Organic and biochar-based fertilizers reshape bacterial communities and enhance fertility in acidic rubber plantation soils

Abstract

Introduction Understanding the effects of different soil amendments on bacterial community structure and diversity in acidic rubber plantation soils is essential for biological remediation and the targeted restoration of these degraded systems. Methods In this study, a 2.5-year long field experiment was conducted in a second-generation 25-year-old rubber plantation at Dongfeng Farm in Jinghong City, southern Yunan, China. The experiment included five fertilization treatments: (1) unfertilized control (CK), (2) microbial fertilizer (T1), (3) biochar-based fertilizer (T2), (4) tobacco ash and oil cake organic fertilizer (T3), and (5) bio-organic fertilizer combined with polyacrylamide (T4). Soil samples were collected from the 0–20 cm layer in October 2022, and bacterial communities were analyzed using Illumina MiSeq high-throughput sequencing. Key environmental drivers were identified by integrating sequencing data with soil physicochemical properties. Results The application of soil fertilizers significantly altered the tested soil physicochemical properties and bacterial community composition. Compared with CK, T1 and T4 increased soil pH. T2 and T3 significantly enhanced soil organic matter, available phosphorus, and total nitrogen. In addition, T2 specifically increased exchangeable Ca2+ and Mg2+ concentrations and elevated the Chao1 richness index. Both T2 and T3 enriched beneficial taxa, including Proteobacteria and BradyRhizobium, while principal coordinate analysis (PCoA) revealed distinct shifts in bacterial community structure. The T4 treatment resulted in the most complex bacterial co-occurrence network. Mantel tests identified organic matter, total nitrogen, available phosphorus, and available nitrogen as the primary drivers of bacterial diversity. Further analysis using structural equation modeling indicates that soil conditioners alter bacterial community structure and diversity by influencing soil fertility and pH. Discussion Collectively, these findings demonstrate that organic matter, total nitrogen, available phosphorus, and available nitrogen serve as key environmental factors shaping bacterial community structure and diversity in acidic rubber plantation soils. Organic fertilizers and biochar have proven highly effective in enhancing soil fertility and buffering capacity, while significantly increasing the abundance of dominant bacterial taxa. Therefore, organic and biochar-based amendments should be prioritized as effective and sustainable strategies for restoring soil health and promoting continuous soil quality improvement in acidified rubber plantations.