The Physiological Utility of Root Cortical Aerenchyma for Efficient Nitrogen Acquisition in Maize (Zea mays).

Nitrogen stress is a primary constraint for global crop production and therefore human food security. In recent years several billion dollars has been spent on nitrogen fertilizer used in maize production, but only 30-50% of the applied nitrogen fertilizer is taken up by the crop, the remainder causing significant environmental pollution. This emphasizes the need to identify traits that enable plants to acquire nitrogen more efficiently. Root Cortical Aerenchyma (RCA) is known to form in response to hypoxia and the role of RCA in improving oxygen transport to roots under water logging is well documented in many plant species. Interestingly, RCA can also form in response to edaphic stress such as low nitrogen. However, its physiological utility for plants in low N soil is not understood. In this study, we hypothesize that RCA may reduce root metabolic costs and allow for soil exploration at greater depth, which would improve plant nitrogen acquisition. To test the hypothesis, Maize Recombinant Inbred Lines (RILs) of the Intermated B73 x Mo17 (IBM) population contrasting in RCA were grown under low and high N conditions in the greenhouse and in the field. Nitrogen stress increased RCA formation. Increased RCA significantly reduced root segment respiration. With suboptimal N supply, high RCA genotypes had greater rooting depth, greater N acquisition, and greater biomass than low RCA genotypes. Our results indicate that RCA is a promising root trait for improving N acquisition efficiency in maize.