Effects Of UV-B Radiation On Six Annual Species On Qinghai-Tibet Plateau

A decrease in the ozone layer could lead to a significant increase in ultraviolet-B (UV-B) radiation (280-320 nm) reaching the earth's surface. Recently an 'ozone hole' has been discovered above the Qinghai-Tibet Plateau in China. In order to examine the effects of the present and enhanced UV-B radiation on the growth and reproduction of the alpine species on Qinghai-Tibet Pleteau, six alpine meadow annual species Vicia angustifolia Linn, 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 (40.8% reduction by plastic films), ambient and an ambient plus supplemental UV-B radiation (simulating a 9% ozone depletion over Gannan, China, 34°55'N, 2900 m) up to leaf senescence and fruit maturation. The experiment was done in two successive years. Plant height, biomass allocation, flower phrnology, pollen germination and reproductive parameters of the six species were measured. We presented the concept of GRPT (growth rate of pollen tube) and COF (concentration of flowering) and their formulae. The results showed: 1) UV-B effects on plant height of V. angustifolia, P. depressa, and M. sinensis were different with the development of plant growth. Sensitivity of plant height to UV-B radiation depended on not only species but also developing stages. 2) Biomass allocation of the six species was more or less changed by UV-B radiation and the influences were more pronounced in enhanced UV-B treatment than in reduced UV-B treatment compared with ambient control. 3) Onset of flowering in V. angustifolia was significantly delayed by enhanced UV-B radiation but seed yield of it was not changed. Changes in concentration of flowering did not influence the reproductive success of the six species very much. 4) UV-B effects on pollen germination, flowering, and reproduction of the six species were species specific. 5) Successive UV-B effects on plant heights of the six species showed that no matter the effects of the first year UV-B treatment were significant or not, the second year treatment had...