Performance Of Invasive Species And Co-Occurring Native Species Under Nutrient Variability And Competition

When invasive plants arrived at a new habitat, they began to compete with others species,including other invasive plants and native plants or both. Besides their inherent characteristics, and performance in a competition is often affected by environmental factors as well, especially by variable resources. Under the background of global environment change, resource variability tends to be common both spatially and temporally. Resource variability has greatly significant effect on invasive plants and co-occurring native plants. A large amount of researches were focused on the effects of resource spatial variability on plant growth and competition. However, little has been done on the effects of resource temporal variability. In addition, it is uncertain whether resource variability promotes competition or coexistence between invasive and co-occurring native plants due to the complicated interaction between plants and between plants and environment.Among all kinds of resources, nutrient is one of the most effective resources, therefore, we made it a research target. In our study, we selected 6 species, one pair of invasive and native species each in Hydrocotyle Linnaeus, Sp. Pl., Alternanthera Forsk., Wedelia calandulacea. We conducted a greenhouse experiment to examine the effect of invasiveness, nutrient variability, competitor type and their interactions on competition and each species involved. The results showed:1. Invasive focal species had significantly higher number of ramet, biomass, aboveground mass,belowground mass and biomass ratio, aboveground mass ratio, belowground mass ratio than native focal species. Invasive competitors had significantly higher belowground mass than native competitors.Invasive community or community with invasive focal species had significantly higher belowground mass than native community or community with native focal species.2. Belowground mass and R/S ratio of invasive focal species increased while those of native species decreased along with nutrient variability. Belowground mass and R/S ratio of invasive competitors also decreased along with nutrient variability.3. In competition with intraspecific competitors and hetrogenetic competitors, belowground mass and belowground mass ratio of invasive focal species increased while those of native species decreased along with nutrient variability. Difference between invasive and native focal species was the most significant under multiple pulses nutrient supply and it was the least significant under constant nutrient supply. The result was the same for invasive competitors and native competitors.4. Competitor type had a significant effect on number of ramet, biomass, aboveground mass andbelowground mass of competitors. These of mixed competitors, hetrogenetic competitors, congenetic and intraspecific competitor gradually decreased. Competitor type had a significant effect on biomass,aboveground mass and belowground mass of community as well. Those of community with mixed competitors was the highest while community with intraspecific competitors the lowest.