More is not always better: Impact of nutrient-addition on floral traits important for buzz pollination

Abstract

Nutrient addition can affect plant fitness by altering resource allocation to reproduction or modifying floral traits. Alterations in floral attributes, particularly in species that exhibit specialization in specific ecological niches, can disrupt or augment the dynamics of interactions between plants and their pollinators. However, very little is known about how soil enrichment affects the floral characteristics and pollen release dynamics of buzz pollinated plants. Our study analyzed the effects of nutrient enrichment on the reproductive traits of a buzz pollinated plant species. Under greenhouse conditions, we established a phosphorus-rich nutrient gradient to investigate the impact of such enrichment on tomato plants (Solanum lycopersicum). Our study focused on: i) flowering patterns, ii) flower morphology, iii) pollen release from anthers, and iv) pollen quantity and quality (protein concentration). Plants were grown in low, intermediate, and high nutrient conditions, and various functional traits that are essential for buzz pollination were examined. Adding nutrients improved the display of flowers. Morphometric traits important for pollinator attraction and interaction, such as floral diameter, anther-tube width, and petal width, showed an increase in the high nutrient condition. The pollen quality and quantity were found to be unaltered; however, flowers originating from intermediate and high nutrient conditions exhibited reduced pollen release upon buzzing despite possessing ample pollen reserves. Our findings suggest that the positive effects of nutrient addition on floral traits are limited to a narrow range of concentrations. Higher concentrations can diminish these effects and impact the accessibility of pollen, as well as the reproductive performance of plants. In conclusion, based on our results, we predict that changing land use scenarios leading to nutrient accumulation may have significant consequences for plant-pollinator interactions.