Plant growth responses to elevated atmospheric CO2 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.
(© The Author 2016. Published by Oxford University Press on behalf of the Society for Experimental Biology.)