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

Methods The experiment was conducted in a ecological tea plantation located in Pu’er City of Yunnan Province of Camellia sinensis cv. ‘Jinggu Dabai Cha’, where straw compost had been 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 the bacterial 16S rDNA and fungal ITS regions was employed to characterize the root endophytic microbial community. Simultaneously, rhizosphere soil physicochemical properties were determined to analyze the impact of fertilization on microbial diversity and soil fertility.

Results Compared with CK, none of the fertilization treatments had a significant effect on the contents of soil total P (TP) or total K (TK), but they all significantly increased soil available P (AP). Furthermore, OF treatment increased soil pH, whereas CL and CH decreased it. A total of 1687 bacterial operational taxonomic units (OTUs, 115 shared) and 539 fungal OTUs (12 shared) were identified in tea root endophytes across all treatments. Principal coordinate analysis (PCoA) revealed that, except for the OF treatment, fertilization significantly affected the 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 fungi (2.04–3.75). The dominant endophytic bacteria phyla were Proteobacteria and Actinobacteriota, while the dominant endophytic fungi genera were Cephalotheca, Pezicula, and Pseudodactylaria. Redundancy analysis (RDA) demonstrated that rhizosphere soil nutrients were closely correlated with variations in endophytic microbial community structures, explaining 66.54% and 72.20% of the total variation in bacterial and fungal communities, respectively. Specifically, dominant endophytic bacterial genera including Cloacibacterium, Lawsonella, Phenylobacterium, Herbaspirillum, and Thermosporothrix were positively (P<0.05) correlated with soil pH, SOC, AP, TN, but negatively (P<0.05) correlated with TK and AK. 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 the rhizosphere soil of tea plants. Straw compost elevated the rhizosphere soil pH, and its co-application with chemical fertilizers further enhanced soil available K content. The effects of changes in rhizosphere soil pH, organic matter, and available NPK on the composition and diversity of endophytic bacterial communities in tea roots were more pronounced than those on fungi. Chemical fertilizers reduced the richness and diversity of both endophytic bacteria and fungi, whereas straw compost improved these metrics for both microbial groups. Several dominant endophytic bacterial taxa exhibited positive correlations with soil pH, SOC, available P, and total N, but negative correlations with total and available K. Conversely, multiple dominant fungal taxa showed negative correlations with soil SOC and TN, but positive correlations with TK, AK, and AN. Further research is needed to elucidate how fertilization regulates the rhizosphere soil nutrient environment to drive endophytic microbial communities in tea roots, thereby enhancing nutrient uptake, disease resistance, yield, and quality.