Functional role of fire-derived charcoal in boreal forest ecosystem processes

Charcoal is a natural product of wildfires which operate as a major natural disturbance in boreal forested ecosystems. This carbon (C)-rich material is present in most forest soils but its effects on ecosystem processes remain poorly understood. This thesis explores how charcoal, through its characteristics or traits, affects above- and belowground processes in the Swedish boreal forest by using laboratory mesocosm and glasshouse studies and a large field experiment. The relative importance of charring condition and species identity in determining charcoal traits was also investigated. These experiments covered a wide range of humus types, charcoal types and plant species in order to better understand the factors that determine the functional role of charcoal. With regard to aboveground processes, fire-derived charcoal promoted tree seedling growth but had only a minimal effect on seed germination, and plant community characteristics. Belowground processes such as humus decomposition and N mineralization rate were enhanced by the presence of charcoal, even though charcoal had minimal effect on microbial biomass and composition. Charcoal traits were shown to be affected primarily by species identity and to a lesser extent by charring conditions. The magnitude of charcoal effects was influenced by humus type, charcoal type and plant species identity. The mechanisms by which fire-derived charcoal affect ecosystem processes differed between above- and belowground processes; notably, while the effects of charcoal on aboveground processes were linked mostly to the direct input of phosphorus and especially PO43- from charcoal, its effect on belowground processes were mostly determined indirectly through its impact on microbial specific activity. These findings suggest that charcoal is likely to play a role in boreal forest succession, plant-soil feedbacks and ecosystem C dynamics. Moreover, the impacts of charcoal in boreal ecosystems are relevant to better understanding the ecological consequences of forest management practices such as site preparation, prescribed burning, fire suppression and biochar addition. Overall, the findings described in this thesis show that charcoal is a significant component of the C cycle and one that can have strong impacts on boreal ecosystem processes

AFM Analysis on Polymer Optical Micro-Resonators: Investigation on Quality Factor Origin

International audienceThis paper deals with the surface analysis of spherical polymeric optical micro-resonators in order to correlate surface defects with optical characteristics. Atomic force microscopy was used on structures to determine surface quality, which is the main origin of optical scattering losses. Surface morphologies were numerically treated to enable a relevant investigation on surface parameters such as root mean square (RMS) roughness (30.1 +/- 3.0 nm) or correlation length (few microns) necessary to express optical quality factors. A statistical analysis was conducted for calibration of these parameters as a function of cavities' diameter. Results are in perfect agreement with spectral analyses performed in parallel on others structures. This comparison highlights the main role of scattering losses on quality factor origin

Improvement of efficient coupling and optical resonances by using taper-waveguides coupled to cascade of UV210 polymer micro-resonators

International audienceIn this paper, we report the overall design, fabrication and optical characterization of single and multiple resonant micro-structures patterned on the UV210 polymer and shaped by adequate deep-UV lithography procedures. Various families of ring and racetrack forms are investigated with different geometrical dimensions linked to the micro-resonators and the specific taper-waveguides and gaps allowing the optimized coupling. Well defined photonic structures families in the sub-micrometer range obtained by this deep UV-light process are clearly confirmed through scanning electron microscopy. In order to evaluate and quantify the efficiency of the sub-micrometer coupling, the recirculation of the light and the quality of the optical resonance aspects, a global study including top view intensity imaging, spectral measurements and Fast Fourier Transform analysis is performed for all these devices based on single and multiple family resonators. The experimental TE-mode resonance transmissions reveal a complete agreement with the period of the theoretically expected resonances. A maximum value of the quality factor Q = 3.5 x 10^3 at 1035 nm with a 3.2 times higher resonance contrast is assessed for cascade of triple micro-resonators respect to the photonic devices based on only one micro-resonator. In addition, these UV210 circuits made of specific tapers coupling to cascade loops act directly on the improvement of the evanescent coupling and resonances in terms of quality factor and extinction rate, by selecting successively and more precisely the optical mode resonance. All these designs and low cost technological reproducible steps, and furthermore the devices and protocol measurements are markedly suitable for mass fabrication and metrology applications

A novel deep-UV polymer for integrated photonics: waveguides structures towards cascade of multiple micro-resonators

International audienceAn overview of targeted current research on integrated photonics based on the new deep-UV210 organic material is given. We report on the interest in this new material and properties coupled to deep-ultraviolet (DUV) lithography processes towards the realization and optical characterization of sundry photonics structures. Such structures include sub-wavelength waveguides, pedestal and tapers waveguides until serial of optical micro-resonators (MRs) shaped as disk, ring, stadium and racetrack

