Effects Of Nitrogen Deposition And Enhanced UV-B Radiation On The Growth Of Native And Invasive Populations Of Triadica Sebifera

Plant invasion is an important factor of global change,threatening the stability and function of ecosystems.It is important to understand effects of global change on plant invasion and learn more about the physiological and ecological changes of invasive plants for effective control of invasive plants.The major manifestations of current global changes including nitrogen deposition and enhanced ultraviolet（UV-B）radiation intensity.Changes of these external environmental factors will have direct or indirect influence on succession of ecosystem,changes of plant community structure and the growth of individual plants.However,different environmental factors often interact with each other,so the response of plants to environmental factors may be results of interactions among different global change factors.The successful invasion mechanisms were generally proposed as following:the invasive plant after being introduced into the new frontier has improved the adaptive evolution,and further enhanced the competitive ability by the external environmental factors;invasive plants have a strong competitive ability compared with the local non-invasive plants.In this study,seeds of four Chinese tallow（Triadica Sebifera）populations were collected from China（native）and the United States（invasive）in autumn,2015.Greenhouse experiments were conducted in spring,2016.The effects of nitrogen deposition,phosphorus application and soil sterilization on the biomass and growth of different native and invasive populations were studied.Full factorial experimental design was employed.Origin was used as the fixed factor and the population（nested within origins）as the random factor.The net effects of nitrogen deposition,phosphorus application and soil sterilization on the growth of tallow seedlings were analyzed by measuring the biomass and morphological characteristics of the young tallow seedlings.The effects of simulated nitrogen deposition and enhanced UV-B radiation on photosynthetic parameters and growth of different populations of tallow were studied to explore effects of global change on growth of invasive plants.The growth and chlorophyll fluorescence parameters of different populations of tallow（including the maximum quantum yield（F_v/F_m）of optical System II）were studied.Optical system II actual photosynthetic quantum yields(Y（II）,the effects of the initial slope（α）,the potential maximum relative electron transfer rate（ETRmax）and the half full and intensity（I_k）,relative chlorophyll content（SPAD）and plant height were discussed to further expound the mechanism of the successful invasion of the tallow under the background of global change.The results showed that:1.In control soil,the invasive Chinese tallow seedlings were higher in leaf biomass,leaf area and plant height than native seedlings but there is no significant difference in the sterilized soil.Nitrogen deposition significantly increased the aboveground biomass,total biomass,leaf number,leaf area and plant height of the tallow.Phosphorus application significantly increased the biomass of tallow root,stem and leaf biomass.Soil biota promoted the growth of tallow.In the control soil,the invasive populations of tallow outperform the native populations.2.Enhanced UV-B radiation resulted in changes in morphological characteristics and biomass allocation of tallow,with most of the resources were allocated to the leaves to withstand UV-B radiation.Nitrogen deposition induced more aloocations to aboveground,especially leaves,reducing the distribution of underground biomass.Chlorophyll fluorescence parameters of the young tallow seedlings(F_v/F_m,Y（II）,α,ETR_max,I_k),SPAD and plant height were significantly influenced,in which the interaction of UV-B radiation and nitrogen deposition in plant height was significant.Nitrogen deposition and soil sterilization had significant effects in Y（II）,SPAD and plant height.Compared with native tallow,invasive tallow had higher Y（II）and plant height,but it is more sensitive to UV-B radiation stress and has weaker plant-soil feedback effect in SPAD.There was a positive plant-soil feedback effect between the tallow and the native non-rhizosphere soil sterilization.As a result,global changes（increased nitrogen deposition,enhanced UV-B radiation）and soil microorganisms can interact impacting the plant photosynthesis and plant-soil feedback effects and hence successful invasion of Chineses tallow.In conclusion,increased nitrogen deposition and enhanced UV-B radiation may interact with soil microorganism impacting the invasion process of tallow.Plant-soil feedback process and plant photosynthesis both affect successful invasion process of Chinese tallow.