Coupling relationship between plant diversity characteristics and soil physicochemical properties of forest communities in Jiangxi Forest Farm, Yushu Prefecture

Taking Picea likiangensis var. rubescens forest, Juniperus tibetica forest, Betula albosinensis forest, and mixed Picea likiangensis var. rubescens + Betula albosinensis forest in Yushu Jiangxi Forest Farm as research subjects, this study adopted species diversity indices and redundancy analysis (RDA) to investigate the characteristics of shrub and herb layer diversity, soil physicochemical properties, and their interrelationships across different communities. The results showed that a total of 169 seed plant species, including infraspecific taxa, belonging to 46 families and 98 genera were recorded across the four communities. Species richness ranked as follows: Picea likiangensis var. rubescens forest > Juniperus tibetica forest > Betula albosinensis forest > mixed forest. The tree layer had low species richness (1～3 species), and diversity was mainly derived from the shrub and herb layers, with a greater contribution from the herb layer. The Shannon-Wiener index of the shrub layer was highest in the mixed forest (2.94 ± 0.07) and lowest in the Juniperus tibetica forest (2.10 ± 0.09), with significant differences among communities. The Margalef index of the Juniperus tibetica forest (0.96 ± 0.01) was significantly lower than that of the other communities, indicating the strongest environmental filtering effect of its harsh habitat on shrubs. No significant differences in herb layer diversity were detected among communities, and Pielou evenness did not differ significantly between shrub and herb layers. Soil physicochemical properties varied significantly among the four communities. The Picea likiangensis var. rubescens forest exhibited weakly acidic soil (pH = 6.37 ± 1.28), the highest organic carbon (61.61 ± 13.64 g/kg) and total nitrogen (3.40 ± 0.13 g/kg) contents, and the highest non-capillary porosity (55.06 ± 7.83%). The Betula albosinensis forest had the highest total phosphorus (0.63 ± 0.05 g/kg) and available phosphorus (2.66 ± 0.50 mg/kg) contents. Soil nutrient levels were generally lowest in the Juniperus tibetica forest. Redundancy analysis showed that soil bulk density and organic carbon were key factors explaining the variation in shrub and herb layer diversity. Soil physicochemical properties collectively explained a high proportion of the diversity variation (>80%), but the dominant factors differed among community types. The explanatory power was relatively high in the Picea likiangensis var. rubescens forest (>90%). In contrast, shrub layer variation in the Juniperus tibetica forest was less explained by soil chemical properties (58.51%) and was mainly driven by physical properties. Soil water content and pH gained significantly higher importance in the Betula albosinensis forest and mixed forest.