Root physiological adaptations that enhance the grain yield and nutrient use efficiency of maize (Zea mays L) and their dependency on phosphorus placement depth

Root growth demonstrates a high degree of plasticity in response to spatial variations in the availability of vital nutrients, and P fertilizer placement depth affects the development and distribution of plant roots. Optimizing the spatial matching between soil nutrients and the roots of maize plants in order to improve their N and P uptake and utilization capacity is a potential measure for improving the grain yield from summer maize. The spatial distribution profile of N, P and roots in the soil, as well as the roots’ absorption and utilization characteristics with respect to N and P and how these relate to the dry matter accumulation and grain yield formation were evaluated under four different placement depths of 5, 10, 15 and 20 cm (labeled P5, P10, P15, and P20, respectively). Compared with the P5 treatment, the P15 treatment induced a larger root length density, as well as a larger rooting depth. That happened because a higher number of root cortical aerenchyma, combined with a larger cortical cell size, reduces the metabolic cost required to establish them, which drives regulation processes that result in the allocation of more biomass to root proliferation. It also helped plants to maintain a higher level of biomass and N and P accumulation during the later growth period, which in turn increased the N and P assimilation of grain and enhanced the grain yield by 22%, the P recovery efficiency by 74%, the P agronomic efficiency by 150%, and both the partial factor productivity of P and the partial factor productivity of N by 21%. In conclusion, this study demonstrates that placing P fertilizer at a depth of 15 cm promotes root growth by reducing the metabolic cost of having a higher number of root cortical aerenchyma and a larger cortical cell size, and also that it improves the N and P absorption and utilization of roots and synergistically increases the grain yield and nutrient utilization efficiency of the whole plant.