Effects of Nitrogen and Phosphorus Levels on Arbuscular Mycorrhizal Symbiosis and Associated Bacterial Communities in Culture

Arbuscular mycorrhizal (AM) fungi establish mutualistic symbioses with plant roots, enhancing plant growth and improving soil fertility through nutrient exchange. Among these, soil nitrogen (N) and phosphorus (P) are critical for symbiosis formation, directly influencing nutrient uptake and translocation within the symbiotic system. This study aimed to examine the regulatory roles of N and P levels on AM fungal development and associated bacterial communities in culture. Sorghum was used as the host plant in pot experiments with two AM fungi, <i>Rhizophagus irregularis</i> and <i>Funneliformis mosseae</i>, under varying N and P concentrations. The analyzed parameters included mycorrhizal colonization, propagule production, plant biomass, nutrient contents (N, P, and K), and bacterial community diversity. N3P1 treatment (150 mg/L N, 30 mg/L P) yielded the highest colonization rate, spore production, and arbuscule abundance in both AM fungal symbionts. At equivalent N and P concentrations, the N, P, and K contents in inoculated plants were significantly higher than those in controls. AM fungal inoculation markedly increased the bacterial diversity in the culture (Shannon index raised by 15.2-28.7%) and enriched beneficial taxa, such as <i>Bradyrhizobium</i> and <i>Pseudomonas</i>. N and P concentrations substantially influenced AM fungal symbiosis, with optimal development observed under N3P1 conditions. By regulating AM symbiotic establishment, N and P levels reshaped microbial community composition, providing theoretical guidance for industrialized AM fungal cultivation and inoculant production.