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

N 2 O emissions and NO 3 − leaching from two contrasting regions in Austria and influence of soil, crops and climate: a modelling approach

National emission inventories for UN FCCC reporting estimate regional soil nitrous oxide (N 2 O) fluxes by considering the amount of N input as the only influencing factor for N 2 O emissions. Our aim was to deepen the understanding of N 2 O fluxes from agricultural soils, including region specific soil and climate properties into the estimation of emission to find targeted mitigation measures for the reduction of nitrogen losses and GHG emissions. Within this project, N 2 O emissions and nitrate (NO 3 − ) leaching were modelled under spatially distinct environmental conditions in two agricultural regions in Austria taking into account region specific soil and climatic properties, management practices and crop rotations. The LandscapeDNDC ecosystem model was used to calculate N 2 O emissions and NO 3 − leaching reflecting different types of vegetation, management operations and crop rotations. In addition, N input and N fluxes were assessed and N 2 O emissions were calculated. This approach allowed identifying hot spots of N 2 O emissions. Results show that certain combinations of soil type, weather conditions, crop and management can lead to high emissions. Mean values ranged from 0.15 to 1.29 kg N 2 O–N ha −1  year −1 (Marchfeld) and 0.26 to 0.52 kg N 2 O–N ha −1  year −1 (Grieskirchen). Nitrate leaching, which strongly dominated N-losses, often reacted opposite to N 2 O emissions. Larger quantities of NO 3 − were lost during years of higher precipitation, especially if winter barley was cultivated on sandy soils. Taking into account the detected hot spots of N 2 O emissions and NO 3 − leaching most efficient measures can be addressed to mitigate environmental impacts while maximising crop production. © 2018, The Author(s)

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

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

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

Molecular isomerization and fragmentation of polyatomic molecules controlled by inner-valence recollision-ionization

Control over various fragmentation reactions of a series of polyatomic molecules (acetylene, ethylene, 1,3-butadiene) by the optical waveform of intense few-cycle laser pulses is demonstrated experimentally. We show both experimentally and theoretically that the responsible mechanism is inelastic ionization from inner-valence molecular orbitals by recolliding electron wave packets

Enhanced ionization of acetylene in intense laser pulses is due to energy upshift and field coupling of multiple orbitals

Synopsis We describe a new enhanced ionization mechanism for polyatomic molecules. It works via a significant energy up-shift of valence orbitals for stretched bonds and a strong concomitant increase in the coupling between multiple molecular orbitals

Fungal and bacterial utilization of organic substrates depends on substrate complexity and N availability

There is growing evidence of a direct relationship between microbial community composition and function, which implies that distinct microbial communities vary in their functional properties. The aim of this study was to determine whether differences in initial substrate utilization between distinct microbial communities are due to the activities of certain microbial groups. We performed a short-term experiment with beech forest soils characterized by three different microbial communities (winter and summer community, and a community from a tree-girdling plot). We incubated these soils with different 13C-labelled substrates with or without inorganic N addition and analyzed microbial substrate utilization by 13C-phospholipid fatty acid (PLFA) analysis. Our results revealed that the fate of labile C (glucose) was similar in the three microbial communities, despite differences in absolute substrate incorporation between the summer and winter community. The active microbial community involved in degradation of complex C substrates (cellulose, plant cell walls), however, differed between girdling and control plots and was strongly affected by inorganic N addition. Enhanced N availability strongly increased fungal degradation of cellulose and plant cell walls. Our results indicate that fungi, at least in the presence of a high N supply, are the main decomposers of polymeric C substrates

N2_{2}O emissions and NO3_{3}−^{-} leaching from two contrasting regions in Austria and influence of soil, crops and climate: a modelling approach

National emission inventories for UN FCCC reporting estimate regional soil nitrous oxide (N$_{2}$O) fluxes by considering the amount of N input as the only influencing factor for N$_{2}$O emissions. Our aim was to deepen the understanding of N$_{2}$O fluxes from agricultural soils, including region specific soil and climate properties into the estimation of emission to find targeted mitigation measures for the reduction of nitrogen losses and GHG emissions. Within this project, N$_{2}$O emissions and nitrate (NO$_{3}$$^{-}$) leaching were modelled under spatially distinct environmental conditions in two agricultural regions in Austria taking into account region specific soil and climatic properties, management practices and crop rotations. The LandscapeDNDC ecosystem model was used to calculate N$_{2}$O emissions and NO$_{3}$$^{-}$ leaching reflecting different types of vegetation, management operations and crop rotations. In addition, N input and N fluxes were assessed and N$_{2}$O emissions were calculated. This approach allowed identifying hot spots of N$_{2}$O emissions. Results show that certain combinations of soil type, weather conditions, crop and management can lead to high emissions. Mean values ranged from 0.15 to 1.29 kg N$_{2}$O–N ha$^{-1}$ year$^{-1}$ (Marchfeld) and 0.26 to 0.52 kg N$_{2}$O–N ha$^{-1}$ year$^{-1}$ (Grieskirchen). Nitrate leaching, which strongly dominated N-losses, often reacted opposite to N$_{2}$O emissions. Larger quantities of NO$_{3}$$^{-}$ were lost during years of higher precipitation, especially if winter barley was cultivated on sandy soils. Taking into account the detected hot spots of N$_{2}$O emissions and NO$_{3}$$^{-}$ leaching most efficient measures can be addressed to mitigate environmental impacts while maximising crop production