Synergy between TROPOMI sun-induced chlorophyll fluorescence and MODIS spectral reflectance for understanding the dynamics of gross primary productivity at Integrated Carbon Observatory System (ICOS) ecosystem flux sites

An accurate estimation of vegetation gross primary productivity (GPP), which is the amount of carbon taken up by vegetation through photosynthesis for a given time and area, is critical for understanding terrestrial–atmosphere CO2 exchange processes and ecosystem functioning, as well as ecosystem responses and adaptations to climate change. Prior studies, based on ground, airborne, and satellite sun-induced chlorophyll fluorescence (SIF) observations, have recently revealed close relationships with GPP at different spatial and temporal scales and across different plant functional types (PFTs). However, questions remain regarding whether there is a unique relationship between SIF and GPP across different sites and PFTs and how we can improve GPP estimates using solely remotely sensed data. Using concurrent measurements of daily TROPOspheric Monitoring Instrument (TROPOMI) SIF (daily SIFd); daily MODIS Terra and Aqua spectral reflectance; vegetation indices (VIs, notably normalized difference vegetation index (NDVI), near-infrared reflectance of vegetation (NIRv), and photochemical reflectance index (PRI)); and daily tower-based GPP across eight major different PFTs, including mixed forests, deciduous broadleaf forests, croplands, evergreen broadleaf forests, evergreen needleleaf forests, grasslands, open shrubland, and wetlands, the strength of the relationships between tower-based GPP and SIFd at 40 Integrated Carbon Observation System (ICOS) flux sites was investigated. The synergy between SIFd and MODIS-based reflectance (R) and VIs to improve GPP estimates using a data-driven modeling approach was also evaluated. The results revealed that the strength of the hyperbolic relationship between GPP and SIFd was strongly site-specific and PFT-dependent. Furthermore, the generalized linear model (GLM), fitted between SIFd, GPP, and site and vegetation type as categorical variables, further supported this site- and PFT-dependent relationship between GPP and SIFd. Using random forest (RF) regression models with GPP as output and the aforementioned variables as predictors (R, SIFd, and VIs), this study also showed that the spectral reflectance bands (RF-R) and SIFd plus spectral reflectance (RF-SIF-R) models explained over 80 % of the seasonal and interannual variations in GPP, whereas the SIFd plus VI (RF-SIF-VI) model reproduced only 75 % of the tower-based GPP variance. In addition, the relative variable importance of predictors of GPP demonstrated that the spectral reflectance bands in the near-infrared, red, and SIFd appeared as the most influential and dominant factors determining GPP predictions, indicating the importance of canopy structure, biochemical properties, and vegetation functioning on GPP estimates. Overall, this study provides insights into understanding the strength of the relationships between GPP and SIF and the use of spectral reflectance and SIFd to improve estimates of GPP across sites and PFTs.</p

Crystal structure, Hirshfeld surface analysis, and physicochemical studies of a new Cu(II) complex with 2-amino-4-methylpyrimidine

International audienceThe chemical preparation, crystal structure, magnetic study and spectroscopic characterization of the new Cu(II) complex with the monodentate ligand 2-amino-4-methylpyrimidine [Cu2(CH3COO)4(C5N3H7)2] are reported. The copper atoms are surrounded by one nitrogen atom from one 2-amino-4-methylpyrimidine ligand and four oxygen atoms of CH3COO − groups yielding to a penta-coordination of the metal ion. In the structural arrangement, the amino group and the pyrimidine nitrogen atom of neighboring molecules are linked together through a pair of N-H…N hydrogen bonds forming a 1-D corrugated chain running along the [111] direction wherein the complex molecules are located parallel to the (a, c) plane at z = ½. Intermolecular interactions were investigated by Hirshfeld surfaces and contact enrichment tools. Mulliken charge distribution, molecular electrostatic potential (MEP) maps and HOMO and LUMO energy gaps have been computed. The vibrational absorption bands were identified by infrared spectroscopy. Magnetic properties were also studied to characterize the complex

Linking phytoplankton pigment composition and optical properties: A framework for developing remote-sensing metrics for monitoring cyanobacteria

