Preliminary Study On The Nitrogen Cycle Of Spartina Alterniflora Wetlands In Pearl River Esturay

Nitrogen cycle in the wetland ecosystem is one of the most basic components of biogeochemical cycle,especially study on plants which plays an important role in it.This paper presented the nitrogen cycle of Spartina alterniflora wetland at Qi'ao Island,Zhuhai with detections of the nitrogen in plant organs,sediment and the upper cover water for alien plants S.alterniflora as well as the greenhouse gas N₂O emissions.Furthermore,a simulation experiment was set up in greenhouse in Guangzhou University with different salinity?10‰,20‰and 30‰?and water levels?high,medium and low?in order to simulate the tides with drought and salinity stress.Based on the study,we preliminary discuss the mechanism of nitrogen cycle in S.alterniflora wetland,and then explore what the role of nitrogen cycling plays in the biogeochemical cycle.The main research conclusions are as follows:?1?S.alterniflora grass roots is of certain influence to the soil physical and chemical properties,such as decreasing pH value of the soil,which makes the deeper surface soil pH value less than the upper surface soil in the system.And the strong salt excretion of S.alterniflora makes the electrical conductivity Under the surface soil below the upper surface soil's and surface water's.?2?The soil's nitrogen content in S.alterniflora wetland is higher than outside wetland soil's and tidal flat soil's,which indicted that S.alterniflora population has a certain role in promoting sediment nitrogen fixation.In S.alterniflora wetland,the sediment nitrogen content in Zhuhai is relatively higher than those in greenhouse,and higher density of S.alterniflora and its litter as well as the tide have stronger ability of nitrogen input.Overall,the result suggests that S.alterniflora population can significantly increase the soil total nitrogen content.Total nitrogen content on wild S.alterniflora wetland sediment in the winter were significantly higher than those in Spring and Autumn,total nitrogen content of water in Winter were significantly lower than those in Spring and Autumn which showed that in Winter,the nitrogen of soil less transfer to water which led to soil nitrogen content increase and water's reduce.?3?Different water level has less effect on the growth of the S.alterniflora,however,different salinity has greater impact.Salinity of 10‰and 20‰has no obvious difference effects on the growth of S.alterniflora,but salinity of 30‰has obvious inhibitory effect of growth,showed S.alterniflora although have strong secrete salt effect,which can adapt to a certain salinity,but its growth still will be hindered by 30‰of high salinity.?4?S.alterniflora to the absorption of N nutrient elements provided by the environment has certain absorption limit,after more than the absorption limit,plant will not increase with the increase of N content.?5?N₂O emissions is associated with the weather in S.alterniflora wetlands,presented with to a certain extent,associated with the temperature and relative humidity,and the temperature showed positive correlation,and relative humidity showed the negative correlation.The relationship between N₂O emissions and the mechanism of the combined stresses of salinity and drought influence is relatively complex;which still needs further research.?6?In the invasive alien plants S.alterniflora wetlands,the?¹³C composition of sediment,plant root,stem and leaf were higher than native plants Acrostichum aureum,?¹⁵N composition of sediment,plant root and leaf were higher than native plants A.aureum,while the plant stem of A.aureum was higher than S.alterniflora.C/N of S.alterniflora root,stem and soil were lower than A.aureum,while C/N of plant leaves is higher than A.aureum,which indacted that S.alterniflora has higher nitrogen content,better ability to fix nitrogen and better utilization of N.As a C₄plants,S.alterniflora leaves has higher utilization ratio of C than that of C₃ plant because of the different photosynthetic pathway.