Large flowers enhance pollination success and nutrient resorption in Yulania species

Flower size is a key determinant of reproductive success in animal-pollinated plants. However, traditional interpretations of these costs have often overlooked critical aspects of floral investment, including the complex relationships between flower size and factors such as initial resource allocation, floral longevity, resource resorption efficiency and ultimate reproductive output. We studied two Yulania species (Y. liliiflora and Y. soulangeana) to compare large and small flowers in terms of floral traits, pollinator preference, seed set ratio and nutrient resorption. Large flowers exhibited significantly greater floral display area, dry weight and pollen production but shorter longevity than small flowers. Pollinators, particularly bumblebees and honeybees, preferentially visited large flowers first, enhancing cross-pollination. When only large flowers were retained on branches (small flowers bagged), pollinator visitation frequency and seed set ratio of large flowers did not differ significantly from the natural control. In contrast, branches with only small flowers (large flowers bagged) experienced a significant reduction in pollinator visits. Consequently, the seed set ratio of small flowers in the absence of large flowers decreased significantly compared to that of small flowers under natural conditions. This suggests large flowers enhance pollinator attraction, indirectly benefiting neighbouring small flowers. Additionally, large flowers demonstrated significantly higher nutrient resorption efficiency (N, P, chlorophyll, starch, sugars and proteins) from senescing petals than small flowers. These findings indicate that large floral displays are not wasteful but instead optimize nutrient recycling and reproductive success. Floral size variation thus represents an adaptive strategy balancing pollinator-mediated reproduction with efficient resource use. Our study provides new insights into the ecological and evolutionary significance of floral trait variation in perennial plants.