Abstract
Abstract. Biogenic NOx emissions from natural and anthropogenically influenced soils are currently estimated to amount to 9 Tg a−1, hence a significant fraction of global NOx emissions (45 Tg a−1). During the last three decades, a large number of field measurements have been performed to quantify biogenic NO emissions. To study biogenic NO emissions as a function of soil moisture, soil temperature, and soil nutrients, several laboratory approaches have been developed to estimate local/regional NO emissions by suitable upscaling. This study presents an improved and automated laboratory dynamic chamber system (consisting of six individual soil chambers) for investigation and quantification of all quantities necessary to characterise biogenic NO release from soil (i.e. net NO release rate, NO production and consumption rate, and respective Q10 values). In contrast to former versions of the laboratory dynamic chamber system, the four experiments for complete characterisation can now be performed on a single soil sample, whereas former studies had to be performed on four sub-samples. This study discovered that the sub-sample variability biased former measurements of net NO release rates tremendously. Furthermore, it was also shown that the previously reported variation of optimum soil moisture (i.e. where a maximum net NO release rates occur) between individual sub-samples is most likely a methodical artefact of former versions of the laboratory dynamic chamber system. A comprehensive and detailed methodical concept description of the improved laboratory dynamic chamber system is provided. Response of all quantities (necessary to characterise net NO release) to soil temperature and NO mixing ratio of the flushing airstream are determined by automatic monitoring of these variables during one single drying-out experiment with one single soil sample only. The method requires precise measurements of NO mixing ratio at the inlet and outlet of each soil chamber; finally, four pairs of inlet/outlet NO mixing ratios are sufficient to derive all necessary quantities. Soil samples from drylands exhibit particularly low NO production, but even lower NO consumption rates. However, with the improved laboratory dynamic chamber system those low levels can be quantified, as well as corresponding NO compensation point mixing ratios and respective Q10 values. It could be shown that the NO compensation point mixing ratio seems to be generally independent of gravimetric soil moisture content, but, particularly for dryland soils, strongly dependent on soil temperature. New facilities have been included into the improved system (e.g. for investigation of net release rates of other trace gases, namely CO2 and volatile organic compounds – VOCs). First, results are shown for net release rates of acetone (C3H6O), acetaldehyde (C2H4O) and CO2. This new system is thus able to simultaneously investigate potential mechanistic links between NO, multitudinous VOC and CO2.
Highlights
The turnover of nutrients in natural soils is predominantly driven by soil microbes and any control of production and consumption of trace gases in the soil is exerted on the level of microbes’ metabolism
Obvious and large discrepancies have been found between the postulated response of net nitric oxide (NO) release rates to soil moisture, soil temperature, and NO mixing ratio and that observed by earlier versions of the laboratory dynamic chamber system
An improved laboratory incubation system − consisting of six individual soil chambers − is described with respect to design and function, benchmark tests have been performed, and the overall performance of the system has been demonstrated by a series of experiments on five soil samples which are characterised by very contrasting soil properties
Summary
The turnover of nutrients in natural soils is predominantly driven by soil microbes and any control of production and consumption of trace gases in the soil is exerted on the level of microbes’ metabolism. If production of the trace gas in the soil exceeds its consumption, the trace gas will be delivered to the atmosphere. In case of nitric oxide (NO), microbially produced NO is usually released from soils. It is immediately involved in important chemical 2007). For understanding tropospheric chemistry of non-industrialised regions, it is important to know the strength of biogenic NO and VOCs emissions from natural sources. While there is rich literature with respect to soil biogenic NO emissions, relatively little is known about VOC emissions from and VOC deposition to soils
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