Physiological Effect Of Autotoxicity And Allelopathy On Alfalfa And Wheat

This study aimed to understand the effect of different concentrations of plant extracts from alfalfa and wheat on the autotoxicity and allelopathy mechanisms of alfalfa and wheat.Legume crops?Medicago sativa L.cv.Gannong No.2?and gramineous crop?Triticum aestivum L.cv.Longchun BJ103?were used as the tested materials by intraspecific and interspecific irrigating plant extracts from seedlings to simulate continuous cropping and rotation.Additionally,four exogenous autotoxic substances,including cinnamic acid,hydroxamic acid,coumarin and tricin,were selected to study the effects of exogenous substances on the growth of alfalfa and wheat.The results as follows:1.Under the intraspecific irrigation conditions,the germination rate,radicle length and hypocotyl length of the alfalfa receptors was restricted,plant height,root length,plant fresh weight and root fresh weight of seedlings were lower than the control plants.Alfalfa growth was obviously inhibited with the increasing concentrations of plant extracts.When the concentration of alfalfa extracts was greater than 0.1 g·L^-1,the activities of SOD,POD and CAT in alfalfa seedlings decreased while MDA content,H₂O₂ content and relative membrane permeability increased.Different concentrations of wheat extracts had prominent autotoxicity on the wheat receptors,Alfalfa showed a stronger autotoxicity than wheat in the terms of the inhibition of growth rate.The results of stepwise regression analysis showed that SOD activity was a key indicator affecting the autotoxicity of alfalfa and wheat.2.Under the interspecific irrigation conditions,,both alfalfa and wheat showed positive allelopathy when the concentrations of extracts were 0.1 g·L^-1,0.25 g·L^-1 and 0.5 g·L^-1,and the most positive allelopathy was found when the concentration of extracts was 0.25 g.L-1,meanwhile,the increased activities of SOD,POD and CAT of the receptors of alfalfa and wheat caused the decrease in MDA content,H₂O₂ content and relative membrane permeability,thereby promoting growth of the receptor wheat.Compared with the control plants,the germination rate,radicle length,coleoptile length of receptor wheat were 13.80%,18.45%and 15.16%higher,respectively;the plant height,root length,plant fresh weight and root fresh weight were 18.90%,12.47%,14.61%and 11.79%higher,respectively;and the germination rate,length of the embryo root and hypocotyl were 8.60%,32.13%and 29.48%higher,respectively;plant height,root length,plant fresh weight,root fresh weight were 33.06%,37.34%,43.83%and 52.59%higher,respectively.The positive allelopathy of wheat extracts on alfalfa was obviously greater than the positive allelopathy of alfalfa extracts on wheat.When the concentration of extracts was 1 g·L-1,the activities of SOD,POD and CAT decreased while the levels of MDA,H2O2 and the relative membrane permeability signif icantly increased.The effective accumulation of reactive oxygen species destroyed the normal metabolism and inhibited the growth,thus causing the negative allelopathy on alfalfa and wheat with the more prominent effect on alfalfa.The rotation effect of alfalfa and wheat showed a concentration effect of?low boost and high inhibition?.The results of stepwise regression analysis showed that relative membrane permeability,CAT activity,SOD activity were key indicator affecting the allelopathy of alfalfa and wheat.CAT activity,H₂O₂content and relative membrane permeability were key indicator affecting the the allelopathy of alfalfa and whea3.There was a difference effect of exogenous allelopathy substances on alfalfa and wheat.Under the treatments of cinnamic acid,hydroxamic acid,coumarin and tricin,germination index,seed germination,seedling growth and root activityof alfalfa were decreased with the increases in the concentrations of autotoxic substances.Moreover,the results of the effect of four autotoxic substances on wheat growth showed that only the inhibitory effect of coumarin on wheat had a significant concentration effect,while cinnamic acid,hydroxyalbinoic acid and tricin at low concentrations basically had no toxicity effect on the seed germination,seedling growth and root activity of wheat,and only the treatment concentration was up to 0.01g.L^-1 or more showed concentration-dependent inhibition.The effects of four exogenous autotoxic substances on the physiology of alfalfa and wheat were also different.The results of stepwise regression analysis showed that CAT activity was a key indicator affecting the cinnamic acid of alfalfa,and CAT activity was a key indicator affecting the cinnamic acid of wheat.the POD activity was a key indicator affecting the hydroxybenzoic acid of alfalfa,SOD activity and MDA content were key indicator affecting the hydroxybenzoic acid of wheat,relative membrane permeability and CAT activity were key indicator affecting the coumarin of alfalfa,relative membrane permeability and H₂O₂ content were key indicator affecting the coumarin of wheat,SOD activity was a key indicator affecting the tricinof alfalfa,SOD,CAT activity and H₂O₂ content were key indicator affecting the the tricin of wheat.Four exogenous allelopathy substances had a greater effect on the physiology of alfalfa than wheat.