Cr6+对人工湿地薏苡光合特性和微量元素吸收的影响

Effects of Cr6+ on photosynthetic characteristics and trace element absorption of Coix lacryma-jobi in constructed wetland

关键词:  铬, 人工湿地, 光合作用, 微量元素, 抗氧化酶

Key words:  chromium(Cr), constructed wetland, photosynthesis, trace element, antioxidative enzyme

摘要:

为深入了解Cr⁶⁺胁迫对人工湿地植物薏苡光合特性和微量元素吸收的影响,该文通过构筑微型垂直流薏苡(Coix lacryma-jobi)人工湿地,采用1/2 Hoagland's营养液配制的含0、5、20、40 mg·L^-1 Cr⁶⁺废水为灌溉用水,研究铬胁迫对人工湿地植物生长、光合特性、抗氧化酶活性和微量元素吸收等的影响。结果表明:(1)低浓度(5 mg·L^-1)Cr⁶⁺对薏苡的株高、茎粗和分蘖影响不显著,高浓度(20、40 mg·L^-1)Cr⁶⁺则显著抑制薏苡的生长。(2)低浓度Cr⁶⁺处理下,薏苡叶片净光合速率(P_n)、气孔导度(G_s)和蒸腾速率(T_r)有不同程度的提高,提高幅度分别为6.8%～54.8%、13.0%～40.3%和9.1%～36.4%。高浓度Cr⁶⁺处理下,叶片P_n、G_s、T_r等指标显著下降,但叶片胞间CO₂浓度(C_i)则显著提高。(3)薏苡叶片超氧化物歧化酶(SOD)和过氧化物酶(POD)活性均随着处理时间的延长而提高; 低浓度Cr⁶⁺处理下,薏苡叶片SOD活性与对照差异不大,高浓度Cr⁶⁺处理下,SOD活性受到显著抑制。薏苡叶片POD活性和丙二醛(MDA)含量均随Cr⁶⁺处理浓度的提高而提高。(4)高浓度Cr⁶⁺处理显著抑制根系、茎、叶对Cu 、Fe、Mn和Zn的吸收。(5)5、20 mg·L^-1 Cr⁶⁺处理下,人工湿地对Cr⁶⁺去除率最高可达99%,40 mg·L^-1 Cr⁶⁺处理下最高则为86%。综上认为,Cr⁶⁺胁迫导致Fe、Mn、Zn和Cu等元素吸收量显著下降,光合受阻,抗氧化系统受损,植物生长受到抑制,最终导致人工湿地处理含Cr⁶⁺废水的能力下降。

Abstract:

In order to understand the effects of Cr⁶⁺ stress on the photosynthetic characteristics and trace element absorption of Coix lacryma-jobi, we investigated the effects of Cr stress on the growth, photosynthetic characteristics, antioxidant enzyme activity and microelement absorption of C. lacryma-jobi by constructing a miniature vertical flow C. lacryma-jobi artificial wetland with 1/2 Hoagland's nutrient solution containing 0, 5, 20, 40 mg·L^-1 Cr⁶⁺ wastewater as irrigation water. The results were as follows:(1)Low concentration(5 mg·L^-1)of Cr⁶⁺ had no significant effects on plant height, stem thickness and tillering of C. lacryma-jobi, while high concentrations(20, 40 mg·L^-1)of Cr⁶⁺ significantly inhibited the growth of C. lacryma-jobi.(2)Net photosynthetic rate (P_n), stomatal conductance(G_s)and transpiration rate(T_r)of C. lacryma-jobi leaves were increased to different degrees under low Cr⁶⁺ treatment, with the increases ranging from 6.8% to 54.8%, from 13.0% to 40.3% and from 9.1% to 36.4%, respectively. Under the high concentration of Cr⁶⁺ treatment, the P_n, G_s and T_r of leaves decreased significantly, but the intercellular CO₂ concentration(C_i)increased significantly.(3)Both superoxide dismutase(SOD)and peroxidase(POD)activities of C. lacryma-jobi leaves increased with increasing treatment time; SOD activity of C. lacryma-jobi leaves did not significantly differ from the control under low Cr⁶⁺ treatment, and was significantly inhibited under high Cr⁶⁺ treatment. The POD activity and malondialdehyde(MDA)content of C. lacryma-jobi leaves increased with the increase of Cr⁶⁺ treatment concentration.(4)The absorption of Cu, Fe, Mn and Zn by roots, stems and leaves was significantly inhibited by high concentration of Cr⁶⁺ treatment.(5)The removal rate of Cr⁶⁺ by the artificial wetland was up to 99% under 5 and 20 mg·L^-1 Cr⁶⁺ treatments, and 86% under 40 mg·L^-1 Cr⁶⁺ treatment. All the results indicate that Cr⁶⁺ stress leads to a significant decrease in the absorption of Fe, Mn, Zn and Cu, hinders photosynthesis, impairs antioxidant systems and inhibits plant growth, which ultimately leads to a decrease in the ability of the artificial wetland to treat Cr⁶⁺ containing wastewater.