title: Diurnal and spatial variations of soil NOx fluxes in the northern steppe of China.
abstract: NOx emissions from biogenic sources in soils play a significant role in the gaseous loss of soil nitrogen and consequent changes in tropospheric chemistry. In order to investigate the characteristics of NOx fluxes and factors influencing these fluxes in degraded sandy grasslands in northern China, diurnal and spatial variations of NOx fluxes were measured in situ. A dynamic flux chamber method was used at eight sites with various vegetation coverages and soil types in the northern steppe of China in the summer season of 2010. Fluxes of NOx from soils with plant covers were generally higher than those in the corresponding bare vegetation-free soils, indicating that the canopy plays an important role in the exchange of NOx between soil and air. The fluxes of NOx increased in the daytime, and decreased during the nighttime, with peak emissions occurring between 12:00 and 14:00. The results of multiple linear regression analysis indicated that the diurnal variation of NOx fluxes was positively correlated with soil temperature (P<0.05) and negatively with soil moisture content (P<0.05). Based on measurement over a season, the overall variation in NOx flux was lower than that of soil nitrogen contents, suggesting that the gaseous loss of N from the grasslands of northern China was not a significant contributor to the high C/N in the northern steppe of China. The concentration of NOx emitted from soils in the region did not exceed the 1-hr National Ambient Air Quality Standard (0.25 mg/m3).
authors.affiliation: State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China. Electronic address: wangbing@vip.gyig.ac.cn.
authors.forename: Bing
authors.initials: B
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China. Electronic address: lee@mail.gyig.ac.cn.
authors.forename: Xinqing
authors.initials: X
authors.lastname: Lee
authors.affiliation: Landcare Research, Private Bag 11052, Palmerston North 4442, New Zealand.
authors.forename: Benny K G
authors.initials: BK
authors.lastname: Theng
authors.affiliation: State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China.
authors.forename: Jianzhong
authors.initials: J
authors.lastname: Cheng
authors.affiliation: State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China; Graduate University of the Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Fang
authors.initials: F
authors.lastname: Yang
mesh_terms: D000383:Agriculture; D002681:China; D004784:Environmental Monitoring / Q000379:methods*; D065948:Grassland; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009589:Nitrogen Oxides / Q000032:analysis*; D012987:Soil / Q000737:chemistry* / Q000592:standards; D013696:Temperature; D014867:Water / Q000032:analysis
chemical_list: D009589:Nitrogen Oxides; D012987:Soil; D014867:Water
keywords: Desertification; Land-use change; N cycle; Nitrogen oxides