Long-term measurements of NOx and O3 soil fluxes in a temperate deciduous forest

A long-term campaign devoted to the measurement of fluxes of nitrogen oxides and ozone at the surface\r\nof a temperate deciduous forest was carried out from 1st September 2012 to 31st December 2013, using\r\nautomated dynamic chambers.\r\nSoil temperature and water content profiles were recorded near the chambers in order to clarify the\r\nshort-term response of the fluxes to these two variables.\r\nBulk soil resistances against NO, NO2 and O3 emission or deposition were also estimated in order to\r\nunderstand their daily and seasonal variations.\r\nNitric oxide was almost exclusively emitted and the annual average soil emission of 27.4mgNm−2 h−1\r\nwas higher than those for other deciduous European forests. The maximum daily peaks of NO emission\r\nexceeded 100mgNm−2 h−1 during summertime and were close to zero in wintertime.\r\nOn annual basis the N balance of the ecosystem as NOx showed a net emission towards the atmosphere\r\nof 1.1 kgNha−1 yr−1. This result can be explained by the strong N input through wet deposition observed\r\nat this site during the last decades. NO emission fluxes depended exponentially on soil temperature and\r\ndecreased at high levels of soil water content during summertime, suggesting that the main contribution\r\nwas due to aerobic nitrification processes.\r\nSoil deposition fluxes of NO2 and O3 were mainly governed by atmospheric processes related to the\r\natmosphere/soil concentration differences.\r\nSoil resistances against NO2 and O3 deposition showed both diurnal and seasonal variations which\r\ndisagree with the constant values often used in model studies.