Plant biomass responses to elevated CO2 are mediated by phosphorus uptake

Elevated atmospheric CO2 concentrations [CO2] potentially alter carbon (C) and phosphorus (P) cycles in terrestrial ecosystems. Although numerous field experiments and a few meta-analyses have been conducted, it is still largely un-clear how the P cycle affects plant biomass responses under elevated [CO2] globally. Here, we conducted a global syn-thesis by analyzing 111 studies on the responses of above-and belowground P cycling to elevated [CO2], to examine how changes in the P cycle affect the plant biomass response to elevated [CO2]. Our results show that elevated [CO2] significantly increased plant aboveground biomass (+13 %), stem biomass (+4 %), leaf biomass (+11 %), below -ground biomass (+12 %), and the root: shoot ratio (+7 %). Effects of elevated [CO2] on aboveground biomass, below -ground biomass, and root: shoot ratio were best explained by plant P uptake. In addition, elevated [CO2]-induced changes in the aboveground P pool, leaf P pool, and leaf P concentration were modulated by ecological drivers, such as Delta CO2, experimental duration, and aridity index. Our findings highlight the importance of plant P uptake for both above-and belowground plant biomass responses under elevated [CO2], which should be considered in future biosphere models to improve predictions of terrestrial carbon-climate feedbacks.