Effects of fruit load on growth, photosynthesis, biochemical characteristics, and fruit quality of Camellia oleifera

Camellia oleifera Abel is one of the four major woody oil species that produce edible oil from seeds. Nevertheless, its oil yield is comparably low, due to an imbalance in its source–sink relationship caused by its alternate bearing cycle. In this study, we conducted a pot experiment using 5-year-old C. oleifera 'Huaxin' young plants to examine the source–sink relationship and determine the optimal fruit load for oil production that ensures maximum economic value for C. oleifera. From April to October, the C. oleifera young plants were subjected to different leaf:fruit ratios: no fruit (control, CK), low fruit load (FL1, leaf:fruit ratio of 36:1), medium fruit load (FL2, leaf:fruit ratio of 18:1), and high fruit load (FL3, leaf:fruit ratio of 9:1). The results showed that the FL2 and FL3 treatments significantly reduced plant height, stem diameter, and flower bud differentiation from August to October, compared with the control. The net photosynthetic rate (Pn) and stomatal conductivity (Gs) of new leaves on clear days from June to August were decreased in the FL2 and FL3 treatments, compared with the control. Medium and high fruit loads (FL2 and FL3 treatments) and prolonged growth duration led to greater reductions in fruit size, weight, seed kernel oil content, oil production per plant, oil body volume, and distribution area, compared with the FL1 treatment. However, stearic acid and oleic acid contents were significantly higher in camellia oil obtained from the FL1 treatment than in camellia oil obtained from the FL2 and FL3 treatments. Thus, a leaf:fruit ratio of 36:1 is recommended to ensure proper C. oleifera 'Huaxin' growth and yield, and higher fruit loads should be avoided.