Research On The Relationship Between Plant Diversity And Ecosystem Stability In Constructed Wetlands

The relationship between biodiversity and ecosystem stability has fascinated ecologists for more than half a century. Recently, lots of experimental studies measured the stability of the ecosystems by the variability and resistance of biomass production. However, as anthropogenic N enrichment increasingly serious, how the N enrichment affect ecosystem functions and the relationship between diversity and stability are poorly understand.The study used microcosms to simulate constructed wetland (CW), conducted sand culture and hydroponic system.4 species that commonly planted in wetland were chosen as experimental species and 4 species richness levels (1,2,3, and 4) were established. The influent was Hoagland nutrient solution with minor modification as the simulated wastewater. At the beginning, NO3--N was supplied with a concentration of 336 mg L-1. After the microcosms had been established for 74 days, the six replicates were divided equally into two treatments (perturbed and unperturbed). Unperturbed treatment was still supplied with NO3-N while perturbed treatment was supplied with mixed N03--N and NH4+-N with a ratio of NO3--N/NH4+-N as 2:1. We aimed to explore the effects of species richness and identity on the variability and resistance of biomass productivity and N removal. The main results and findings are as follows:1. Ammonium perturbation could reduce the N removal efficiency of both sand culture and hydroponic system. However, ammonium perturbation did not affect above and belowground biomass. Diversity could buffer the perturbation effect of ammonium on N removal in hydroponic system.2. Species richness reduced the coefficient of variation (CV) of belowground biomass, NO3- and TIN removal in hydroponic system. The presence of Phragmites australis and Coix lacryma-jobi could also reduce the CV of NH4+ and TIN removal. The CV of nitrogen (N) removal of sand culture was not significant affected by species richness. The presence of Coix lacryma-jobi increased the CV of NO3- and TIN removal. These results indicated that species identity surpasses species richness as a key driver of CV of N removal in sand culture.3. Resistance of belowground biomass in hydroponic system and aboveground biomass in sand culture were both negatively dependent on species richness. The resistances of N removal were not respond to species richness in both sand culture and hydroponic system while were significantly affected by Phragmites australis and Coix lacryma-jobi. The presence of Phragmites australis increased the resistance of NO3- and TIN removal in hydroponic system while decreased the resistance of NH4+ removal in sand culture. The presence of Coix lacryma-jobi increased the resistance of NH4+ removal in hydroponic system while decreased the resistance of NO3- and TIN removal in sand culture. These results indicated that species identity surpasses species richness as a key driver of the resistance of N removal in both sand culture and hydroponic system.4. Resistances of above and belowground biomass in hydroponic system was negatively dependent on the initial state of biomass without perturbation. The resistances of effluent NO3- and TIN concentration was positively dependent on the initial concentration without perturbation. Resistances of aboveground biomass, effluent NO3- and TIN concentration in sand culture was negatively dependent on the initial state without perturbation. These results indicated that the resistance of certain function is dependent on the initial state of this function.This study explored the relationship between plant diversity and ecosystem stability under ammonium perturbation in CW microcosms. The results extend the understanding on the resistance of ecosystem with new functions and perturbations and finds general picture of the relationship between diversity and stability. It also provided reference for improving the removal efficiency and stability of CWs.