Temporal trends in N₂O flux dynamics in a Danish wetland – effects of plant‐mediated gas transport of N₂O and O₂ following changes in water level and soil mineral‐N availability

Abstract

Temporal trends of N 2 O fluxes across the soil-atmosphere interface were determined using continuous flux chamber measurements over an entire growing season of a subsurface aerating macrophyte (Phalaris arundinacea) in a nonmanaged Danish wetland. Observed N 2 O fluxes were linked to changes in subsurface N 2 O and O 2 concentrations, water level (WL), light intensity as well as mineral-N availability. Weekly concentration profiles showed that seasonal variations in N 2 O concentrations were directly linked to the position of the WL and O 2 availability at the capillary fringe above the WL. N 2 O flux measurements showed surprisingly high temporal variability with marked changes in fluxes and shifts in flux directions from net source to net sink within hours associated with changing light conditions. Systematic diurnal shifts between net N 2 O emission during day time and deposition during night time were observed when max subsurface N 2 O concentrations were located below the root zone. Correlation (P < 0.001) between diurnal variations in O 2 concentrations and incoming photosynthetically active radiation highlighted the importance of plantdriven subsoil aeration of the root zone and the associated controls on coupled nitrification/denitrification. Therefore, P. arundinacea played an important role in facilitating N 2 O transport from the root zone to the atmosphere, and exclusion of the aboveground biomass in flux chamber measurements may lead to significant underestimations on net ecosystem N 2 O emissions. Complex interactions between seasonal changes in O 2 and mineral-N availability following near-surface WL fluctuations in combination with plant-mediated gas transport by P. arundinacea controlled the subsurface N 2 O concentrations and gas transport mechanisms responsible for N 2 O fluxes across the soil-atmosphere interface. Results demonstrate the necessity for addressing this high temporal variability and potential plant transport of N 2 O in future studies of net N 2 O exchange across the soil-atmosphere interface.

Spatiotemporal Variations in Nitrous Oxide Emissions from an Open Fen on the Qinghai–Tibetan Plateau: a 3-Year Study

“…N 2 O emissions vary considerably and have been influenced by several key factors, such as soil WFPS, pH, C supply, and the weather conditions (Lin et al 2009;Jørgensen et al 2012). However, in this study we only observed significant relation between N 2 O emissions and the 5 cm soil temperatures in 2005.…”

“…Moreover, temporal dynamics of soil water regime in wetland soils is sensitive to seasonal and inter-annual weather patterns, which will affect the environmental drivers for N-transformation processes (Jørgensen et al 2012). On the plateau, the precipitation trend since 1960 has shown an overall slight increase with highly seasonal and inter-annual variations Kang et al 2010) and this trend will continue in the future (Piao et al 2010).…”

“…For example, constructed wetlands, lakes, and rice paddies are significant sources of N 2 O due to high nitrogen loading (Lilkanen and Martikainen 2003;Xu et al 2004;Sovik and Klove 2007). About N 2 O fluxes in wetlands, great spatial and temporal variation was found in many studies (Sovik et al 2006;Song et al 2008;Allen et al 2011;Jørgensen et al 2012). Several factors dominantly control N 2 O production, including soil moisture content, the standing water depth, plant growth pattern, O 2 availability, soil labile carbon, and nitrogen (Lilkanen and Martikainen 2003;Song et al 2008;Burgin and Groffman 2012).…”

“…. Wetlands, however, due to their high water table and low oxygen (O 2 ) availability, are usually regarded as a low source or even a sink of N 2 O (Tauchnitz et al 2008), while wetland soils can also be significant sources of N 2 O given favorable conditions for N 2 O production (Lilkanen and Martikainen 2003;Jørgensen et al 2012). For example, constructed wetlands, lakes, and rice paddies are significant sources of N 2 O due to high nitrogen loading (Lilkanen and Martikainen 2003;Xu et al 2004;Sovik and Klove 2007).…”

Effect of reed canary grass cultivation on greenhouse gas emission from peat soil at controlled rewetting

“…Next, the transport of oxygen to anaerobic zones stimulates heterotrophic degradation of organic matter, but at the same time stimulates oxidation of CH 4 (Kao-Kniffin et al, 2010) and suppress CH 4 production due to increase in redox potential (Laanbroek, 2010;SuttonGrier and Megonigal, 2011). RCG may further increase the emissions of reduced soil gases as the aerenchyma tissues act as a conduit for the direct transport of, for example, CH 4 and N 2 O produced in soil (Joabsson et al, 1999;Jørgensen et al, 2012). Also, RCG can decrease N 2 O emissions by assimilation of mineral N, which reduces the availability of electron acceptors (nitrate) for denitrifying microorganisms (Roobroeck et al, 2010).…”