Elevated CO₂ and nitrogen addition have minimal influence on the rhizospheric effects of Bothriochloa ischaemum

The influence of elevated CO₂ and nitrogen (N) addition on soil microbial communities and the rhizospheric effects of Bothriochloa ischaemum were investigated. A pot-cultivation experiment was conducted in climate-controlled chambers under two levels of CO₂ (400 and 800 μmol mol^-1) and three levels of N addition (0, 2.5, and 5 g N m^-2 y^-1). Soil samples (rhizospheric and bulk soil) were collected for the assessment of soil organic carbon (SOC), total N (TN), total phosphorus (TP), basal respiration (BR), and phospholipid fatty acids (PLFAs) 106 days after treatments were conducted. Elevated CO₂ significantly increased total and fungal PLFAs in the rhizosphere when combined with N addition, and N addition significantly increased BR in the rhizosphere and total, bacterial, fungal, Gram-positive (G⁺), and Gram-negative (G^-) PLFAs in both rhizospheric and bulk soil. BR and total, bacterial, G⁺, and G⁺/G^- PLFAs were significantly higher in rhizospheric than bulk soil, but neither elevated CO₂ nor N addition affected the positive rhizospheric effects on bacterial, G⁺, or G⁺/G^- PLFAs. N addition had a greater effect on soil microbial communities than elevated CO₂, and elevated CO₂ and N addition had minor contributions to the changes in the magnitude of the rhizospheric effects in B. ischaemum.