Search

Elevated tropospheric ozone(O3) and enhanced atmospheric nitrogen(N) deposition exert great impact on the physiology of forest trees.The respective effects of these two pollutants have been studied thoroughly during the past couple of decades.However,little information is available concerning their combined effects on the physiology of subtropical evergreen trees.In the present study,O3 effects on Cinnamomum camphora,a native evergreen tree species,widely distributed in subtropical region,were investigated under enhanced N loads.One-year-old seedlings were adopted and the experiment was carried out in open-top chambers(OTCs).O3 fumigation regimes were set at ambient air(AA),ambient air plus 60 nmol/mol(AA+60) and ambient air plus 120 nmol/mol(AA+120);N load levels were set at 0(CK),30 and 60 kg · hm-2 · a-1,designated as N0,N30 and N60,respectively.Membrane lipid peroxidation,foliar chlorophyll and ascorbic acid contents as well as the total antioxidant capacity were examined after treatments for one growing season(May 5-September 10,2009).Foliar MDA(malondialdehyde) concentration was significantly enhanced by AA+120 treatment,but changed little in AA+60.Neither N30 nor N60 affected foliar MDA concentration significantly.Chlorophyll a content significantly decreased under both AA+60 and AA+120 treatments,and was significantly lower in the latter than in the former.Both N30 and N60 significantly increased chlorophyll a content,and the increment under N60 was significantly greater than that under N30.Chlorophyll b was also significantly increased by both N30 and N60,while was only significantly decreased by AA+120 rather than by AA+60.AA+120,as well as N60,significantly decreased chlorophyll a/b,which,however,was affected by neither AA+60 nor N30.The effects of elevated O3 and enhanced N on foliar carotenoid content were similar to those on Chlorophyll a content: significant treatment effects(O3 and N) with significant differences between treatment levels(AA+60 and AA+120,or N30 and N60).Besides,AA+120 significantly increased the total antioxidant capacity,on which,however,the effect of AA+60 was not significant.Significant difference of the total antioxidant capacity was not found either between AA+60 and AA+120,or among the N treatments.There were no significant interactions detected between O3 and N on foliar MDA,chlorophyll content and the total antioxidant capacity in our study.However,the effects of elevated O3 on the reduced(ASC) and total ascorbic acid() content were significantly modified by N loads.Under N0,both AA+60 and AA+120 significantly reduced the foliar ASC content,which,however,was significantly increased by AA+120 under N30 and N60.AA+60 also tended to increase the ASC content under enhanced N,although its effect was not significant.The effects of elevated O3 on under different N loads were similar to those on ASC,although they were of no statistical significance.Enhanced N loads strengthened the tolerance of C.camphor to O3 through increasing the foliar ASC content.