Rhizosphere Soil Fungal Community Patterns and Drivers in Chinese Fir Plantations Across Developmental Stages

The composition, richness, and diversity of rhizosphere fungal communities play significant roles in plant development in Chinese fir plantations. Understanding their structure and assembly, along with their relationship to soil physicochemical properties and root traits, is essential for maximizing the benefits of fungal symbionts for Chinese fir trees. Hence, fungal communities in two soil layers (0–20 cm and 20–40 cm) at four plantation developmental stages were analyzed using internal transcribed spacer rRNA gene sequencing. Soil physicochemical properties and root traits were examined to determine the main fungal community drivers. Our results revealed that fungal communities were significantly influenced by stand developmental stage, rhizosphere, and soil depth. Fungal biomass was highest at the young stand stage, whereas the α-diversity and evenness of the surface rhizosphere soil fungi remained stable across stages. With increasing stand age, the fungal community structure shifted from aggregated to dispersed. Co-occurrence network analysis demonstrated that stand development promoted network connectivity and modularity, with tighter local associations and distinct core functional consortia formed in the mature and over-mature stages. The proportion of positive links and positive cohesion increased along the stand developmental gradient, indicating a shift from competitive to cooperative interspecific interactions. Ascomycota and Basidiomycota consistently dominated soil fungal communities regardless of stand age, whereas Mortierellomycota and Chytridiomycota displayed sensitivity to stand development despite their low relative abundance. Soil physicochemical properties (total carbon, potassium, dissolved organic carbon, and phosphorus) were the primary drivers of rhizosphere fungal community dynamics and regulated fungal assembly by controlling soil resource availability. Additionally, the structural configuration of the fungal community was found to be intricately linked to root biomass and morphological traits.