Impact of ultraviolet-B radiation on plant-pollinator interactions

Ozone in the stratosphere screens much of our planet's surface from the harmful effects of ultraviolet-B radiation (UV-B: 320-280 nm wavelengths). Intensified UV-B is known to be detrimental to vegetative growth of plants. Research reported here demonstrates that intensified ultraviolet-B radiation can also delay flowering, diminish pollen production and reduce lifetime flower production in healthy Phacelia campanularia (Hydrophyllaceae) and meadowfoam, Limnanthes alba (Limnanthaceae), two plants visited by a solitary bee, Osmia lignaria propinqua Cresson (Megachilidae). Pollinator reproductive responses to forage plants subjected to intensified UV-B depend on the length of time between pollinator emergence and the time when UV-B first affects pollen production for floral host plants.; Intensified UV-B did not substantially affect the production of nectar and pollen of the two plant species or their potential dietary value to bees. However, intensified UV-B elicited idiosyncratic responses in flowering phenology and flower production from the two annual plants. As UV-B dosage increased, L. alba plants were less likely to flower, but those that did flower suffered no delays in flowering or reduction of lifetime flower production. Conversely, the same proportions of P. campanularia plants flowered under all UV-B treatments, but this species experienced delayed onset to bloom and produced fewer flowers at greater UV-B intensities. Overall, our results showed that intensified UV-B can alter some flowering traits that impinge upon plant competition for pollinator services, as well as plant and pollinator reproductive success.; Pollinator (Osmia lignaria) reproductive success was not altered by UV-B because female bees completed their nests before UV-B affected their meadowfoam host. Although female bees removed 93% of pollen resources by day's end, fecundity appeared constrained by the time it took females to mature eggs. Female offspring received more maternal provisioning effort than male siblings. Despite the rearing of larger female offspring, three times more males than females were produced. Although increasingly male-bias sex ratios are associated with bee populations experiencing resource limitation, there was no evidence of pollen limitation due to UV-B damage to host plants. Greater male production probably resulted from a larger percentage of unmated females in our small bee population.