Laboratory measurements of nitric oxide release from forest soil with a thick organic layer under different understory types

[摘要] Nitric oxide (NO) plays an important role in the photochemistry of thetroposphere. NO from soil contributes up to 40% to the global budget ofatmospheric NO. Soil NO emissions are primarily caused by biologicalactivity (nitrification and denitrification), that occurs in the uppermostcentimeter of the soil, a soil region often characterized by high contentsof organic material. Most studies of NO emission potentials to date haveinvestigated mineral soil layers. In our study we sampled soil organicmatter under different understories (moss, grass, spruce and blueberries) ina humid mountainous Norway spruce forest plantation in the Fichtelgebirge(Germany). We performed laboratory incubation and flushing experiments usinga customized chamber technique to determine the response of net potential NOflux to physical and chemical soil conditions (water content andtemperature, bulk density, particle density, pH, C/N ratio, organic C, soilammonium, soil nitrate). Net potential NO fluxes (in terms of mass of N)from soil samples taken under different understories ranged from1.7–9.8 ng m⁻² s⁻¹ (soil sampled under grass and moss cover),55.4–59.3 ng m⁻² s⁻¹ (soil sampled under spruce cover), and43.7–114.6 ng m⁻² s⁻¹ (soil sampled under blueberry cover) atoptimum water content and a soil temperature of 10 °C. The water contentfor optimum net potential NO flux ranged between 0.76 and 0.8 gravimetricsoil moisture for moss covered soils, between 1.0 and 1.1 for grass coveredsoils, 1.1 and 1.2 for spruce covered soils, and 1.3 and 1.9 for blueberrycovered soils. Effects of soil physical and chemical characteristics on netpotential NO flux were statistically significant (0.01 probability level)only for NH₄⁺. Therefore, as an alternative explanation for thedifferences in soil biogenic NO emission we consider more biological factorslike understory vegetation type, amount of roots, and degree ofmycorrhization; they have the potential to explain the observed differencesof net potential NO fluxes.

[学科分类] 地球化学与岩石