Effects Of UV-B Radiation On Photosynthesis, Growth And Reproduction Of Three Annuals In Alpine Meadow

In this study, the effects of ambient and elevated UV-B radiation on photosynthesis, growth and reproduction of Vicia angustifolia L. of one and two generation were investigated to better understand the influence of UV-B radiation on Alpine meadow plant in the Tibetan Plateau. Field experiments were conducted under three UV-B treatments: UV-B filtering, UV-B supplement and ambient UV-B, and, furthermore, successive generation was carried through the UV-B treatments, and, simultaneously, reverse experiments of the F1 generation of the reduced/elevated-UV-B -treated plants went along. Comparing UV-B filtering with ambient UV-B treatment, effects of UV-B radiation were seen;comparing UV-B supplement with ambient UV-B treatment, effects of elevated UV-B radiation simulating 9% ozone depletion could be estimated;Additional reversion experiments was used to test the variability of the filial generation. Main results as follows:(1) concerning plant through one-year filtering treatment, ambient UV-B had positive effect on photosynthesis and water use efficiency , and negative effect on morphological development, biomass production and reproduction of Vicia angustifolia L., and thus, plants under ambient treatment showed lower individual fitness;(2) compared to plant under ambient UV-B treatment, the variational direction of the successive generation under UV-B filtering treatment accorded with plant only through one-year filtering treatment, with the extents more or less reinforcing except transpiration, showing the progressive effects of ambient UV-B by generation;(3) the seeds of the plant under UV-B filtering treatment in the first year had been sown back under ambient UV-B treatment, and the mature plant hadn't completely come back to the physiological and growth state under ambient UV-B radiation: the values of all variables were significantly different from those under ambient UV-B treatment, except net photosynthetic rate, leaf area, plant height and root/shoot length ratio, which implied the inherited variability in the filial generation;(4) under one-generation supplement treatment simulating 9% ozone depletion, leaf area, plant height, root length decreased, and net photosynthetic rate, biomass production and allocation andreproductive production remained unaffected, and specific leaf area reduced offering protection from UV-B damage, but root/shoot length ratio, underground/aboveground biomass ratio, and water use efficiency decreased, implying limited water use;(5) after two generation under UV-B supplement treatment, compared with only through one-generation such treatment, values of most variables of the plant were more close to those under ambient UV-B treatment, and biomass accumulation, reproductive allocation and production were even more, suggesting the filial generation could adapt better to elevated UV-B radiation;(6) also, the filial generation of the plant through UV-B filtering treatment in the first year re-cultivated under ambient UV-B treatment hadn't completely returned to the environmental state: the values of all variables, except net photosynthetic rate, leaf area, plant height and root/shoot length ratio, were significantly different from those under ambient UV-B treatment, which indicated the inherited variability in the filial generation.Synthetically, it can be concluded that Vicia angustifolia L. growing in the Tibetan Plateau is able to acclimatize itself to alteration in environmental UV-B radiation with various potential mechanisms.Also, we compared the effects of ambient and enhanced UV-B radiation on the photosynthesis, growth and reproduction of Malva verticilla var. chinensis and Elsholtzia densa Benth, and compared the susceptivities and the adaptive manners and abilities of the two species responding to UV-B radiation. Main results as follows:(i) under ambient treatment, relative to filtering treatment, in M. verticilla, specific leaf area was decreased, photosynthesis enhanced, water use efficiency lower, biomass portioning to fruit and root a bit more, and, in E. densa, photosynthesis is slightly reduced, water use efficiency unaffected, biomass portioning to fruit and root a bit more, and it could be seen that the susceptivity and adaptability of M. verticilla was ecumenic, and as for E. densa, the susceptivity was weaker and the adaptability better;(ii) under supplement treatment, in M. verticilla, the root turned longer but thinner, transpiration and water use efficiency lower, biomass accumulation somewhat less, reproductionalmost unaffected, and, in E. densa, the morphological development was inhibited, underground/ aboveground biomass ratio, photosynthesis and water use efficiency decreased, and it could be seen that the susceptivity of E. densa was better than M. verticilla, and the adaptability was weaker;(iii) the two-way ANOVA analysis showed that specific leaf area, lef area, root/shoot length ratio, net photosynthetic rate, stomatal conductance, water use efficiency is more sensitive to UV-B variation, esp. the latter three parameters, so that they could be used as the indicators to judge the two species' UV-B susceptivity;(iv) for the two species, the dose of elevated UV-B radiation in our experiment could impose small stress, and if the dose got higher, it would result in UV-B damage, especially in E. densa.