Effects of reduced, ambient, and enhanced UV-B radiation on pollen germination and pollen tube growth of six alpine meadow annual species

Six alpine meadow annual species Vicia angustifolia L. ex Reichard. (Leguminosae), Poa annua L. (Gramineae), Polygonum aviculare L. (Polygonaceae), Plantago depressa Willd. (Plantaginaceae), Elsholtzia densa Benth. (Labiatae), and Malva sinensis Cav. (Malvaceae) were grown in the field under reduced and ambient ultraviolet-B (UV-B) levels, and an ambient plus supplemental UV-B radiation, simulating a 9% ozone depletion over Gannan, China (102°53′E, 34°55′N, 2900 m above sea level). Pollen grains were collected at full florescence at 10:30-11:00 a.m. in fine day and then the pollen germination and pollen tube growth were measured. Species-specific effects were observed and distributed both positive and negative responses to the treatments. Enhanced UV-B radiation significantly (p < 0.05) reduced pollen germination and pollen tube growth in V. angustifolia compared with ambient and reduced UV-B radiations. Pollen germination of P. annua and P. aviculare as well as pollen tube growth of P. annua and M. sinensis were significantly increased by enhanced UV-B radiation compared with the control. Meanwhile, no significant effect was found in pollen germination and pollen tube growth in P. depressa and E. densa by enhanced UV-B radiation compared with ambient control. Pollen germination in P. annua, P. aviculare, and E. densa and pollen tube growth in P. annua and E. densa were higher in pollen collected from the plant treated with reduced UV-B radiation than in pollen from plants grown in ambient conditions, and no significant negative effect was found in pollen germination and pollen tube growth by reduced UV-B radiation compared with the control in the tested species. Growth rate of pollen tube was much higher in V. angustifolia, P. annua, and P. aviculare in comparison to that in P. depressa, E. densa, and M. sinensis. Our results suggested that pollen of some species in Qinghai-Tibet Plateau were relatively tolerant to UV-B radiation in comparison to pollen of the species in lower altitude. In the future, the different responses among species to changed UV-B radiation may lead to a change in the competitive balance and species composition in natural communities on Qinghai-Tibet Plateau if UV-B radiation is increased.