| In recent years, Ultraviolet-B radiation reaching the earth surface was significantly enhanced as a result of that the ozonosphere was severely destroyed.UV-B radiation have significant effects on the plants on the ground. However, the plant is not under the influence of a single environmental factor, Global environmental change is the compound effect of multiple factors, and enhanced UV-B radiation is just one aspect of global environmental change. The response of plants to enhanced UV-B radiation also depends on the surrounding other environmental factors, such as temperature. Temperature is an important factor for the growth and development of plant. However, in recent years with the global warming increasing, high temperature has become one of the important limiting factors for plant growth and development.Wheat (small weir 926) was selected for this study as the material which grows in the artificial climate chamber.The effects of growth and photosynthesis of wheat seedlings exposed to the enhanced UV-B radiation (8.82kJ.m-2d-1)under different temperatures(21℃,26℃,31℃,36℃) have been studied and discussed in this study, in hope that the results can provide evidence for the correct assessment of biological effects under the interaction of the enhanced UV-B radiation and the global warming.The major results are as follows:1, Along with the temperature increasing from 21℃to 31℃, the height, root length, growth potential, biomass, the fresh weight of aboveground and underground parts of the wheat seedling, the dry weight of wheat seedlings increased significantly; when the temperature rose to 36℃, these indices were significantly reduced. It suggests that increasing the temperature properly will promote the growth of wheat seedlings, the best growth conditions of the wheat seedlings is in 31℃, When the temperature further rose to 36℃, the growth of wheat seedlings will be inhibited.2, Enhanced UV-B radiation have a certain inhibitory effect on growth of wheat seedlings,but the degree of inhibition are different under different temperatures. The damage of the growth of wheat seedlings caused by UV-B radiation is the biggest in 21℃.With the temperature rising to31℃, the degree of inhibition is reduced gradually.when the temperature reaches 36℃, the degree of inhibition has significantly increased.It show that raising the temperature appropriately can increase the plant resistance to UV-B radiation, while the high temperatures and UV-B radiation synergistic combined effect of the plant growth. 3, Along with the temperature raising from 21℃to 31℃(T21-T31), the net photosynthetic rate (Pn), stomatal conductance (Gs), photosynthesis (Ao), carboxylation efficiency (CE), Rubisco content and the content of photosynthetic pigment increased gradually, when the temperature rose to36℃(T36),accompanied by significant reduction of Pn, Gs, Ao, CE, Rubisco content and the content of photosynthetic pigment. It shows that raising temperature appropriately is beneficial to the photosynthesis of wheat seedlings, and photosynthesis increased because of both stomatal factors and non-stomatal factors; Reduction of photosynthesis in high temperature (T36) is also the result of both stomatal and non-stomatal factors. Meanwhile the results also show that the effect of different temperatures on growth of plant under different temperatures is related to the effect of different temperatures on photosynthesis of plant.However, along with the temperature rising from T21 to T26, accompanied by the increase of photosynthetic rate, the intercellular CO2 concentration (Ci) increased, and stomatal limitation (Ls) is decreased. It suggests that the stomatal factors is dominant in this period;when the temperature rose to 31℃, accompanied by a further increase in Pn, Meanwhile Ci was significantly lower, Ls has no significant change; when the temperature reaches to 36℃, along with Pn and Gs significantly reduced, while Ci was significantly increased. This indicates that non-stomatal factors is the dominant one in this period(26-36℃).Along with the temperature raising, the limiting factor of photosynthesis changes from the stomata factor to the non-stomatal factors obviously. Meanwhile, at different temperatures, a high degree of correlation of Pn and Ao, CE, Rubisco content is always present, indicating that the content of Rubisco is the main non-stomatal factors leading to changes in photosynthetic capacity.4, Enhanced UV-B radiation has a certain inhibition on photosynthesis of wheat seedlings, while the degree of inhibitions are different under different temperatures. The inhibition of the photosynthesis of wheat seedlings caused by UV-B radiation is the biggest in 21℃(T21).Along with the temperature rising to 31℃(T31), the degree of inhibition is reduced gradually, when the temperature reaches 36℃(T36), the degree of inhibition has significantly increased. It shows that raising the temperature appropriately can alleviate the damage on the photosynthesis caused by UV-B radiation. But the high temperature and UV-B radiation are synergistic co-inhibition of photosynthesis. Meanwhile the results also show that the effect of UV-B radiation on growth of plant under different temperatures is related to the effect of UV-B radiation on photosynthesis of plant.In the T21-T26, the decrease of Pn caused by UV-B radiation was along with Ci's significantly lower and Ls significant increasing, It indicates that the decrease of photosynthetic rate(T21-T26) is mainly owing to stomatal factors; under T31, Pn was decreased by UV-B radiation, while Ci and Ls did not change significantly; under T36, Pn was decreased by UV-B radiation,while Ci was significantly increased. This indicates that when temperature is higher than T31, the decrease of Pn caused by UV-B radiation is mainly owing to non-stomatal factors. At the same time,,the effect of UV-B radiation to Pn, Ao, CE, Rubisco content have a high degree of correlation.So the decrease in Rubisco content is an important non-stomatal factors of photosynthesis under UV-B radiation. |
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