Plasticity of maize (Zea mays) roots depends on water content in nitrogen fertilized soil

Maize (Zea mays) roots grow in response to the soil nitrate (NO₃⁻) concentration, to optimize nitrogen (N) uptake. However, soil water content may influence plastic root responses by regulating plant N demand. This study aimed to identify the morphological and anatomical plasticity of maize roots affecting their hydraulic conductance with variable N fertilizer rates and soil water contents. Maize root growth was assessed in response to variable soil water content and N fertilizer rates. The growth chamber experiment was factorial with N fertilizer (equivalent to 85–170 kg N ha^− 1) × water treatments (soil water potential at -5 kPa and − 15 kPa), with five replicates per treatment. Field plots were fertilized with 0, 30, 40, or 50 kg N ha^− 1, banded at seeding in four replicated blocks, in 2021 and 2022. In relatively wet soil (-5 kPa), pot-grown maize had 23% longer lateral roots, 16% greater lateral root surface area, and 15% more crown root number with 170 kg N ha^− 1 than 85 kg N ha^− 1. In relatively dry soil (-15 kPa), lateral root surface area and crown roots were similar with both N fertilizer levels. In the wetter growing season (2022), field-grown maize with 30–40 kg N ha⁻¹ had 21–25% longer lateral roots on the seminal and crown roots than with 0 kg N ha^− 1. Maize had higher hydraulic conductance in wetter soil, which was positively correlated with N uptake in pot and field conditions. Maize roots show more growth plasticity to N fertilizer treatments in wetter soil conditions, indicating that water management is the key to optimize root development for maximum N uptake.