| How exotic pests adapted to the new environment to establish populations and continue to expand was an important hot issue in the research of invasive biology.Large-scale biogeographic comparisons showed that many exotic harmful plants had invaded a certain region from their"hometown" and had undergone changes in their adaptive characteristics,such as natural enemy resistance and interaction with rhizosphere soil microorganisms,which laid the foundation for their subsequent regional expansion of biological ecology.Previous studies indicated that Ageratina adenophora showed adaptive changes that were favorable for expansion in the invasive areas,such as increased allelopathy and decreased resistance to specific natural enemies.Recently,we found that A.adenophora could promote the increase of the beneficial rhizosphere Bacillus cereus through root exudates,and this change had a positive feedback effect on its own growth.Whether the interaction between A.adenophora and rhizosphere microorganisms changes before and after the invasion,and what the feedback effects of B.cereus on them were the scientific questions of this thesis.Therefore,in this study,three populations(M1,M2,M3;C1,C2,C3)from the native areas in Mexico and the invasive areas of Yunnan in China were used as materials.The common garden method was used to detect the differences of the contents of B.cereus in the roots and rhizosphere soil ofA.adenophora of the native and invasive populations.The physicochemical indicators of the rhizosphere soil,and the effects of plant leaves leachates and root exudates treatments on the contents of B.cereus in the rhizosphere soil were determined.The effects of B.cereus on the growth of A.adenophora seedlings of different populations and the degradation of two main allelochemicals in the rhizosphere were tested.The difference evaluation results maybe enrich the ecological adaptation mechanism of the populations before and after the invasion of A adenophora,and the scientific basis for the ecological control of A.adenophora based on the regulation of rhizosphere microorganism environment was laid ultimately.The main results were as followed:1)We determined and compared the contents of B.cereus in the roots and rhizosphere soil of A.adenophora of the native and invasive populations,as well as the soil treated with leaves leachates and root exudates of A.adenophora plants of different populations by molecular quantitative techniques.The results showed that the total contents of B.cereus in the roots of A.adenophora of invasion populations was significantly higher than that of the invasion populations,and the contents of B.cereus in the roots of various populations of A.adenophora of invasion populations were all higher than the native populations.Among them,the contents of B.cereus of C2 population was 10-fold higher than that of the M1 population.The comparison of the contents of B.cereus in the rhizosphere soil of A.adenophora at different times and densities in greenhouses showed that the two invasive populations(C2,C3)were higher than the two native populations(M1,M3),especially between the biennial populations with a density of 10 plants/m2.The treated soil by leaves leachates and root exudates of different populations of A.adenophora showed that the contents of B.cereus in the soil of native populations were higher than that the invasive populations to varying degrees.The difference in the treatment of root exudates was more significant,which may be one of mechanisms for quick environmental adaption of newly invasive plants arose from promoting beneficial rhizosphere bacteria.The results of the determination and comparison of the soil physicochemical indicators of the two extracts showed that the NO3--N and AP contents of the C1 population in the leaves leachates treatment group were 4 mg/kg and 18 mg/kg,respectively,which were the highest among the six populations.They were 4%,14%,15%and 51%,19%,44%higher than M1,M2,and M3 respectively.The root exudates treatment showed that C3 population had the highest moisture content,NH4+-N,AP,and AK,which were higher than the populations of M1,M2,and M3 were 11%,16%.47%,and 89%respectively.These results indicated that the main internal mechanism for the invasive populations to promote the growth of beneficial bacteria by changing the physical and chemical properties of the soil2)We detected the effects of B.cereus on the growth of A.adenophora seedlings of different populations by the B.cereus addition/exclusion method;and the HPLC technology was used to compare the effects of degradation of B.cereus treatment on two main allelochemicals of the rhizosphere.The results showed that:B.cereus had a positive effect on the physiological indicators of various populations.Compared with sterilized soil treatment,sterilized soil added with B.cereus treatment could increase the germination rate of seeds of various populations by more than 10%.except for population M1,of which M3 was the most obvious increase of 49%,C3 increased by 27%.The root exudates treatment,except C3 increased by 17%,the germination rate of other populations all decreased.Adding bacteria solution treatment increased the shoot length of various populations,and increased the root length of the M1 population and the invasive populations.In the determination of the shoot length,the root exudations treatment had a negative impact on the A.adenophora of native populations,but it increased the shoot length of the invasive populations B.cereus had effects on the degradation of two allelochemicals(DTD,HHO).The invasive populations of A.adenophora had a higher ability to degrade DTD and HHO than the native populations.During most of the determination time,there was a significant difference between the sterilized soil treatment with B.cereus solution and the sterilized soil treatment,especially the C3 population,which the DTD content was 124%,100%and 222%lower than the sterilized soil treatment after 72 h,96 h and 120 h,respectively.After 96 h and 120 h,the HHO content of C3 population by the sterilized soil treatment with B.cereus solution was 174%and 305%lower than the sterilized soil treatment.These results confirmed that the positive feedback effects of B.cereus on the A.adenophora populations in the invasion areas were more significant,and the promotion of the degradation of rhizosphere allelochemicals were more obvious to reduce the autotoxic effects.It was an important basis for the control technology of A.adenophora based on rhizosphere soil microbial environment regulation in the invasive areas. |
PDF Full Text Request