Arbuscular mycorrhiza enhances maize grain yield and nitrogen uptake during the grain filling stage with contrasting nitrogen status in two types of soils

Arbuscular mycorrhizal fungi (AMF) generally improve crop nutrient acquisition and grain yield, especially under nutrient deficiency. It is uncertain, however, whether and how AMF colonization affects maize nitrogen (N) uptake during grain filling stage and grain yield under varying soil N status. To investigate this role under the conditions of poor and rich agricultural soils, two pot experiments were conducted with AMF inoculated and non-inoculated maize growing at low (180 kg N hm) and high N (270 kg N hm) input and two different nutrient areas. Compared to the non-inoculation treatment, AMF inoculation increased maize grain yield, plant biomass, and N accumulation during the filling stage under different soil N conditions. Other responses included increasing root length, root surface area, activities of grain nitrate reductase, nitrite reductase, glutamine synthetase, glutamate synthase (GOGAT) and their gene expressions. All enzyme activities and GOGAT gene expression were significantly correlated with grain yield. Grain yield and N accumulation were significantly higher at the nutrient rich site than poor site. Inoculation with AMF significantly increased grain yield with either lower or higher N input at both sites, whereas increased efficiency was greater with lower N input than higher N input. These results showed that AMF inoculation can increase maize yield and N uptake during the filling stage through regulating root traits and grain N metabolic enzyme activities and their gene expressions independent of soil N status. This enhances our knowledge of the role of AMF in the context of conventional agricultural management.