Effects of combined application of nitrogen, phosphorus, and potassium fertilizers on tea (Camellia sinensis) growth and fungal community

Fertilization is an effective strategy for enhancing tea yield and quality. In practice, fertilizer application in tea plantations is often characterized by N, P, or K deficiencies, which suppress tea growth. Fertilization also exerts indirect effects on tea yield and quality by affecting the microbial community in the soil which is critical for regulating nutrient cycling and soil multiplication. Due to their tolerance to adverse environments in tea plantations including low pH and high aluminum and fluorine content, fungi are strongly associated with tea growth and are involved in the decomposition of pruning residues. To elucidate the poorly understood effects of different fertilizer combinations on soil fungi and tea, soil and plant samples were collected from a five-year (2016–2020) field experiment involving combined application of N, P, and K fertilizers (NF: no fertilizer; PK, NK, and NP: fertilization under conditions of N, P, and K deficiency, respectively; and NPK: fertilization with N, P, and K). Yield and quality differences between NPK and PK were more significant than those between NPK and NK, and NPK and NP. Of these three nutrients, N was the primary limiting factor for tea growth and N deficiency had more significant effects on fungal diversity than P or K deficiencies. N addition accelerated soil acidification and promoted native soil organic carbon decomposition, thereby decreasing the fungal diversity and modifying fungal community composition and structure. Moreover, in the PK (N deficiency) treatment, the fungal network had the lowest modularity, indicating that N deficiency reduced the resistance of fungal communities to external disturbances. The relationship between tea and fungi at different soil depths revealed that yield and amino acid content of tea were more strongly correlated with fungi in the topsoil than in the subsoil. This indicates that soil samples collected from the top layer are more informative for investigating the relationship between tea and soil. Overall, these findings deepen our understanding of how combined fertilization affects tea growth and soil quality, thereby guiding optimal fertilization strategies toward maximization of tea yield and quality and minimization of environmental risks.