Physiological And Biochemical Responses Of Cinnamomum Camphora To Nitrogen Dioxide Induced Stress

As the amount of motor vehicles increases rapidly in the world,the emission of nitrogen dioxide(NO₂) has been enhanced and the following environmental problems,such as the acid rain and O₃ pollution,are getting more and more severe.As the development of phytoremediation,the usage of plants with high absorbency to certain air pollutant in atmospheric pollution control has become a new and rapidly strengthened subject,of which the study on the assimilation of NO_x was a focus. Using open-top chambers,we studied the absorbency and resistance to NO₂ for main landscaping plants in Zhejiang Province,selected plants of high resistance and absorbency,and built up plant configurations of greenbelt in living district for the main purpose of removing NO₂.The results may provide references in the planning of city greening.NO₂ fumigations at low concentrations(0.1,0.5 and 4.0μl·l^-1) in the period of 60 days and high concentrations(9.0,13.5,18.0,22.5 and 27.0μl·l^-1) in the period of 3 days were also implemented to study on the growth,N accumulation and NR activity,photosynthesis,oxidative stress and antioxidative responses of 1-year Cinnamomum camphora seedling.Information concluded from this part of study will be helpful to identify the resistance of plant to NO₂;it will also provide a base for further study of the NO₂ resisting mechanism in plant on cellular or molecular level.1.Selection of plants with high resistance and absorbency to NO₂.We studied the resistances and absorbencies to NO₂ of 38 landscaping plants,which were widely planted in Zhejiang Province in artificial fumigation method.According to the results of system cluster analysis,resistances and absorbencies of the participants was graded to five levels:strong,moderately strong,mid-level,moderately weak,and weak.The times to resist NO₂ of these 38 participants were ranged from 97 h to 25.5 h. Moreover,the absorbencies to NO₂ of these 38 plants were also different,of which the strongest was 404.5%and the lowest was 0.07%.In the experiment,focusing on the family,the resistances in plants in Lauraceae and Theaceae,which have leathery leaf, were stronger than that in Hamamelidaceae,which has papery leaf.2.Plant configurations of greenbelt in living district.Basing on the results above, the pollution situation in living district,and the principles of landscape designing and community ecology,we selected plants including Aceraceae fabric,Sapindus mukorossi,Loropetalum chinense var.rnbrum,Pyracantha fortuneana,Camellia japoica,Ophiopogon japonicus,et.al,and built up 5 configurations of grass,shrub and tree species,such as "Magnolia grandiflora+S,mukorossi+L,chinense var.rnbrum+P.fortuneana+ C.japoica+O,japonicus".We also estimated the absorbency of greenbelt with the configuration of "C.camphora+Sophura japonica+L. chinense var.rnbrum+P.fortuneana+C,japoica+O.japonicus " to be 1 045.47 kg NO₂·hm^-2·y^-1 in maximum.3.Growth and N accumulation.In the first 30 d of low-concentration fumigation,0.1, 0.5 and 4.0μl·l^-1 NO₂ showed insignificant effects on the growth of C.camphora seedlings;in the following 30 d,4.0μl·l^-1 NO₂ showed obvious inhibition on it,0.5 and 0.1μl·l^-1 NO₂ showed obvious promotion on it.In the low-concentration fumigation,0.1 and 0.5μl·l^-1 NO₂ obviously enhanced the nitrate reductase(NR) activities and N contents in leaves of C.camphora seedlings,4.0μl·l^-1 NO₂ enhanced the N contents while inhibited the NR activities.In the high-concentration fumigation, as the NO₂ concentration of treatments rose up,the NR activities first dropped slightly, then fluctuated acutely,and the N contents rose gradually.4.Photosynthesis.In the low-concentration fumigation,the diurnal variation of net photosynthetic rate(P_n) presented two-peaks with an obvious midday depression;0.5μl·l^-1 NO₂ increased the P_n,the maximum of P_n reached 8.542μmolCO₂·m^-2s^-1;4.0μl·l^-1 NO₂ decreased the P_n in most period of time;while the effect of 0.1μl·l^-1 NO₂ varied with time period;fumigation with 0.5 and 4.0μl·l^-1 NO₂ increased the maximum and minimum values of stomatal conductance(G_s)and intercellular CO₂ concentration(C_i),while 0.1μl·l^-1 NO₂ increased the maximum and minimum values of C_i,but decreased the maximum and minimum values of G_s.At the middle and late stages of fumigation,the mean P_n of the seedlings treated with 0.5μl·l^-1 NO₂ was significantly higher than that treated with 0.1 and 4.0μl·l^-1 NO₂.At the earlier stage of fumigation,0.5 and 4.0μl·l^-1 NO₂ significantly decreased the maximal PSâ…¡efficiency(F_v/F_m);and at the later stage,4.0μl·l^-1 NO₂ treatment still decreased the F_v/F_m significantly.In tile high-concentration fumigation,NO₂ of every concentration inhibited the photosynthesis,and the diurnal variation of net photosynthetic rate(P_n) presented one-peak in 22.5 and 27.0μl·l^-1 NO₂ treatments.The decreases in photosynthesis in this experiment were mainly due to nonstomatal limitation factors. According to the parameter values of model variational curve of P_n with photosynthetically active radiation(PAR),0.5μl·l^-1 NO₂ increased the utilization of weak light,strong light and PAR in the seedlings,while 4.0μl·l^-1 NO₂ showed contrary effects on them.5.Oxidative stress and antioxidative response.In the first 30 d of low-concentration fumigation,0.1,0.5 and 4.0μl·l^-1 NO₂ showed negative effects on the health of the C. camphora seedlings,which were reflected by the reduced chlorophyll contents,the enhanced superoxide dismutase(SOD) activities and the significantly increased malondialdehyde(MDA) contents.In the following 30 d,0.5μl·l^-1 NO₂ showed positive effects on the health of the seedlings,as the SOD activities were enhanced continuously,the ascorbate(AsA) contents and the glutathione reductase(GR) activities were enhanced,the oxidative stress still existed,while the chlorophyll contents recovered and the growth were promoted;4.0μl·l^-1 NO₂ showed negative effects on the health of the seedlings,which was reflected by the apparently reduced chlorophyll contents,the inhibited growth and the highest MDA contents among the treatments,although the SOD activities were at high level,the AsA contents and GR activities fluctuated acutely and asynchronously;0.1μl·l^-1 NO₂ showed the weakest effects on the health of the seedlings among the treatments,as the chlorophyll contents were insignificantly affected,the MDA contents and the SOD activities were the lowest among the treatments.In the high-concentration fumigation,the tendency of SOD activities and AsA contents in the seedlings presented one-peak,reached the maximum values at the level of 9.0 and 13.5μl·l^-1 NO₂,respectively;the GR activities fluctuated slighter than the former two indexes.As the NO₂ concentration arrived at 22.5μl·l^-1,the SOD activities and AsA contents in the seedlings fell much,and the MDA contents reached the maximum value.The toxic critical values of atmospheric NO₂ in inducing oxidative injury to C.camphora seedlings were 0.5-4.0μl·l^-1·60 d and 18.0-22.5μl·l^-1·3 d.SOD activity in the C.camphora seedlings responded steadily on the oxidative stress induced by NO₂.