Transcriptomic and metabolomic profiles of Zea mays fed with urea and ammonium

The simultaneous presence of different N-forms in the rhizosphere leads to beneficial effects on nitrogen (N) nutrition in plants. Although widely used as fertilizers, the occurrence of cross connection between urea and ammonium nutrition has been scarcely studied in plants. Maize fed with a mixture of urea and ammonium displayed a better N-uptake efficiency than ammonium- or urea-fed plants (Buoso et al., Plant Physiol Biochem, 2021a; 162: 613\u2013623). Through multiomic approaches, we provide the molecular characterization of maize response to urea and ammonium nutrition. Several transporters and enzymes involved in N-nutrition were upregulated by all three N-treatments (urea, ammonium, or urea and ammonium). Already after 1 day of treatment, the availability of different N-forms induced specific transcriptomic and metabolomic responses. The combination of urea and ammonium induced a prompt assimilation of N, characterized by high levels of some amino acids in shoots. Moreover, ZmAMT1.1a, ZmGLN1;2, ZmGLN1;5, ZmGOT1, and ZmGOT3, as well transcripts involved in glycolysis-TCA cycle were induced in roots by urea and ammonium mixture. Depending on N-form, even changes in the composition of phytohormones were observed in maize. This study paves the way to formulate guidelines for the optimization of N fertilization to improve N-use efficiency in maize and therefore limit N-losses in the environment

Réalisation de micro-résonateurs organiques par procédés hybrides : Nouvelles perspectives en photonique intégrée

L’article consiste en une étude de micro-résonateurs (MRs) sphériques fabriqués à partir d’un matériau organique : le polymère NOA (Northland Optical Adhesive). Les auteurs présentent en un premier lieu le circuit micro fluidique spécialement adapté à la création de gouttes sphériques MRs.L’excitation des modes de galerie permet de déterminer les rayons des sphères. Dans une intégration photonique et pour un meilleur confinement, les sphères sont excitées en utilisant un guide d’onde réalisé par technique de « spin coating » à l’aide de polymère SU8 (bisphénol A d’éther glycide). Le couplage est réalisé à l’aide d’ondes évanescentes circulant du guide vers la sphère. La photographie des sphères excitées (pour deux configurations différentes all-pass ou add-drop) met en évidence les modes optiques situés à la surface des sphères synonymes de modes de galerie. L’analyse spectrale du signal à la sortie du guide met en évidence la présence de pics confirmant l’excitation de cette catégorie de modes au sein de la structure. Ces mesures, à l’aide de l’intervalle spectrale libre permettent de remonter aux diamètres des sphères. Les valeurs déterminées sont en bon accord avec celles mesurées à l’aide de la microscopie optique

Identification of dichloroacetic acid degrading Cupriavidus bacteria in a drinking water distribution network model

Aims: Bacterial community structure and composition of a drinking water network were assessed to better understand this ecosystem in relation to haloacetic acid (HAA) degradation and to identify new bacterial species having HAA degradation capacities. Methods and Results: Biofilm samples were collected from a model system, simulating the end of the drinking water distribution network and supplied with different concentrations of dichloroacetic and trichloroacetic acids at different periods over the course of a year. The samples were analysed by culturing, denaturing gradient gel electrophoresis (DGGE) and sequencing. Pipe diameter and HAA ratios did not impact the bacterial community profiles, but the season had a clear influence. Based on DGGE profiles, it appeared that a particular biomass has developed during the summer compared with the other seasons. Among the bacteria isolated in this study, those from genus Cupriavidus were able to degrade dichloroacetic acid. Moreover, these bacteria degrade dichloroacetic acid at 18°C but not at 10°C. Conclusions: The microbial diversity evolved throughout the experiment, but the bacterial community was distinct during the summer. Results obtained on the capacity of Cupriavidus to degrade DCAA only at 18°C but not at 10°C indicate that water temperature is a major element affecting DCAA degradation and confirming observations made regarding season influence on HAA degradation in the drinking water distribution network. Significance and Impact of the Study: This is the first demonstration of the HAA biodegradation capacity of the genus Cupriavidu

An Extended Network of Genomic Maintenance in the Archaeon Pyrococcus abyssi Highlights Unexpected Associations between Eucaryotic Homologs.

In Archaea, the proteins involved in the genetic information processing pathways, including DNA replication, transcription, and translation, share strong similarities with those of eukaryotes. Characterizations of components of the eukaryotic-type replication machinery complex provided many interesting insights into DNA replication in both domains. In contrast, DNA repair processes of hyperthermophilic archaea are less well understood and very little is known about the intertwining between DNA synthesis, repair and recombination pathways. The development of genetic system in hyperthermophilic archaea is still at a modest stage hampering the use of complementary approaches of reverse genetics and biochemistry to elucidate the function of new candidate DNA repair gene. To gain insights into genomic maintenance processes in hyperthermophilic archaea, a protein-interaction network centred on informational processes of Pyrococcus abyssi was generated by affinity purification coupled with mass spectrometry. The network consists of 132 interactions linking 87 proteins. These interactions give insights into the connections of DNA replication with recombination and repair, leading to the discovery of new archaeal components and of associations between eucaryotic homologs. Although this approach did not allow us to clearly delineate new DNA pathways, it provided numerous clues towards the function of new molecular complexes with the potential to better understand genomic maintenance processes in hyperthermophilic archaea. Among others, we found new potential partners of the replication clamp and demonstrated that the single strand DNA binding protein, Replication Protein A, enhances the transcription rate, in vitro, of RNA polymerase. This interaction map provides a valuable tool to explore new aspects of genome integrity in Archaea and also potentially in Eucaryotes