Unlocking Mechanisms for Soil Fertility Enhancement in Tropical Forests Restored From Non‐Native Rubber Plantations: Microbes as the Key Drivers

ABSTRACT Forest restoration is a well‐established approach for effective soil rehabilitation, yet how soil microorganisms influence soil fertility at the soil aggregate microscale during tropical forest restoration remains unclear. We investigated the changes in soil microbial diversity and composition across four forest types: a tropical rainforest, a rubber monoculture plantation, and two restored types (natural restoration of rubber monoculture and natural restoration of rubber tree with tea tree intercropping). Results showed that soil fertility (soil organic C, total N, and total P), pH, and electrical conductivity (EC) exhibited increasing trends following forest restoration or decreasing soil aggregate fractions. Forest restoration and soil aggregate fractions were identified as the key predictors of microbial community structure. This relationship may be attributed to enhanced resource availability caused by increased plant diversity, pH, and EC in the restored forests. Smaller aggregates provide physical protection and retain more nutrients, thereby promoting microbial activity and diversity. PLS‐PM showed that microbes constituted the primary contributor among all the factors driving soil fertility. Strong positive correlations were observed between soil fertility and microbial communities, particularly in the dominant phyla and microbial networks. Specifically, the abundance of r‐strategy bacteria (Bacteroidota, Actinobacteria, and Proteobacteria) increased with forest restoration and decreasing aggregate size fractions. Similarly, fungal K‐strategists (Basidiomycota) increased following forest restoration, whereas fungal r‐strategists (Mortierellomycota) increased in the smaller aggregate size fractions. Microbial networks became more complex and tighter with forest restoration and decreasing aggregate size fractions. These shifts in microbial life strategies and co‐occurrence patterns likely enhance the formation of microbial‐derived organic matter, improve the efficiency of resource allocation and ecological signal transmission, and thereby promote soil fertility accumulation. Overall, this study highlights the critical role of forest restoration in abandoned rubber plantations in reshaping soil microbial communities and emphasizes the potential of soil microbes as indicators of soil resilience and health.