The effects of ultraviolet-B radiation and intraspecific competition on growth, pollination success, and lifetime female fitness in Phacelia campanularia and P. purshii (Hydrophyllaceae)

While a considerable amount of attention has been devoted to the effects that increased ultraviolet-B (UV-B) radiation has on vegetative plant growth and physiological function, the impact that UV-B may have on plant fitness has been the focus of fewer studies, with attention given primarily to a few crop species. Further, the possible interactions between UV-B and additional potential stresses found in natural environments have rarely been studied experimentally. Because the reported effects of increased UV-B on plant growth and fitness have been highly variable, studies that focus on factors that may lead to these differences in results are important for the formulation of accurate predictions about future plant success under varying UV-B levels. We examined the effects of UV-B dose and intraspecific competition on growth, phenology, pollen production, pollination success, fruit and seed production, and offspring quality in two species of Phacelia. Increased UV-B was neutral or beneficial for all traits, while competition was neutral or detrimental. There were no significant interactions between UV-B and competition in the parental generation. Phacelia campanularia offspring were unaffected by parental competition, but derived indirect beneficial effects on germination, growth, and fitness traits from parental enhanced UV-B.