Soil and vegetation-atmosphere exchange of NO, NH3, and N2O from field measurements in a semi arid grazed ecosystem in Senegal. (May 2017)

• Record Type: Journal Article
• Authors: Delon, C.; Galy-Lacaux, C.; Serça, D.; Loubet, B.; Camara, N.; Gardrat, E.; Saneh, I.; Fensholt, R.; Tagesson, T.; Le Dantec, V.; Sambou, B.; Diop, C.; Mougin, E.
• Is Part Of: Atmospheric environment. Volume 156(2017)
• Page Start: 36
• Page End: 51
• Publication Date: 2017-05
• Subjects: Nitrogen compound exchanges -- Semi arid tropical ecosystem -- Biogenic emissions -- Litter emissions -- Soil respiration -- Soil processes of nitrogen release; Air -- Pollution -- Periodicals; Air -- Pollution -- Meteorological aspects -- Periodicals; 551.51
• DOI: 10.1016/j.atmosenv.2017.02.024
• Languages: English
• ISSNs: 1352-2310

Abstract

Abstract: The alternating between dry and wet seasons and the consecutive microbial responses to soil water content in semiarid ecosystems has significant consequences on nitrogen exchanges with the atmosphere. Three field campaigns were carried out in a semi arid sahelian rangeland in Dahra (Ferlo, Senegal), two at the beginning of the wet season in July 2012 and July 2013, and the third one in November 2013 at the end of the wet season. The ammonia emission potentials of the soil ranged from 271 to 6628, indicating the soil capacity to emit NH3 . The ammonia compensation point in the soil ranged between 7 and 150 ppb, with soil temperatures between 32 and 37 °C. Ammonia exchange fluctuated between emission and deposition (from −0.1–1.3 ng N.m −2 s −1 ), depending on meteorology, ambient NH3 concentration (5–11 ppb) and compensation point mixing ratios. N2 O fluxes are supposed to be lower than NO fluxes in semi arid ecosystems, but in Dahra N2 O fluxes (5.5 ± 1.3 ng N m −2 s −1 in July 2013, and 3.2 ± 1.7 ng N m −2 s −1 in November 2013) were similar to NO fluxes (5.7 ± 3.1 ng N m −2 s −1 in July 2012, 5.1 ± 2.1 ng N m −2 s −1 in July 2013, and 4.0 ± 2.2 ngN m −2 s −1 in November 2013). Possible reasons are the influence of soil moisture below the surface (where N2 O is produced) after the beginning of the wet season, the potential aerobic denitrification in microsites, the nitrifier denitrification, and nitrification processes. The presence of litter and standing straw, and their decomposition dominated N compounds emissions in November 2013, whereas emissions in July 2012 and 2013, when the herbaceous strata was sparse, were dominated by microbial processes in the soil. CO2 respiration fluxes were high in the beginning (107 ± 26 mg m −2 h −1 in July 2013) and low in the end of the wet season (32 ± 5 mg m −2 h −1 in November 2013), when autotrophic and heterotrophic activity is reduced due to low soil moisture conditions These results confirm that contrasted ecosystem conditions due to drastic changes in water availability in semi arid regions have important non linear impacts on the biogeochemical nitrogen cycle. Highlights: At the beginning of the wet season, soil microbial activity is reactivated. Significant emissions of NO and CO2 occur and are linked by microbial processes. Litter and straw play an important role in emitting NH3 and NO (end of wet season). NH3 bidirectional exchange is highlighted and both emission and deposition occur. N2 O and NO fluxes are equivalent: denitrification occurs at low soil moisture levels.