International audienceThis study has been performed in the framework of a research program aiming to develop a low-cost aerial sensor for the monitoring of cyanobacteria in freshwater ecosystems that could be used for early detection. Several empirical and mechanistic remote-sensing tools have been already developed and tested at large scales and have proven useful in monitoring cyanobacterial blooms. However, the effectiveness of these tools for early detection is hard to assess because such work requires the detection of low concentrations of characteristic pigments amid complex ecosystems exhibiting several confounding factors (turbidity, blooms of other species, etc.). We developed a framework for performing high-throughput measurements of the absorbance and reflectance of small volumes (~= 20 mL) of controlled mixtures of phytoplankton species and studied the potential of this framework to validate remote-sensing proxies of cyanobacteria concentration. The absorption and reflectance spectra of single and multiple cultures carried a specific signal that allowed for the quantitative analysis of culture mixes. This specific signal was shown to be related to known pigment absorbance spectra. The concentrations of chlorophyll-a and -b, phycocyanin and phycoerythrin could be obtained from direct absorbance measurements and were correlated with the concentration obtained after pigment extraction (R2 ≥ 0.96 for all pigments). A systematic test of every possible two-band and three-band normalized difference between optical indices was then performed, and the coincidental correlation with chlorophyll-b (absent in cyanobacteria) was used as an indicator of non-specificity. Two-band indices were shown to suffer from non-specificity issues and could not yield strong and specific relationships with phycocyanin or phycoerythrin (maximum R2  0.8)

Towards long-term standardised carbon and greenhouse gas observations for monitoring Europe's terrestrial ecosystems : a review

Research infrastructures play a key role in launching a new generation of integrated long-term, geographically distributed observation programmes designed to monitor climate change, better understand its impacts on global ecosystems, and evaluate possible mitigation and adaptation strategies. The pan-European Integrated Carbon Observation System combines carbon and greenhouse gas (GHG; CO2, CH4, N2O, H2O) observations within the atmosphere, terrestrial ecosystems and oceans. High-precision measurements are obtained using standardised methodologies, are centrally processed and openly available in a traceable and verifiable fashion in combination with detailed metadata. The Integrated Carbon Observation System ecosystem station network aims to sample climate and land-cover variability across Europe. In addition to GHG flux measurements, a large set of complementary data (including management practices, vegetation and soil characteristics) is collected to support the interpretation, spatial upscaling and modelling of observed ecosystem carbon and GHG dynamics. The applied sampling design was developed and formulated in protocols by the scientific community, representing a trade-off between an ideal dataset and practical feasibility. The use of open-access, high-quality and multi-level data products by different user communities is crucial for the Integrated Carbon Observation System in order to achieve its scientific potential and societal value.Peer reviewe

Potential of proximal teledetection and modeling as a way to assess canopy structure and functioning

L anticipation des effets des changements climatiques nécessite une bonne compréhension dufonctionnement carboné des écosystèmes continentaux. L une des principales contraintes liées àl étude de ces écosystèmes est la forte variabilité à la fois spatiale et temporelle de leurs flux decarbone et de leurs réponses aux contraintes abiotiques. L usage de méthodes de télédétectionoptiques pourrait permettre de suivre de façon spatialisée le fonctionnement des couverts végétaux.Ce travail vise à évaluer le potentiel de méthodes de télédétection pour décrire la structure et lefonctionnement de couverts végétaux à des échelles spatiales et temporelles variées. Pour ce faire,les relations entre indices optiques et phénomènes biologiques ont été étudiées en suivant unedémarche de transfert d échelle, des échelles les plus fines aux plus larges. Il a été montré que le PRI(Photochemical Reflectance Index), utilisé en tant qu indicateur du LUE (Light Use Efficiency), est parnature un signal composite qui reflète principalement la régulation du rendement de laphotosynthèse sur des échelles de temps fines, et la structure et composition biochimique ducouvert à l échelle de la saison. L analyse de courbes de réponse du PRI au PAR (PhotosyntheticallyActive Radiation) a permis de déconvoluer ces deux sources de variabilité, via l introduction duconcept de PRI0 ou PRI d une feuille idéalement adaptée à l obscurité. Ce PRI0, capturant la variabilitédu PRI indépendante du LUE, a pu être mesuré à l échelle de la feuille, et estimé à l échelle de jeunescouverts végétaux et de la parcelle. Cette variabilité a pu être expliquée à l échelle de la feuille et dejeunes couverts végétaux par les variations du contenu en pigment des feuilles. A l échelle depeuplements adultes et de l année, elle résulte cependant d effets combinés de la compositionbiochimique et de la structure des couverts qui n ont pu être séparés. Ces effets sont susceptiblesaux échelles larges de masquer en bonne partie, voire de biaiser la relation entre PRI et LUE. Il a enoutre été montré que la représentativité du PRI est limitée aux strates supérieures des canopées etdépend de la structure du couvert et du climat lumineux, ce qui peut limiter son intérêt en tantqu estimateur du LUE à l échelle de l écosystème. Ces résultats soulignent la nécessité de prendre encompte la structure et la composition biochimique des couverts végétaux dans le cadre d uneutilisation du PRI en tant que proxy du LUE de l écosystème.In order to assess the effect of global warming, a good understanding of carbon functioning ofterrestrial ecosystems is needed. The study of terrestrial ecosystem carbon fluxes and responses toabiotic stress remain challenging due to their high spatial and temporal variability. The use of remotesensing may help us to describe those sources of variability. The aim of this work is to assess thepotential of remote sensing as a way to describe canopy structure and functioning over a broadrange of temporal and spatial scales. The relationships between optical indices and biologicalphenomenon were investigated over a range of increasing scales. The PRI (PhotochemicalReflectance Index), used as a proxy of the LUE (Light Use Efficiency) was shown to be a compositesignal, mainly impacted by the regulation of the LUE at short time scales, and by canopy structureand pigment content at seasonal scale. The analysis of PRI response to PAR (PhotosyntheticallyActive Radiation) allowed us to deconvolve those two sources of variability thanks to theintroduction of the PRI0 defined as the PRI of ideally dark adapted leaves. The PRI0 was shown toefficiently describe the LUE unrelated PRI variability, and could be measured at leaf scale, andestimated at the leaf, canopy and stand scales. This variability could be explained by changes in leafpigment content over the growing season at leaf and canopy scales. At the stand scale and over theyear, this LUE independent PRI variability resulted from combined effects of canopy structure andpigment content, which could not be separated. These effects may result in biased or masked PRIversus LUE relationships at larges scales. Moreover, it was shown that the in-situ PRI measurementsmainly responded to the LUE of sunlit leaves, depending on canopy structure and sky conditions. Thismay considerably hamper the use of the PRI as a proxy of the whole ecosystem LUE. These resultsillustrate the need to take canopy structure and pigment content into account while using the PRI asa proxy of the ecosystem LUE.PARIS11-SCD-Bib. électronique (914719901) / SudocSudocFranceF

