Effects of Mixed Forest Formation on Rhizosphere Nutrients and Arbuscular Mycorrhizal Fungal Diversity of oil Camellia

In this study, we examined rhizosphere soil and absorptive roots from oil Camellia plantations, wild oil Camellia pure forests, and their mixed forests with Pinus massoniana and Cunninghamia lanceolata under identical environmental conditions. We analyzed major nutrient contents in the rhizosphere soil, isolated AMF spores for morphological identification, and assessed mycorrhizal colonization in absorptive roots. The results showed that after wild oil Camellia was mixed with the two coniferous species, the contents of available nutrients (NH₄ ⁺ , NO₃⁻, available potassium) increased significantly. Typical arbuscular mycorrhizal structures were observed in all four types of oil Camellia forests, and both the colonization rate and arbuscule abundance were significantly higher in mixed forests than in pure forests, with the mixed stand involving Cunninghamia lanceolata showing the strongest promotion of mycorrhiza formation. The highest AMF spore density in rhizosphere soil occurred in the wild oil Camellia /P. massoniana mixed forest. Morphological identification revealed 86 AMF species belonging to 2 phyla, 2 classes, 6 orders, 12 families, and 22 genera, and the AMF community diversity and evenness were higher in mixed forests than in pure forests. Correlation analysis indicated significant positive relationships between soil available nutrient contents and mycorrhizal colonization rate, spore density, and diversity indices. Overall, the establishment of mixed forests can improve rhizosphere nutrient availability and AMF diversity in oil Camellia.