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  • 1
    Language: English
    In: Sci Rep, 2017, Vol.7(1), pp.13243-13243
    Description: Naturally produced by microbial processes in soil, nitrous oxide (NO) is an important greenhouse gas contributing to climate change. Accordingly, there is a need to accurately quantify the capability of forest ecosystems to exchange NO with the atmosphere. While NO emissions from soils have been well studied, trees have so far been overlooked in NO inventories. Here, we show that stems of mature beech trees (Fagus sylvatica) may act as a substantial sink of NO from the atmosphere under conditions of soils consuming NO. Consistent consumption of NO by all stems investigated (ranging between −2.4 and −3.8 µg m h) is a novel finding in contrast to current studies presenting trees as NO emitters. To understand these fluxes, NO exchange of photoautotrophic organisms associated with beech bark (lichens, mosses and algae) was quantified under laboratory conditions. All these organisms were net NO sinks at full rehydration and temperature of 25 °C. The consumption rates were comparable to stem consumption rates measured under field conditions. Cryptogamic stem covers could be a relevant sink of NO in European beech forests.
    Keywords: Article;
    ISSN: 2045-2322
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  • 2
    Language: English
    In: Journal of Plant Nutrition and Soil Science, February 2018, Vol.181(1), pp.31-35
    Description: Quantifying and understanding fluxes of methane (CH) and carbon dioxide (CO) in natural soil–plant–atmosphere systems are crucial to predict global climate change. Wetland herbaceous species or tree species at waterlogged sites are known to emit large amounts of CH. Upland forest soils are regarded as CH sinks and tree species like upland beech are not known to significantly emit CH. Yet, data are scarce and this assumption needs to be tested. We combined measurements of soil–atmosphere and stem–atmosphere fluxes of CO and CH and soil gas profiles to assess the contribution of the different ecosystem compartments at two upland beech forest sites in Central Europe in a case study. Soil was a net CH sink at both sites, though emissions were detected consistently from beech stems at one site. Although stem emissions from beech stems were high compared to known fluxes from other upland tree species, they were substantially lower compared to the strong CH sink of the soil. Yet, we observed extraordinarily large CH emissions from one beech tree that was 140% of the CH sink of the soil. The soil gas profile at this tree indicated CH production at a soil depth 〉 0.3 m, despite the net uptake of CH consistently observed at the soil surface. Field soil assessment showed strong redoximorphic color patterns in the adjacent soil and supports this evaluation. We hypothesize that there is a transport link between the soil and stem the root system representing a preferential transport mechanism for CH despite the fact that beech roots usually do not bear aerenchyma. The high mobility of gases requires a holistic view on the soil–plant–atmosphere system. Therefore, we recommend including field soil assessment and soil gas profiles measurements when investigating soil–atmosphere and stem–atmosphere fluxes to better understand the sources of gases and their transport mechanisms.
    Keywords: Ch 4 ; Soil Gas Profile ; Gas Flux ; Stem Gas Flux ; Co 2 ; Methanogenesis
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 3
    Language: English
    In: 2D profiles of CO2, CH4, N2O and gas diffusivity in a well aerated soil: measurement and Finite Element Modeling. Agricultural and Forest Meteorology, 247., NetherlandsElsevier. (2017).
    Description: Peer reviewed
    Keywords: Life Sciences :: Environmental Sciences & Ecology ; Sciences Du Vivant :: Sciences De L'Environnement & Écologie
    Source: ORBi (Open Repository and Bibliography), University of Liège
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  • 4
    Language: English
    In: Agricultural and Forest Meteorology, 15 February 2019, Vol.265, pp.424-434
    Description: Molecular diffusion is commonly assumed as main physical process of gas transport in soils. However, non-diffusive gas transport processes like the so-called pressure-pumping effect can affect soil gas transport significantly. The pressure-pumping effect has only been detected indirectly and the underlying mechanisms remain unclear. Using a novel method the soil gas transport at a conifer forest site was monitored over a seven-week period. Airflow and air pressure were simultaneously measured above and below the forest canopy and air pressure was also measured in the soil. During episodes of high above-canopy wind speed, the effective soil gas diffusivity temporarily increased due to pressure-pumping. The enhancement of the gas transport rate in the topsoil reached up to 30%. We found that the best meteorological proxy explaining this effect was related to air pressure fluctuations measured at soil surface and not the mean wind speed directly above ground. While sub-canopy wind speeds continuously decreased from the bottom of the tree crown to the soil surface, amplitudes of the air pressure fluctuations were nearly constant in the whole sub-canopy profile and in the soil. We hypothesize that the air pressure fluctuations responsible for pressure-pumping are related to characteristics of above-canopy airflow rather than to airflow directly above the soil surface.
    Keywords: Pressure-Pumping ; Soil Gas Transport ; Air Pressure Fluctuations ; Tracer Gas ; Agriculture ; Meteorology & Climatology
    ISSN: 0168-1923
    E-ISSN: 1873-2240
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