Physiological and lipid metabolic basis of nitrogen-enhanced thermotolerance in Camellia reticulata

Endemic to southwestern China, Camellia reticulata is valued as an ornamental species and for its nutritionally superior camellia oil. However, high temperature stress threatens the growth and economic value of this woody oilseed tree. Preliminary experiments revealed that nitrogen addition enhances thermotolerance in C. reticulata, but the specific mechanisms underlying this effect remain unknown. This study aims to elucidate how nitrogen supply enhances thermotolerance in C. reticulata , focusing on the coordinated regulation of photochemical performance, carbohydrate metabolism, and lipid remodeling. A four-treatment experiment was conducted: ambient temperature without (control) or with nitrogen addition, and high temperature without or with nitrogen addition. Under high temperature, nitrogen supply alleviated photosystem II photoinhibition without affecting the decline in non-photochemical quenching, maintained pectin integrity, and attenuated the reduction in phospholipids (phosphatidylcholine, PC; phosphatidylglycerol, PG; phosphatidylinositol, PI) and glycolipids (monogalactosyldiacylglycerol, MGDG; digalactosyldiacylglycerol, DGDG; sulfoquinovosyldiacylglycerol, SQDG). Furthermore, via significant nitrogen–temperature interactions, it stabilized the PC/phosphatidylethanolamine ratio, elevated phosphatidylserine (PS) content above the control level, limited excessive unsaturation of phosphatidic acid, PC, and PS, and increased diacylglycerol/triacylglycerol ratio. Nitrogen application as a main effect, independent of temperature, reduced the unsaturation of PG and glycolipids, thereby restricting excessive membrane fluidity under heat stress. In conclusion, nitrogen supply represents an effective agronomic strategy to enhance thermotolerance in C. reticulata through coordinated regulation of photochemical efficiency, pectin metabolism, and lipid remodeling. These findings provide a theoretical basis for improving nitrogen nutrition management and cultivation of C. reticulata under global warming.