Plant origin and irrigation influence floral resource value and pollinator attraction to ornamental plants

Irrigation and plant origin are key factors influencing plant growth, development, and reproductive strategies. These same factors may also affect the floral resource value of plants to pollinators, influencing the efficacy of pollinator plantings for conservation or enhancement. While these factors have been studied separately, few studies have examined how plant origin influences plant responses to irrigation for floral traits such as nectar and pollen. In this study, we evaluated 10 native and 10 non-native plants to Florida under two different irrigation treatments and measured floral density, floral display, floral resources (nectar and pollen), and pollinator visitation rates and diversity in an open field study. There was strong to very strong evidence that native plants produced higher floral densities and displays, along with greater amounts of pollen per plot, and attracted a higher number and diversity of pollinators as compared to non-native plants. Additionally, there was weak to moderate evidence that fully irrigated plants produced higher nectar volumes and pollen quantities per plot as well as pollen with higher protein content as compared to partially irrigated plants. However, there was no evidence that native and non-native plants responded differently to irrigation treatment. Additionally, individual pollinator guilds responded differently to origin and irrigation, highlighting the complexity of plant-pollinator interactions. We conclude that native plants consistently produce more flowers and attract a greater number and diversity of pollinators while irrigation affects the production and resource value of pollen and nectar. These findings emphasize the importance of considering both plant origin and irrigation on resource availability of flowers when selecting pollinator-friendly plants under varying climates and management regimes.