The Carbon Dioxide Flux In Mangrove Forest Ecosystem And Its Responses To Climate Change

The research on greenhouse gas emissions is a hot issue nowadays.As an important source of greenhouse gases(GHG)in the atmosphere,wetlands have always attracted much attention of researchers.Mangrove wetlands has extremely high primary productivity,and the researches on the carbon dioxide(CO2)flux of coastal wetlands suggested the uncertainly their role as carbon sink/source.The Zhangjiang Estuary Mangrove Reserve is the most important coastal wetland in Fujian Province,as one of the mangrove nature reserve in China.The dominant mangrove species are Kandelia obovata,Aegiceras corniculatum and Avicennia marina.In this study,a set of in-situ CO2 flux measurement point were set under the Eddy tower of mangroves in Zhangjiang Estuary,and the all-day measurement of CO2 exchange were taken on the canopy,stems and soil surface of the mature plants in these three species in each month for one year.In Zhangjiang Estuary,a set of platforms simulating future sea-level rise scenarios were used to discuss the characteristics of CO2 flux.In Aojiang Estuary of Wenzhou,the northmost location in planting Kandelia obovata,the Open-Top Chambers(OTC)were used to mimic the warming condition,and measurements of CO2 flux were taken.The results were as the follows.1.On the soil surface of mangrove wetlands,the average annual CO2 flux in the soi1 was 3.90 g CO2 m-2 d-1,and the largest annual CO2 emissions occurred in July at 10.17 g CO2 m-2 d-1.Soil CO2 flux was significantly correlated with soil temperature and air temperature.2.There was a significant positive correlation between the CO2 flux and the air temperature.There was a significant difference among in the CO2 fluxes of different mangrove species.The CO2 flux of Aegiceras corniculatum population was the significantly lowest within the three mangrove species.3.The diurnal variation of CO2 flux in the plant canopy showed a "U-shape"characteristic,which is significantly related to the photosynthetically active radiation and the air temperature.There was no significant difference in the CO2 flux among the different mangrove plants.4.Sea-level rise led to the prolonged flooding time and increased flooding depth,which has a certain inhibitory effect on the growth of mangrove plants in Zhangjiang Estuary.However,the different water level treatments had no significant effects on the mangrove wetland CO2 flux.5.The increasing temperature in the OTC in Aojiang Estuary promoted the growth rates of Kandelia obovata seedlings,while the increasing temperature also promoted the CO2 emission from the mangrove soil surface.The positive effects of carbon accumulating by plant growth may be counteracted by the negative effects of significant increasing of GHG emission in future warming and sea-level rise scenarios.