A Preliminary Study On Responses Of Photosynthetic Assimilation To Air Nitrogen Dioxide In Leaves Of Coleus Blumei

Along with the advancement of industrialization and urbanization in China, energy resource consumption continues to increase, air pollution is increasingly aggravating, sulfur dioxide, nitrogen oxides and particulate matter (PM10and PM2.5) regional atmospheric pollutants characterized by environment problem increasingly prominent, harm people’s health, affect social harmony and stability. Nitrogen dioxide is major component of oxynitride amd comes from high temperature combustion process. Nitrogen dioxide is not only the factor of acid rain but also changes the competition and compositon between wetland and terrestrial plant species. Take advantage of assimilative capacity to repair environmental pollution has been frontier subject in recent years, and study of NO2assimilation is one of the hotspot. In order to study the effects of NO2fumigation on the photosynthetic physiological and the resistance of Coleus blumei with different colors in Harbin, the artificial open top fume device was used. The influences of spraying Na2S and NaHSO3on the Coleus blumei which were undergoing NO2fumigation processing were evaluated. In this article, red and yellow Coleus blumei planting in Harbin city were taken as experiment materials and the photosynthetic parameters, chlorophyll fluorescence parameters, chlorophyll content and nitrate reductase were mesured. The main results were as follows:The effects of NO2fumigation processing on photosynthetic physiology of red and yellow Coleus blumei were studyed. After NO2fumigation, the net photosynthetic rates (Pn) of two kinds of Coleus blumei were reduced obviously. The Pn of both color Coleus blumei were reduced gradually with the extension of fumigation time. The Pn of red Coleus blumei reduced from9.87to4.91μmolCO2·m2·g-1, and the Pn of yellow Coleus blumei reduced from9.67to3.19μmolCO2·m2·-1. Early NO2fumigation processing (1h), the Pn of both color Coleus blumei were reduced unconspicuous. Extending fumigation time, the Pn were reduced obviously and the minimum values were observed after fumigating for4h. The trends of Gs and Tr were the samillar to that of Pn. The nitrate reductase activities (NRA) of red and yellow Coleus blumei were reduced dramatically after fumigating for2h, and the NRA of red Coleus blumei was higher than that of yellow Coleus blumei. This illustrated that Coleus blumei could consume some of absorbed NO2through nitrogen metabolism for shortdated NO2fumigation processing. However, long-term NO2fumigation leads to close the stoma and reducing the absorbtion of NO2. The maximum light energy conversion efficiency (Fv/Fm) of Coleus blumei treated with NO2for a long time reduced significantly and the value of red Coleus blumei was higher than that of yellow Coleus blumei. The change of qP was small before fumigating for2h for red Coleus blumei and1h for yellow Coleus blumei. The qP values of two Coleus blumei began to decline after that time, and the minimum values of0.586for red and0.386for yellow were measured after fumigating for4h. During NO2fumigation processing, ETR, chlorophyll a, chlorophyll b and total chlorophyll content of two colors Coleus blumei were decreased gradually. This indicated that the photoinhibition happened to two colors Coleus blumei after NO2fumigation, and the photoinhibition to yellow Coleus blumei was more serious than red Coleus blumei.Normal photorespiration is conducive to the nitrate nitrogen assimilation of absorbed NO2. After spraying photorespiration promoter sodium sulphide (Na2S) and inhibitor sodium bisulfite (NaHSO3), the leaves were fumigated by NO2. After spraying Na2S, the Pn, Ci, Cs and Tr of red Coleus blumei were higher than those of without spraying Na2S, respectively; the Fv/Fm, φ PS Ⅱ, qP, ETR, total chlorophyll content and NRA also had obviously improved. Comparison between varieties, red Coleus blumei increased more than yellow Coleus blumei. After spraying photorespiration inhibitors NaHSO3, the indicators reduced significantly, and red Coleus blumei reduced obviously than those of yellow Coleus blumei. This indicated that photorespiration played an important role in nitrogen assimilation of absorbed NO2. On the one hand, absorbed NO2was transfered into NO3-induced the NRA, accelerated the nitrogen metabolism, avoiding the NO2damage to cells. On the other hand, photorespiration provided the electron acceptor NADP+to light reaction, provided Pi for dark reaction rapidly, thereby promoting energy use and reducing the occurrence of photoinhibition.In conclusion, short-term NO2fumigation, nitrogen metabolism will exhaust part of NO2, but long time of NO2fumigation would lead to stomatal closure, reducing the electron transfer rate and PS Ⅱ maximum light energy conversion efficiency, photoinhibition. Sodium sulphide (Na2S) can alleviate the photoinhibition, and sodium bisulfite (NaHSO3) increased photoinhibition which demonstrated that photorespiration plays an important role in NO2assimilation. Therefore, the ability of NO2assimilation can bu used to screening strong resistance of plant variety.