Non-Targeted Metabolomic Analyses Provide Insights into Exogenous Trehalose-Mediated Heat Stress Tolerance in Tea Plants (Camellia sinensis L.)

Global warming exacerbates high-temperature stress, disturbing the growth, metabolic homeostasis and quality formation of tea plants (Camellia sinensis L.). Trehalose, a multifunctional osmolyte, can enhance abiotic stress tolerance, but its systematic metabolic mechanism against heat damage in tea remains unclear. Here, we applied integrated gas chromatography–mass spectrometry (GC-MS) and liquid chromatography–mass spectrometry (LC-MS) non-targeted metabolomics to compare control (CK), heat-stressed (T), and trehalose-treated heat-stressed (TT) tea leaves. We identified 163 differential volatile metabolites in GC-MS and 1619 differential non-volatile metabolites in LC-MS. Metabolite classification showed that organic oxygen compounds dominated differential volatile metabolites, while lipids and lipid-like molecules dominated differential non-volatile metabolites. The Kyoto Encyclopedia of Genes and Genomes enrichment showed that alanine, aspartate and glutamate metabolism, arginine biosynthesis, aminoacyl-tRNA biosynthesis, and flavone and flavonol biosynthesis were core shared pathways. Quantitatively, exogenous trehalose under heat stress significantly increased carbohydrate accumulation, restored lipid homeostasis, and elevated alanine, arginine, and related intermediates, thereby maintaining carbon–nitrogen balance. Trehalose also remodeled the amino acid substrate pool for aminoacyl-tRNA biosynthesis. In flavonoid metabolism, trehalose enhanced high-antioxidant flavonoid aglycones while reducing most glycosides and inhibiting excessive hydroxylation of flavonols. Although total flavonoid content decreased in TT relative to T, this reflected alleviated oxidative damage and reduced dependence on flavonoid-based defense. Combined with total amino acid and flavonoid quantifications, we conclude that exogenous trehalose enhances tea plant thermotolerance by coordinately regulating primary amino acid metabolism and secondary flavonoid metabolism. These findings provide a theoretical basis for using trehalose in heat-resistance cultivation and quality improvement of tea plants.