| With the development of industry and the use of pesticides and fertilizers in agriculture,heavy metals are increasingly harmful to soil.At present,phytoremediation,as a kind of bioremediation,has attracted much attention because of its low pollution and sustainability.Many scholars have found that Populus alba ×P.berolinensis(PAB)has fast growth,high yield and strong stress resistance,and its rhizome can enrich a large amount of heavy metals,which is the dominant tree species used to control heavy metal pollution in soil.However,there are few studies on the effect of complex heavy metal pollution on insect resistance of PAB.Therefore,three kinds of Cd(0.5 mg/kg,1.5 mg/kg,2.5 mg/kg)and Zn(300 mg/kg,500 mg/kg,700 mg/kg)were added to the soil of one-year-old PAB by orthogonal experiment design(3 x 3).After 30,40 and 50 days of stress,the effects of Cd and Zn stress on the growth and development of PAB,the accumulation ability of heavy metals and chemical defense,and the growth and detoxification ability of the larvae of gypsy moth feeding on its leaves were analyzed.1?The growth and development level of PAB seedlings and Cd enrichment ability in leaves were significantly reduced under Cd and Zn stress.Under Cd and Zn stress,the plant height,root length,dry weight and fresh weight of rhizome and leaf of PAB seedlings gradually decreased with the increase of Cd and Zn content.And the plant height,root length,dry weight and fresh weight of rhizome and leaf under high Cd and Zn stress were significantly lower than those under medium and low content stress(P<0.05),and the growth and development indexes under combined Cd and Zn stress were lower than those under single stress(P<0.05).Among them,under high Cd and Zn stress,plant height,root length,stem and leaf dry weight and fresh weight were significantly lower than those of the control group(P<0.05);under low Cd and Zn stress,only root dry weight and leaf dry weight were significantly different from those of the control group(P<0.05);under medium Cd and Zn stress,root length,stem and leaf dry weight were significantly lower than those of the control group(P<0.05).After 30,40 and 50 days of Cd and Zn stress,the contents of Cd and Zn in leaves of each stress group increased with the increase of Cd and Zn contents in soil,and under high Cd stress,the contents of Zn in leaves were significantly higher than those under medium and low Cd stress(P<0.05);the combined stress of Cd and Zn inhibited the accumulation of Cd in leaves,but had no significant effect on the accumulation of Zn in leaves.2?The activity of defense proteins in leaves of PAB were significantly reduced under the compound stress of Cd and Zn.Under Cd and Zn combined stress,the activities of defense proteins and the contents of secondary metabolites in leaves of PAB decreased with the increase of Cd and Zn combined stress,and the activities of defense enzymes and protease inhibitors and the contents of secondary metabolites in leaves of PAB under high Cd and Zn combined stress were significantly lower than those under medium and low content combined stress(P<0.05).The activities of PAL,PPO,catalase,peroxidase(POD),trypsin inhibitor(TI)and chymotrypsin inhibitor(CI)were significantly lower than those of the control group(P<0.05)after 30,40 and 50 days of combined stress with moderate and high Cd and Zn content(P<0.05),and after 50 days of combined stress with low Cd and Zn content,the activities of PAL,PPO,catalase,POD,TI and CI were significantly lower than those of the control group(P<0.05).PAL activity was significantly lower than that of control group(P<0.05).3?The content of secondary metabolites in leaves of PAB were significantly reduced under compound stress of Cd and Zn.Under the combined stress of Cd and Zn,the content of secondary metabolites in leaves of PAB decreased with the increase of Cd and Zn contents,and the content of secondary metabolites in leaves of PAB under the combined stress of high Cd and Zn contents was significantly lower than that under the combined stress of medium and low contents(P<0.05).The content of flavonoids and lignin was significantly lower than that of control group(P<0.05)after 30,40 and 50 days,and the content of flavonoids after 30 and 40 days was also significantly lower than that of control group(P<0.05)under the combined stress of Cd and Zn.4?The growth and development level and detoxification ability of gypsy moth larvae feeding on leaves of PAB were reduced under the compound stress of Cd and Zn.The body length,body weight and head width of the 3rd and 4th instar gypsy moth larvae decreased with the increase of Cd and Zn contents under the combined stress of Cd and Zn.The body length,body weight and head width under high concentration stress were significantly lower than those under low concentration stress(P<0.05).The body weight,body length and head width of 3rd and 4th instar gypsy moth larvae under high Cd and Zn stress were significantly lower than those of the control group(P<0.05).The activities of detoxification enzymes and antioxidant enzymes of the 3rd and 4th instar larvae of gypsy moth first increased and then decreased with the increase of Cd and Zn contents.Among them,the activity of detoxifying enzymes under low zinc stress was significantly higher than that of control group(P<0.05).In conclusion,Cd and Zn combined stress significantly inhibited the growth and development level of PAB seedlings,and reduced the accumulation ability of cadmium in leaves.Compound stress of Cd and Zn significantly reduced the activity of defense proteins and the content of secondary metabolites in leaves of PAB,and showed a certain concentration and time effect Cd and Zn combined stress inhibited the growth and development of gypsy moth larvae,and promoted the detoxification ability of gypsy moth larvae first and then inhibited.Therefore,it can be predicted that the outbreak trend of gypsy moth feeding on silver poplar in heavy metal contaminated soil will be weakened. |
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