| Lilium davidii var.unicolor salisb is known as‘vegetable ginseng'.In recent years,due to the surge of demand,continuous cropping obstacle has become a common problem.Therefore,it is of great practical significance to study the effect and mechanism of continuous cropping obstacle of Lanzhou lily based on autotoxic effect.Firstly,we conduct a pot experiment to explore the negative effect of autotoxic substances on the growth,production and quality of Lanzhou lily which exist in the soil containing fresh Lanzhou lily stubble and soil from fields where Lanzhou lily has been cultivated for 2 or 4 years.At the same time,we study the effect of water extracts of different organs and rhizosphere soil of different continuous cropping years on the seedlings growth of lily and identify the chemical substances.On this basis,we select the typical autotoxic substances and study the direct effect of these typical autotoxic substances on the growth of lily by using hydroponic test.This paper is funded by the National Natural Science Foundation Project?31560380?.The main results are as follows:1.The results of diaphragm chamber test show that the autotoxic substances in continuous cropping soil can cut down production and quality of lily by reducing the antioxidant enzyme activity of lily plant,damaging free radical metabolic balance and damaging the structure and function of the cell membrane,and this effect increases with the extension of continuous years.In the seedling stage,bulb growth stage and maturity stage,the changes of physiological and biochemical characteristics of lily leaves in all treatments are basically the same.With increase in number of continuous cropping years,the enzyme activity of catalase?CAT?and superoxide dismutase?SOD?decrease,the enzyme activity of peroxidase?POD?firstly increases and then decreases,the content of proline,soluble sugar and malondialdehyde?MDA?and the relative conductivity increase.In the bulb growth stage,the total chlorophyll content?Chl?,net photosynthetic rate?Pn?,stomatal conductance?Gs?,and transpiration rate?Tr?decrease gradually,and the intercellular CO2 concentration?Ci?increases with the extension of continuous cropping years.The main physiological factors affecting net photosynthetic rate in all treatments are transpiration rate?Tr?and water utilization efficiency?WUE?.In treatments of continuous cropping system for 2 or 4 years,the total sugar content decrease by 5.38%and11.42%,the sugar content decrease by 13.10%and 40.48%,and the crude fat content increase respectively by 35.90%and 61.54%compared with those in non-replant lily.Both of the increase or decrease extent show significant at P<0.05.2.The results of study on the autotoxic effect of water extracts from different organs and soil in Lanzhou lily show that the water extracts of the stem and leaf,root and bulb of Lanzhou lily showed inhibitory effect on the seedlings growth of lily,and there was a concentration effect.When the concentration is greater than 100 mg·mL-1,the seedling length,fresh weight,root length and root fresh weight of lily seedlings are significantly decreased in each treatment?P<0.05?.With the concentration of water extracts increasing,three enzyme activity of CAT,POD and SOD firstly increase and then decrease,and the MDA content and the relative conductivity change to the opposite tendency.The content of proline and soluble sugar increase significantly?P<0.05?when the concentration is morn than 100 mg·mL-1.Under the same concentration condition,the autotoxic effect of stem and leaf water extract is the strongest,followed by the autotoxic effect of root water extract,and the effect of bulb water extract is the weakest.The seedling growth of Lanzhou lily is promoted at low concentration,and inhibited at high concentration by the water extracts of soil collected from fields where Lanzhou lily have been cultivated for 0,2 or 4 years and the higher the concentration of the water extracts,the stronger the inhibitory effect is.When the concentration is increased to 300 mg·ml-1,the seedling length,fresh weight,root length and root fresh weight of lily seedlings are significantly decreased in each treatment?P<0.05?.The changes in three enzyme activity of CAT,POD and SOD are consistent as the concentration of water extracts increase.POD firstly increase and then decrease,and CAT and SOD continue to rise.The contents of proline,soluble sugar and MDA increase with the concentration of water extracts increasing,and when the concentration is 200300 mg·mL-1,the increase extent show significant at P<0.05.3.The results of the identification of various organs in Lanzhou lily and the soil in different continuous years show that there are variability in the types and amounts of autotoxic substances contained in different tissues,which is the reason that causes the difference in the autotoxic effect of the water extracts of stems and leaves,root and bulbs of Lanzhou lily.There are 32 species in the stems and leaves of lily,23 species in the root,and only 14 compounds in the bulb,and the similarity coefficient is 23.08%.The compounds identified from the three organs mainly include 2,3-butanediol,toluene,3-methylcyclopentane-1,2-dione,dodecenyl succinic anhydride,syringaldehyde,vanillin,antioxidant 2246,diisobutyl phthalate,dibutyl phthalate and dioctyl terephthalate,benzoic acid,hydrocinnamic acid,trans-Cinnamic acid,2-methoxy-4-?1-propenyl?