Fungi Dominated the Incorporation of (13)C-CO(2) into Microbial Biomass in Tomato Rhizosphere Soil under Different CO(2) Concentrations

An elevated CO(2) (eCO(2)) fumigation experiment was carried out to study the influence of various CO(2) concentrations on microorganisms involved in the incorporation of root-derived C in greenhouse soil systems. In this study, 400 and 800 µmol·mol(−1) CO(2) fumigation treatments were conducted during tomato planting. Phospholipid fatty acid (PLFA) profiling based on the stable isotope probing (SIP) technique was applied to trace active microorganisms. The absolute total abundance of (13)C-PLFAs was much higher under eCO(2) treatment. Most of the (13)C-CO(2) was incorporated into the (13)C-PLFAs 18:2ω6,9 (fungi), 16:0 (general PLFA), 18:1ω9c (Gram-negative bacteria, G(−)) and i17:0 (Gram-positive bacteria, G(+)) via rhizodeposition from tomato under ambient CO(2) (aCO(2)) and eCO(2) treatments, suggesting similar responses of active microorganisms to different CO(2) treatments. However, the fungi (characterized by the (13)C-PLFA 18:2ω6,9) played a much more dominant role in the incorporation of root-derived C under eCO(2). Actinomycetes, marked by the (13)C-PLFA 10-Me-18:0, occurred only on labeling day 15 under the eCO(2) treatment, indicating that the actinomycetes fed on both soil organic carbon and fresh rhizodeposition. It was indicated that eCO(2) significantly affected microbial biomass and microbial community structures involved in the incorporation of (13)C-CO(2) via tomato root secretions, as supported by Adonis analysis and the Mantel test.