| The impact of global climate change on the human environment is receiving increasing attention.Studies have shown that increased temperatures and nitrogen deposition can have an impact on plant growth.Biological invasions can lead to the loss of biodiversity in invaded areas,posing a serious threat to the structure and function of ecosystems and agricultural and livestock production,and causing huge economic losses.In recent years,the interaction between global climate change factors and plant invasions has attracted increasing attention and has become a research hotspot in global ecology.As an arid and semi-arid region in western China,the Yili River Valley in Xinjiang,with its advantageous geographical location and suitable climate,coupled with its long borderline and its complex topographical and geomorphological environment,has rapidly developed into a major area for invasive alien organisms and a source of secondary spread in the western region of China in recent years.Therefore,studies on nitrogen deposition and warming in the Yili Valley have been conducted to investigate whether the two changing environmental factors affect the life history traits of invasive plants,such as seedling growth and establishment,resource allocation and reproduction,and the results will help to understand the bioecological response patterns and invasion mechanisms of invasive plants under nitrogen deposition and warming environments.In this study,Xanthium spinosum,a common and malignant invasive plant in the Ili Valley,was used as a research object to simulate nitrogen deposition and warming and their combined effects in the laboratory to investigate its effects on the growth,material production and distribution,and physiological and ecological characteristics of seedlings of X.spinosum at the individual,modules,physiological and population levels.This study will provide basic information for further research on its invasion and dispersal mechanisms of X.spinosum and provide a scientific basis for the prevention and control of the X.spinosum.The following results were obtained from the indoor simulation experiments.(1)Under moderate nitrogen deposition,seedlings showed growth of main root,taller plants,more leaves,thicker stems and more spines,and the quantitative characteristics of the modules were suppressed under high levels of nitrogen deposition.The accumulation of biomass of roots,stems and leaves all increased significantly under moderate nitrogen deposition,and decreased significantly under high nitrogen deposition.It showed that moderate nitrogen deposition favours seedling biomass accumulation,while high nitrogen deposition acts as a suppressor.The chlorophyll content,soluble sugars and soluble protein content in the leaves were significantly increased under nitrogen deposition,and NR and GS activities were significantly enhanced.It showed that suitable nitrogen deposition increases the content of free amino acids and the activity of the main nitrogen metabolizing enzymes,which promoted the efficiency of the use of available nitrogen and supplied the plant with rapid growth.The plant is able to increase photosynthesis and occupy a more favourable ecological position,strengthening its dominant position in the community and facilitating its invasion.(2)Daytime warming(DW)promotes thickening of the basal diameter of seedlings,growth of the main root,increase in plant height,increase in the number of leaves and increase in spines,while morphological characteristics were suppressed under nighttime warming(NW)and all-day warming(AW).NW significantly increased leaf biomass allocation,DW increased stem biomass allocation and AW increased root biomass allocation.The chlorophyll levels were significantly increased in leaves under DW and NW,but not significantly different from the control under AW.It is shown that DW and NW enhance its adaptation to strong light and promote its growth.Soluble sugar and soluble protein contents in leaves were significantly increased by DW and AW.The activity of both NR and GS enzymes in the leaves was significantly enhanced under different modes of warming,improving the efficiency of nitrogen use by the plants.(3)The combined effect of warming and nitrogen deposition increased seedling height and increased leaf and spur,while basal diameter and main root length were significantly reduced compared to the control group.The combined effect of warming and nitrogen deposition significantly increased the accumulation of root,stem and leaf biomass in X.spinosum seedlings,but root biomass accumulation and distribution decreased significantly compared to the control.This showed that the two synergistically contribute to the accumulation of biomass in the seedlings of X.spinosum,increasing stem and leaf biomass distribution.The combined warming and nitrogen deposition significantly increased the chlorophyll content,soluble sugar and soluble protein content of the seedlings,and significantly enhanced the activity of NR and GS enzymes in the leaves,indicating that the two synergistically promoted the smooth and effective operation of the plant N metabolic system and supplied the plant with rapid growth.The present experiments suggest that warming and nitrogen are conducive to the invasion of the X.spinosum,and under the present environmental conditions,it is urgent to strengthen the ecological management of X.spinosum. |
