Drought stress and intercropping affect pollinator behavior via altered plant and flower traits in a legume

Climate change is a threat to agriculture and humankind. Sustainable cropping systems can enhance the resistance of crops against extreme weather events. The effects of drought stress on flower traits of insect-pollinated crops grown in sole stands and intercrops have rarely been studied, though. In this field study, we investigated how drought stress alters plant and flower traits of faba beans and the resulting pollinator behavior in faba bean sole crops and in faba bean–wheat intercrops. Plant height was reduced by drought stress and in intercrops (vs. sole crops). The number of open flowers per plant was unaffected by drought stress but reduced in intercrops. Drought stress increased the nectar sugar concentration but did not alter nectar volume and pollen production. Faba beans grown in intercrops produced higher nectar, sugar, and pollen grain amounts compared to sole crops. Drought stress effects on plant and flower traits were not affected by intercropping. Drought stress reduced the plant and flower visitation frequency by bumblebees. Although intercropping plots were visited less frequently, the individual flowers were visited more frequently than flowers in sole crops. The bumblebees’ nectar robbing activity increased with plant height and flower sugar amount. Our study shows that drought stress reduces crop plant growth and reduces pollinator visitation to crop flowers. Faba bean flowers in intercrops seem to be more attractive to bumblebees than flowers in sole crops, potentially enhancing pollination. The potential of intercropping should further be investigated in terms of mitigating detrimental effects of climate change on crop plants.