Plant growth responses to elevated atmospheric CO(2) are increased by phosphorus sufficiency but not by arbuscular mycorrhizas

Capturing the full growth potential in crops under future elevated CO(2) (eCO(2)) concentrations would be facilitated by improved understanding of eCO(2) effects on uptake and use of mineral nutrients. This study investigates interactions of eCO(2), soil phosphorus (P), and arbuscular mycorrhizal (AM) symbiosis in Medicago truncatula and Brachypodium distachyon grown under the same conditions. The focus was on eCO(2) effects on vegetative growth, efficiency in acquisition and use of P, and expression of phosphate transporter (PT) genes. Growth responses to eCO(2) were positive at P sufficiency, but under low-P conditions they ranged from non-significant in M. truncatula to highly significant in B. distachyon. Growth of M. truncatula was increased by AM at low P conditions at both CO(2) levels and eCO(2)×AM interactions were sparse. Elevated CO(2) had small effects on P acquisition, but enhanced conversion of tissue P into biomass. Expression of PT genes was influenced by eCO(2), but effects were inconsistent across genes and species. The ability of eCO(2) to partly mitigate P limitation-induced growth reductions in B. distachyon was associated with enhanced P use efficiency, and requirements for P fertilizers may not increase in such species in future CO(2)-rich climates.