title: A relative method for measuring nitric oxide (NO) fluxes from forest soils.
abstract: Many forest ecosystems in the world are suffering from high load of nitrogen (N) deposition and acting as potential contributors to atmospheric nitric oxide (NO), which regulates the oxidative capacity of the troposphere. However, the observation of NO flux with traditional dynamic chamber method is laborious in the forest ecosystem, particularly when the electric power generation system is unavailable. In this work, a relative method based on Fick's law of diffusion was developed to measure NO fluxes from forest soils. This method describes the relationship between NO and other trace gases, such as N2O or CO2, concerning gas fluxes and gas concentration gradients between the uppermost soil layer and the atmosphere. This relative method can be expressed as two forms: based on the directly obtained soil gas and based on the equilibrium gas at soil water surface. To testify the applicability of this method, both laboratory and field experiments were conducted with soil from an N-saturated subtropical forest in Southwestern China. The results demonstrate that the NO fluxes measured based on the later form agreed well with those observed by chamber method, with the deviation rates of around 9% and 30%, respectively. In conclusion, this relative method provides a sound methodological basis for interpreting NO flux variations in the field, especially in N-saturated forest ecosystems, and allows an improvement of statistical N-budget in the world.
authors.affiliation: Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Jiaqi
authors.initials: J
authors.lastname: Wang
authors.affiliation: Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China. Electronic address: zhangxsh@rcees.ac.cn.
authors.forename: Xiaoshan
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
authors.forename: Zhangwei
authors.initials: Z
authors.lastname: Wang
authors.affiliation: Norwegian University of Life Sciences, postbox 5003, Ås 1432, Norway.
authors.forename: Ronghua
authors.initials: R
authors.lastname: Kang
keywords: Diffusion model; Field measurements; Forest ecosystem; Laboratory studies; Nitric oxide (NO); Soil-atmosphere exchange