Diurnal dynamics of CH4, CO2 and N2O fluxes in the saline-alkaline soils of the Yellow River Delta, China

Salt-affected soils are extensively present and constitute about 7% of total land surface. However, our knowledge about greenhouse gas (GHG) turnover between the atmosphere and the saline soils is very limited. In order to evaluate the potential of GHG consumption in saline soils, we measured gas fluxes of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) from the soil surface to the atmosphere under saline-alkaline mudflat and various community types in the Yellow River Delta in China. In general, the emissions of GHG of different ecosystems showed a unique peak diurnal pattern, with the peak at 13:00h and the lowest value at 07:00h. The CH4 and N2O emission of different ecosystems followed the order: saline-alkaline mudflat>T. chinensis>S. salsa>P. australis, while the CO2 emission followed the order: T. chinensis>P. australis>S. salsa >saline-alkaline mudflat. On the whole, saline-alkaline mudflat and different vegetations acted as CO2 and N2O source in spring, while saline-alkaline mudflat and P. australis communities acted as CH4 source and CH4 sink, respectively. However, T. chinensis and S. salsa communities acted as CH4 sink before 12:00h and CH4 source after 12:00h. Although measurements of the CO2, CH4 and N2O fluxes were taken simultaneously, CH4 and N2O fluxes were strongly correlated with soil moisture, temperature and electrical conductivity, while no significant correlation was found between CO2 flux with above environmental factors. These results probably suggest that factors other than soil temperature, moisture and salinity exerted a larger impact on fluxes than on CH4 and N2O release and/or that there were not enough samples for CO2 flux measurements because of its higher spatial and temporal variability.