| The northeast grassland ecosystem is one of the largest grassland ecosystems in China,which is called as China’s "big granary",and it supports a series of animal husbandry and agricultural economic activities.So,it has very important ecological significance to China’s ecological security construction,animal husbandry and agricultural economic development,and social sustainability.Freeze-thaw and allelopathy are the two main ecological stress factors in the northeast grassland ecosystem of China.However,previous studies mostly focused on the effects of a single factor of freeze-thaw or allelopathy on plants,and little attention was paid to the combined stress of freeze-thaw and allelopathy on grassland plants,which was not conducive to the scientific management of grassland ecosystems in high-latitude regions including grassland fragile ecological zones and northeast grassland.In this study,rye(Secale cereale L.)was used as experimental material,and artemisinin and Ambrosia trifida L.extract were used as allelopathic factors.By simulating the freeze-thaw environment indoors,the physiological effects of combined stress of freeze-thaw and allelopathy on rye seedlings under two different freeze-thaw patterns,single freeze-thaw cycle and multiple freeze-thaw cycles,were explored.To determine the changes of physiological characteristics in the leaves of rye seedlings.The main results were as follows:(1)Single Freeze-thaw Cycle: Under allelopathy stress,the activities of malondialdehyde(MDA),soluble protein(SP),superoxide dismutase(SOD)and catalase(CAT)in rye seedlings significantly increased 18.6～110.0%,the respiratory rate(Rr)significantly decreased 15.0～22.9%.Under single freeze-thaw cycle stress,the contents of MDA and SP in rye seedlings increased first and then decreased with the freeze-thaw process(first freezing and then thawing),significantly increased21.8～96.7%,while SOD,CAT and Rr decreased first and then increased,SOD and CAT activities increased 0.4～73.0%,Rr significantly decreased 40.7～57.0%.During the freezing stage,combined stress of freeze-thaw,artemisinin,A.trifida extract(FT-CS)had the greatest effect on MDA content of rye seedlings,which increased by 150.4%(P < 0.05),resulting in severe membrane lipid peroxidation in cells of rye seedlings,and at the same time significantly inhibited the SOD activity,which decreased by 13.3%(P < 0.05).During the thawing stage,the freezing pressure was reduced,and the activities of SOD and CAT in rye seedlings were restored to a certain extent,so as to alleviate the reactive oxygen species stress induced by FT-CS.(2)Multiple Freeze-thaw Cycles: Under allelopathic stress,the MDA content,soluble sugar(SS)content,SOD and CAT activities of rye seedlings significantly increased 40.4～161.9%,and the net photosynthetic rate(Pn)significantly decreased57.9～84.9%.Under multiple freeze-thaw cycles stress,the physiological responses of rye seedlings to different stresses were showed as combined stress of multiple freezethaws,artemisinin and A.trifida extract(FTs-CS)> combined stress of multiple freezethaws and A.trifida extract(FTs-AES)> multiple freeze-thaws(FTs)> combined stress of multiple freeze-thaws and artemisinin(FTs-AS).In the FTs-AS treatment,the activities of SS and antioxidant enzymes SOD and CAT in rye seedlings significantly increased by 128.7%,63.4%,and 141.8%,respectively(P < 0.05),indicating that artemisinin could significantly improve the osmotic regulation ability and antioxidant enzyme activity of rye seedlings under multiple freeze-thaw environments.FTs-CS had the strongest promoting effect on the MDA content of rye seedlings,which increased by 293.7%(P < 0.05),and the SOD activity,CAT activity,and photosynthetic parameters of rye seedlings significantly reduced by 20.6～98.8%,indicating that FTsCS could cause greater damages to the physiology of rye seedlings.In summary,whether it was single freeze-thaw or multiple freeze-thaws,there is a strong synergistic interaction effect between the indoor simulated freeze-thaw environment and the combined allelopathy of artemisinin-A.trifida extract on rye seedlings.Combined stress of freeze-thaw-artemisinin-A.trifida extract caused the most serious physiological damage to rye seedlings,which destroyed the cell membrane structure of rye seedlings,aggravated cell water loss,and inhibited the activities of antioxidant enzymes.Thus,in the management of grassland ecosystem in Northeast China,the interaction effect between freeze-thaw and allelopathy on grassland plants should be considered.Especially,during the period of frequent freeze-thaw cycles in winter,it is necessary to remove Artemisia annua L.and A.trifida plants including their rhizosphere soil in time,so as to avoid the grassland ecological disaster caused by the freeze-thaw combined stress. |
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