| Pinus massoniana is the most widely distributed,the highest degree of comprehensive utilization conifer species in south area in our country,having fast-growing,high–yield,droughtresistant,east-updating,and other excellent features.Whether there is a continuous degradation and the rhizosphere environment how to change after the successive planting of Pinus massoniana has become the problem to be solved urgently.At present,there are few studies on the root exudates and its rhizosphere effect of Pinus massoniana.Adopting the method of space replace time and sample plot couples,take the 1st and 2nd generations of pinus massoniana as study objects,collecting its rhizosphere soil and using organic extraction,GC-MS and biological detection technology,this thesis discusses the chemical composition of root exudates of 1st and 2nd Pinus massoniana plantations with different seasons and different ages and study the allelochemicals after the successive rotation.By setting high(1 mg·mL-1),medium(0.5 mg·mL-1)and low(0.25 mg·mL-1)in three concentrations of rhizosphere soil extract and three kinds of allelochemicals to understand the allelopathy effects on seeds and seedlings of Pinus massoniana.In addition,study on the changes of soil nutrients,enzyme activities andmicroorganisms in rhizosphere soil after successive planting of Pinus massoniana,the effects of root exudates on rhizosphere microecological environment were discussed.It provides scientific basis and theoretical guidance for the future maintenance and sustainable management of Pinus massoniana.The main results are showed as follows:(1)Through ethanol extraction,varieties of 1st and 2nd Pinus massoniana plantation rhizosphere soil extracts contain respectively 46 and 49 components,while there contain respectively 36 and 37 components by using methanol.Two kinds of extraction methods are the highest relative content of acid substances.Therefore,in terms of the amount and the categories of components,ethanol extraction performs better than methanol.The number of soil extracts in the rhizosphere soil of the two generations were increased with age,and showed the seasonal variation which is spring>autumn>summer.The chemical constituents of rhizosphere soil extracts of 1st and 2nd generations with different age and different seasons were mainly acids and esters,among them,relatively high content of acid substances are palmitic acid,stearic acid and dehydroabietic acid.Compared with the 1st generation,the number of extracts in the 2nd generation rhizosphere soil increased,in particular,the type and content of organic acids are increased.Comparison of GC-MS results of rhizosphere soil extracts of 1st and 2nd Pinus massoniana plantation,the allelochemicals substances accumulated in rhizosphere soil after Pinus massoniana successive planting were palmitic acid,2,4-Di-tert-butylphenol,(Z)-9-Octadecenamide etc.(2)The allelopathic effect of rhizosphere soil extracts on the seed germination and seedling growth of the 1st and 2nd generations was the highest,medium concentration inhibition,low concentration promotion,the results of germination and shoot growth were treated by rhizosphere soil extracts of 2nd generation of Pinus massoniana were better than those of 1st generation.The effects of different concentrations of rhizosphere soil extract of Pinus massoniana on the seedling height,ground diameter and aboveground biomass of Pinus massoniana seedlings were promoted in different degrees,and the effect was enhanced with the concentration reduction.The overall performance for the 2nd generation is better than 1st generation,the differences between the intergenerational of all indicators were not significant,indicating that there was no obvious autotoxicity of Pinus massoniana replanting for the second generation.(3)Under the three treatments of high,medium and low concentration levels,three kinds of allelochemicals have allelopathic effect with different degrees on seeds and seedlings.At the high concentration,the three allelochemicals had inhibitory effects on seed germination and seedling growth,and the inhibitory effect was 2,4-Di-tert-butylphenol>palmitic acid>(Z)-9-Octadecenamide.Under low concentration level,palmitic acid and(Z)-9-Octadecenamide could promote seed germination rate and seedling growth index,the enhancement of palmitic acid is more obvious.Three concentrations of(Z)-9-Octadecenamide have negative effect on the seed vigor index,germination index and radicle length,while different concentrations of 2,4-Di-tert-butylphenol inhibited the seed germination,seedling height,ground diameter and aboveground biomass of Pinus massoniana,and the inhibitory effect increased with the increase of concentration.(4)The pH value of rhizosphere soil in middle-aged and mature forest of Guangxi,mature forest of Guizhou was decreased with the successive planting.The contents of soil organic matter,total N,total P,total K and available K in rhizosphere soil were decreasing of the 2nd generation of middle-aged and mature forests in Guangxi,while the content of available N and available P in the soil increased.Compared with Guangxi,the content of soil organic matter,total N,total P and available nutrient in mature forest of Guizhou were increased after successive planting,but the content of total K decreased with the increase of planting algebra.(5)The microorganism quantity and enzyme activity in rhizosphere soil in mature forest of 2nd generation of Guizhou higher than 1st generation.The number of actinomycetes in rhizosphere soil of middle-aged and the activity of polyphenol oxidase,acid phosphatase of middle-aged and mature forest of Guangxi performance the characteristic is 2nd generation less than 1st generation,while other microorganism quantity and enzyme activity of 2nd generation higher than the 1st.The correlation analysis showed that there were significant negative correlation between microorganism and enzyme with the pH,and significant positive correlation with organic matter,total N,total P and available K in soil.(6)The microorganism quantity and enzyme activity in mature forest of Pinus massoniana in Guizhou have obvious seasonal variation.The quantity of microorganism was summer>spring> autumn.The peak period of soil urease,catalase and acid phosphatase activity was summer,and the peak period of polyphenol oxidase activity was autumn.The quantity of bacteria,fungi,actinomycetes and the activities of urease,polyphenol oxidase,acid phosphatase and catalase in the rhizosphere soil of 2nd generation were higher than the 1st in different seasons.(7)The nutrient content,microorganism quantity and enzyme activity of rhizosphere soils were higher than those of non-rhizosphere soils,indicating that the root exudates of Pinus massoniana had rhizosphere positive effect on soil environment. |
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