The direct evaluation of attosecond chirp from a streaking measurement

We derive an analytical expression, from classical electron trajectories in a laser field, that relates the breadth of a streaked photoelectron spectrum to the group-delay dispersion of an isolated attosecond pulse. Based on this analytical expression, we introduce a simple, efficient and robust procedure to instantly extract the attosecond pulse's chirp from the streaking measurement.Comment: 4 figure

Validating soil denitrification models based on laboratory N2 and N2O fluxes and underlying processes: evaluation of DailyDayCent and COUP models

Denitrification is an anaerobic key process by microbes where the NO3- is step-by-step reduced and emitted as NO, N2O and finally N2 gas from the soil. Accurate knowledge on denitrification dynamics is important because the N2O is further reduced to N2 and constitutes the main emission source of this greenhouse gas from agricultural soils. Hence, our understanding and ability to quantify soil denitrification is crucial for mitigating nitrogen fertilizer loss as well as for reducing N2O emissions. Models can be an important tool to predict mitigation effects and help to develop climate smart mitigation strategies. Ideally, commonly used biogeochemical models could provide adequate predictions of denitrification processes of agricultural soils but often simplified process descriptions and inadequate model parameters prevent models from simulating adequate fluxes of N2 and N2O on field scale. Model development and parametrization often suffers from limited availability of empirical data describing denitrification processes in agricultural soils. While in many studies N2O emissions are used to develop and train models, detailed measurements on NO, N2O, N2 fluxes and concentrations and related soil conditions are necessary to develop and test adequate model algorithms. To address this issue the coordinated research unit „Denitrification in Agricultural Soils: Integrated Control and Modelling at Various Scales (DASIM)” was initiated to more closely investigate N-fluxes caused by denitrification in response to environmental effects, soil properties and microbial communities. Here, we present how we will use these data to evaluate common biogeochemical process models (DailyDayCent, Coup) with respect to modeled NO, N2O and N2 fluxes from denitrification. The models are used with different settings. The first approximation is the basic “factory” setting of the models. The next step would show the precision in the results of the modeling after adjusting the appropriate parameters from the result of the measurement values and the “factory” results. The better adjustment and the well-controlled input and output measured parameters could provide a better understanding of the probable scantiness of the tested models which will be a basis for future model improvement

Enzymaktivitäten in Schwarzerden des Pannonischen Raumes: Bedeutung von Niederschlagsregime und Bodentyp

Klimaszenarien für den Pannonischen Raum weisen auf eine Zunahme der Länge und Anzahl der Trockenperioden und auf eine Konzentration der Niederschläge auf wenige Ereignisse hin. Ziel der Studie war es, die Auswirkungen von klimainduziertem Stress und Starkregenereignissen auf mikrobielle Eigenschaften in landwirtschaftlichen Böden zu erfassen. Von Oktober 2011 bis November 2016 wurden hierzu in einem Freilandversuch mit kontrollierter Beregnung mehrmals pro Jahr unter anderem Enzymaktivitäten (Cellulase, Xylanase, Protease, Peroxidase und Phenoloxidase) bestimmt. Als Versuchsstandort diente die Lysimeteranlage Hirschstetten im Nordosten Wiens. Je drei Lysimeter pro Bodentyp (Feuchtschwarzerde, sandiger und tiefgründiger Tschernosem) wurden Trockenperioden und Starkregenereignissen unterworfen („dry“; Variante D). Die Beregnungsmenge und -verteilung für die übrigen Lysimeter (Kontrolle) orientierte sich am langjährigen Niederschlagsmittel. Die Enzymaktivitäten zeigten keine ausgeprägte zeitliche Dynamik mit Ausnahme der Enzyme des Kohlenstoffkreislaufs. Die Cellulaseaktivität war 2015 im Frühjahr und Spätherbst gegenüber den Probenahmeterminen im Sommer in allen drei Böden um das Zwei- bis Fünfzehnfache erhöht. Im Gegensatz hierzu wurden für die Xylanaseaktivität die höchsten Werte im Sommer 2015 registriert. Im Frühjahr 2014 war die Xylanaseaktivität in den Proben der D-Variante nicht nachweisbar. Das Niederschlagsregime hatte kaum Auswirkungen auf die gemessenen Enzymaktivitäten. Von einzelnen Probenahmeterminen abgesehen, konnte für keinen der drei Böden Unterschiede zwischen den Varianten festgestellt werden. Der Bodentyp beeinflußte die Aktivtäten der unspezifischen Enzyme Peroxidase und Phenoloxidase. Beide Enzyme zeigten im Mittel höhere Aktivitäten in den Proben des tiefgründigen Tschernosems als in denen des sandigen Tschernosems bzw. der Feuchtschwarzerde. Die vorliegenden Ergebnisse liefern keinen Hinweis darauf, daß die für den Pannonischen Raum erwarteten Modifikationen des Niederschlagsregimes die enzymatische Aktivität landwirtschaftlich bedeutsamer Böden verändern werden

