Abstract
Capturing the full growth potential in crops under future elevated CO2 (eCO2) concentrations would be facilitated by improved understanding of eCO2 effects on uptake and use of mineral nutrients. This study investigates interactions of eCO2, soil phosphorus (P), and arbuscular mycorrhizal (AM) symbiosis in Medicago truncatula and Brachypodium distachyon grown under the same conditions. The focus was on eCO2 effects on vegetative growth, efficiency in acquisition and use of P, and expression of phosphate transporter (PT) genes. Growth responses to eCO2 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 CO2 levels and eCO2×AM interactions were sparse. Elevated CO2 had small effects on P acquisition, but enhanced conversion of tissue P into biomass. Expression of PT genes was influenced by eCO2, but effects were inconsistent across genes and species. The ability of eCO2 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 CO2-rich climates.
Highlights
Dramatic increases in atmospheric concentrations of carbon dioxide (CO2) since pre-industrial times are predicted to produce CO2 levels of ~500 to ~900 ppm by the end of this century, according to different climate scenarios (IPCC, 2013)
This study investigates interactions of elevated CO2 (eCO2), soil phosphorus (P), and arbuscular mycorrhizal (AM) symbiosis in Medicago truncatula and Brachypodium distachyon grown under the same conditions
The ability of eCO2 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 CO2-rich climates
Summary
Dramatic increases in atmospheric concentrations of carbon dioxide (CO2) since pre-industrial times are predicted to produce CO2 levels of ~500 to ~900 ppm by the end of this century, according to different climate scenarios (IPCC, 2013). Elevated CO2 concentrations (eCO2) are expected to increase growth of C3 plants primarily because the current CO2 concentration is suboptimal for the Rubisco enzyme that catalyzes carbon fixation; in particular, eCO2 will competitively inhibit the oxygenation reaction and so reduce CO2 loss and energy costs associated with photorespiration. Other factors in the growth environment such as soil phosphorus (P) levels will influence the magnitude of the ‘carbon fertilizer’ effects on future crop productivity (Cavagnaro et al, 2011; Pandey et al, 2015b) and many soils are already characterized by decreasing P availability (Obersteiner et al, 2013) Global abundance of such soils may further increase as rock P is non-renewable on a human time scale (Scholz and Wellmer, 2013), or because P fertilizer becomes prohibitively expensive for farmers, especially in developing countries. Possible requirements for higher inputs of P fertilizers under eCO2 conditions could even accelerate the depletion of rock P reserves
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