Contrasting Responses of Multispatial Soil Fungal Communities of Thuja sutchuenensis Franch., an Extremely Endangered Conifer in Southwestern China.

Thuja sutchuenensis Franch. is an endangered species in southwest China, distributed sporadically in mountainous areas. Soil property and soil fungal community play a crucial role in plant growth and survival. Nevertheless, understanding soil properties and the soil fungal community in the areas where T. sutchuenensis is distributed is extremely limited. Hence, this study collected a total of 180 soil samples from five altitudinal distribution areas (altitudinal gradients) and three vertical depths throughout four horizontal distances from the base of each tree. The results found that altitudinal gradients and vertical depths altered soil properties, including pH, organic matter content, water content, total nitrogen, phosphorus, and potassium, and available nitrogen, phosphorus, and potassium. The fungal alpha diversity indexes (Chao1 and Shannon) and beta diversity were dramatically decreased with elevation. In addition, high altitudes (2,119 m) harbored the highest relative abundance of ectomycorrhizal fungi (27.57%) and the lowest relative abundance of plant-pathogenic fungi (1.81%). Meanwhile, we identified a series of fungal communities, such as Tomentella, Piloderma, Cortinarius, Sebacina, and Boletaceae, that play an essential role in the survival of T. sutchuenensis. The correlation analysis and random forest model identified that water content and total phosphorus showed strong relationships with fungal characteristics and were the primary variables for Zygomycota and Rozellomycota. Collectively, the findings of this integrated analysis provide profound insights into understanding the contrasting responses of T. sutchuenensis soil fungal communities and provide a theoretical basis for T. sutchuenensis habitat restoration and species conservation from multispatial perspectives. IMPORTANCE The present study highlights the importance of fungal communities in an endangered plant, T. sutchuenensis. Comparative analysis of soil samples in nearly all extant T. sutchuenensis populations identified that soil properties, especially soil nutrients, might play critical roles in the survival of T. sutchuenensis. Our findings prove that a series of fungal communities (e.g., Tomentella, Piloderma, and Cortinarius) could be key indicators for T. sutchuenensis survival. In addition, this is the first time that large-scale soil property and fungal community investigations have been carried out in southwest China, offering important values for exploring the distribution pattern of regional soil microorganisms. Collectively, our findings display a holistic picture of soil microbiome and environmental factors associated with T. sutchuenensis.

Comparative Analyses of Rhizosphere Bacteria Along an Elevational Gradient of Thuja sutchuenensis.

Thuja sutchuenensis Franch. is an endangered species in southwestern China, primarily distributed in 800-2,100 m of inaccessible mountainous areas. Rhizosphere soil physicochemical properties and bacterial communities play an essential role in managing plant growth and survival. Nonetheless, the study investigating rhizosphere soil properties and bacterial communities of T. sutchuenensis is limited. The present study investigated soil properties, including soil pH, organic matter, water content, nitrogen, phosphorus, and potassium contents, and bacterial communities in nearly all extant T. sutchuenensis populations at five elevational gradients. Our results demonstrated that the increase in elevation decreased rhizosphere and bulk soil phosphorus content but increased potassium content. In addition, the elevational gradient was the dominant driver for the community composition differentiation of soil bacterial community. Proteobacteria and Acidobacteria were the dominant bacterial phyla distributed in the rhizosphere and bulk soils. Co-occurrence network analysis identified key genera, including Bradyrhizobium, Acidicapsa, Catenulispora, and Singulisphaera, that displayed densely connected interactions with many genera in the rhizosphere soil. The dominant KEGG functional pathways of the rhizosphere bacteria included ABC transporters, butanoate metabolism, and methane metabolism. Further correlation analysis found that soil phosphorus and potassium were the dominant drivers for the diversity of soil bacteria, which were distinctively contributed to the phylum of Planctomycetes and the genera of Blastopirellula, Planctomycetes, and Singulisphaera. Collectively, this comprehensive study generated multi-dimensional perspectives for understanding the soil bacterial community structures of T. sutchuenensis, and provided valuable findings for species conservation at large-scale views.