Greenhouse gas emissions from Savanna (Miombo) woodlands: responses to clearing and cropping

Natural vegetation represents an important sink for greenhouse gases (GHGs); however, there is relatively little information available on emissions from southern African savannas. The effects of clearing savanna woodlands for crop production on soil fluxes of N2O, CO2 and CH4 were studied on clay (Chromic luvisol) and loamy sand (Ferric acrisol) soils in Zimbabwe. Maize (Zea mays L.) was the test crop. Gas samples were measured from undisturbed, cleared and cultivated woodlands using the static chamber methodology involving gas chromatography for ample air analysis. Site and climatic variables were particularly important determinants of GHG emissions. Over an average of 154 days emissions of 0.8 – 2.5 kg N2O-N ha-1, 1146 – 2847 kg CO2-C ha-1 and 7.4 – 38.5 kg CH4-C ha-1 were estimated during a season that followed a relatively drier one. Fertiliser-N significantly increased GHG emissions on cropped plots (clay soil). The undisturbed woodland with a relatively higher tree density (loamy sand) was an important GHG source. The high CH4 fluxes from woodlands provide ground based validation of satellite observations of CH4 hotspots in sub-Saharan Africa, and have considerable implications on regional GHG balance

GREENHOUSE GAS EMISSIONS FROM SAVANNA (MIOMBO) WOODLANDS: RESPONSES TO CLEARING AND CROPPING

Natural vegetation represents an important sink for greenhouse gases (GHGs); however, there is relatively little information available on emissions from southern African savannas. The effects of clearing savanna woodlands for crop production on soil fluxes of N2 O, CO2 and CH4 were studied on clay (Chromic luvisol) and loamy sand (Ferric acrisol) soils in Zimbabwe. Maize ( Zea mays L.) was the test crop. Gas samples were measured from undisturbed, cleared and cultivated woodlands using the static chamber methodology involving gas chromatography for ample air analysis. Site and climatic variables were particularly important determinants of GHG emissions. Over an average of 154 days emissions of O.8 \u2013 2.5 kg N2O-N ha-1, 1146 \u2013 2847 kg CO2-C ha-1 and 7.4 \u2013 38.5 kg CH4-C ha-1 were estimated during a season that followed a relatively drier one. Fertiliser-N significantly increased GHG emissions on cropped plots (clay soil). The undisturbed woodland with a relatively higher tree density (loamy sand) was an important GHG source. The high CH4 fluxes from woodlands provide ground based validation of satellite observations of CH4 hotspots in sub-Saharan Africa, and have considerable implications on regional GHG balance.La v\ue9g\ue9tation naturelle repr\ue9sente une source importante de gaz \ue0 effet de serre (GES) ; Par ailleurs, il existe relativement peu d\u2019informations disponibles sur les \ue9missions dans les savanes sud africaines. Les effets du d\ue9boisement de la savane pour la production agricole sur le flux du sol de N2O, CO2 et de CH4 ont \ue9t\ue9 \ue9tudi\ue9s sur les sols argileux (luvisol chromique) et sablo limoneux (acrisol ferrique) au Zimbabwe. La plante test consid\ue9r\ue9e \ue9tait ma\uefs ( Zea mays L.). Des \ue9chantillons de gaz \ue9taient collect\ue9s des for\ueats non perturb\ue9es, d\ue9frich\ue9es et cultiv\ue9es en utilisant la m\ue9thode de la Chambre statique impliquant le gaz chromatographie pour l\u2019analyse de l\u2019air. Le site et les variables climatiques \ue9taient particuli\ue8rement des d\ue9terminants importants des \ue9missions de gaz \ue0 effets de serre. Sur une moyenne de 154 jours des \ue9missions de O.8 \u2013 2.5 kg N2O-N ha-1, 1146 \u2013 2847 kg CO2 -C ha-1 et 7.4 \u2013 38.5 kg CH4-C ha-1 \ue9taient estim\ue9es au cours d\u2019une saison qui a suivi celle relativement la plus s\ue8che. L\u2019engrais N significativement augment\ue9 les \ue9missions de gaz \ue0 effets de serre sur les parcelles cultiv\ue9es (sol argileux). Le sol (sablo-limoneux) sous for\ueats non perturb\ue9es avec relativement une plus grande densit\ue9 d\u2019arbres \ue9tait une source importante de gaz \ue0 effets de serre. Les flux \ue9lev\ue9s de CH4 en condition de v\ue9g\ue9tation naturelle fournit une base de validation des observations satellitaires du CH4 en Afrique subsaharienne, et ont une des implications sur la balance r\ue9gionale des gaz \ue0 effets de serre

Greenhouse gas emissions from savanna (miombo) woodlands. Responses to clearing and cropping

