Allelopathic Effects Of β-sitosterol In Mirabilis Jalapa L. On Soybean And Maize When Treated With Cadmium

Cadmium（Cd）pollution in soil and invasion of alien plants have become important environmental problem,which seriously endangers the production of agriculture,forestry and animal husbandry.At present,there have been relevant studies on the remediation of heavy metal pollution in soil by invasive alien plants,but there are few reports on whether invasive alien plants will have adverse effects on agricultural production during remediation.Therefore,Mirabilis jalapa L.an ornamental invasive plant,was selected as the research object,and soybean and maize were used as allelopathic to study the allelopathic effects.First,under different 0–5mg·L^-1 Cd concentration treatments,using hydroponics to culture the root exudates of Mirabilis jalapa L.were measured,and their allelopathic effects on soybean and maize were determined.Secondly,using soil culture test,we cultivated Mirabilis jalapa L.in 0–25 mg·kg^-1 Cd-contaminated soil,and planted soybean and maize on the soil that had been cultivated with Mirabilis jalapa L..The pre-cultivation soil was divided into rhizosphere and non-rhizosphere,and sterilized and non-sterilized treatments were performed.The soil without Mirabilis jalapa L.was used as a control to study the effect of Mirabilis jalapa L.planting soil on 2 crops.Finally,the root exudates of Mirabilis jalapa L.in hydroponics and soil culture were collected,and the sterol allelopathic substances in the plants and root exudates were analyzed and determined.Under a certain concentration of Cd treatment,the allelopathic effect ofβ-sitosterol was further explored by exogenously adding a certain concentration(0-2mg·L^-1)ofβ-sitosterol,and the resistance of the two crops to allelopathy was determined.Oxidase（peroxidase POD,catalase CAT,superoxide dismutase SOD）,malondialdehyde（MDA）,chlorophyll content,root activity,soluble sugar and proline changes.The main findings of the paper show that:1.The Mirabilis jalapa L.was tolerant to Cd under the treatment of 0–5 mg·L^-1Cd,and its growth was not severely inhibited.Under Cd treatment,Mirabilis jalapa L.root exudates showed allelopathic inhibitory effects on soybean germination potential and germination rate.From the allelopathic response index（RI）,under 3 mg·L^-1 Cd treatment,Mirabilis jalapa L.root exudates had an allelopathic inhibitory effect on soybean germination potential and germination rate.Soybean germination potential had the greatest allelopathic inhibitory effect（RI=-65.85%）,while maize seed germination rate,seedling height,and root length still showed allelopathic promotion even when treated with high concentration of Cd(5 mg·L^-1).With the increase of Cd concentration,the effect of Mirabilis root exudates on soybean was greater than that in maize.In addition,the effects of Mirabilis jalapa L.root exudates on the physiology of soybean and maize were also different.Under the treatment of 1 mg·L^-1Cd-induced root exudates,the SOD activity of soybean seedling leaves was significantly increased compared with the control.Under the root exudates induced by3 and 10 mg·L^-1 Cd,the POD activity of the seedling leaves was significantly lower than that of the control;the MDA content of soybean seedling leaves was induced by0 mg·L^-1 Cd and 5 mg·L^-1 Cd.The root exudates of 3 mg·L^-1 Cd-induced root exudates were significantly lower than the water control,and the MDA content was significantly higher than that of the control.The Mirabilis jalapa L.root exudates had no significant effect on antioxidant enzyme activity,malondialdehyde,chlorophyll content,root activity,proline and soluble sugar in leaves of maize seedlings.2.In the soil culture experiment,under sterilization conditions,in the rhizosphere and non-rhizosphere soil that had grown Mirabilis jalapa L.under 2 mg·kg^-1 Cd pollution,the allelopathy index SE of soybean was significantly lower than that of the control（without Cd addition）.while the SE value of soybean under 25 mg·kg^-1 Cd pollution was significantly higher than that of the control,and the SE in the non-rhizosphere soil was significantly lower than that in the rhizosphere soil（P<0.05）.Under unsterilized conditions,the SE of soybeans in the rhizosphere and non-rhizosphere soil of Mirabilis jalapa L.under different Cd contamination conditions were all less than 0 mg·kg^-1Cd contamination,under 2 mg·kg^-1 and 25mg·kg^-1 Cd contamination,and the SE was significantly lower than 0,The allelopathic comprehensive index of maize in sterilized rhizosphere,unsterilized rhizosphere and non-rhizosphere soil were all greater than under different Cd contamination.It can be seen that in different Cd-contaminated soils,the independent allelopathic effects of Mirabilis jalapa L..3.Under hydroponic conditions,with the increase of Cd treatment concentration,under 5 mg·L^-1Cd treatment,the content ofβ-sitosterol in the roots of Mirabilis jalapa L.was significantly lower than the control,while the content ofβ-sitosterol in root exudates was significantly higher than the control.Similarly,under soil culture conditions,the content ofβ-sitosterol in the root exudates of Mirabilis jalapa L.under the treatment of 25 mg·kg^-1Cd was significantly higher than that of the control.That is,with the increase of Cd treatment concentration,the roots of Mirabilis jalapa L.will secrete moreβ-sitosterol.Sinceβ-sitosterol was only detected in the root exudates of Mirabilis jalapa L.,it can be seen thatβ-sitosterol in sterols can enter the environmental medium through the roots.When 0.125 mg·L^-1β-sitosterol was added exogenously,the seed germination and seedling growth of soybean and maize were significantly inhibited,while otherβ-sitosterol treatment concentrations promoted the growth of maize seedlings,while soybean was affected by different treatments.degree of allelopathic inhibition.The MDA content of soybean leaves was significantly higher than that of the control under the treatment of 0.125 mg·L^-1β-sitosterol,while the change of maize MDA content was not significant.At the same time,the contents of chlorophyll a and carotenoid in soybean and maize seedlings were significantly decreased compared with the control under low and high concentrations ofβ-sitosterol treatment.Different concentrations ofβ-sitosterol had different allelopathic effects on the two crops under Cd treatment,and the allelopathic inhibitory effect on soybean was higher than that in maize.To sum up,although Mirabilis jalapa L.still secretes the allelochemicalβ-sitosterol under Cd stress,it has an allelopathic effect on crops and provides a strong support for its successful invasion of new habitats,and ecological risks still exist.However,choosing suitable low-accumulation maize and intercropping can still turn harm into benefit.