Bad Homburg vor der Höhe, Germany
Bad Homburg vor der Höhe, Germany

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Bucher S.F.,Friedrich - Schiller University of Jena | Bucher S.F.,University of Regensburg | Auerswald K.,TU Munich | Tautenhahn S.,Friedrich - Schiller University of Jena | And 7 more authors.
Plant Ecology | Year: 2016

Stomata are mediators of gas exchange and thus important for photosynthesis and plant performance. The aim of this study was to analyze the ecological explanatory power of the stomatal pore area index (SPI) calculated via stomatal size and density. We studied the SPI on sun leaves of 22 herbaceous species on 22 study sites being distributed along two elevational gradients in the northern Alps ranging from 700 to 1800 m a.s.l.. We analyzed its correlation with other functional traits related to plant performance namely specific leaf area (SLA), area-based leaf nitrogen and carbon (Narea and Carea, respectively) as well as carbon discrimination Δ13C within as well as between species. On a subset of four species we also measured light-saturated net photosynthetic rate at ambient CO2 concentration (Asat) and stomatal conductance on all sites. We found that SPI was positively correlated with Asat, yet the relation was weaker than expected. The reaction of SPI along the elevational gradients was highly species-specific and related to variations in other investigated leaf traits. The relationship with functional traits, however, differed between the inter- and intraspecific level in strength and direction. SPI was positively related to Narea and Carea and negatively with SLA and Δ13C for most species. However, we found no significant relation considering species mean values for Δ13C and Narea. The relation of SPI to SLA was the most consistent displaying no difference when comparing the relation between and within species. This research shows that different processes may act on different organizational levels leading to the detected differences in trait–trait correlations on the inter- and intraspecific levels. It may have important consequences also for macroecological and modelling studies. © 2016 Springer Science+Business Media Dordrecht


Kok J.F.,University of California at Los Angeles | Kok J.F.,Cornell University | Mahowald N.M.,Cornell University | Fratini G.,University of Tuscia | And 10 more authors.
Atmospheric Chemistry and Physics | Year: 2014

Simulations of the dust cycle and its interactions with the changing Earth system are hindered by the empirical nature of dust emission parameterizations in weather and climate models. Here we take a step towards improving dust cycle simulations by using a combination of theory and numerical simulations to derive a physically based dust emission parameterization. Our parameterization is straightforward to implement into large-scale models, as it depends only on the wind friction velocity and the soil's threshold friction velocity. Moreover, it accounts for two processes missing from most existing parameterizations: a soil's increased ability to produce dust under saltation bombardment as it becomes more erodible, and the increased scaling of the dust flux with wind speed as a soil becomes less erodible. Our treatment of both these processes is supported by a compilation of quality-controlled vertical dust flux measurements. Furthermore, our scheme reproduces this measurement compilation with substantially less error than the existing dust flux parameterizations we were able to compare against. A critical insight from both our theory and the measurement compilation is that dust fluxes are substantially more sensitive to the soil's threshold friction velocity than most current schemes account for. © Author(s) 2014.


Brummer C.,Thunen Institute of Climate Smart Agriculture TI AK | Marx O.,LI COR Biosciences GmbH | Kutsch W.,Thunen Institute of Climate Smart Agriculture TI AK | Ammann C.,Swiss Federal Research Station Agroscope ART | And 3 more authors.
Tellus, Series B: Chemical and Physical Meteorology | Year: 2013

