Integrated nitrogen management using Azospirillum lipoferum and arbuscular mycorrhizal fungi improves physiological traits and maintains sesame ( Sesamum indicum L.) yield under deficit irrigation

Abstract

Drought stress constrains sesame (Sesamum indicum L.) productivity in arid regions, whereas excessive reliance on chemical nitrogen fertilizers raises environmental concerns. This study evaluated whether microbial inoculation with Azospirillum lipoferum and arbuscular mycorrhizal fungi (AMF) could partially compensate for reduced nitrogen input under different irrigation regimes. A two-year field experiment was conducted using three levels of soil moisture depletion and seven nitrogen management treatments. Drought stress reduced relative water content, chlorophyll-related traits, and seed yield, while increasing ion leakage and antioxidant enzyme activity. AMF root colonization also declined progressively with increasing drought severity, but was enhanced by microbial inoculation, particularly under the combined application of 50% chemical nitrogen, A. lipoferum, and AMF. The combined treatment improved several physiological traits compared with the unfertilized control. However, the highest seed yield (1050 kg ha−1) was obtained under full chemical nitrogen. Under moderate drought, the combined treatment produced a yield statistically comparable to full nitrogen despite a 50% reduction in fertilizer input. Moreover, AMF root colonization was positively associated with relative water content, photosynthetic performance, and seed and oil yields, indicating coordinated responses under the experimental conditions. Integrated nitrogen management may therefore reduce fertilizer input while maintaining acceptable yield under moderate drought, but it should be regarded primarily as a strategy to improve input efficiency rather than maximize productivity.