Semidwarf winter wheat roots contain fewer organic acids than wild-type varieties under phosphorus stress

Organic acids are exuded by plant roots into the rhizosphere for a variety of reasons, including nutrient acquisition. The most frequently reported organic acids are those involved in the Krebs cycle and other important biochemical pathways that are responsible for the production of important plant metabolites, including oxalic, malic, and citric acid. Many studies report increased citric and malic acid exudation when plants are P-deficient. Because plant breeding is typically carried out under heavily fertilized conditions, it is possible that wheat (Triticum aestivum L.) breeders have unintentionally selected for varieties with decreased nutrient acquisition capability from soil organic matter and soil colloids. In this study, we evaluated a diverse panel of 10 winter wheat cultivars, which included wild-type (tall) and semidwarf varieties, for organic acid content. Plants were grown in solution culture with and without P for 24 d. Thirty 1-cm root tips were bulked per sample and the extracts were analyzed by high-performance liquid chromatography for citric, malic, and oxalic acid content. Under P deficiency, total organic acid content differed between wild-type and semidwarf varieties, with wild-type cultivars containing more organic acids in the root tips. This difference in total production was driven by oxalic acid, whereas citric and malic acid concentrations were conserved. Unlike citric and malic acid, oxalic acid is not necessary for major metabolic processes and therefore may be expendable. Breeding for semidwarf wheat corresponds with unintentional changes to root system function that could impact nutrient acquisition and other rhizosphere processes.