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.