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Arbuscular mycorrhizal(AM)fungi and nitrogen-fixing bacteria play important roles in plant growth and recovery in degraded ecosystems.The desertification in karst regions has become more severe in recent decades.Evaluation of the fungal and bacterial diversity of such regions during vegetation restoration is required for effective protection and restoration in these regions.Therefore,we analyzed relationships among AM fungi and nitrogen-fixing bacteria abundances,plant species diversity,and soil properties in four typical ecosystems of vegetation restoration(tussock(TK),shrub(SB),secondary forest(SF),and primary forest(PF))in a karst region of southwest China.Abundance of AM fungi and nitrogen-fixing bacteria,plant species diversity,and soil nutrient levels increased from the tussock to the primary forest.The AM fungus,nitrogen-fixing bacterium,and plant community composition differed significantly between vegetation types(p < 0.05).Plant richness and pH were linked to the community composition of fungi and nitrogen-fixing bacteria,respectively.Available phosphorus,total nitrogen,and soil organic carbon levels and plant richness were positively correlated with the abundance of AM fungi and nitrogen-fixing bacteria(p < 0.05).The results suggested that abundance of AM fungi and nitrogen-fixing bacteria increased from the tussock to the primary forest and highlight the essentiality of these communities for vegetation restoration.