Living Cortical Area in Roots Influences Root Respiration and Drought Tolerance in Maize.

Edaphic stresses such as drought and deficiency of mineral nutrients are major limitants of agricultural production worldwide, and are of particular import for subsistence farmers whose access to irrigation and fertilizers is often very limited. A variety of architectural and anatomical root traits have been shown to be potentially important in mitigating the effects of edaphic stresses. Root cortical aerenchyma (RCA) is one such anatomical trait that can reduce root respiration, potentiate greater root length, and increase tolerance of drought, as well as of low availability of nitrogen and phosphorus. However, the effect of RCA has been variable. We propose that a superior predictor of root respiration costs, and tolerance of edaphic stresses is the area of root cortex left after the formation of RCA - the living cortical area (LCA). LCA integrates root diameter, stele diameter, and aerenchyma formation. Evidence from field and greenhouse trials suggests that genotypes with high LCA are able to maintain greater root length and thus achieve greater growth under drought treatment compared to genotypes with lower LCA. LCA was also found to be a better predictor of root respiration than RCA.