Effects Of Soil Microorganism And Invasive Plant Diversity On The Native Pterocypsela Laciniata Growth Under Invasions: Responses Through Plant-Soil Feedback

Plant invasion is a key element in defining the community structure and dynamics which has become a major concern for ecosystem restoration.Plant invasion provokes changes in the composition and structure with regards to the soil microbial community,which is considered as one of the most important determinants of plant growth and invasive plant success.The effects of soil microorganisms in plant competition have been recently studied for a better understanding of plant invasion and to provide solutions for invasive plant management and control as well as ecosystem restoration and biodiversity.It is well known that plant species are differently affected by soil microorganisms,and changes in soil conditions may affect interspecific competition,especially the native plant growth under invasion.Thereby plant-soil feedback was added to the previous concepts explaining invasive plant success,as it is currently considered as a new vision for agriculture sustainability by addressing population demand for food production and ecosystem services.However,a large number of studies have been focused on the invasive plants by neglecting the native plant response.Moreover,many uncertainties still exist on the impact of soil microorganisms on the native plant growth under single and co-invasion despite the large number of studies that have been previously done in this domain.Understanding the concept of plant invasion and soil microorganism impact on the native plant-soil feedback would be a significant step forward in invasive plant management and control as well as ecosystem restoration.However further researches are needed,to comprehend and elucidate the effects of invasive plant identity and diversity and soil microorganism's impact on the native plant growth.In this study,the native plant Pterocypsela laciniata,which is largely distributed in Shandong,Zhejiang,Jiangxi and in Jiangsu province,was chosen as the native target plant.This work aims to determine i)the impact of soil microorganisms on the native P.laciniata response under single and co-invasion in different soil conditions,ii)the effects of soil microorganisms on the native plant response through plant-soil feedback,and iii)the impacts of invasive plant identity and diversity on the native P.laciniata growth under invasion.The following are how this work has been carried out:Firstly the effects of soil microorganisms on the native P laciniata growth in monoculture and under single and co-invasion with the invasives Solidago canadensis and Aster subulatus Michx was studied in natural soil,nutrient soil,and nutrient sterilized soil.The results suggest that the native P.laciniata obtains its highest competitive ability under single invasion compared to the co-invasion.Moreover,the nutrient sterilized soil presents the optimal growth condition of our target plant,followed by the natural soil.No significant difference between the invasive plant effects on the native plant response was observed,depending on the identity of the invasive plant.The native plant response was more impacted by the soil microorganisms than exotic plant identity and the type of invasion.Secondly,the effect of the soil microorganisms on the native plant response through plant-soil feedback using the soil conditioned in the first experiment(chapter 2)was carried out.We noticed that the individual feedback of the native P.laciniata experiment is affected by soil properties and also the magnitude and direction of change,which differ between soils depending on the conditioning phase.The pronounced positive feedback observed in nutrient sterilized soil might be due to the positive plant-soil interaction in the conditioning phase.On the contrary,the negative feedback observed under the soils conditioned by co-invasion is due to the lack of soil microorganism caused by their excessive use during the conditioned phase.Finally,insight was taken from the first experiment to investigate the impact of invasive plant identity and diversity on the native target plant P.laciniata by conducting a mixing planting experiment using four invasive plants,i.e.,S.canadensis(Sc),A.subulatus Michx(At)Biden pilosa(Bp)and Amaranthus retroflexus(Am)in which treatments consisted of different levels(1:1,1:2,1:3 and 1:4)of invasive plants richness and different combinations.Our experiment revealed that the native plant P.laciniata response depends on the identity of the invasive plants,their diversity,and abundance.We also observed a pronounced negative effect on the invasive plant under S.canadensis invasion or in combination with other invasive plants.The impact of invasion on P.laciniata depends on the invasive plant identity and diversity.The most surprising result was that invasive plant diversity increases the native plant biomass.Moreover,the invasive plant diversity positively affects the native plant response at a specific level of invasive plant richness.The invasive plant's diversity in high density reduces the native plant growth rate.Although the invasive plant diversity increases the native plant response,it would be more valuable to do more investigations among the invasive plants to find the most beneficial combination which could be more useful for the native plant and harmful to the invasive plant to support the invasive plant's management and control as well as to reduce the native plant's extinction.