Aiming at the industrial problems of low yield, low efficiency and high labor cost in the management of Camellia oleifera forests, this study explored the regulatory effects of mechanized fertilization in autumn on photosynthetic carbon assimilation capacity, oil synthesis and yield of four major promoted C. oleifera cultivars in Hunan Province, so as to provide a theoretical and technical basis for yield and quality improvement as well as precision fertilization of C. oleifera.

Fourteen-year-old C. oleifera forests of four cultivars, namely ‘Huashuo’, ‘Huajin’, ‘Huaxin’ and ‘Xianglin 210’, were selected as test materials. The mechanized fertilization experiment was conducted in late September 2024. Three treatments were set up, including compound fertilizer (CF), phosphorus-potassium fertilizer (PP) and no-fertilizer control (CK). Photosynthetic gas exchange parameters (net photosynthetic rate, transpiration rate, stomatal conductance, intercellular CO₂ concentration, water use efficiency, etc.), chlorophyll content, yield per unit area, fruit oil content and fatty acid composition were determined in late October before fruit harvesting and early December.

Compared with CK, CF treatment increases the chlorophyll content, net photosynthetic rate, stomatal conductance, intercellular CO₂ concentration, water use efficiency, kernel oil content, oleic acid proportion, linoleic acid proportion and total polyphenol content of all C. oleifera cultivars in late October. In particular, the chlorophyll content of ‘Huaxin’ and ‘Huajin’ is significantly improved (P<0.05), and the net photosynthetic rate and water use efficiency values of ‘Huaxin’, ‘Huashuo’ and ‘Xianglin 210’ also rise significantly (P<0.05). PP treatment extremely and significantly enhances the chlorophyll content of two late-maturing cultivars (‘Huashuo’ and ‘Xianglin 210’) (P<0.05), promotes linoleic acid synthesis in ‘Huaxin’, ‘Huajin’ and ‘Xianglin 210’, and markedly improves the yield of ‘Xianglin 210’. In early December, compared with CK, CF treatment continuously and significantly increases the chlorophyll content of ‘Huajin’, ‘Huashuo’ and ‘Xianglin 210’, and all cultivars maintain high levels of net photosynthetic rate and water use efficiency. PP treatment sustainably elevates the chlorophyll content of the two late-maturing cultivars ‘Huashuo’ and ‘Xianglin 210’ with significant differences (P<0.05).

Autumn application of compound fertilizer (CF) significantly improves the photosynthetic efficiency, chlorophyll content and oil quality of C. oleifera, which is regarded as the optimal fertilization scheme. Phosphorus-potassium fertilizer (PP) exerts remarkable effects on linoleic acid synthesis, yield and kernel oil content of ‘Huaxin’, ‘Huajin’ and ‘Xianglin 210’. In summary, compound fertilizer is recommended as the first choice for field application, and phosphorus-potassium fertilizer can be additionally applied before fruit harvesting according to the botanical characteristics of specific cultivars.