The Effects Of Plant Invasion On Relationship Between Biodiversity And Productivity

In recent decades, the invasion of exotic species into assemblages of native plants is a pervasive and widespread phenomenon. Biological invasions distinctly affect the stability and productivity of the native communities by modifying their diversity and function. The relationships between diversity, productivity and invasibility have been attracted considerable attention. When invading the new ecological system, the exotic species can expand promtly and cause the loss of biodiversity through competing the resources (such as water, light and nutrient) with native plantsand restraining native plants. Accordingly, it is very important to study whether the invasive plants have impacts on the relationship between diversity and productivity. The effects of invasive plants on the relationship between diversity and productivity is illustrated from two following experiments:Firstly, in the semi-natural field experiment, the effects of many invasive plants on the relationship between diversity and productivity was conducted as invasive plants spread freedom in the field; secondly, the effects of one invasive plant Alternanthera philoxeroid.es on biodiversity and productivity was studied by pot experiments. Although most studies have focused on the effect of invasive plants on native plants or communities, the effect of community diversity on invasive plants’offspring performances are very few, it is urgent to understand the effects of species diversity on the seed performances of invasive species. Therefore, the effect of species diversity on the seed weight and germination characteristics of two invasive plants were also concerned in the third experiment. The main results were showed as follows:1) effects of many invasive plants on the relationship between species diversity and productivity.In 2008, we established 108 plots (3 m×3 m) at The Chinese academy of agricultural sciences langfang base, hebei province. After clearing all plants in the plots, six invasive and six native species were randomly planted to the 108 plots, respectively And each species planted nine replicated plots. This study lasted five years and no anthropogenic activities were conducted throughtout the whole experiment. The number of species and biomass of each plot were surveyed in 2013 after five years of free spreading of species. Two invasive plants, Bidens pilosaand Flaveria bidentis, which distributed more than 50%(54 plots) of the total plots, were selective to study the effects of many invasive plants on the relationship between species diversity and productivity. The results showed thatrelationships between species diversity and biomass of the plots distributed by the two invasives were both negatively correlated.2 Effects one invasive plant on the relationship between species diversity and productivity.In the pot experiment, we established artificial communities with a design of four levels of 1,2,4 and 6 species of only native species and corresponding mixtures of Allernanthera Philoxeroides and native species in each pot (0.5 m×0.8 m) were established, respectively, and six replicated pots for each treatment. The aboveground biomass and total biomass of each pot were harvested after five months. The results showed that 1) the relationships between biodiversity and the aboveground biomassas well asthe total biomass were positively correlated.2) the relationships between biodiversity and the aboveground biomassas well asthe total biomass were negatively correlated.3 Effects of biodiversity on the seed weight and germination characteristics of the invasive plantsThe relationships between diversity and seed weight, germination percent, germination rate and initial germination time of Bidens pilosa and Flaveria bidentis were investigated as the first experiment, respectively. The results showed that 1) seed weight of Bidens pilosa was not affected by species diversity; while germination percent of Bidens pilosa was negatively corrected with the biodiversity of invasive species, and initial germination time of Bidens pilosa were positively correlated with bioversity of invasive species, native species and total species; 2)seed weight, germination percent and germination speed of Flaveria bidentis were negatively corrected with the biodiversity of native species and total species, and initial germination time of Flaveria bidentis were positively correlated with bioversity of native species and total species.The effect of invasive plant on the relationship between species diversity and productivity were mainly studied in this thesis, and the results indicated whether single or multiple invasive plants could lead to a negative correlation between species diversity and productivity, and the germination indexes of invasive plants were inhibited by diversity of invasive plant, native plant and the total plant.