Low phosphorus supply constrains plant responses to elevated CO 2 : A meta-analysis

Phosphorus (P) is an essential macro-nutrient required for plant metabolism and growth. Low P availability could potentially limit plant responses to elevated carbon dioxide (eCO ), but consensus has yet to be reached on the extent of this limitation. Here, based on data from experiments that manipulated both CO and P for young individuals of woody and non-woody species, we present a meta-analysis of P limitation impacts on plant growth, physiological, and morphological response to eCO . We show that low P availability attenuated plant photosynthetic response to eCO by approximately one-quarter, leading to a reduced, but still positive photosynthetic response to eCO compared to those under high P availability. Furthermore, low P limited plant aboveground, belowground, and total biomass responses to eCO , by 14.7%, 14.3%, and 12.4%, respectively, equivalent to an approximate halving of the eCO responses observed under high P availability. In comparison, low P availability did not significantly alter the eCO -induced changes in plant tissue nutrient concentration, suggesting tissue nutrient flexibility is an important mechanism allowing biomass response to eCO under low P availability. Low P significantly reduced the eCO -induced increase in leaf area by 14.3%, mirroring the aboveground biomass response, but low P did not affect the eCO -induced increase in root length. Woody plants exhibited stronger attenuation effect of low P on aboveground biomass response to eCO than non-woody plants, while plants with different mycorrhizal associations showed similar responses to low P and eCO interaction. This meta-analysis highlights crucial data gaps in capturing plant responses to eCO and low P availability. Field-based experiments with longer-term exposure of both CO and P manipulations are critically needed to provide ecosystem-scale understanding. Taken together, our results provide a quantitative baseline to constrain model-based hypotheses of plant responses to eCO under P limitation, thereby improving projections of future global change impacts.