Temporal trends in N sub(2)O flux dynamics in a Danish wetland - effects of plant-mediated gas transport of N sub(2)O and O sub(2) following changes in water level and soil mineral-N availability

• Published in: Global change biology 2012-01, Vol.18 (1), p.210-222
• Main Authors: Jorgensen, Christian Juncher, Struwe, Sten, Elberling, Bo
• Format: Article
• Language: English
• Subjects: Phalaris arundinacea
• ISSN: 1354-1013; 1365-2486
• DOI: 10.1111/j.1365-2486.2011.02485.x

Temporal trends of N sub(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 sub(2)O fluxes were linked to changes in subsurface N sub(2)O and O sub(2) concentrations, water level (WL), light intensity as well as mineral-N availability. Weekly concentration profiles showed that seasonal variations in N sub(2)O concentrations were directly linked to the position of the WL and O sub(2) availability at the capillary fringe above the WL. N sub(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 sub(2)O emission during day time and deposition during night time were observed when max subsurface N sub(2)O concentrations were located below the root zone. Correlation (P < 0.001) between diurnal variations in O sub(2) concentrations and incoming photosynthetically active radiation highlighted the importance of plant-driven subsoil aeration of the root zone and the associated controls on coupled nitrification/denitrification. Therefore, P. arundinacea played an important role in facilitating N sub(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 sub(2)O emissions. Complex interactions between seasonal changes in O sub(2) and mineral-N availability following near-surface WL fluctuations in combination with plant-mediated gas transport by P. arundinacea controlled the subsurface N sub(2)O concentrations and gas transport mechanisms responsible for N sub(2)O fluxes across the soil-atmosphere interface. Results demonstrate the necessity for addressing this high temporal variability and potential plant transport of N sub(2)O in future studies of net N sub(2)O exchange across the soil-atmosphere interface.