The amount and timing of reactive nitrogen exchange between agricultural land and the atmosphere play a key role in evaluating ecosystem productivity and in addressing atmospheric nitrogen budgets and transport. With the recent development of the Total Reactive Atmospheric Nitrogen Converter (TRANC) apparatus, a methodology has been provided for continuous measurement of the sum of all airborne nitrogen containing species (σNr) allowing for diurnal and seasonal investigations. We present σNr concentration and net flux data from an 11-month field campaign conducted at an arable field using the TRANC system within an eddy-covariance setup. Clear diurnal patterns of both σNr concentrations and fluxes with significant dependencies on atmospheric stability and stomatal regulation were observed in the growing season. TRANC data were compared with monthly-averaged concentrations and dry deposition rates of selected Nr compounds using DELTA denuders and ensemble-averages of four inferential models, respectively. Similar seasonal trends were found for Nr concentrations from DELTA and TRANC measurements with values from the latter being considerably higher than those of DELTA denuders. The variability of the difference between these two systems could be explained by seasonally changing source locations of NOx contributions to the TRANC signal. As soil and vegetation Nr emissions to the atmosphere are generally not treated by inferential (dry deposition) models, TRANC data showed lower monthly deposition rates than those obtained from inferential modelling. Net σNr exchange was almost neutral (~0.072 kg N ha-1) at the end of the observation period. However, during most parts of the year, slight but permanent net σNr deposition was found. Our measurements demonstrate that fertilizer addition followed by substantial σNr emissions plays a crucial role in a site's annual atmospheric nitrogen budget. As long-term Nr measurements with high temporal resolution are usually cost and labour-intensive, field application of the TRANC helps improve the understanding of ecosystem functioning, atmospheric transport and revising definitions of ecosystem-specific critical loads at a relatively moderate operational cost level. © 2013 C. Brümmer et al.


Marx O.,LI COR Biosciences GmbH | Brummer C.,Johann Heinrich Von Thunen Institute | Ammann C.,Swiss Federal Research Station Agroscope ART | Wolff V.,Swiss Federal Research Station Agroscope ART | Freibauer A.,Johann Heinrich Von Thunen Institute
Atmospheric Measurement Techniques | Year: 2012

The input and loss of plant available nitrogen (reactive nitrogen: N r) from/to the atmosphere can be an important factor for the productivity of ecosystems and thus for its carbon and greenhouse gas exchange. We present a novel converter for reactive nitrogen (TRANC: Total Reactive Atmospheric Nitrogen Converter), which offers the opportunity to quantify the sum of all airborne reactive nitrogen compounds (∑N r) in high time resolution. The basic concept of the TRANC is the full conversion of all N r to nitrogen monoxide (NO) within two reaction steps. Initially, reduced N r compounds are being oxidised, and oxidised N r compounds are thermally converted to lower oxidation states. Particulate N r is being sublimated and oxidised or reduced afterwards. In a second step, remaining higher nitrogen oxides or those generated in the first step are catalytically converted to NO with carbon monoxide used as reduction gas. The converter is combined with a fast response chemiluminescence detector (CLD) for NO analysis and its performance was tested for the most relevant gaseous and particulate N r species under both laboratory and field conditions. Recovery rates during laboratory tests for NH3 and NO 2 were found to be 95 and 99%, respectively, and 97% when the two gases were combined. In-field longterm stability over an 11-month period was approved by a value of 91% for NO 2. Effective conversion was also found for ammonium and nitrate containing particles. The recovery rate of total ambient N r was tested against the sum of individual measurements of NH 3, HNO 3, HONO, NH 4 +, NO 3 -, and NO x using a combination of different well-established devices. The results show that the TRANC-CLD system precisely captures fluctuations in ∑N r concentrations and also matches the sum of all individual N r compounds measured by the different single techniques. The TRANC features a specific design with very short distance between the sample air inlet and the place where the thermal and catalytic conversions to NO occur. This assures a short residence time of the sample air inside the instrument, and minimises wall sorption problems of water soluble compounds. The fast response time (e-folding times of 0.30 to 0.35 s were found during concentration step changes) and high accuracy in capturing the dominant N r species enables the converter to be used in an eddy covariance setup. Although a source attribution of specific N r compounds is not possible, the TRANC is a new reliable tool for permanent measurements of the net ∑N r flux between ecosystem and atmosphere at a relatively low maintenance and reasonable cost level allowing for diurnal, seasonal and annual investigations. © Author(s) 2012.


