臭氧浓度升高对香樟叶片光合色素及抗过氧化的影响及其氮素响应

为阐明氮(N)沉降条件下我国亚热带典型常绿树种香樟(Cinnamomum camphora)的臭氧(O3)胁迫响应特征,以1年生幼苗为试验对象,采用开顶气室(OTC)进行模拟研究。O3处理设大气O3(AA)、大气O3+60 nmol/mol(AA+60)、大气O3+120nmol/mol(AA+120)3个水平;N素以硝酸铵(NH4NO3)溶液形式施加,施N量设0(N0)、30(N30)、60(N60)(kg.hm-.2a-1)3个水平。主要考察了叶片膜质过氧化、光合色素、胞质抗坏血酸含量及总抗氧化能力的胁迫响应特征。结果表明:一个生长季(2009年5月15日—2009年9月10日)高浓度O3处理导致试验幼苗叶肉细胞膜脂过氧化程度显著加剧,叶绿素a、叶绿素b、类胡萝卜素含量显著降低;N素施加显著提高了叶绿素含量,但未改变细胞膜脂过氧化水平。叶片总抗氧化能力在AA+120处理下显著提高,但未受N施加影响。还原型抗坏血酸含量在N0处理下随O3浓度升高而降低;在N30及N60处理下随O3浓度升高而增高。施N可通过提高叶片抗坏血酸含量来增强香樟对O3升高的适应能力。研究结论可为O3与N复合污染下,我国亚热带地区典型常绿树种的保护提供科学参考。

Effects of elevated ozone on foliar chlorophyll content and antioxidant capacity in leaves of Cinnamomum camphora under enhanced nitrogen loads

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 (ASC+DHA]) 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 ASC+DHA] 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.