Effects And The Mechanisms Of Different Degrees Of Drought On The Growth Competitiveness Of Invasive Plant Species Amaranthus Spinosus L. And Native Plant Species A.tricolor L. And Soil Enzyme Activities

In recent years,biological invasion caused by invasive plant species has posed a serious threat to environmental health and ecological security.Additionally,the occurrence frequency and persistent period of drought and the area affected by drought are increasing in the global scope mainly due to the intensification of global climate change,especially the changes in precipitation patterns.However,drought may significantly affect the physiological and ecological characteristics of invasive plant species and native plant species which has the potential to alter the invasion process of those invaders.Therefore,it is necessary to explore the effects of drought on the growth competitiveness of invasive plant species and native plant species as well as soil enzyme activities to clarify the driving mechanism underlying the successful invasion of invasive plant species under drought.This study was performed via a competitive cultivation experiment using the notorious invasive plant species Amaranthus spinosus L.and the native plant species A.tricolor L.with three patterns of plant cultivation,i.e.,(I)monocultural A.spinosus(six seedlings);(II)monocultural A.tricolor(six seedlings),and(III)co-cultivated A.spinosus(three seedlings)and A.tricolor(three seedlings).The seedlings of the two Amaranthus species were treated with three degrees of drought,i.e.,(I)control(one hundred percent of the normal annual precipitation of the study area;pretend the condition without drought);(II)light degree of drought(sixty percent of the normal annual precipitation of the study area;pretend the condition with light drought);(III)heavy degree of drought(twenty percent of the normal annual precipitation of the study area;pretend the condition with heavy drought).This study focused on the differences in the physiological and ecological characteristics,soil physicochemical properties,and soil enzyme activities between the invasive plant species A.spinosus and the native plant species A.tricolor under different degrees of drought via a panoramic comparative analysis.The purpose of this study was to illuminate the mechanism underlying the successful invasion of invasive plant species under different degrees of drought.The results of this project can build solid theoretical support for further explanation of the driving mechanism driving the successful invasion of invasive plant species and provide a strong practical basis for the establishment of biosafety early warning and prevention as well as the control management represented by biological invasion caused by invasive plant species in China in the new era.The main results of this study are as follows:1.The effects of different degrees of drought on the physiological and ecological characteristics of the invasive plant species A.spinosus and the native plant A.tricolor and the mechanisms:(1)The invasive plant species A.spinosus and the native plant species A.tricolor tend to diverge functionally.Thus,the dissimilarity in the physiological and ecological characteristics of the invasive plant species A.spinosus and the native plant species A.tricolor supports the similarity limitation hypothesis,which can enable the invasive plant species A.spinosus to gain stronger growth competitiveness.(2)The competitive power for sunlight acquisition,the leaf shape variation level,and the leaf photosynthetic ability of the invasive plant species A.spinosus are significantly greater than those of the native plant species A.tricolor.Accordingly,the competitive power for sunlight acquisition,the leaf shape variation level,and the leaf photosynthetic ability may be the main physiological and ecological characteristics that affect the growth competitiveness of the invasive plant species A.spinosus.(3)Different degrees of drought significantly inhibit the competitive power for sunlight acquisition,the plant photosynthetic area,the stem support intensity,the leaf water content,the leaf photosynthetic ability of the invasive plant species A.spinosus and the native plant species A.tricolor,and the extent of inhibition enhances with the increases in the degree of drought.(4)The biomass stability of the co-cultivated invasive plant species A.spinosus is obviously higher than that of monocultural invasive plant species A.spinosus under drought.Meanwhile,drought stress was more intense on native plants that coexisted with invasive plants.Further,the growth competitiveness of invasive plant species A.spinosus is significantly greater than that of native plant species A.tricolor under drought.Hence,drought may be benefit to the invasion process of the invasive plant species A.spinosus.2.The effects of different degrees of drought on the soil physicochemical properties and soil enzyme activities of the invasive plant species A.spinosus and the native plant species A.tricolor and the mechanisms:(1)Different degrees of drought significantly reduce the soil acidity,soil moisture,and soil water-soluble salt content.,and the impact amplitude rises as the degree of drought increases.(2)Different degrees of drought significantly increase hydrolysis power of sucrose and urea,which can accelerate the material transformation and absorption,and will be beneficial to improve the competitive ability of A.spinosus.(3)The soil water-soluble salt content and the hydrolysis power of sucrose in the soil of the monocultural invasive plant species A.spinosus are significantly greater than those of the monocultural native plant species A.tricolor under different degrees of drought.(4)The effects of different treatments on soil moisture content,electrical conductivity and soil urease activity may be one of the important reasons for the differences in the physiological and ecological characteristics between invasive plant A.spinosus and native plant A.tricolor.In conclusion,the key physiological and ecological characteristics of invasive plant A.spinosus are significantly higher than that of native plant A.tricolor.Meanwhile,the functional traits of invasive plant A.spinosus and native plant A.tricolor are different,and drought may be beneficial to the invasion process of invasive plant A.spinosus.The difference of soil moisture content,soil electrical conductivity and soil urease activity under different treatments was the important reason for the differences in physiological and ecological characteristics between the invasive plant A.spinosus and native plant A.tricolor.