Soil salinity effects on pollen and pollinator visitation in a buzz-pollinated glycophyte, Solanum carolinense

Human activity has significantly altered the salt cycle, affecting an estimated 2.5 billion acres of soil worldwide. Elevated soil salinity is a well-known plant stressor, but it may also affect interactions between plants and insects, which are often sodium limited. Elevated sodium in nectar can increase pollinator visitation, but no previous study has examined the effects of elevated soil salinity on visitation by pollen-collecting bees.

Our study tested whether increased soil salinity impacts pollen sodium and Bombus spp. visitation to Solanum carolinense, a buzz-pollinated perennial wildflower that rewards pollinators only with pollen. Soil salinity around the root zone of Solanum carolinense growing wild in an early successional field was artificially increased with a salt solution to observe changes in pollen sodium and other cations, pollen viability, and pollinator visitation.

Salt addition to the soil increased soil salinity by over five-fold, but there was no effect on the sodium levels of S. carolinense pollen. The salt treatment had no effect on pollinator visitation or pollen viability.

Although high soil salinity has been shown to increase nectar sodium levels and thus pollinator visitation, we infer from our results that S. carolinense is able to largely exclude sodium from its pollen, preventing high salinity soil from affecting pollinator attraction and pollen viability.