Nicolini G.,University of Tuscia | Nicolini G.,Euro Mediterranean Center for Climate Change | Castaldi S.,Euro Mediterranean Center for Climate Change | Castaldi S.,The Second University of Naples | And 4 more authors.
Atmospheric Environment | Year: 2013

The use of micrometeorological (MM) techniques for methane (CH4) and nitrous oxide (N2O) flux measurements in terrestrial ecosystems is increasing and a general outline which summarizes key results is needed. This work provides an overview of the current status of global flux measurements of CH4 and N2O by MM techniques in terrestrial ecosystems. Published studies were grouped into four main terrestrial land cover categories and the reported flux ranges, the consistency of different MM approaches over the same ecosystem types, the variability of the MM technique performances as regards the flux detection limit and environmental conditions, were analysed. Furthermore, the issue of the comparability between MM and soil chambers measurements was evaluated. The existing dataset, although temporally and spatially limited, shows that CH4 and N2O fluxes are extremely variable in both time and space with mean fluxes spanning within interquartile ranges of 1.33÷5.45, 11.02÷68.48, 5.38÷29.28, 13.87·103÷47.60·103nmolCH4m-2s-1 in forest, wetlands, croplands and artificial lands respectively, and of 0.09÷0.42, 0.24÷1.47, 9.13÷20.89nmolN2Om-2s-1 in forest, croplands and artificial lands (no published works were found for wetlands). When environmental conditions were comparable, a general agreement of flux ranges was found within each ecosystem type, in particular when estimates were based on accurate footprint analysis. Exceptions were mainly related to site-specific aspects or to particular measurement periods. Not all the measurement set-ups were suitable for all ecosystems, environmental conditions, turbulence characteristics and flux intensity, however the latest technological improvements make the detection of fluxes feasible virtually in all ecosystems. MM studies of CH4 and N2O fluxes were unevenly distributed around the globe and, in particular, were lacking in sensitive areas like Africa, South America and Central Asia. © 2013 Elsevier Ltd.


Gioli B.,CNR Institute for Biometeorology | Toscano P.,CNR Institute for Biometeorology | Zaldei A.,CNR Institute for Biometeorology | Fratini G.,LI COR Biosciences GmbH | Miglietta F.,CNR Institute for Biometeorology
Energy Procedia | Year: 2013

Eddy covariance (EC) flux measurements of CO2, CH4 and particles in densely urbanized area in Florence are reported, and partitioned into emission categories. CO2 fluxes are a net source to the atmosphere, with small inter-annual variability and high seasonality. CH4 fluxes represent about 8% of CO2-equivalent emissions, and do not exhibit significant seasonality. Heating and road traffic account for 68% and 32% of observed CO2 emissions, respectively, and for 14% of CH4 emissions, while gas network leakages are responsible for the residual. Particle fluxes exhibit a pronounced weekend decrease, highlighting that the main contribution to emissions comes from road traffic. © 2013 The Authors. Published by Elsevier Ltd.


Brilli F.,University of Antwerp | Brilli F.,CNR Institute of Agro-environmental and Forest Biology | Gioli B.,CNR Institute for Biometeorology | Zona D.,University of Sheffield | And 7 more authors.
Agricultural and Forest Meteorology | Year: 2014

Emission of carbon from ecosystems in the form of volatile organic compounds (VOC) represents a minor component flux in the global carbon cycle that has a large impact on ground-level ozone, particle and aerosol formation and thus on air chemistry and quality. This study reports exchanges of CO2 and VOC between a poplar-based short rotation coppice (SRC) plantation and the atmosphere, measured simultaneously at two spatial scale, one at stand level and another at leaf level. The first technique combined Proton Transfer Reaction "Time-of-Flight" mass spectrometry (PTR-TOF-MS) with the eddy covariance method, to measure fluxes of a multitude of VOC. Abundant fluxes of isoprene, methanol and, to a lesser extent, fluxes of other oxygenated VOC such as formaldehyde, isoprene oxidation products (methyl vinyl ketone and methacrolein), methyl ethyl ketone, acetaldehyde, acetone and acetic acid, were measured. Under optimal environmental conditions, isoprene flux was mostly controlled by temperature and light. Differently, methanol flux underwent a combined enzymatic and stomatal control, together involving environmental drivers such as vapour pressure deficit (VPD), temperature and light intensity. Moreover fair weather condition favoured ozone deposition to the poplar plantation.The second technique involved trapping the VOCs emitted from leaves followed by gas chromatography-mass spectrometry (GC-MS) analysis. These leaf-level measurements showed that emission of isoprene in adult leaves and of monoterpenes in juvenile leaves are widespread across poplar genotypes. Detection of isoprene oxidation products (iox) emission with leaf-level measurements confirmed that a fraction of isoprene may be already oxidized within leaves, possibly when isoprene copes with foliar reactive oxygen species (ROS) formed during warm and sunny days. © 2013 Elsevier B.V.


