桉树混交林在促进土壤养分循环、提高生产力和生态系统功能等方面有重要作用。菌根共生是影响混交林种间互作关系的重要因素。然而，不同菌根类型的混交树种对桉树人工林土壤微生物群落结构及功能的影响尚缺乏研究。该研究以桉树纯林及其与降香黄檀（Dalbergia odorifera，固氮-丛枝菌根树种）、火力楠（Michelia macclurei，丛枝菌根树种）、麻栎（Quercus acutissima，外生菌根树种）的混交林为研究对象，利用宏基因组测序技术，探究4种不同林型土壤微生物群落多样性、结构功能、细菌-真菌共现网络模式差异及其与土壤养分的关系。结果表明：混交林显著提高土壤微生物群落物种丰富度，改变微生物功能，增加微生物共现网络复杂性。降香黄檀与桉树混交林土壤微生物丰富度、细菌群落好氧化能异养和发酵功能基因相对丰度、真菌-细菌微生物共现网络模块度均最高；土壤细菌、真菌群落结构与其他3种林型差异显著。火力楠与桉树、麻栎与桉树混交林土壤细菌、真菌的碳氢化合物降解、氮固定、甲烷氧化功能基因相对丰度均高于桉树纯林。外生菌根树种（麻栎）与桉树混交林土壤微生物共现网络边数、平均度及网络稳定性最高，其核心微生物丰度与$NO^{-}_{3}$水平显著相关。丛枝菌根树种（降香黄檀、火力楠）与桉树混交林土壤核心微生物丰度与$NO^{+}_{4}$水平显著相关。

Mixed-species plantations can promote soil nutrient cycling， productivity， and ecosystem functions. Mycorrhizal associations play important roles in affecting species coexistence and nutrient cycling in mixed plantations. However， our understanding on the effects of mixed tree species with different mycorrhizal types on soil microbial community associated with soil nutrients of Eucalyptus plantations remains limited. In this study， we conducted metagenomic sequencing to investigate the changes in soil microbial community structure and functions， co-occurrence networks between bacteria and fungi， and their relationships with soil nutrients for one monospecific Eucalyptus plantation and three mixed Eucalyptus plantations with different mycorrhizal tree species， including Dalbergia odorifera（arbuscular mycorrhizal and N₂-fixing， AM-NF）， Michelia macclurei（arbuscular mycorrhizal， AM）， and Quercus acutissima（ectomycorrhizal， ECM）. The results indicated that the mixed stands significantly increased the richness of soil microbial community， enhanced the abundance of genes related to soil nutrient cycling， and increased the complexity of microbial co-occurrence networks. The mixed plantations of Eucalyptus with D. odorifera had the highest soil microbial richness， relative abundance of bacterial community associated with aerobic chemoheterotrophy and fermentation， and the modularity of fungal-bacterial co-occurrence network； meanwhile， either the bacterial or fungal communities were significantly different from the other three plantations. The mixed Eucalyptus plantations with M. macclurei or Q. acutissima species had the highest abundance of microbial functional genes such as hydrocarbon degradation， nitrogen fixation， and methanotrophy. In addition， the microbial co-occurrence networks in the mixed Eucalyptus plantations with Q. acutissima have the highest number of edges， average degree， and network stability. The richness of key microbes in co-occurrence networks was closely correlated with soil $NO^{-}_{3}$ level. However， the richness of microbial community of the networks in the mixed Eucalyptus plantations with D. odorifera and M. macclurei was largely associated with soil $NO^{+}_{4}$ level.