ABSTRACT Natural vegetation represents an important sink for greenhouse gases (GHGs); however, there is relatively little information available on emissions from southern African savannas. The effects of clearing savanna woodlands for crop production on soil fluxes of N 2 O, CO 2 and CH 4 were studied on clay (Chromic luvisol) and loamy sand (Ferric acrisol) soils in Zimbabwe. Maize (Zea mays L.) was the test crop. Gas samples were measured from undisturbed, cleared and cultivated woodlands using the static chamber methodology involving gas chromatography for ample air analysis. Site and climatic variables were particularly important determinants of GHG emissions. Over an average of 154 days emissions of 0.8 -2.5 kg N 2 O-N ha -1 , 1146 -2847 kg CO 2 -C ha -1 and 7.4 -38.5 kg CH 4 -C ha -1 were estimated during a season that followed a relatively drier one. Fertiliser-N significantly increased GHG emissions on cropped plots (clay soil). The undisturbed woodland with a relatively higher tree density (loamy sand) was an important GHG source. The high CH 4 fluxes from woodlands provide ground based validation of satellite observations of CH 4 hotspots in sub-Saharan Africa, and have considerable implications on regional GHG balance. Key Words: Carbon dioxide, methane, nitrous oxide, Zimbabwe RÉSUMÉ La végétation naturelle représente une source importante de gaz à effet de serre (GES) ; Par ailleurs, il existe relativement peu d'informations disponibles sur les émissions dans les savanes sud africaines. Les effets du déboisement de la savane pour la production agricole sur le flux du sol de N 2 O, CO 2 et de CH 4 ont été étudiés sur les sols argileux (luvisol chromique) et sablo limoneux (acrisol ferrique) au Zimbabwe. La plante test considérée était maïs (Zea mays L.). Des échantillons de gaz étaient collectés des forêts non perturbées, défrichées et cultivées en utilisant la méthode de la Chambre statique impliquant le gaz chromatographie pour l'analyse de l'air. Le site et les variables climatiques étaient particulièrement des déterminants importants des émissions de gaz à effets de serre. Sur une moyenne de 154 jours des émissions de 0.8 -2.5 kg N 2 O-N ha -1 , 1146 -2847 kg CO 2 -C ha -1 et 7.4 -38.5 kg CH 4 -C ha -1 étaient estimées au cours d'une saison qui a suivi celle relativement la plus sèche. L'engrais N significativement augmenté les émissions de gaz à effets de serre sur les parcelles cultivées (sol argileux). Le sol (sablo-limoneux) sous forêts non perturbées avec relativement une plus grande densité d'arbres était une source importante de gaz à effets de serre. Les flux élevés de CH 4 en condition de végétation naturelle fournit une base de validation des observations satellitaires du CH 4 en Afrique subsaharienne, et ont une des implications sur la balance régionale des gaz à effets de serre

Carbon-nitrogen interactions in European forests and semi-natural vegetation - Part 2: Untangling climatic, edaphic, management and nitrogen deposition effects on carbon sequestration potentials

The effects of atmospheric nitrogen deposition (N$_{dep}$) on carbon (C) sequestration in forests have often been assessed by relating differences in productivity to spatial variations of N$_{dep}$ across a large geographic domain. These correlations generally suffer from covariation of other confounding variables related to climate and other growth-limiting factors, as well as large uncertainties in total (dry+wet) reactive nitrogen (N$_{r}$) deposition.We propose a methodology for untangling the effects of N$_{dep}$ from those of meteorological variables, soil water retention capacity and stand age, using a mechanistic forest growth model in combination with eddy covariance CO$_{2}$ exchange fluxes from a Europe-wide network of 22 forest flux towers. Total N$_{r}$ deposition rates were estimated from local measurements as far as possible. The forest data were compared with data from natural or semi-natural, non-woody vegetation sites. The response of forest net ecosystem productivity to nitrogen deposition (dNEP= dN$_{dep}$) was estimated after accounting for the effects on gross primary productivity (GPP) of the co-correlates by means of a meta-modelling standardization procedure, which resulted in a reduction by a factor of about 2 of the uncorrected, apparent dGPP/dN$_{dep}$ value. This model-enhanced analysis of the C and N$_{dep}$ flux observations at the scale of the European network suggests a mean overall dNEP/dN$_{dep}$ response of forest lifetime C sequestration to N$_{dep}$ of the order of 40–50 g C per g N, which is slightly larger but not significantly different from the range of estimates published in the most recent reviews. Importantly, patterns of gross primary and net ecosystem productivity versus N$_{dep}$ were non-linear, with no further growth responses at high N$_{dep}$ levels (N$_{dep}$ >2.5–3 gNm$^{-2}$ yr$^{-1}$) but accompanied by increasingly large ecosystem N losses by leaching and gaseous emissions. The reduced increase in productivity per unit N deposited at high N$_{dep}$ levels implies that the forecast increased N$_{r}$ emissions and increased Ndep levels in large areas of Asia may not positively impact the continent’s forest CO$_{2}$ sink. The large level of unexplained variability in observed carbon sequestration efficiency (CSE) across sites further adds to the uncertainty in the dC/dN response