Les respirations autotrophe et hétérotrophe du sol dans une chênaie tempérée

Dans le contexte des changements climatiques, la compréhension du fonctionnement du sol est devenue cruciale car la respiration du sol (RS) peut déterminer l état de source ou de puits de C des écosystèmes continentaux. En effet, RS contribue à la respiration écosystémique à hauteur de 40 à 70%. Affiner notre compréhension des processus impliqués dans le fonctionnement du sol est en grande partie déterminé par notre capacité à étudier séparément les composantes autotrophe et hétérotrophe de RS, et leurs réponses faces aux variations des facteurs environnementaux. Les objectifs de cette étude étaient de décomposer RS en ses composantes autotrophe (RA) et hétérotrophe (RH) d une part ; et de déterminer l effet de variations de facteurs biotiques et abiotiques sur le fonctionnement du sol d autre part. Cette étude s est principalement déroulée dans une forêt tempérée décidue (forêt de Barbeau, site FR-Font, Réseau CarboEurope-IP). La décomposition de RS en RA et RH a mis en jeu la méthode des Trench plot couplée à des mesures de RS et l utilisation des isotopes stables du C en abondance naturelle. Ce couplage entre différentes techniques a permis de tester l impact de l exclusion racinaire sur la composition isotopique du CO2 sortant du sol (). Les résultats ont permis de montrer que RH contribuait à hauteur de 40 à 60% de RS. RS augmente avec la température du sol ; cette augmentation étant modulée par l humidité du sol. Au contraire, l exclusion racinaire n a pas affecté , ce qui laisse supposer que la différence de composition isotopique entre RA et RH est trop faible pour décomposer précisément RS dans des écosystèmes forestiers sans alternance entre types photosynthétiques. Les effets des variations des facteurs biotiques sur le fonctionnement du sol ont été étudiés via une modification quantitative des allocations de litière foliaire au sol, et par un suivi mensuel de RS et ; ainsi que de la structure des communautés bactériennes (BCS) du sol et de la litière. Les résultats montrent que RS augmente de façon non proportionnelle à la quantité de litière allouée. Cette augmentation a été reliée à un priming effect (PE). L intensité des flux de CO2 issus du sol minéral et de la litière n ayant pas été affectée par le traitement, le PE a été localisé dans du sol profond et comme utilisant du C récalcitrant. De plus, n a pas été affecté par le traitement, laissant supposer que le PE a des sources de C ayant un proche de celle des autres sources de CO2. Néanmoins, les BCS du sol et de la litière ont été significativement modifiées par le traitement, mettant en avant de potentielles variations de fonctionnement du sol. Cette hypothèse est appuyée par la mise en évidence d un lien statistique entre les variations de BCS et d intensité et de composition isotopique du flux de CO2 dans la litière. L ensemble de ces résultats traduit l importance d études intégrées de la RS. En effet, une meilleure compréhension du fonctionnement du sol et de ses variations face aux changements climatiques nécessite d être en mesure de prendre en compte à la fois les variations d intensité et de composition isotopique du flux de CO2 sortant du sol, ceci parallèlement à la variabilité du système sol en terme de diversité spécifique et d activité enzymatique des communautés microbiennes.Nowadays, a better understanding of soil functioning has become crucial in the context of climate change because soil respiration (RS) can determine the source or sink status of terrestrial ecosystems. Indeed, RS accounts for 40 to 70% of total ecosystem respiration. A better understanding of RS processes is mainly determined by our ability to disentangle its autotrophic (RA) and heterotrophic (RH) components and to study their response to variations of environmental factors. The aims of this study were to partition RS into RA and RH, and to determine the effects of biotic and abiotic factors variations on soil functioning. This study took place in a deciduous temperate forest (Barbeau forest, site FR-Font, CarboEurope-IP Network). To partition RS, a trenching approach with RS measurements (chamber and soil CO2 gradients) was adopted and coupled to the use of C stable isotopes in natural abundance. This allowed testing