Arbuscular Mycorrhizal Fungi and Their Relationships with the Soil Nutrients and Heavy Metals in Ancient Trees in Blue-Crowned Laughingthrush Habitats

The fragile ancient 'Shuikoulin' forests, which provide critical habitats for the critically endangered Blue-crowned Laughingthrush, are increasingly degraded by soil contamination and heavy metal pollution. This study examines the rhizosphere environment of four key ancient tree species in the bird's core habitat, focusing on soil properties, heavy metal accumulation, and the structure of arbuscular mycorrhizal (AM) fungal communities. The results revealed that <i>Liquidambar formosana</i> showed the highest total nitrogen (TN) and available phosphorus (AP), whereas <i>Quercus chenii</i> had the lowest soil organic matter (SOM). The primary heavy metal contaminant across all tree species was Cd (<i>Igeo</i> > 2), followed by the metalloid As. We detected 41 AM fungal species spanning 7 genera, with <i>Glomus</i> dominating (84.19% relative abundance). OTU richness was highest in <i>Cinnamomum camphora</i> and <i>L. formosana</i> (110 each), followed by <i>Q. chenii</i> (88) and <i>Castanopsis sclerophylla</i> (75). Structural equation modeling indicated that soil nutrients (TN, TP, AP, SOM) suppressed the accumulation of V, Cr, Ni, and Cu, thereby indirectly favoring <i>Glomus</i> and <i>Paraglomus</i>. In contrast, higher pH and total potassium (TK) levels promoted Co and Zn bioavailability and negatively affected <i>Acaulospora</i> and other minor genera. Tree species identity directly modulated these interactions. Our findings demonstrate that ancient tree species shape AM fungal assembly through distinct rhizosphere geochemical niches, providing a mechanistic basis for restoring degraded habitats critical to endangered species conservation.