Objectives This study investigated the effects of different fertilization practices on rhizosphere soil nutrient status and root endophytic microbial community structure in tea plants, aiming to provide a scientific basis for sustainable improvement of soil fertility and high-quality, high-yield tea production.

Methods A field experiment was conducted in an ecological tea plantation of Camellia sinensis cv. ‘Jinggu Dabai Cha’ in Pu’er City, Yunnan Province, where straw compost had been continuously applied for many years. Six fertilization treatments were established: no fertilization control (CK), straw compost fertilizer (OF), compound microbial organic fertilizer (CM), low-N compound fertilizer (CL), high-N compound fertilizer (CH), and co-application of high-N compound fertilizer and straw compost (COF). High-throughput sequencing of bacterial 16S rDNA and fungal ITS regions was performed to characterize the root endophytic microbial community structure. In addition, rhizosphere soil physicochemical properties were analyzed to evaluate the effects of fertilization on microbial community diversity and soil fertility.

Results Compared with CK, none of the fertilization treatments significantly affected soil total phosphorus (TP) or total potassium (TK) contents, whereas all treatments significantly increased soil available phosphorus (AP) content. The OF treatment significantly increased soil pH, while CL and CH treatments significantly decreased it. A total of 1,687 bacterial operational taxonomic units (OTUs, including 115 shared OTUs) and 539 fungal OTUs (including 12 shared OTUs) were identified from tea root endophytes across all treatments. Principal coordinate analysis (PCoA) revealed that, except for the OF treatment, fertilization significantly altered the community structures of both endophytic bacteria and fungi, with the first two axes explaining 63.99% and 56.95% of the total variation, respectively. The Shannon diversity index of endophytic bacteria (3.61–4.01) was consistently higher than that of endophytic fungi (2.04–3.75). The dominant endophytic bacteria phyla were Proteobacteria and Actinobacteriota, while the dominant endophytic fungi genera included Cephalotheca, Pezicula, and Pseudodactylaria. Redundancy analysis (RDA) demonstrated that rhizosphere soil nutrients were closely associated with variations in endophytic microbial community structures, explaining 66.54% and 72.20% of the variation in bacterial and fungal communities, respectively. Dominant endophytic bacterial genera, including Cloacibacterium, Lawsonella, Phenylobacterium, Herbaspirillum, and Thermosporothrix, were positively correlated with soil pH, SOC, AP, TN, but negatively correlated with TK and AK (P<0.05). In contrast, dominant endophytic fungal taxa such as Diaporthe, Fusidium, Dothideomycetes, and Mycenaceae were predominantly negatively correlated with SOC and TN, yet positively correlated with TK, AK, and AN contents.

Conclusions Fertilization significantly increased the contents of available N and available P in tea rhizosphere soil. Straw compost increased rhizosphere soil pH, and its combined application with chemical fertilizer further enhanced soil available potassium content. Variations in rhizosphere soil pH, organic matter, and available NPK contents had stronger effects on the composition and diversity of root endophytic bacterial communities than on fungal communities. Chemical fertilizers reduced the richness and diversity of both endophytic bacteria and fungi, whereas straw compost promoted the richness and diversity of both microbial groups. Several dominant endophytic bacterial taxa were positively correlated with soil pH, SOC, AP, and TN but negatively correlated with TK and AK. Conversely, multiple dominant fungal taxa were negatively correlated with SOC and TN but positively correlated with TK, AK, and AN contents. Further studies are required to elucidate how fertilization regulates the rhizosphere soil nutrient environment and drives root endophytic microbial communities to enhance nutrient acquisition, yield, and quality of tea plants.