The Emission Of N₂O From The Chongming Dongtan Wetland Under Different Plants

N₂O is one of the important greenhouse gases,which has great influence of the temperature of the globe.Wetland as one of the important ecosystem,whose different types overlying plants' effect of N₂O flux is still lack of study.Taking the Chongming Dongtan wetland as a typical area,and choosing Phragrnites australis and Scirpus mariqueter as an example,this article discussed the regular contribution factor of N₂O emission.Some achievements were described as below:There has obvious space-time variance of N₂O emission in Chongming Dongtan wetland.Totally The high tidal flat with Phragmites australis is represented as release, which mean annual N₂O flux is 96.95 mg·m^-2·h^-1,and the high tidal flat with no plant is represented as absorbability,which mean annual N₂O flux is -1.587 mg·m^-2·h^-1;the middle tidal flat with Scirpus mariqueter is represented as weak release,which mean annual N₂O flux is 1.54 mg·m^-2·h^-1,and the middle tidal flat with no plant has a significantly higher flux,which mean annual N₂O flux is 36.63 mg·m^-2·h^-1;the low tidal flat's annual N₂O flux is 3.38 mg·m^-2·h^-1.So we can find that the Phragmites australis accelerated the N₂O flux, and the Scirpus mariqueter is on the contrary.The N₂O is both release and absorbed intense in July,while other time is opposite weaker.Correlation analyze indicated that there don't has obvious linearity relation of the temperature and the N₂O flux;when the temperature is less than 25℃,both the release and absorbed of N₂O is low and when the temperature exceed 25℃,the N₂O flux is significantly enlarged.The absorbability and distribution of N by plant presented obvious phasic as the plant grows.When the plant grows,the N in plant is diluted,so the content of N is negative correlation of the biomass and height of plant.The N storage capacity of Phragmites australis in Chongming Dongtan wetland is 18920.19t in August,and the Scirpus mariqueter's is 25141.11t in September,which is a big build-up of nitrogen cycle in wetland,and is also a big contribution of the physicochemical property of the wetland.The Correlation analyze indicated that the most important contribution physicochemical property of N₂O flux is NH₄ content,OC content,Eh and water content. The topsoil of sediment under P.australis has higher NH₄-N contents witch promoted the emission of N₂O;while the S.mariqueter is the other way round.The cover of P.australis promoted the emission of N₂O flux;while the S.mariqueter is the other way round,the high and middle tidal flat's plant-sediment system has high water content because the water holding capacity of plant,which promoted the denitrification and N₂O flux.The Eh of the topsoil of sediment under plant have a low average and no more than 200mV,so it make against the denitrification and N₂O flux.The plant's influence to the physicochemical property of sediment is very complex and difficult in difficult type of plant.As a whole,the P.australis promoted N₂O flux and the S.mariqueteis is on the contrary.