Abstract:

Aims: Flower orientation is shaped by both biotic and abiotic factors, reflecting their adaptation to the environment. Such variation may influence floral traits and pollinator visitation, ultimately affecting plant reproductive success. However, the effect of within-individual variation in flower orientation on pollinator visitation and pollination efficiency remains understudied in woody plants. Prunus mume f. purpurea is a woody species with important ornamental and economic value. It exhibits three different flower orientations (upward, horizontal, and downward) within a single plant. It is an ideal model for exploring the effects of flower orientation on pollinator visitation and pollination efficiency. 

Methods: In this study, we investigated the proportion of flowers with different orientations and quantified the floral traits, floral longevity, pollen viability, stigma receptivity, and the pollination characteristics. 

Results: Our results showed that proportion of downward-oriented flowers (53.17% ± 1.82%) was significantly higher than that of horizontal (29.75% ± 1.73%) and upward-oriented (17.08% ± 1.33%) flowers. Significant differences in floral traits were observed among the three flower orientations. Specifically, downward-oriented flowers exhibited greater male reproductive resource investment than horizontal and upward-oriented flowers, including longer stamens, a higher number of stamens, and greater pollen production. Downward-oriented flowers also exhibited significantly longer floral longevity, as well as higher stigma receptivity and pollen viability compared to horizontal and upward- oriented flowers. Apis cerana was identified as the primary pollinator of P. mume f. purpurea. Apis cerana visited downward-oriented flowers significantly more frequently, spent significantly more time per visit, and transferred significantly more pollen grains per visit than it did with upward-oriented flowers. 

Conclusion: In conclusion, our findings demonstrate that the differentiation in floral traits of different orientations in P. mume f. purpurea influences pollinator visitation behavior. Therefore, our study suggests that the proportion of downward-oriented flowers in P. mume f. purpurea may enhance reproductive success as an adaptive strategy.

Key words: flower orientation, Prunus mume f.purpurea, floral traits, pollination efficiency