-phenol,2-methoxy-4-vinylphenol,dodecanoic acid,tetradecanoic acid etc,most of these are reported as autotoxic substances.Antioxidant 2246 and dioctyl terephthalate are present in all organs and have relatively high relative contents.With the prolongation of continuous cropping years,the increase in the variety and quantity of autotoxic substances in the rhizosphere soil lead to the strongest autotoxic effect of soil water extract in 4 years of continuous cropping,followed by 2 years of soil water extract,followed by positive soil water extracts.In the harvesting period,17 species,15 species,and 9compounds are identified from soil of continuous cropping for 4,2,0 years.The similarity coefficient is only 6.67%.The main compounds present in the treated soil include1,2,3-trimethylbenzene,dioctyl terephthalate,toluene,2,3-butanediol,p-xylene,antioxidant2246 etc.Antioxidant 2246 and dioctyl terephthalate are also present in all treated soils and have relatively high relative contents.In growth period,19 species,15 species,and 11compounds are identified from soil of continuous cropping for 4,2,0 years.The similarity coefficient is only 14.29%.The main compounds present in the treated soil include 2,3-butanediol,1,4-xylene,2,6-dibutyl toluene,dioctyl phthalate,isooctyl alcohol,antioxidant2246,dibutyl phthalate and dioctyl dioctyl phthalate etc.Most of them have also been reported as autotoxic substances.4.The results of the study on the autotoxic effect and mechanism of the typical autotoxic substances are that the autotoxic substances firstly exert autotoxicity on the cell membrane,induce the increase of membrane lipid peroxidation,and promote the damage of cell membrane structure and function of lily plants.Different structures of autotoxic substances have different effect on the growth of lily.In the concentration range of 0.025 mg·mL-1,2,3-butanediol has the promoting effect on the seedlings growth of lily and the promoting effect decrease with the concentration increasing.Under lower concentration,dioctyl terephthalate and antioxidant2246 do not show the inhibitory effect,which actually has the promotion effect.But at high concentration,they show inhibitory effect,but the inhibitory effect of dioctyl terephthalate is stronger than 2,3-butanediol.With the increase of solution concentration,the activity changes of CAT,POD and SOD in lily seedlings treated with 2,3-butanediol are less.The activity of POD in the seedlings treated with antioxidant 2246 is significantly reduced at 5 mg·ml-1.The activity of three enzymes in the seedlings treated with dioctyl terephthalate firstly increase and then decrease with the increase of solution concentration and when the concentration was 5mg·mL-1,the activity of CAT,POD and SOD significantly fall by 58.34%,39.09%and 44.25%.The contents of MDA in three treatments decrease,and the contents of soluble protein change to the opposite tendency.When the concentration reaches 5 mg·mL-1,the content of MDA in lily seedlings of dioctyl terephthalate and antioxidant 2246 treatments increase by 69.09%and37.95%,and the content of soluble protein decrease by 36.60%and 15.84%respectively.Both of the increase or decrease extent show significant at P<0.05.When dioctyl Terephthalate?D?and antioxidant 2246?A?with different autotoxic effect are cross-tested at concentrations of 0.2 and 5 mg·mL-1,the physiological and biochemical characteristics of lily seedlings do not change significantly,and It is determined that the solution of D0.2A5,D5A0.2 and D5A5 have a certain inhibitory effect on the growth of lanzhou lily seedlings,but the degree of inhibition is not obvious compared with the control.For different growth indicators,when the above two compounds are applied alone,if the direction of action is the same,additive effect is not exhibited under the condition of co-application,and if two compounds have opposite directions under single application conditions,they show some antagonistic effect under the mixed condition.5.Based on the above results,it is concluded that autotoxicity is an important reason for the occurrence of continuous cropping disorder of Lanzhou lily.The metabolites of various organs of lily plants and the accumulation of autotoxic components in continuous cropping soil are the material basis of autotoxicity.Autotoxic substances can inhibit the growth of lily seedlings and eventually cause a decline in the production and quality of Lanzhou lily by inducing the peroxidation of lily seedlings,inhibiting the activity of antioxidant enzymes,destroying the integrity of cell membrane,and reducing the photosynthetic ability of lily leaves. |
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