Beauveria bassiana enhances maize nitrogen use efficiency and soil nitrogen cycling under elevated CO2

Rising atmospheric carbon dioxide concentrations significantly alter crop nitrogen utilization, posing a challenge to agricultural sustainability. While the entomopathogenic fungus Beauveria bassiana is known to colonize plants endophytically and promote growth, its capacity to regulate nitrogen dynamics under climate change scenarios remains unclear. This study investigated the interactive effects of B. bassiana colonization and elevated carbon dioxide on maize nitrogen metabolism. Using open-top chambers to simulate ambient and elevated (600 ppm) carbon dioxide environments combined with 15 N isotope tracing, we analyzed nitrogen migration, transformation, and soil microbial responses. Results indicated that fungal colonization significantly enhanced nitrogen uptake and assimilation under both carbon dioxide levels, with amplified effects observed under elevated concentrations. The endophyte optimized nitrogen allocation within the plant, increasing grain nitrogen content and boosting the activity of key metabolic enzymes such as nitrate reductase and glutamine synthase. Concurrently, inoculation reshaped the rhizosphere microbial community and improved soil physicochemical properties, thereby increasing nitrogen retention and reducing losses. Notably, B. bassiana mitigated the nitrogen dilution effect typically induced by elevated carbon dioxide, resulting in superior biomass accumulation and nitrogen use efficiency. These findings reveal that utilizing beneficial endophytic fungi can synergistically optimize plant nitrogen physiology and soil nutrient cycling in high-carbon environments, offering a promising strategy to maintain crop yields and reduce fertilizer inputs in future climate regimes.