Observations of oxidation products above a forest imply biogenic emissions of very reactive compounds

International audienceVertical gradients of mixing ratios of volatile organic compounds have been measured in a Ponderosa pine forest in Central California (38.90° N, 120.63° W, 1315m). These measurements reveal large quantities of previously unreported oxidation products of short lived biogenic precursors. The emission of biogenic precursors must be in the range of 13-66µmol m-2h-1 to produce the observed oxidation products. That is 6-30 times the emissions of total monoterpenes observed above the forest canopy on a molar basis. These reactive precursors constitute a large fraction of biogenic emissions at this site, and are not included in current emission inventories. When oxidized by ozone they should efficiently produce secondary aerosol and hydroxyl radicals

Observations of oxidation products above a forest imply biogenic emissions of very reactive compounds

International audienceMeasurements of volatile organic compounds in a pine forest (Central California, 38.90° N, 120.63° W, 1315 m) reveal large quantities of previously unreported oxidation products of short lived biogenic precursors. The emission of biogenic precursors must be in the range of 13?66 µmol m?2 h?1 to produce the observed oxidation products. That is 6?30 times the emissions of total monoterpenes observed above the forest canopy on a molar basis. These reactive precursors constitute the largest fraction of biogenic emissions at this site, and are not included in current emission inventories. When oxidized by ozone they should efficiently produce secondary aerosol and hydroxyl radicals

Quantitative Shape-Classification of Misfitting Precipitates during Cubic to Tetragonal Transformations: Phase-Field Simulations and Experiments

The effectiveness of the mechanism of precipitation strengthening in metallic alloys de-pends on the shapes of the precipitates. Two different material systems are considered: tetragonal γ′′ precipitates in Ni-based alloys and tetragonal θ′ precipitates in Al-Cu-alloys. The shape formation and evolution of the tetragonally misfitting precipitates was investigated by means of experiments and phase-field simulations. We employed the method of invariant moments for the consistent shape quantification of precipitates obtained from the simulation as well as those obtained from the experiment. Two well-defined shape-quantities are proposed: (i) a generalized measure for the particles aspect ratio and (ii) the normalized λ2, as a measure for shape deviations from an ideal ellipse of the given aspect ratio. Considering the size dependence of the aspect ratio of γ′′ precipitates, we find good agreement between the simulation results and the experiment. Further, the precipitates’ in-plane shape is defined as the central 2D cut through the 3D particle in a plane normal to the tetragonal c-axes of the precipitate. The experimentally observed in-plane shapes of γ′′-precipitates can be quantitatively reproduced by the phase-field model. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

Light and Dehydration but Not Temperature Drive Photosynthetic Adaptations of Basal Streptophytes (Hormidiella, Streptosarcina and Streptofilum) Living in Terrestrial Habitats

Streptophyte algae are the ancestors of land plants, and several classes contain taxa that are adapted to an aero-terrestrial lifestyle. In this study, four basal terrestrial streptophytes from the class Klebsormidiophyceae, including Hormidiella parvula; two species of the newly described genus Streptosarcina (S. costaricana and S. arenaria); and the newly described Streptofilum capillatum were investigated for their responses to radiation, desiccation and temperature stress conditions. All the strains showed low-light adaptation (I k < 70 μmol photons m −2  s −1 ) but differed in photoprotective capacities (such as non-photochemical quenching). Acclimation to enhanced photon fluence rates (160 μmol photons m −2  s −1 ) increased photosynthetic performance in H. parvula and S. costaricana but not in S. arenaria, showing that low-light adaptation is a constitutive trait for S. arenaria. This lower-light adaptation of S. arenaria was coupled with a higher desiccation tolerance, providing further evidence that dehydration is a selective force shaping species occurrence in low light. For protection against ultraviolet radiation, all species synthesised and accumulated different amounts of mycosporine-like amino acids (MAAs). Biochemically, MAAs synthesised by Hormidiella and Streptosarcina were similar to MAAs from closely related Klebsormidium spp. but differed in retention time and spectral characteristics in S. capillatum. Unlike the different radiation and dehydration tolerances, Hormidiella, Streptosarcina and Streptofilum displayed preferences for similar thermal conditions. These species showed a temperature dependence of photosynthesis similar to respiration, contrasting with Klebsormidium spp. and highlighting an interspecific diversity in thermal requirements, which could regulate species distributions under temperature changes. © 2018, The Author(s)