Effects Of Environmental Variation On The Relationship Between Biodiversity And Productivity

Due to the unprecedented species extinction rate, the effects of biodiversity on the ecosystem function have been the focus of ecological research for nearly 30 years. However, there has been substantial debate on the relationship between biodiversity and productivity until recently. Many researchers insist on that the higher the productivity, the better, and the value of biodiversity is promoting productivity. As a consequence, ecologists try to prove the promotion of biodiversity on productivity from different angles, and ignore others relationship between biodiversity and productivity. But I consider that understanding the relationship between biodiversity and productivity in the right way and studying how the relationship between biodiversity and productivity change along the environment are the best way to recognize the value of biodiversity. Artificial grassland experiments are always disturbed by weeds, which exaggerates the positive relationship between biodiversity and productivity. But we can understand'diversity-productivity'relationship accurately by eliminating weed interference. I performed an experiment using four common herbaceous species (Bidens pilosa, Pennisetum alopecuroides, Mosla dianthera and Ambrosia artemisiifolia), with different levels (1,2,3 and 4) of species richness and composition. Each community was grown in different nutrient levels and different levels of water. The research was to study how the relationship between biodiversity and productivity changes along environment. In order to eliminate weed interference, soils were irradiated by ?-ray to make weed seeds inactive before experiment. Relative Neighbour Effect (RNE) was used to quantify the interspecies relationship, Ymix is the performance per plant, in this case biomass, for a plant individual growing in a mixed community, Yiso is the performance per plant for a plant individual growing alone). And the results are shown below:(1) Simple linear regression model were used to analyze the relationship between biodiversity and productivity first. The relationship between biodiversity and productivity is positive under control (no fertility), however, there is no relationship between biodiversity and productivity in 1 Hoagland's nutrient solution added treatment, and the productivity increases with diversity slightly significantly in 5 Hoagland's nutrient solution added treatment; the relationship between biodiversity and productivity is uncorrelated under each levels of water. But the results is different when applying linear mixed model to analyze them, namely the positive relationship between diversity and productivity is decreasing after ruling out the effect of plant density.(2) The relationship between the value of RNE and nutrient levels is U-shaped, but water has no significant effect on RNE. The values of RNE in each species richness and the slope of'diversity-productivity' relationship between the adjacent levels of diversity is positively related (P< 0.045), which indicates that the increasing RNE (the increasing frequency of facilitation) will strengthen the positive correlation between diversity and productivity gradually.(3) The coefficient of variation, standard deviation and range of plant community productivity across water treatments or nutrient treatments increase with diversity, and part of them are significantly positive related (P< 0.05). In consequence, biodiversity decreases the stability of plant community in changing environment.The research shows that the positive relationship between diversity and productivity is not a common form and the promoting effect of biodiversity on productivity is limited. However, the result that biodiversity decreases the stability is conflicted with other researchers' viewpoint, and the mechanism remains to be further studied.