O_3胁迫对三种楠木幼苗光合作用的影响及伤害症状

[目的]随着全球O_3浓度升高,O_3胁迫对植物影响的研究已成为研究的热点之一。我国的相关研究较少,主要以农作物为主,且大多局限在北方地区。本研究探讨O_3胁迫下,亚热带三种楠木幼苗光合作用的变化规律及其可见伤害症状,以期为后续研究提供理论依据。[方法]以一年生亚热带乡土树种桢楠、闽楠和刨花楠幼苗为材料,采用开顶式气室(OTCs),研究低浓度O_3、环境大气、100 n L·L-1O_3、150 n L·L-1O_3处理对光合作用的影响及伤害症状。[结果]研究表明:(1)O_3胁迫下,三种楠木幼苗的光合作用受到一定的抑制,气孔导度和净光合速率的相关性降低,对光合有效辐射的利用范围整体减小,出现了明显的光抑制现象。O_3浓度越高,对桢楠和刨花楠光合作用的抑制效果越明显,而100 n L·L-1O_3处理对闽楠光合作用的抑制效果较150 n L·L-1O_3处理明显。环境大气中的O_3浓度均值较低,但由于其较高的O_3浓度峰值,仍对三种楠木幼苗的光合作用产生了一定的抑制。与环境大气相比,低浓度O_3处理通过消除较高的O_3浓度峰值从而缓解了O_3对光合作用的不利影响。(2)O_3胁迫下,桢楠叶片出现褪绿、黄斑和坏死斑的症状,闽楠叶片出现褪绿、黄斑和水渍的症状,刨花楠叶片出现红褐色斑、水渍、坏死斑、卷曲皱缩、失水萎蔫的症状。三种楠木幼苗叶片的伤害症状随O_3浓度的增加而更明显。[结论]三种楠木幼苗叶片的光合作用均受到O_3的抑制,并出现了伤害症状,可作为O_3污染的指示树种。光合作用对O_3敏感性的关系为:刨花楠闽楠桢楠,其中刨花楠对O_3更敏感,伤害症状也较多样,因此指示O_3污染的效果更好。

Effects of Elevated O3 Level on Photosynthesis and Injury of Phoebe and Machilus Seedlings in Subtropical China

[Objective] To study the effects of O₃ on the change law of photosynthesis and occurrence of visible symptoms. [Methods] One-year-old seedlings of Phoebe zhennan S. Lee et FNWei, Phoebe bournei(Hemsl.) Yang and Machilus pauhoi Kanehira, the native tree species in subtropical regions, were exposed to the O₃ concentrations gradient consisting of low O₃ treatment, non-filtered treatment, 100 nL·L^-1 and 150 nL·L^-1 O₃ by using open-top chambers. [Results] (1) the decrease in photosynthesis of the three tree species was related to non-stomatal factors. Elevated O₃ caused a decrease in the degree of correlation between net photosynthetic rate and stomatal conductance, reduced the using range of photosynthetically available radiation (PAR) as a whole, induced obviously the photo inhibition and weakened the photosynthetic acclimation of plants accordingly. The negative effects on Phoebe zhennan and Machilus pauhoi seedlings were more serious with higher O₃ concentration, however, the negative effects of 100nL·L^-1 O₃ on Phoebe bournei were more serious than 150nL·L^-1 O₃. In non-filtered treatment, although the mean O₃ concentration was low, to some extent, O₃ had negative effects on seedlings as a result of its higher peak O₃ concentration. Relative to non-filtered treatment, low O₃ treatment reduced the damage of O₃ by eliminating relative high O₃ peak concentration. (2) Under O₃ stress, obvious visible symptoms were found in the three tree species, including chlorosis, macular and necrosis in the leaves of Phoebe zhennan, chlorosis, macular and water stains in the leaves of Phoebe bournei, brown-red spots, water stains, necrosis, crimp and wilt in the leaves of Machilus pauhoi.[Conclusion] Elevated O₃ resulted in the decrease of photosynthesis and visible symptoms in the leaves of the three tree species, and all these species can be used as bioindicators of O₃ pollution. Sensitive degree to O₃ among the three tree species was determined based on photosynthesis: Machilus pauhoi > Phoebe bournei > Phoebe zhennan. Machilus pauhoi has better indicating effect due to greater O₃-sensitivity and more serious injury symptoms.