Community assembly of bacterial generalists and specialists and their network characteristics in different altitudinal soils on Fanjing Mountain in Southwest China

Recent evidence suggests that Abies fanjingshanensis, endemic to China's Fanjing Mountain—a UNESCO World Heritage site—is facing a worrying decline. It is postulated that this decline is intricately linked to soil conditions. In response, this study has categorized microbial communities as generalists or specialists within soils from varying altitudes and has examined their relationship with soil nutrient status, as well as their implications for species extinction and diversification rates. Our findings indicate that low-altitude soils provide a more expansive and significant ecological niche for both specialist and generalist species compared to those from mid- and high-altitudes. Moreover, microbial diversity was markedly higher in the low-altitude soils. Soil pH emerged as the predominant factor influencing microbial communities across all elevations. In accordance with pH variations, species turnover rates followed an ascending order from low to high altitudes, corroborated by the specialization rates of generalists, which were 16.83, 1.50, and 3.06 times higher in low-, mid-, and high-altitude soils, respectively. Network stability analysis revealed that low-altitude soils exhibited greater robustness compared to their higher altitude counterparts. These results suggest that low-altitude soils on Fanjing Mountain present a more favorable environment for soil bacterial growth, potentially elucidating the marked decline of rare plant species in the mid- and high-altitude regions. This research contributes to a more nuanced understanding of the interplay between microbial communities and soil nutrition on Fanjing Mountain, with broader implications for the conservation of rare montane flora.