Interactive effects of Nutrient Enrichment and Water Scarcity on Floral signaling and visitation

- Floral traits remain an underexplored frontier in global change biology compared to their vegetative counterparts. As anthropogenic change involves simultaneous shifts in resource availability, focusing on isolated stressors may overlook complex biological responses. Characterizing the interactive effects of these stressors is therefore crucial to move beyond additive models and accurately predict the stability of pollination services in a transforming world. - The individual and interactive effects of nutrient enrichment and water scarcity were investigated on the floral traits and pollinator visitation rates of five grassland species. - While species identity emerged as the dominant driver of overall trait variation, across-species responses were also present. Among the abiotic drivers, nutrient enrichment emerged as the primary influence, significantly increasing flower number and achromatic contrast while decreasing floral area, chromatic contrast and chroma. Conversely, water scarcity primarily reduced plant height and increased floral chroma and hue. The two factors also often interacted in their effects. The changes in visual traits scaled up to changes in pollinator visitation, but the specific effects were largely species-specific. - Ultimately, our findings demonstrate that anthropogenic stressors act in divergent ways to reshape floral phenotypes and pollinator visitation, advancing our understanding of plant-pollinator interactions under compounding global pressures.