus enrichment on grassland productivity

By combining a global meta-analysis of nutrient-addition experiments with a five-year field experiment in the Inner Mongolia grassland, we show that combined N and P addition synergistically increases both community aboveground net primary productivity (ANPP) and ecosystem WUE. The synergistic responses of ANPP are primarily driven by enhanced WUE, as indicated by the strong coupling between the N–P interactive effects on ANPP and those on WUE. Shifts in community structure—reflected by an increased grass/forb ratio—serve as a bridge linking nutrient-induced soil environmental changes to improvements in WUE.