Nodal Root Growth Angle Influences Nitrogen Acquisition and Competition In Maize (Zea mays).

Maize ecosystems cover 1% of the Earth’s land area and have major impact on terrestrial carbon and nitrogen cycles. Upwards of 50% of applied nitrogen may be lost to volatilization and leaching causing environmental pollution. Root system architecture (RSA) is the spatial deployment of roots. Shoot-borne nodal roots form the majority of the maize root system’s backbone. Nodal root growth angle (NRGA) plays a large role in determining the distribution of maize roots in soil. We hypothesized that shallow angled roots would capture more nitrogen in the shallow layers of soil, while steeper angles would allow leaching nitrogen to be captured. Mixtures of maize genotypes having phenotypes contrasting in NRGA were hypothesized to decrease competition and increase stand level performance. Field and simulation experiments were conducted across a range of soil types and nitrogen levels to test these hypotheses. Six genotypes exhibiting shallow or steep NRGAs were planted as monocultures and mixtures in a clay soil in Pennsylvania and a sandy soil in South Africa in a split plot design with low and high nitrogen. Structural-functional modeling in SimRoot evaluated these hypotheses in varying soil types, nitrogen regimes, and root phenotypes. NRGA affected N acquisition and competition for N among maize plants. The utility of NRGA for N acquisition varied among soil types and N regimes. Maize mixtures exhibited complementarity for N acquisition.  In conclusion, optimal root system architectures are context-dependent and nodal root growth angle is an important regulator of maize N acquisition efficiency. Genetic monocultures may lack functional diversity needed for optimal productivity and efficiency.