Effects of nitrogen-phosphorus imbalance on plant biomass production: a global perspective

Background and aimsUnparalleled inputs of anthropogenic nitrogen (N) and phosphorus (P) cause a strong N-P imbalance in terrestrial ecosystems. However, the effects of N-P imbalance on plant biomass production remains unclear.MethodsGiven that tissue N:P ratio may serve as an indicator of plant N or P limitations, we compiled a dataset reporting aboveground biomass (AGB) and tissue N:P ratio simultaneously from worldwide N addition experiments and explored the relationship between the responses of AGB and tissue N:P ratio to N enrichment.ResultsThe N-induced changes in AGB exhibited an asymptotic relationship (i.e., Michaelis-Menten function) with changes in tissue N:P ratio, indicating a progressive P limitation with increasing N. Our results further revealed that plant N and P status was related to the changes in soil inorganic N and P concentrations. Soil N increased while soil P remained unchanged with increasing N rate, thus resulting in an unbalanced soil N and P as N continues to increase.ConclusionsThis study is the first to report the influences of human-induced N-P imbalance on plant biomass production at the global scale. The biomass-N:P ratio relationship needs to be considered for reliable predictions of the future global carbon dynamics under global change.