Journal research area: Ecophysiology and Sustainability Root cortical aerenchyma enhances nitrogen acquisition from low nitrogen soils in maize (Zea mays L.)

Suboptimal nitrogen availability is a primary constraint for crop production in developing nations, while in rich nations intensive nitrogen fertilization carries substantial environmental and economic costs. Understanding root phenes that enhance nitrogen acquisition is therefore of considerable importance. Structural-functional modeling predicts that root cortical aerenchyma (RCA) could improve nitrogen acquisition in maize. We evaluated the utility of RCA for nitrogen acquisition by physiological comparison of maize Recombinant Inbred Lines (RILs) contrasting in RCA grown under suboptimal and adequate N availability in greenhouse mesocosms and in the field in the USA and South Africa. Nitrogen stress increased RCA formation by 200% in mesocosms and by 90-100% in the field. RCA formation substantially reduced root respiration and root N content. Under low N conditions, RCA formation increased rooting depth by 15% to 31%, increased leaf N content by 28% to 81%, increased leaf chlorophyll content by 22%, increased leaf CO2 assimilation by 22%, increased vegetative biomass by 31% to 66%, and increased grain yield by 58%. Our results are consistent with the hypothesis that RCA improves plant growth under N limiting conditions by decreasing root metabolic costs, thereby enhancing soil exploration and N acquisition in deep soil strata. Although potential fitness tradeoffs of RCA formation are poorly understood, increased RCA formation appears be a promising breeding target for enhancing crop nitrogen acquisition.