Changes of soil microbial biomass carbon and community composition through mixing nitrogen-fixing species with Eucalyptus urophylla in subtropical China

• Mixed Eucalyptus with N-fixing tree species can enhance the soil C sequestration.
• Mixing with N-fixing tree species significant effect on soil microbial characters.
• Positive effect of the enhanced soil N availability caused by N-fixing species.
• These findings are importance for shaping sustainable management of plantations.

In this study we examined the effects of mixing N-fixing species with Eucalyptus on microbial biomass carbon (MBC) and phospholipid fatty acid (PLFA) composition using a comparative experiment of an 8-year-old pure Eucalyptus urophylla plantation (PP) and an 8-year-old mixed E. urophylla and Acacia mangium plantation (MP) in Guangxi Zhuang Autonomous Region, southern China. Additionally, a trench control experiment was conducted to distinguish the effects of roots on MBC and community structure. The results showed that the number and abundance of PLFAs and MBC were higher in MP than that in PP. The soil TOC, NH4-N, NO3-N, TN and litterfall mass were significantly higher in surface soil (0–10 cm) in MP; whereas the C/N ratios of soil and litterfall were significantly lower by 37.6% and 78.5%, respectively, in MP than in PP. MBC at the surface soil (0–10 cm) was significantly higher by 9.0% in MP than in PP. Principal Component Analysis (PCA) indicated that soil microbial community structure differed between the two plantations, and between the trenched and untrenched plots. Redundancy analysis (RDA) also revealed that C/N ratios of soil and litterfall, TOC, NH4-N, litterfall mass and NO3-N were key factors affecting the soil microbial community regardless of plantation types.Our study suggests that mixing N-fixing species into E. urophylla plantations can enhance soil C sequestration by increasing TOC and MBC, as well as through increased soil microbial community diversity and abundance. Findings from this study could assist sustainable management of Eucalyptus plantations for biomass carbon production, soil C sequestration and retention.