Corresponding fungal RDA revealed even stronger explanatory power, as the first two axes accounted for 82.81% of fungal community variance (RDA1: 62.82%, RDA2: 19.99%) with a highly significant model fit (R 2 = 0.592, p = 0.001, F = 2.813).
These shifts suggest a weak trend toward lower soil nutrient availability rather than a clear successional reorganization.
Although stochastic processes (e.g., dispersal limitation) exerted decisive dominance over fungal community assembly across all terraced citrus orchards, the relative contribution of deterministic processes—particularly heterogeneous selection—exhibited an increasing trend in older citrus orchards (Y8–Y12), becoming more pronounced than that in younger citrus orchards, where AK explained 27.9% of the βNTI variation (Fig. 8 B).
From Y3 to Y12, the number of Acidobacteriota nodes in microbial co-occurrence networks first increased then decreased, while their interactions with other microbial groups showed a trend of initial strengthening followed by weakening.