[Effects of Biochar Amendment on Microbial Community Structure in Purple Soils with Varying Acidification Levels]

Biochar， as a soil amendment， plays an important role in increasing soil pH and promoting microbial diversity. An indoor incubation experiment combined with high-throughput sequencing was conducted to investigate the effects of biochar addition on soil pH， organic matter content， and microbial community structure in purple soils with different acidification degrees， aiming to elucidate the response characteristics of purple soils to biochar input under varying acidification conditions and to provide a theoretical basis for improving soil fertility and promoting sustainable utilization of purple soils. Biochar was added at 3% of the dry soil weight and incubated for 63 days under laboratory conditions. The treatments included three acidification levels： T1， severe acidification （pH=4.48）； T2， moderate acidification （pH=4.90）； and T3， slight acidification （pH=5.82）. The results showed that： ① Under equal biochar application， compared with pre-incubation values， soil pH increased significantly in all treatments by 0.09， 0.34， and 0.37 units for T1， T2， and T3， respectively （P<0.05）. Organic matter increased by 70.13%-118.98%， with the highest increase observed in moderately acidified soil. ② Microbial community structures differed markedly among the three acidification levels， and greater acidification reduced microbial richness. Both bacterial richness （Chao1） and diversity （Shannon） followed the order T3>T2>T1； fungal richness （Chao1） followed T3>T2>T1， while fungal diversity （Shannon） followed T3>T1>T2. ③ The dominant bacterial phyla in all treatments were Proteobacteria and Chloroflexi， while the dominant fungal phyla were Ascomycota， Basidiomycota， and Mortierellomycota. ④ Biochar addition altered microbial community structures across different acidification levels， with dominant microbial taxa shifting along the soil pH gradient and more complex and stable co-occurrence networks forming under near-neutral conditions. ⑤ Redundancy analysis revealed that pH， TN， AP， C/N， and β-glucosidase were the main factors shaping bacterial community structure， whereas TN， C/N， cellobiohydrolase， and sucrase were the main factors influencing fungal community structure. In conclusion， biochar application improved soil pH， organic matter， and total nitrogen contents； altered microbial community succession and network characteristics； and thereby enhanced soil ecological health.