if root exclusion significantly affected the C stable isotopic composition of soil CO2 efflux (). Results showed that RS was significantly affected by trenching and that RH accounted for 40 to 60% of RS. They also showed that RS increased with soil temperature, this increase being modulated by soil moisture. On the contrary, was not affected by root exclusion; leading to the conclusion that differences in between RA and RH are probably too small to confidently partition soil respiration in forest ecosystems.The effects of biotic factors variations on soil functioning were studied by quantitatively modifying the amount of leaf litter reaching the soil, and by a manual monthly monitoring of RS and ; and the bacterial community structure (BCS) in soil and litter. Results show that RS increased non-proportionally to leaf litter amount. This increase was attributed to a priming effect (PE). The intensity of the CO2 efflux from mineral soil or leaf litter was independent of the treatment, suggesting that the PE occurred in deeper soil horizons and consumed old organic C. was not affected by treatment, leading to the conclusion that the isotopic composition of CO2 corresponding to the priming effect was close to other CO2 sources. Nevertheless, soil and litter BCS were significantly affected by leaf litter treatment, leading to potential variations in soil functioning. Moreover, a significant statistical link between litter BCS and litter CO2 efflux intensity and isotopic composition highlighted the link between microbial diversity variations and variations in soil functioning. All these results underline the importance of integrated studies when considering RS. To better understand soil functioning and its response to climate change, it seems necessary to take into account both the variability of the intensity of soil CO2 efflux and the variability of the soil system in terms of microbial diversity and enzymatic activities.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Mesure de l'indice foliaire en forêt

National audienceL'indice foliaire des peuplements forestiers, s'il est largement admis comme étant un paramètre clé du fonctionnement des couverts forestiers, n'est pas mesuré en routine et ne fait pas partie des descripteurs usuels des peuplements. pourtant, l'indice foliaire peut caractériser précisément un état sanitaire, une sylviculture, une perturbation des peuplements. En outre, c'est un élément important de l'extrapolation des mesures écophysiologiques et biochimiaques et une aide substantielle pour toute entreprise de changement d'échelle. Cette sous-utilisation de l'indice foliaire est sans doute due à une méconnaissance des métrologies qui permettent son estimation. Dans cet esprit, l'objectif de cette synthèse est de proposer un précis méthodologique à l'usage des utilisateurs. Notre document s'est voulu aussi complet que possible. Il comporte plusieurs parties, que le lecteur pourra parcourir indépendamment selon ses connaissances et ses besoins

Explaining the variability of the photochemical reflectance index (PRI) at the canopy-scale: Disentangling the effects of phenological and physiological changes

International audienc

Experimental study of the energy balance of unheated greenhouse under hot and arid climates: Study for the night period of winter season

AbstractIn regions with warm and hot climates as is the case of several countries of the Mediterranean basin, it is interesting to study the energy balance inside a greenhouse and to quantify the heat transfers along the building components (roof, walls and ground) in winter and during night time. The present experimental work was conducted in an unheated glasshouse without crop in the region of Batna, Algeria. Three types of measurements were done from January to March: the first one is at a cloudy night; the second one at a windy night and the third one at a cloudless night. The results indicate that the greenhouse ground is considered as a significant heat source which can compensate the energy losses through the walls especially during a night preceded by a significant diurnal insulation. In addition, the convection heat transfer coefficients inside and outside the greenhouse were estimated and analysed. A good agreement with the models reported in the literature was found