| Since the implementation of the project of returning cultivated land to forestry on the Loess Plateau,as a suitable species,Alfalfa has been planted in large quantities.According to the different planting years(1 years,10,20,30)of alfalfa in loess area,we used different polar extracts(ethyl acetate and methylene chloride)to extract their rhizosphere soil,and analyzed the contents and differences of root exudates by GC-Ms.At the same time,we extracted the alfalfa root exudates under hydroponics by indoor artificial simulation,and treated with different concentrations to soil,then analyzed the changes of soil available nutrients and enzyme activity.Finally we analyzed the root exudates which under hydroponics treatment by GC-Ms.The conclusions are as follows:1.The root exudates of alfalfa mainly contain alkanes,esters,alcohols,acids,phenols,ketones,and ethers.The proportion of alkane compounds in the all compounds extracted by methylene chloride and ethyl acetate is above 75%.The content of heneicosane was the largest,and its content increased with the growth of planting years.2.The results of extraction show that the comparison of the number of species by extracted is 30 years> 10 years> 20 years> 1 year.The number of 10-year and 20-year compound species was almost the same among them.And the 30-year compound species was significantly higher than 1 year(P <0.05).The proportion of root exudates of alfalfa planted with 10,20 and 30 years in dichloromethane extraction results in a relatively large proportion of heneicosane,hexacosane and tetracosane,alfalfa secretion in turn with diethyl phthalate,1.54-dibromo-tetradecane,eicosane,hexacosane,such as a large proportion of the proportion.The results of ethyl acetate extraction show that the relative content of heneicosane was the largest in the four years of extraction,which accounting for 8.82%,11.5%,17.85% and 25.69%,then followed by tetracontane and hexacosane.However,comparing with the results of methylene chloride,it extracted relatively few species.3.The alkane compounds accounted for 89.5% of the total species in alfalfa root extraction by methylene chloride under the hydroponic conditions.Among the acidic,neutral,and alkaline components extracted from ethyl acetate,the alkane compounds accounted for 78.1%,75.1%,and 87.5% of the total material species,and still be the main substances.In addition,a small amount of lipids,alcohols,acids,amides were also found.There are six kinds of common substances in the acidic,neutral,and alkaline components in the ethyl acetate phase,including five alkane compounds and one lipid compound.They are respectively butyric acid-2-methyl-Esters,2,2,4,6,6-pentamethyl-heptane,eicosane,pentadecane,pentacosane,and tetradecane.In the methylene chloride phase,the relative content of hydrocarbons in each component is above 94%.Most of them are saturated chain alkanes and a few are unsaturated hydrocarbons and naphthenes.It can be seen that the hydrocarbons account for a large proportion.4.After adding different concentrations of alfalfa root exudates in the soil,the content of soil microbial carbon,nitrate nitrogen,available phosphorus,and quick-acting potassium increased to some extend compared to the control treatments(P < 0.05),but there was no significant changes of organic matter and ammonium nitrogen content.In terms of enzyme activity,the urease content was significantly lower(P < 0.05)than that of the control at low,medium,and high concentrations;the invertase content was significantly lower at medium and high concentrations(P <0.05);The content of phosphatase was significantly lower than that of the control under medium concentration treatment,but significantly increased under high concentration treatment(P < 0.05).In addition,the content of glucosidase,cellobiohydrolase,and acetylglucososidase were no significant difference between the three treatments. |
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