Nitrogen Fertilizer Exerts Little Impact on Highbush Blueberry Floral Chemistry, Pollinator Visitation, Yield, and Fruit Quality.

Abstract

Plants allocate chemical resources to nectar and pollen rewards to entice pollinators to flowers and encourage pollination success. However, plant mineral nutrients, when deficient or applied in excess using fertilizers, could affect the chemistry of nectar and pollen and, subsequently, pollinator preferences for the flowers; therefore, cross-pollination, yield, and quality of fruits. In this study, we analyzed the chemical composition of nectar and pollen and the rates of pollinator visitation in commercial fields of northern highbush blueberry (Vaccinium corymbosum L.) cultivar Duke supplemented with nitrogen fertilizer at three progressive rates. We further integrated these studies with measurements of transcript abundance of nitrogen and proline transporters, and affinity scores of transporter proteins for nitrate. Our analysis revealed moderate variation of proline, dehydroascorbate, and succinate concentration in nectar but no changes in the pollen chemistry and honey bee visitation or the yield and quality of berries. Our findings suggest that applying low rates of nitrogen fertilizer (33-55 kg N ha^-1) can sustain the chemical quality of nectar and pollen, attract enough honey bee pollinators to support pollinator services, and ultimately maintain blueberry yield and quality.