Research On The Mechanism Of Biodiversity-Nitrogen Removal In Constructed Wetlands

Global nutrient pollution has strengthened the need of ecosystem service for eutrophication mitigation. Recent researches have confirmed that ecosystems with high biodiversity are more efficient at removing nutrient from environment. This has led to the trials that the biodiversity effect for over-depletion might be a useful tool for nutrient management, but the existed biodiversity effects (such as complementarity effect and sampling effect) have been limitations of explanation under high nitrogen level. Here we use microcosm with1,2,3and4plant species and an unplanted microcosm to examine the mechanism of biodiversity effect on ecosystem functioning (such as nitrogen removal, productivity, denitrification). Nitrogen removal and the related plant uptake and denitrification were measured by using both mass balance approach and15N signatures. We found that,(1) Nitrogen removal in nitrate treatment is significant higher than that in NO3-/NH4+ratios2:1treatment (P<0.05);(2) Nitrogen removal in substrate system is significant higher than that in hydroponic system (P<0.05);(3) As increasing number of species richness, though the intensity of plant uptake and denitrification showed approximate sampling effect, the nitrogen purifying function of the whole ecosystem present resource-use complementarity determined by the two processes, that is, non-linear emergence effect was produced in the cross-integrated processes;(4) The effect of the four species present or not on the nitrogen processes of the ecosystem was significantly different (P<0.05), moreover, there were three different N processes caused by three plant species of them-C. lacryma-jobi which strongly assimilate nitrate but restrain the microbial nitrification and denitrificaton in rhizosphere (Type â… ), P. australis which facilitate denitrification and utilize ammonium (Type â…¡), and A. calamus facilitate nitrification but cannot utilize ammonium (Type â…¢;(5) Coexistence model indicate that Type â…  and â…¡ cannot coexist because the failed competition of Type â…¡ under the condition that nitrate was the unique nitrogen resource. But Type â…  and â…¡ can coexist when Type â…¢ exist in the community for the new niche produced by ammonium mineralized by organic nitrogen. These complicated relationship mentioned above suggested that there are more than three functional plant species could ensure the nitrogen function of the two subsystems, thereby produce the integrated processes of purifying function. Therefore, to ensure existence of inferior species, CWs may need to be maintained by artificial regulation, which would maintain higher diversity to enhance the wastewater purifying function.