Physiological And Growth Responses Of Winter Wheat To Ozone Stress And The Optimization Of Flux Model

In recent decades, human activities accelerate changes in atmospheric composition. Atmospheric nitrogen oxides and volatile organic compounds increased, resulting in near surface atmospheric ozone concentrations increased rapidly, the instantaneous peak concentration of atmospheric near surface O3reached100-200nl/L. Our research group used the OTC field experiment, laboratory and other methods, set the O3with different concentration gradients, launched a few years research of effects of enhanced O3on physiology and ecology of winter wheat, based on the field test data for three years, this paper analysised photosynthetic and stomatal characteristics of winter wheat and its optical response mechanism in the condition of ozone pollution. Discussed the effects of ozone stress on photosynthetic production and dry matter accumulation of winter wheat. Studied on the change of the ozone absorption flux of winter wheat based on its detoxification mechanism. Calculated ozone absorption flux from the two aspects of stomatal uptake and detoxification of apoplast, layed the foundation for improving the accuracy of ozone assessment and opened up a new perspective for the study on crop ozone deposition. The main results are as follows:(1). According to the measured data of diurnal changes in stomatal conductance, net photosynthesis rate and transpiration rate of winter wheat at its grain filling stage. Stomata maintained maximum opening at noon. The maximum stomatal conductance of every treatment groups are as follows:CK>150ppb>100ppb. The net photosynthetic rate of CK group had two peaks, the peaks appeared at10:48and14:24, after the12:00appeared "nap" phenomenon. By comparison, there was no "nap" phenomenon in100ppb group and150ppb group.(2). According to the analysis of stomatal limitation, two reliable judgment standards to determine the main reason of decrease of photosynthetic rate of winter wheat winter wheat is stomatal factors or non stomatal factors are as follows:Ci decreased and Ls increased indicate that stomatal limitation is the main reason; Ci increased and Ls decreased indicate that non stomatal factors leading to photosynthesis decline.(3). Many factors influence stomatal conductance of leaves of plants, including temperature, light, CO2concentration and water content of leaf. The mechanism of guard cell which control stomatal movement is more complex.(4). According to the response of photosynthetic rate and stomatal conductance to light, O3has significant stress effect on potential maximum photosynthetic capacity and maximum stomatal conductance of winter wheat. With the process of growth period, maximum photosynthetic rate of every treatment groups decreased, and the relationship of their maximum photosynthetic rate is CK>100ppb>150ppb. The light compensation point (LCP) and dark respiration (Rd) has good correlation.(5). O3can accelerate the aging of winter wheat leaf, decrease the leaf area and photosynthetic time. Ozone has effects on winter wheat dry matter accumulation. O3stress significantly inhibited the potential maximum accumulation of total dry weight of winter wheat. O3treatment also affect the accumulation and distribution of grain dry weight. O3caused the stress response of winter wheat photosynthetic production in the early of fumigation, so that the growth rate of100ppb group and150ppb group were higher than CK group.Then, ozone damage the photosynthetic system caused the growth rate lower than the CK group, and the difference gradually increased.(6). The mechanism of plant defense needs photosynthetic products to provide sufficient raw materials, photosynthesis is energy source of plant detoxification and self healing. The ratio between the photosynthetic rate and the ozone absorption corresponding to the plant sensitivity to ozone. From this point of view, ozone injury threshold should be a function of plant photosynthetic rate.(7). According to the calculation of SODA model, The thickness of cell wall and the concentration of ASC in cell wall is the main factor to determine plant detoxification ability of apoplast. In addition, many factors such as the regeneration of cytosol DHA, the recharge rate of cell wall ASC, the distribution of leaf totle ASC in cell components, biological permeability of membrane and subcellular pH value all have vital important effect on plant detoxification capacity.