Impact Of Tropospheric Ozone On Leaves Of Subtropical Woody Plants In China

During recent years, the increase of ozone precursor for photochemical reactions has made plants suffering from ozone stress in the troposphere more and more serious. Ozone pollution has been considered to be the primary cause of forest degradation and tree dieback in Eastern and Western Europe and throughout the United States.based on field investigation of some botanic gardens, people’s parks, college campuses and mountain areas in subtropics of china, in combination of ozone concentration monitoring data from April to August of Nanchang city, representing the subtropical urban areas in China, the temporal and spatial distribution characteristics and the effects of tropospheric ozone on plants were studied with the criteria of an ozone injury assessment manual. Meanwhile measured hyperspectral reflectance of leaves using the portable spectrometer, extracted the reflectance of red edge position, analyzed the variation of spectral signature in the before and after ozone injured, then calculated the effect of O3 injury to chlorophyll content of leaves incorporating the generalized model of Chlorophyll-reflection spectrum.Results showed that:(1) there are at least 84 kinds of woody plants are sensitive to tropospheric ozone, include both 66 ozone indicator plants, such as Magnolia subsp and Machilus ichangensis et al, and 18 ozone suspected plants, such as Broussonetia papyri/era and Sophora japonica et al, with the typical symptoms which include chlorosis, colored spots and patches, and exsciccation of the margin between the veins of the upper leaf surface. And this study suggests that the assessment method of ozone injured severity rank based on 7 classes is more reasonable.(2) The ozone concentration of suburb region was significantly higher than that of the urban and the exurban regions in Nanchang city. The highest average concentration of ozone occurred in June, and the value of AOT40 reached 35.5 mg·m-3·h which was well over the thresholds of 19.6 mg·m-3·h. But in the field, surprisingly,as it is influenced greatly by the environmental factors, the occurrence of ozone injury is not completely positively correlated with ozone concentration. (3) Under the ozone stress, high spectral reflectance has appeared great changes which contain that the spectrum reflectance has obviously increased between the visible spectrum 450-680nm, and the red edge position has highly significantly drifted to the left, meanwhile, the estimated result, based on the generalized model of chlorophyll-reflection spectrum:y=-0.12212 e900554x+ 2.3421, showed that the tropospheric ozone has led to chlorophyll content extremely dramatically reduced and caused severely impact on plant growing in the field.