Studies On Changes In Atmospheric Greenhouse Gas Fluxes From Soils Of Kandelia Obovata Mangrove Forests With The Development Of Restored Vegetation In Jiulong River Estuary

In order to understand the spatial and diurnal variations of greenhouse gas fluxes from mangrove soils, the fluxes of N2O, CH4and CO2were measured in one Kandelia obovata mangrove forest in Jiulong River estuary, China, when mangrove soils were exposed to air during one tidal cycle on spring or neap day in summer. Based on that study, effect of age of restored mangrove forests on the atmospheric greenhouse gas fluxes from soils were investigated, choosing one bare flat (KO), one26-year old restored forest (K26) and one50-year old restored mangrove forest (K50) as well as one natural mature forest (MF) as representative forests. Seasonal variations of greenhouse gas fluxes and soil parameters from all these mangrove forests with different ages were measured. The correlation relationships between greenhouse gas fluxes and soil parameters were tested in order to understand the variation of greenhouse gas fluxes with the development of restored mangrove forests.There were no significant differences in the fluxes of N2O, CH4and CO2from different study sites (inner site and outer site) in the present mangrove forest during the spring day of summer. It was the same for the fluxes of N2O and CH4during the neap day, while CO2showed significantly higher fluxes at the inner site than the outer site. Significantly diurnal variations of fluxes of the three greenhouse gases in one tidal cycle were not found during the neap day. Moreover, the average fluxes of N2O and CH4were similar between spring and neap days, while fluxes of CO2were a little higher on neap day than on spring day. The soil temperature and inorganic nitrogen contents were important factors that affect the diurnal variations of the greenhouse gas fluxes.As for the effect of age of restored mangrove forests on the fluxes of atmospheric greenhouse gases from soils, annual fluxes of N2O, CH4and CO2ranged from0.17to0.76μmol m-2h-1,4.52to73.27μmol m-2h-1and-0.22to4.35mmol m-2h-1, respectively. Fluxes of the three greenhouse gases differed significantly among sampling seasons, as well as among restored forests with different ages. In general, fluxes of the three greenhouse gases were highest in summer and lowest in winter. Meanwhile, fluxes of CH4and CO2increased with the development of restored forests, but fluxes of N2O from soils firstly decreased after the replanting of vegetation and then increased with the later development of vegetation. Total CO2-equivalent fluxes of the three gases from soils of restored forests with different ages, indicating their global warming potential, ranged from82.33to674.92mg CO2m-2h-1, and CO2was the most dominant in the total flux in all mangrove forests. Therefore, total CO2-equivalent fluxes also increased with the development of restored forests.Soils were also sampled after the sampling of greenhouse gases. Soil parameters of Eh, water content, pH, ammonia nitrogen, nitrate nitrogen, organic carbon, total nitrogen, total phosphorus and ratio of carbon and nitrogen were analyzed. All soil parameters showed significant differences among sampling seasons, while soil total nitrogen was an exception. Significant variations of soil parameters among restored forests with different ages were found though different soil parameters showed different variation patterns. Soil ammonia nitrogen contents firstly decreased after the replanting of vegetation and then increased with the later development of vegetation, like the variation of N2O fluxes. The value of soil pH decreased with the development of vegetation, while soil organic carbon content, total nitrogen content and ratio of carbon and nitrogen increased with the development of vegetation. Furthermore, fluxes of N2O among restored forests with different ages were significantly correlated with the contents of soil ammonia nitrogen, while fluxes of CH4and CO2were significantly correlated with the contents of soil organic carbon and total nitrogen.As a summary, with the development of restored mangrove forests, soil parameters varied and those soil parameters were vital factors that caused the variations of greenhouse gas fluxes from mangrove soils.