Arbuscular Mycorrhizal Fungi Can Increase Nitrogen Use Efficiency in Aerobically Grown Rice Under Water‐Limited Conditions

Abstract

Rice is a vital staple crop for more than half of the global population, but water limitations threaten its production under flooded conditions. A transition to aerobic production of rice would ease water limitations but may increase nutrient management issues. Arbuscular mycorrhizal (AM) fungi could help by boosting nutrient and water uptake, but little is known about nitrogen (N) dynamics in these systems. We used a precision irrigation platform to apply watering treatments in combination with three soil N application treatments (160 kg urea ha −1 , 320 kg urea ha −1 or split applications of 160 kg urea ha −1 twice each) inoculation with AM fungi ( Rhizophagus irregularis ), and three commercial rice varieties: Reiziq, Topaz, and Viand. Water availability was a stronger determinant of grain biomass production than N application or AM fungal inoculation. Inoculation with AM fungi led to increased grain N concentration and N use efficiency in some varieties under water‐limiting conditions. Nitrogen availability determined how much water was used by the plants, and a mid‐development N application triggered increased plant water use, stomatal conductance and carbon assimilation, regardless of water availability. We conclude that AM fungal inoculation may support aerobic rice production, but that the benefits will likely be limited under low N availability.