Effects of arbuscular mycorrhizal fungi on carbon assimilation and ecological stoichiometry of maize (Zea mays) under combined abiotic stresses

Arbuscular mycorrhizal fungi (AMF) enhance plant tolerance to abiotic stresses like salinity and improve crop yield. However, their effects are variable, and the underlying cause of such variation remains largely unknown. This study aimed to assess how drought modified the AMF effect on plant resistance to high calcium-saline stress. A pot experiment was performed to examine how AMF inoculation affects the growth, photosynthetic activity, nutrient uptake, and C:N:P stoichiometric ratio of maize under high calcium stress and contrasting water conditions. The results showed that high calcium stress significantly reduced mycorrhizal colonization, biomass accumulation, C assimilation rate, and C:N stoichiometric ratio in plant tissues. Besides, the adverse effects of calcium stress on photosynthesis were exacerbated under drought. AMF inoculation profoundly alleviated such reductions under drought and saline stress. However, it barely impacted maize performance when subjected to calcium stress with well-watered conditions. Moreover, watering changed AMF impact on nutrient allocation in plant tissues. Under well-watered conditions, AMF stimulated P accumulation in roots and plant growth, but did not induce leaf P accumulation proportional to C and N, resulting in increased leaf C:P and N:P ratios under high calcium stress. In contrast, AMF decreased N content and the N:P ratio in leaves under drought. Overall, AMF inoculation improved maize resistance to calcium salt through enhanced photosynthesis and modulation of nutrient stoichiometry, particularly under water deficit. This study highlighted the regulatory role of AMF in carbon assimilation and nutrient homeostasis under compound stresses, which provides significant guidance on crop yield improvement in saline and arid regions.