Plant biomass responses to elevated CO are mediated by phosphorus uptake.

Elevated atmospheric CO concentrations [CO] 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 unclear how the P cycle affects plant biomass responses under elevated [CO] globally. Here, we conducted a global synthesis by analyzing 111 studies on the responses of above- and belowground P cycling to elevated [CO], to examine how changes in the P cycle affect the plant biomass response to elevated [CO]. Our results show that elevated [CO] significantly increased plant aboveground biomass (+13 %), stem biomass (+4 %), leaf biomass (+11 %), belowground biomass (+12 %), and the root: shoot ratio (+7 %). Effects of elevated [CO] on aboveground biomass, belowground biomass, and root: shoot ratio were best explained by plant P uptake. In addition, elevated [CO]-induced changes in the aboveground P pool, leaf P pool, and leaf P concentration were modulated by ecological drivers, such as ΔCO, experimental duration, and aridity index. Our findings highlight the importance of plant P uptake for both above- and belowground plant biomass responses under elevated [CO], which should be considered in future biosphere models to improve predictions of terrestrial carbon-climate feedbacks.