Effects of Rice Straw Biochar Application Rates on Soil Aggregate Biogeochemistry and Linkages to Microbial Community Structure and Enzyme Activities

Biochar, a widely adopted soil amendment, has been widely recognized for its potential to improve crop yields and soil nutrients significantly. This enhancement is primarily attributed to the crucial role of soil microorganisms, whose contribution to soil fertility is significant and often underappreciated. However, the effects of varying biochar application rates on soil functional biota, particularly within aggregates that expand soil spatial heterogeneity, remain unclear. Understanding the relationship between nutrient dynamics and microbial community composition in these aggregates is essential for comprehending the intricate connections between soil microbiomes and related biogeochemical cycles. This study utilized long-term experimental soils, including treatments with no fertilizer, chemical fertilizer alone, and chemical fertilizer combined with rice straw biochar at gradient application rates (22.5, 45, 90 t·hm-2). The responses of microbial community structure and soil enzyme activities in whole soil and aggregates to different biochar application rates were investigated. Results showed that, compared to NPK treatment, biochar significantly increased bacterial and fungal diversity in macroaggregates. It also notably increased the relative abundance of Proteobacteria and Ascomycota in soil and aggregates, and at the same time reduced the relative abundance of Chloroflexi and Basidiomycota. Furthermore, carbon and phosphorus cycle-related enzyme activities increased significantly with higher biochar application rates. However, the activity of NAG, a nitrogen cycle-related enzyme, decreased as biochar application increased. Mantel analysis revealed that the relationship between microorganisms, enzyme activity, and soil nutrients was closest at a biochar application rate of 45 t·hm-2. Structural equation modeling demonstrated that macroaggregates exhibited the most complex nutrient accumulation relationships, with bacterial and fungal diversity promoting nutrient accumulation. In conclusion, moderate biochar application induced the most intricate and closely connected microbial networks in macroaggregates, promoting soil nutrient cycling.

生物炭，作为一种被广泛采用的土壤改良剂，因其显著提升作物产量和土壤养分潜力的潜力而受到广泛关注。此种提升主要归功于土壤微生物的至关重要作用，其对土壤肥力的贡献巨大且常被低估。然而，不同生物炭施用率对土壤功能生物群落的影响，尤其是在扩大土壤空间异质性的团聚体中，尚不明确。理解这些团聚体中养分动态与微生物群落组成之间的关系，对于揭示土壤微生物群落与相关生物地球化学循环之间复杂联系至关重要。本研究采用了长期实验土壤，包括无肥料处理、单一化学肥料处理以及化学肥料与梯度的稻秆生物炭混合施用处理（22.5、45、90 t·hm-2）。本研究调查了微生物群落结构和土壤酶活性在整体土壤和团聚体中对不同生物炭施用率的响应。结果显示，与NPK处理相比，生物炭显著增加了宏观团聚体中的细菌和真菌多样性。同时，生物炭也显著增加了土壤和团聚体中变形菌门（Proteobacteria）和子囊菌门（Ascomycota）的相对丰度，并相应地降低了放线菌门（Chloroflexi）和伞菌门（Basidiomycota）的相对丰度。此外，随着生物炭施用率的提高，碳和磷循环相关酶的活性显著增加。然而，与氮循环相关的酶NAG的活性随着生物炭施用率的增加而降低。Mantel分析表明，在生物炭施用率为45 t·hm-2时，微生物、酶活性和土壤养分之间的关系最为密切。结构方程模型表明，宏观团聚体表现出最复杂的养分积累关系，其中细菌和真菌的多样性促进了养分积累。综上所述，适度的生物炭施用诱导了宏观团聚体中最复杂且联系紧密的微生物网络，促进了土壤养分循环。