Analysis of the Effects of pH on Rhizosphere Soil Protein Functions and Tea Plant Growth Using Soil Proteomics Technology

Soil acidification is a major environmental issue facing tea plantations in China. However, the molecular mechanisms by which acidification affects tea plant growth through rhizosphere microbial functional proteins remain unclear. In this study, tea plantation soils with different pH gradients were selected. Tea plant growth indicators, soil available nutrient contents, microbial abundance, and microbial physiological indicators were comprehensively measured, and metaproteomics was employed to analyze soil protein composition, functions, and microbial origins. The results showed that as soil pH increased from 3.54 to 5.37, the leaf chlorophyll content, leaf area, hundred-bud weight, and yield of tea plants were all significantly increased (p < 0.05). Soil available nitrogen, phosphorus, and potassium contents, as well as microbial biomass carbon, nitrogen, and phosphorus, also significantly increased in parallel. The abundances of bacteria and actinomycetes increased with rising pH, whereas fungal abundance decreased. A total of 6558 soil proteins were identified by metaproteomics, among which 236 were characterized as signature proteins (VIP > 1). Functional enrichment analysis revealed that proteins significantly upregulated with increasing pH were mainly enriched in pathways such as cysteine and methionine metabolism, galactose metabolism, and glycerophospholipid metabolism, with sulfur-containing amino acid metabolism contributing as much as 88.31%. Microbial source tracking indicated that Bacillus and Burkholderia were the primary contributors to these signature proteins; their abundances were significantly higher in the pH 5.37 treatment than in the low-pH treatment, with contribution rates of 100% and 43.73%, respectively. Partial least squares structural equation modeling (PLS-SEM) further revealed that signature microorganisms sequentially promoted microbial physiological indicators, nutrient availability, and tea plant growth by positively influencing the abundance and function of signature proteins. In conclusion, increasing soil pH to 5.37 can enhance the nutrient cycling capacity in the rhizosphere and increase tea yield. This phenomenon is closely related to the increase in the number of Bacillus and Burkholderia species, as well as the enhancement of key pathways such as sulfur-containing amino acid metabolism. This study provides molecular targets and a theoretical basis for the ecological remediation of acidified tea plantation soils.