Fixation of CO2 by soil fungi: contribution to organic carbon pool and destination of fixed carbon products.

Dark microbial CO₂ fixation plays a crucial role in soil organic carbon (SOC) sequestration, but the fungus contributions to this process in varying agroecosystems remain unclear. This study investigated fungal CO₂ fixation in 29 soil samples collected from the major agricultural regions across China. Phospholipid fatty analysis-stable isotope probing revealed variations in fungal fixation by 2.2 to 65.5% of the total microbial CO₂ fixation. CO₂ assimilation of ten fungal strains belonging to the phyla Ascomycota and Basidiomycota was determined in three different media using an isotope labeling experiment. Trichocladium uniseriatum had the highest CO₂ fixation capacity. T. uniseriatum had the reductive tricarboxylic acid cycle (rTCA) for CO₂ assimilation associated with sulfite metabolism. T. uniseriatum was thus selected for use in soil inoculation experiments, aimed to trace the fractionation of its fixed carbon in SOC. The CO₂ fixation rate of T. uniseriatum was 0.07–0.09 μg C per g of soil per day. Notably, 77–82% of the fixed C was partitioned into the mineral-associated soil organic carbon. This study highlights the significance of fungal CO₂ fixation in soil carbon sequestration. [ABSTRACT FROM AUTHOR]