Budishchev A.,VU University Amsterdam | Mi Y.,VU University Amsterdam | Van Huissteden J.,VU University Amsterdam | Belelli-Marchesini L.,VU University Amsterdam | And 6 more authors.
Biogeosciences | Year: 2014

Most plot-scale methane emission models - of which many have been developed in the recent past - are validated using data collected with the closed-chamber technique. This method, however, suffers from a low spatial representativeness and a poor temporal resolution. Also, during a chamber-flux measurement the air within a chamber is separated from the ambient atmosphere, which negates the influence of wind on emissions. Additionally, some methane models are validated by upscaling fluxes based on the area-weighted averages of modelled fluxes, and by comparing those to the eddy covariance (EC) flux. This technique is rather inaccurate, as the area of upscaling might be different from the EC tower footprint, therefore introducing significant mismatch. In this study, we present an approach to validate plot-scale methane models with EC observations using the footprint-weighted average method. Our results show that the fluxes obtained by the footprint-weighted average method are of the same magnitude as the EC flux. More importantly, the temporal dynamics of the EC flux on a daily timescale are also captured (r2 = 0.7). In contrast, using the area-weighted average method yielded a low (r2 = 0.14) correlation with the EC measurements. This shows that the footprint-weighted average method is preferable when validating methane emission models with EC fluxes for areas with a heterogeneous and irregular vegetation pattern. © Author(s) 2014. CC Attribution 3.0 License.


Ammann C.,Federal Research Station Agroscope ART | Wolff V.,Federal Research Station Agroscope ART | Marx O.,LI COR Biosciences GmbH | Brummer C.,Johann Heinrich Von Thunen Institute | Neftel A.,Federal Research Station Agroscope ART
Biogeosciences | Year: 2012

The (net) exchange of reactive nitrogen (Nr) with the atmosphere is an important driver for ecosystem productivity and greenhouse gas exchange. The exchange of airborne Nr includes various trace compounds that usually require different specific measurement techniques, and up to now fast response instruments suitable for eddy covariance measurements are only available for few of these compounds. Here we present eddy covariance flux measurements with a recently introduced converter (TRANC) for the sum of all Nr compounds (σNr). Measurements were performed over a managed grassland field with phases of net emission and net deposition of σNr and alternating dominance of oxidized (NOX) and reduced species (NH3). Spectral analysis of the eddy covariance data exhibited the existence of covariance function peaks at a reasonable time lag related to the sampling tube residence time under stationary conditions. Using ogive analysis, the high-frequency damping was quantified to 19%-26% for a low measurement height of 1.2 m and to about 10% for 4.8 m measurement height. σNr concentrations and fluxes were compared to parallel NO and NO2 measurements by dynamic chambers and NH3 measurements by the aerodynamic gradient technique. The average concentration results indicate that the main compounds NO 2 and NH3 were converted by the TRANC system with an efficiency of near 100%. With an optimised sample inlet also the fluxes of these compounds were recovered reasonably well including net deposition and net emission phases. The study shows that the TRANC system is suitable for fast response measurements of oxidized and reduced nitrogen compounds and can be used for continuous eddy covariance flux measurements of total reactive nitrogen. © 2012 Author(s).

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