Pb^(2+)、Cd^(2+)复合胁迫对桑树光合作用的影响

Effects of Pb^(2+) and Cd^(2+) combined stress on photosynthesis of Morus alba

【目的】土壤重金属污染日益严重,重金属对植物的影响备受关注。目前,研究多限于重金属单一胁迫对植物的影响,但土壤重金属污染存在形式并不是只有一种重金属,而是由多种重金属复合而成,研究重金属单一胁迫与复合胁迫对植物生长及光合作用的影响与差异很有必要。【方法】本研究以桑树幼苗为实验材料,通过添加不同质量分数的Pb2+和Cd2+进行桑树幼苗土培实验,分析单一胁迫与复合胁迫对桑树幼苗生长指标、光合色素含量和光合作用指标的影响与差异。【结果】Pb2+单一胁迫降低了桑树叶绿素含量和类胡萝卜素含量,Cd2+单一胁迫对叶绿素含量是"低促高抑",对类胡萝卜素而是随Cd2+含量的增加抑制作用增强。复合胁迫对桑树光合色素含量起到抑制作用,且程度强于单一胁迫。桑树叶片的光饱和点(LSP)、最大净光合速率(Pnmax)、暗呼吸速率(Rd)及表观量子效率(φ)均受到重金属胁迫的抑制作用,且随含量增大,抑制作用增强。单一胁迫和复合胁迫对桑树叶片净光合速率(Pn)、气孔导度(Gs)、胞间CO2浓度(Ci)以及蒸腾速率(Tr)均起到抑制作用,从而显著地限制了桑树的生长。【结论】重金属单一胁迫及复合胁迫对桑树幼苗的生长指标、光合色素含量以及光合作用均有抑制作用,且重金属含量越高,桑树幼苗受到的抑制作用越强,复合胁迫对桑树幼苗的抑制作用存在协同效应,毒害程度强于单一胁迫;在重金属胁迫条件下,桑树表现出了较强的耐重金属性。

[Objective] Heavy metals in soil become more serious and the effects of heavy metals on plant are high profile. At present,most studies pay attention to the effects of single heavy metal stress on plants. Compound contamination of heavy metals is one of the important soil contamination types.Therefore,it is critical to investigate the effects of combined heavy metal contaminants on soil.[Method] Morus alba seedlings were treated with different concentration gradients of Pb2 ＋and Cd2 ＋separately and in combination, to investigate the effects of heavy metals on growth indices, the photosynthetic pigment content and its photosynthesis index in leaves of Morus alba. [Result]Photosynthetic pigment of Morus alba leaves decreased significantly under Pb2 ＋single stress. Chlorophyll contents increased under low concentration and decreased under high concentration while carotenoids content decreased significantly under Cd2 ＋single stress. Inhibition exists in the effect of compound heavy stress on photosynthetic pigment content and is stronger than one of single stress. Light saturation point（ LSP）,light compensation point（ LCP）,maximum net photosynthetic rate（ Pnmax）,dark respiration rate（ Rd）,apparent quantum yield（ φ） decreased as concentration of heavy metals increasing. Heavy metal stress all suppressed on net photosynthetic rate（ Pn）,intercellular CO2 concentration（ Ci）,stomatal conductance（ Gs） and transpiration rate（ Tr） of mulberry leaves and inhibited leaf biomass and plant height. [Conclusion] Both single and compound heavy metal stress all suppressed height growth,photosynthetic pigment content and photosynthesis index in leaves of Morus alba. The higher the concentration of heavy metals is,the stronger the inhibition on mulberry is. It shows a synergistic effect of Pb2 ＋and Cd2 ＋compound stress. Mulberry shows stronger resistance to heavy metal stress.