Study On The Adaptive Mechanism Of Invasive Plant Bidens Pilosa To Soil At Different Recovery Stages After Fire Disturbance

Fire disturbance is one of the major factors affecting geochemical cycles,not only affecting soil seed banks and microbial communities,but also causing fluctuations in nutrients,water and other resources,often by disrupting the inherent equilibrium state of plant communities,and thus promoting invasion of exotic plants.In-depth understanding of exotic plant adaptations and their invasion mechanisms in the context of global climate change,and effective prediction,prevention and management of invasive species has become an important ecological problem that ecologists need to address.The analysis of the invasion risk of species in the context of fire disturbance and the exploration of its formation mechanism is also one of the hot spots in the research of global change ecology.Based on the above background,in this study,after fieldwork and literature research,the invasive plant Bidens pilosa L.was selected for greenhouse control experiments in soils 1,4,9 and 31 years after fire disturbance.By measuring the plant type,physiology and biomass of B.pilosa and soil physicochemical properties,we firstly analyzed whether the soil conditions after fire disturbance were more favorable for the colonization of B.pilosa and its dynamic changes with the years of recovery after fire disturbance;secondly,we elucidated the invasion mechanism of invasive plants after fire disturbance from the perspective of soil fungi and seed bank.The main findings are as follows:(1)Different adaptations of Bidens pilosa to soils with different restoration years after fire disturbance.Compared to non-fire disturbed,aboveground biomass,belowground biomass and total biomass of B.pilosa increased significantly at 1,4,9 and 31 years after fire disturbance,indicating that fire disturbed soils are conducive to B.pilosa colonization.The physicochemical properties of the soils differed among the different restoration years after fire disturbance,which also differed in their effects on B.pilosa.Compared with the control group,the nitrogen content of above-ground parts of B.pilosa decreased significantly at 1,4 and 9 years after fire disturbance,while there was no significant change in the nitrogen content of above-ground parts at 31 years after fire disturbance.The phosphorus content and pH of the original soil were higher than those of the non-fire disturbed soil at 4 years after fire disturbance,and the net photosynthetic rate and total chlorophyll content of the ghost grouse were significantly higher than those of the control.The results indicated that after fire disturbance,B.pilosa more nutrients from the soil and increased the content of photosynthetic pigments,which in turn increased the photosynthetic rate and total biomass of B.pilosa significantly higher than that of the control.In addition,with the increase of restoration years after fire disturbance,soil carbon,nitrogen and phosphorus contents gradually increased,and the biomass of B.pilosa was significantly higher than that of the control group,indicating that the colonization ability of B.pilosa in fire disturbed soil may be enhanced with the increase of restoration years.(2)Deseedbanking and fungicide treatments had significant effects on functional traits of Bidens pilosa.The seed bank removal treatment significantly increased net photosynthetic rate.aboveground biomass and total biomass of B.pilosa 4 years after fire disturbance,and significantly increased aboveground N and P content of B.pilosa 9 years after fire disturbance;the seed bank removal treatment did not significantly affect the plant size and biomass index of B.pilosa 1 and 31 years after fire disturbance.As an important link in the soil restoration mechanism after fire disturbance,the germination and growth process of the seed bank,which is an important link in the soil to influence the invasion of exotic plants,competed with the B.pilosa and was able to deter the colonization and invasion of exotic plants to a great extent.The fungicide treatment significantly reduced the subsurface phosphorus content 1 year after fire disturbance and the total biomass 4 and 9 years after fire disturbance,but the fungicide treatment did not significantly affect the indicators of B.pilosa 31 years after fire disturbance.Soil fungi play an important role in the growth of B.pilosa,and the fungicide treatment may have removed many beneficial fungi that play an important role in the colonization of B.pilosa and contribute to the invasion of B.pilosa in fire-disturbed soils.The ability of B.pilosa to colonize fire-disturbed soils may increase as the number of years of recovery after fire disturbance varies.Seed bank and fungicide treatments had a greater effect on B.pilosa at 4 and 9 years after fire disturbance,but a smaller effect at 1 and 31 years after fire disturbance.The study of the e ffects of fi re disturbance on the invasion mechanism of exotic plants can help to elucidate the biological invasion mechanism and the evolutionary pattern of species under the disturbance of human activities,provide an in-depth understanding of the invasion mechanism of exotic plants in the areas where fire disturbance occurs,and provide an effective scientific basis and theoretical guidance for the prediction and prevention and control of exotic plant invasion.