Continuous Moderate Organic–Inorganic Fertilization Optimizes Soil Bacterial Communities in Camellia oleifera Plantations Through Macro-Nutrient Enrichment and Micronutrient Selectivity

Abstract

Fertilization is vital for improving the productivity of Camellia oleifera, a high-value woody oilseed crop. Yet, the prolonged influence of varying nutrient management regimes on edaphic microbial communities in subtropical plantation ecosystems has not been fully elucidated. To address this gap, we implemented a three-year field study with six amendment treatments: organic fertilizer (OF), organic–inorganic compound fertilizer (SF), a no-fertilizer control (CK), and three SF rates-low (F1), medium (F2), and high (F3). By combining random forest, redundancy analysis [RDA], and structural equation modeling [SEM] in a multi-model framework, total nitrogen (TN), total phosphorus (TP), and organic matter (OM) were identified as the main drivers of overall bacterial diversity. Importantly, RDA further revealed that specific micronutrients—particularly available iron (AFe) and available copper (ACu)—exerted significant selective pressures on community composition at the phylum level, notably correlating with Acidobacteria (AFe) and Proteobacteria (ACu). The moderate F2 treatment achieved optimal bacterial richness and enrichment of copiotrophic taxa (Proteobacteria, Gemmatimonadetes), comparable to F3, while avoiding over-fertilization risks. We conclude that the balanced supply of macro-elements (OM, TN, TP) combined with adequate chelated micronutrients (Fe, Cu, Mn, Ca, Mg) in the compound fertilizer contributes to F2’s superior performance, enhancing both overall community diversity and specific functional guilds. This study provides a nuanced, multi-factorial framework for precision nutrient management in C. oleifera plantations.