[Effects of Land Use Intensity on the Microbial Community Structure in Purple Soil]

Soil microbial community structure and function are critical factors in maintaining soil health， productivity， and regulating global carbon and nitrogen cycles. To clarify the regulatory mechanisms of land use intensity on microbial community structure and function in purple soil， a long-term field experiment was conducted， integrating high-throughput sequencing and functional prediction. Six treatments were investigated： fallow （CK）， low-intensity （P1）， low-moderate intensity （P2）， moderate-intensity （P3）， moderate-high intensity （P4）， and high-intensity （P5） utilization. The study analyzed changes in soil nutrient characteristics， microbial diversity， community structure， and function. The results demonstrated that： ① High-intensity land use （P5） significantly reduced soil pH and organic matter content （P < 0.05） but increased available nutrient levels （P < 0.05）. Notably， the increment of alkaline hydrolyzable nitrogen in deep soil （20-40 cm） under P5 （147%） was significantly higher than that in surface soil （77%）， indicating a more pronounced impact of land use intensity on deep soil nutrient dynamics. ② As land use intensity increased， bacterial α and β diversity indices initially increased and then decreased. The number of unique bacterial amplicon sequence variants （ASVs） in P2 decreased by 68% （2 126 ASVs） compared to that in CK （6 633 ASVs）， reflecting a trend toward community homogenization. Dominant phyla shifted from Actinobacteriota to Chloroflexi， with a significant increase in the relative abundance of FCPS473 at the genus level.③ Functional prediction revealed that high-intensity utilization （P5） significantly enhanced the abundance of defense mechanisms and secondary metabolic genes， while core metabolic functions （e.g.， energy conversion） remained stable. Microbial network analysis further indicated reduced network complexity （31% fewer edges） and diminished functional redundancy under P5. In conclusion， high-intensity land use drives microbial diversity loss and functional specialization in purple soil through acidification， nutrient imbalance， and organic matter depletion. Optimizing fertilization regimes and cropping patterns， particularly by controlling land use intensity at the P2 level and integrating organic-inorganic fertilizer applications， is recommended to sustain soil ecological health.