Responses of soil organic carbon decomposition and microbial community to the addition of plant residues with different C:N ratio

Changes in plant residue quality caused by global change may affect the cycle of soil organic carbon by priming effect in terrestrial ecosystems. However, how residue C:N ratio affects priming effect is not fully understood. To assess how plant residues with different C:N ratios influence priming effect, three 13C-enriched maize straw residues were added to soils and then incubated for 120 d. Soil carbon dioxide efflux and microbial community composition were measured. Addition of maize residues with low C:N ratio induced positive priming effect in the first 23 d of the incubation, whereas addition of maize residues with high C:N ratio induced negative priming effect in the first 60 d, followed by positive priming effect. At the end of incubation, relative priming effects induced by maize residues with C:N ratios of 27.6, 16.9 and 10.3 were −31.5%, 13.5% and 21.5%, respectively. Adding residues also increased the microbial biomass but reduced the bacteria:fungi ratio. Moreover, adding residues except maize residues with C:N ratio of 10.3 significantly decreased the ratio of Gram-positive to -negative bacteria. Most residue-C utilized by microorganisms was incorporated into the 16:0 and 18:1ω9c phospholipid fatty acids, and 67.9% of this residue-C was incorporated into bacterial phospholipid fatty acids. Our results suggest that C:N ratios of residue input to soils affect the magnitude and direction of priming effect and alter the composition and structure of soil microbial community.