The Allelopathy Of Eucalyptus Grandis X E.urophylla Leaves And Its Relationship With Soil Microbes

Plant allelopathy is closely related to soil microbes.A thorough understanding of the interaction between allelochemicals and microbes is essential for further study on the mechanism of plant allelopathy.Although many researches on the allelopathy of Eucalyptus have been reported,it is still rare studies on the correlation between soil microbes and eucalyptus allelopathy due to the complexity of soil ecosystem and experimental methods.Therefore,on one hand,the effects of Eucalyptus grandis x E.urophylla on the growth of native plant seedlings in Guangxi was investigated,and the effects of different soil-derived microorganisms on the activity,transformation and persistence of the allelochemicals of E.grandis x E.urophylla were studied.The other hand,the effect of allelochemicals on soil microbes was discussed from the aspects of soil microbial function and the diversity of bacterial community structure.Consequently the mutual relation of allelochemicals and soil microbes were discussed from the above researches,which will provide basis to further explore the mechanism and pathways of Eucalyptus allelopathy.The results will have important theoretical and practical significance to comprehensively understand the ecological effects of E.grandis x E.urophylla.The main results are as follows: 1.Effects of E.grandis x E.urophylla on the growth of native underground plantseedlings in GuangxiBy comparing the allelopathic effects of different E.grandis x E.urophylla leaves(green leaves,yellow leaves,gray leaves)in different way of treatments(pouring extract,laying leaves,leaves mixed in the soil)on the growth of Euodia lepta,Cipadessa baccifera and Rhus chinensis,it was found that the effect of pouring extract and laying leaves on the growth of recipient plants was not obvious.However,the high concentration of gray leaves and yellow leaves after decomposed in the soil 45 d,significantly inhibited the growth of seedlings and inhibition increased as the decomposition time prolonging.In the whole experimental stage old leaves did not inhibit the seedling growth.But the three leaves significantly inhibited the growth of the Euodia lepta roots.The results showed that the origin and the mode of treatment of E.grandis x E.urophylla leaves resulted in different allelopathy.2.Allelopathy of E.grandis x E.urophylla leaves on Chinese cabbage and functionaldiversity of soil microorganismBy comparing the allelopathic effect of E.grandis x E.urophylla leaves in different soils,we can see that soil microbes have the effect of reducing allelopathy,and the effect of different soil microbes is different.The initial decomposition of E.grandis x E.urophylla leaves inhibited the germination and growth of Chinese cabbage,and inhibition was weakened or became promoting effect as the decomposition time increased and by the microbial effect.The inhibition allelopathic effect of E.grandis x E.urophylla leaves in unsterilized soils of Ecucalyptus,cedar and native plant mixed forests plantations,on the germination and growth of Chinese cabbage,was lower than that in sterilized soils,and the promoting allelopathic effect was stronger than the latter.However,in the soil of wasteland,soil sterilization treatment did not cause significant differences on allelopathy of E.grandis x E.urophylla leaves.Through the biolog technique,it was found that when the E.grandis x E.urophylla leaves were relative fully decomposed in the soils of Eucalyptus forest,cedar forest and native plant mixed forests(20 d),they could promote the soil microbial activity(AWCD),but in the same decomposition time,soil microbes was still inhibited in wasteland soil.The fragmentation of E.grandis x E.urophylla leave also had a certain effect on the diversity index of soil microbes,which showed no obvious effect on Shannon index,the greatest impact on McIntosh index,and following Simpson index,indicating that the homogeneity of the microbial community and the dominance of the common species are affected.3.Effects of E.grandis x E.urophylla leave on structure diversity of soil bacteriamicrobialThe effects of the decomposition of E.grandis x E.urophylla leaves on the bacterial microbes of Eucalyptus,cedar,native plant mixed forest and wasteland soils were studied by high-throughput sequencing.It was found that structures of bacterial microbe in Eucalyptus,native plant mixed forest and wasteland soils was similar,which is obvious difference from that in cedar soils.Proteobacteria,Acidobacteria,Actinobacteria,Firmicutes,Verrucomicrobia,Bacteroidetes,Chloroflexi,Gemmatimonadetes,Planctomycetes belong to the preponderant categories in the tested samples.The E.grandis x E.urophylla leaves did not cause significant changes in the number of soil bacteria after a period of decomposition in soils,but the percentage of proteobacteria was increased and the content of actinomycetes was decreased.E.grandis x E.urophylla leaves decomposed in original forestry soils made the soil bacteria abundance and diversity increased,and when the soil microorganisms recultured in the sterile soil,the addition of E.grandis x E.urophylla leaves make their abundance and diversity reduce except for that of wasteland soil.The decomposition of E.grandis x E.urophylla leaves caused soil bacteria changes in the genus level.This experiment shows more changes in abundance,but this change also varied with the different of soil bacteria origins.The results showed that the decomposition products of E.grandis x E.urophylla leaves had a certain effect on the community structure of soil microbial.4.the effect of different chemical composition of extracts on the allelopathy of Chinesecabbage and soil microbesE.grandis x E.urophylla leave extract had a certain allelopathic effect on Chinese cabbage and the diversity of soil microbial function.Compared with the control group,the inhibitory effect of 40% and 80% methanol fractions of the HP-20 resin on the seed germination and seedling fresh weight was higher than that of the 20% methanol,but was lower than that of the total extract.Aqueous extract has the function of promoting the diversity of soil microbial function,and the function of HP-20 resin adsorption fraction on the microbes is more obvious.In general,the inhibitory effect of the fraction adsorbed by the resin is stronger than that of the unadsorbed components.5.the direct effect of microorganisms on the chemical composition of the extract and theeffect of allelopathyThe experiment that the microorganisms cultured in the E.grandis x E.urophylla leaves' s extract confirmed that the microorganisms have the ability to alter the chemical composition of the extract,and this ability varies from microbial sources.After the chemical composition of the extract is changed by the microorganism,its allelopathic effect on the cabbage is reduced.In conclusion,this study confirmed that the organic constituents of E.grandis x E.urophylla leave were the material basis of its allelopathy.Soil microbes had the effect of reducing the allelopathic effect of E.grandis x E.urophylla leaves on Chinese cabbage,and the effect of soil microbes was different.While E.grandis x E.urophylla leaves were decomposed in soils,the functional diversity of soil microbes and the structure of bacteria were also affected.