Abstract: Pollen flow between alfalfa (Medicago sativa L.) cultivars has raised great concerns due to its potential impacts on alfalfa seed production and ecological and evolutionary effects. This study was conducted to explore the pollen release and dispersal patterns of alfalfa that was driven by pollinating bees under different weather conditions (buoyant turbulent or pressure-driven nonturbulent conditions) using the Rotorod pollen collector. The results showed that regardless of honeybee (Apis mellifera L.) or bumblebee (Bombus terrestris L.), the pollen release pattern of alfalfa driven by pollinating bees initially increased from the morning at 8:00 (about 30 pollens·m^-3·h^-1) to the noon at 13:00 (about 1100 pollens·m^-3·h^-1) (reaching the peak at 13:00), and decreased subsequently. The concentration of alfalfa pollen dispersed from the pollen source decreased with increasing the distance from the pollen source edge. The directional effect on pollen concentration out of the pollen source was showed. Under the present experimental conditions, the potential distance of pollen dispersal from pollen source was 18 m. Additionally, compared to honeybees, bumblebees are better adapted to the different weather conditions, especially the pressure-driven nonturbulent conditions. In summary, the results in this study would be helpful for better understanding the pollen-mediated pollen flow, developing strategies to limit the pollen flow, and thus providing the valuable reference for proper using of different pollinating bees in alfalfa.

Key words: Alfalfa, Pollen dispersal, Aerodynamics, Italian bee, Bumblebee

摘要： 紫花苜蓿(Medicago sativa L.)品种间的花粉漂移，对苜蓿的制种具有重要影响；且其潜在的生态、进化学效应引起学者担忧。本试验利用Rotorod花粉收集器探究不同天气条件下不同蜂类驱动的苜蓿花粉释放和扩散规律。结果表明：不论意大利蜜蜂或熊蜂，它们引起的花粉释放模式为随日时间变化花粉浓度先增后减，即从8:00(约30 pollens·m^-3·h^-1)到13:00(约1100 pollens·m^-3·h^-1)浓度逐渐增加(13:00达到峰值)，之后降低；苜蓿花粉扩散随距离增加浓度减小且浓度大小具有方向性倾向。本试验条件下，苜蓿花粉最大扩散距离为18 m。相较于意蜂，熊蜂更能适应不同天气条件，尤其是高气压、强风天气。本研究结果有助于加深对苜蓿花粉介导的基因漂移的认识，为制定限制花粉漂移策略及科学利用蜂类授粉提供参考。

关键词: 紫花苜蓿, 花粉扩散, 空气动力学, 意大利蜜蜂, 熊蜂