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

- The priming effect is negatively related to the residue C:N ratio.
- The majority of priming effect occurred in the early stage of incubation.
- Most residue-C was incorporated into the 16:0 and 18:1ω9c phospholipid fatty acids.
- Fungi play important function in priming effect.

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.