Mechanisms of Cultivation Chronosequence on Distribution Characteristics of Arbuscular Mycorrhizal Fungi in Tea Plantations, South Henan, China

The vital role of arbuscular mycorrhizal (AM) fungi in tea plant growth is well established; however, the mechanisms underlying how increasing cultivation chronosequence (CC) influences AM fungal distribution remain unclear. An investigation was conducted to investigate the temporal dynamics of AM fungal indices and soil properties across a 100-year tea CC (10-, 30-, 60-, and 100-year CC) in Xinyang Maojian tea (Camellia sinensis L.) plantations (Xinyang, Henan Province, China). Principal coordinate analysis was conducted to reveal the significant reorganization of AM fungal indices during early-to-mid stages (PCoA1: 89.2%, p < 0.05), with triphasic development. Mycorrhizal colonization (MC), hypha biomass (hypha), and spore density (SD) surged by 100% during 10–30 years; SD peaked at 60 years (164 spores g−1) before declining, while glomalin-related soil protein (GRSP) accumulated significantly only at 100 years (p < 0.05). Concurrently, soil acidification (pH decreased from 6.37 to 4.84) and phosphorus depletion (AP from 119.6 mg kg−1 to 32 mg kg−1) intensified by 60 years, contrasting with the significant accumulations of soil organic organisms (SOM) (from 10.6 g kg−1 to 36.4 g kg−1), electrical conductivity (EC) (from 0.019 to 0.050 mS·cm−1), and microaggregate accumulation (MAR) (from 25.8% to 40.3%) during the period. The linear regression model was performed to validate the significant effects (p < 0.05) of CC on the AM indices (MC, SD, hypha, and GRSP) and soil physiochemical characteristics (EC, moisture, and SOM). Variance partitioning attributed 97.4% of the total variation, while interactions among cultivation ages, nutrient characteristics (SOM and AP), and non-nutrient characteristics (pH, EC, moisture, and aggregates) accounted for 23.0%. To identify the driving factors of AM fungi indices, Pearson correlation and redundancy analysis (RDA) were performed, and EC (26.5%) and pH (20.9%) were identified as the paramount regulators of hyphal integrity and colonization efficiency. It was found that 60 years worked as a critical transition point for targeted interventions (e.g., organic amendments and pH buffering) to mitigate rhizosphere dysfunction and optimize mycorrhizal services in perennial monocultures.