The Responses Of Winter Wheat Leaf Chlorophyll Fluorescence Parameters And Photosynthesis To Shading And Elevated O₃Concentration

Aerosol effect is one of the major environmental issues of concern to the world in recent years, and atmospheric aerosol through direct or indirect effects to affect crop; meanwhile, surface ozone concentration elevated year by year, high ozone concentration had been a serious threat to crop yield. In order to future research the influence of reduced solar radiation and increased ozone concentration on photosynthesis and fluorescence characteristics of crops, in this paper, the field experiment of difference shading and difference ozone concentration (natural light and ambient air, CK;20%natural light and ambient air, T1;20%natural light and100nL·L-1O3, T2;20%natural light and150nL·L-1O3, T3; nature light and100nL·L-1O3, T4;40%natural light and100nL·L-1O3, T5) based on open top chamber (OTC) and shade nets had been presented, photosynthesis and fluorescence characteristics of the different leaves were measured by Diving-PAM fluorometer and photosynthesis system, and make a thorough inquiry to the influence of reduced solar radiation and increased ozone concentration on photosynthesis and fluorescence characteristics of wheat, the relation of fluorescence characteristics and photosynthetic rate, the results in the paper are as follows:(1) The simulated elevate of O3concentration in shading caused a wide range of effects including actual photochemical efficiency and electron transport rate reductions and light-harvesting efficiency increased, light tolerance is reduced; minimalfluorescence、 maximalfluorescence-. potential photochemical activity and efficiency of primary conversion of light energy have no significant change in the early growth stage, but decreased significantly in the late growth stage; photochemical quenching decrease and non-photochemical quenching increase, the light energy used in antenna heat dissipation and others increased, while the photochemical efficiency decreased; the excitation energy distribution between PS Ⅱ and PS Ⅰ had a significant change. The increased ozone concentration could cause a serious damage to winter wheat, through self-regulation to alleviate the damage in the early growth stage, but because of the cumulative of ozone, resulting in the damage to photosynthetic in the latter growth stage.(2) The simulated increased of shading in ozone stress caused maximum photochemical efficiency and light-harvesting efficiency reductions; the efficiency of charge separation and electron transport rate decreased in the early growth stage, but increased significantly in the late growth stage; electron transport rate increased significantly of40%shading in the late growth stage; in the energy distribution,20%shading could enhanced photochemical quenching in the early growth stage, but shading could decreased in the late growth stage non-photochemical quenching. Shading could create serious damage to wheats, but wheats have considerable self-protection capacity.(3) Using the experimental data of YangMai13, the effects of elevate of O3concentration on maximum leaf net photosynthetic rate and actual quantum efficiency of PS II and the relationship of both factors were quantified, independent data were used for quantitative relationship validation. The results indicated that the coefficient of determination (R2) and the root mean square error (RMSE) based on1:1line between the estimated and measured values of maximum leaf net photosynthetic rat and actual quantum efficiency of PS Ⅱ are0.886and0.80, and2.887umolCO2·m-2·s-1and0.002. On this basis, using actual quantum efficiency of PS Ⅱ calculate maximum leaf net photosynthetic rate by quantitative relationship, analysis of the actual value and the calculated value showed that the coefficient of determination (R2) and the root mean square error (RMSE) based on1:1line between the estimated and measured values of maximum leaf net photosynthetic rate are0.921and2.127umolCO2·m-2·s-1.