In the present study, Rhododendron rex soil from Jiaozishan national nature reserve and Xiaobaicaoling in Yunnan province of China was selected as the research object. Physicochemical properties and high-throughput sequencing techniques were used to analyze soil nutrients and microbial diversity to explore the soil nutrients and microbial community characteristics of Rhododendron rex in central Yunnan, and provide theoretical reference for future research on ex-situ conservation, bionic cultivation and artificial propagation of Rhododendron rex. Results showed that the Rhododendron rex soil in central Yunnan was acidic, and the contents of various nutrients in the soil were high and correlated with each other. The abundance of fungi was higher than that of bacteria, while the diversity of bacteria was higher than that of fungi. There was a correlation between soil nutrients and microbial community characteristics. The dominant phyla of soil bacteria were Acidobacteria, Proteobacteria and Actinobacteria, and the sum of relative abundance was 78.97%. The dominant phyla of fungi were Ascomycota and Basidiomycota, and the sum of relative abundance was 94.89%.

Increasing severity of drought stress due to global change and extreme weather has been affecting the biodiversity, function, and stability of forest ecosystems. However, despite being an important component in the alpine and subalpine vegetation in forest ecosystems, Rhododendron species have been paid rare attention in the study of molecular mechanism of tolerance or response to drought. Herein, we investigated the correlation of transcriptomic changes with the physiological and biochemical indicators of Rhododendron rex under drought stress by using the co-expression network approach and regression analysis. Compared with the control treatment, the number of significantly differentially expressed unigenes (DEGs) increased with the degree of drought stress. The DEGs were mainly enriched in the cell wall metabolic process, signaling pathways, sugar metabolism, and nitrogen metabolism. Coupled analysis of the transcriptome, physiological, and biochemical parameters indicated that the metabolic pathways were highly correlated with the physiological and biochemical indicators under drought stress, especially the chlorophyll fluorescence parameters, such as the actual photosynthetic efficiency of photosystem II, electron transport rate, photochemical quenching coefficient, and the maximum quantum efficiency of photosystem II photochemistry. The majority of the response genes related to the metabolic pathways, including photosynthesis, sugar metabolism, and phytohormone signal pathway, were highly expressed under drought stress. In addition, genes associated with cell wall, pectin, and galacturonan metabolism also played crucial roles in the response of R. rex to drought stress. The results provided novel insight into the molecular response of the alpine woody species under drought stress and may improve the understanding of the response of forest ecosystems to the global climate change.