Nutrient Limitations and Bacterial Community Dynamics in Rhizosphere Versus Non-Rhizosphere Soils of Camellia tetracocca Across Plantation Types and Habitats

Despite the ecological and economic importance of Camellia tetracocca, a rare ancient tea germplasm endemic to karst areas, variation in rhizosphere effects across plantation types and associated soil ecological coupling patterns remain poorly understood. This exploratory study compared physicochemical, biochemical, and bacterial community traits between rhizosphere and non-rhizosphere soils across three C. tetracocca plantation types—wild millennium ancient (MA), century-old cultivated (CC), and modern cultivated (CT)—representing a stand-age and management gradient. Soil nutrient pools, extracellular enzyme activities, bacterial diversity, and taxonomic composition were measured, and permutational multivariate analysis of variance (PERMANOVA), Mantel tests, and co-occurrence networks were integrated to characterize interactive linkages among soil abiotic and biotic variables. Results showed that soil organic matter (SOM) and total nitrogen concentrations in CT were 2.7-fold and 1.6-fold greater than those in MA, respectively. Nutrient limitation patterns diverged by habitat and stand age: non-rhizosphere soils of MA exhibited phosphorus limitation, whereas MA rhizosphere soils and all soils from CC and CT were dominated by nitrogen limitation. Explicit quantification of the rhizosphere effect (RE) revealed complex, indicator-specific patterns rather than a uniform age trend: MA showed the strongest positive RE for available phosphorus (+82.19%) and C-cycling hydrolases (βG: +18.82%, CBH: +29.98%), whereas polyphenol oxidase was the only enzyme showing a consistent increase in RE with cultivation age (MA < CC < CT). PERMANOVA indicated that plantation type explained the largest proportion of variation in bacterial community composition (R2 = 0.400, p < 0.001), whereas habitat (rhizosphere vs. non-rhizosphere) had no significant overall effect (p = 0.829). Mantel tests and network analysis revealed that SOM, rather than pH, was the strongest correlate of microbial community structure in these karst soils, and rhizosphere microhabitats strengthened tight correlations among soil nutrients, enzyme activities, and bacterial communities. These findings advance understanding of age-associated rhizosphere response patterns in rare ancient tea ecosystems and provide theoretical support for germplasm conservation and sustainable management of karst tea plantations.