Bargsten, A; Falge, E; Huwe, B; Meixner, FX: Laboratory measurements of nitric oxide release from forest soil with a thick organic layer under different understory types, Biogeosciences - Discussion, 7, 203–250 (2010), doi:http://www.biogeosciences-discuss.net/7/203/2010/bgd-7-203-2010.pdf [Link]
Nitric oxide (NO) plays an important role in the photochemistry of the troposphere. NO from soil contributes up to 40% to the global budget of atmospheric NO. Soil NO emissions are primarily caused by biological activity (nitrification and denitrification), that occurs in the uppermost centimetres of the soil, a soil region often characterized by high contents of organic material. Most studies of NO emission potentials to date have investigated mineral soil layers. In our study we sampled soil organic matter under different understories (moss, grass, spruce and blueberries) in a humid mountainous Norway spruce forest plantation in the Fichtelgebirge (Germany). We performed laboratory incubation and fumigation experiments using a customized chamber technique to determine the response of net potential NO flux to physical and chemical soil conditions (water content and temperature, bulk density, particle density, pH, C/N ratio, organic C, soil ammonium, soil nitrate). Net potential NO fluxes (in terms of mass of N) from soils of different understories ranged from 1.7–9.8 ngm−2 s−1 (grass and moss), 55.4–59.3 ngm−2 s−1 (spruce), and 43.7–114.6 ngm−2 s−1 (blueberry) at optimum water content and a soil temperature of 10 C. The water content for optimum net potential NO flux ranged between 0.76 and 0.8 gravimetric soil moisture for moss, between 1.0 and 1.1 for grass, 1.1 and 1.2 for spruce, and 1.3 and 1.9 for blueberries. Effects of soil physical and chemical characteristics on net potential NO flux were statistically significant (0.01 probability level) only for NH+4. Therefore, the effects of biogenic factors like understory type, amount of roots, and degree of mycorrhization on soil biogenic NO emission are discussed; they have the potential to explain the observed different of net potential NO fluxes. Quantification of NO emissions from the upmost soil layer is therefore an important step to quantify soil NO emissions in ecosystems with substantial organic soil horizons.
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