Nectar characteristics and pollination ecology of Camellia perpetua in South China

• Camellia perpetua show a significant rise in avian floral visitation frequency, fruit and seed set in winter as opposed to summer. • The seasonal visitation in birds visitation rates coincided with the higher volume and sucrose proportion of nectar in winter. • This seasonal differentiation in floral nectar traits seemed to be associated with different pollinator functional groups. Temporal variation in floral nectar properties and their effects on reproductive success in plants that flower from winter to summer remain poorly understood. Camellia perpetua (Theaceae) blooms almost year-round in the karst regions of Guangxi, South China. Nectar characteristics and pollinator visits were observed in two populations: in the Guilin Botanical Garden (GBG) and PaiRu Village, Chongzuo White-Headed Langur National Reserve (PRV). Nectar is secreted in the buds of C. perpetua approximately 4–5 h before opening. The total nectar volume per flower was higher in winter (453.66 ± 4.67 μL) than in summer (129.14 ± 4.48 μL). Nectar secretion decreased during the day but increased in the evening. The amount of sucrose /(fructose + glucose) ratio was significantly higher in winter (49.69 ± 2.56) than in summer (6.99 ± 0.42). The glutamic acid content was higher in summer than in winter. During the summer and winter flowering seasons, birds ( Aethopyga christinae [the fork-tailed sunbird] in the GBG and PRV) and three bee species (in the GBG: Apis cerana, Apis mellifera ligustica , and Nomia chalybeata ) were the primary visitors. The frequency of birds visiting flowers, fruit and seed set was significantly higher in winter than in summer in both populations. Furthermore, the seed set was significantly higher in PRV than in the GBG. The higher floral visitation rates by birds during winter compared to summer were associated with a larger volume and higher proportion of sucrose in the nectar during that season. This seasonal differentiation in floral nectar traits seemed to be associated with different pollinator functional groups. However, further studies are needed to determine whether factors other than the variation in nectar traits, such as temperature, play a role.