Natural wetlands act as both sources and sinks of greenhouse gases such as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) from the soil to the atmosphere. Production and consumption of these gases in the soil are controlled by a series of highly dynamic and interrelated processes involving plants, soil and microorganisms. These processes are regulated by different
physio-chemical drivers such as soil moisture content, soil temperature, nutrient and oxygen (O2) availability. In wetlands, the position of the free standing water level (WL) influences the spatiotemporal variation in these drivers, thereby influencing the net emission or uptake of greenhouse gas.
In this PhD thesis the complex aspects in the exchange of N2O across the soil-atmosphere is investigated with special focus on the spatiotemporal variations in drivers for N2O production and consumption in the soil and their relation to observed flux patterns. It is demonstrated how the seasonal variations in N2O emissions are linked to the subsurface concentrations of N2O at the capillary fringe above the WL by regulating the apparent diffusion rates of oxygen (O2) into the soil which availability regulates sequential nitrification-denitrification processes in the soil.
It is shown that fast acting N-transformation processes both produce and consume large concentration of N2O over short distances in response to rapid WL variations, and that these processes are crucial for explaining the spatiotemporal variation in observed net N2O dynamics.
Similarly, plant-mediated gas transport by the subsurface aerating macrophyte Phalaris arundinacea played a major part in regulating and facilitating emissions of greenhouse gases across the soil-atmosphere interface.
It is concluded that the spatiotemporal distribution of dominating N2O producing and consuming processes below the surface, in combination with the variations in the diffusive exchange rates due to soil water content and apparent diffusivity, control the magnitude and timing of N2O emissions to the atmosphere in close connection with the plant-mediated gas transport. It is evident, that the
inclusion of the aboveground biomass in these types of flux measurements is essential to avoid significant underestimations of net N2O fluxes, whereas an inadequate sampling frequency or nonuniform temporal coverage could impose an undesirable bias to the net flux estimates.