Les métaux lourds et les changements climatiques: Une histoire complexe qui continue à s'écrire

Les émissions de métaux par voies naturelles et par les activités humaines sont à l’origine de multiples problématiques environnementales souvent bien connues du public. Les changements de la législation de nombreux pays au cours des dernières décennies ont permis des avancées notables pour réduire les émissions et pour traiter ces polluants métalliques. Or, en raison des changements climatiques, de nouvelles sources anthropiques (d’origine humaine) ainsi que naturelles de contaminants métalliques émergent. Les conséquences, encore difficiles à évaluer, pourraient être importantes pour, notamment, la préservation de la qualité de l’eau et la sécurité alimentaire. Au-delà de la toxicité, il existe de multiples autres facettes de la contamination métallique de l’environnement par l’Homme. En effet, de nombreux métaux sont des nutriments essentiels au fonctionnement de microorganismes contrôlant des étapes clés du cycle du carbone (production ou séquestration du dioxyde de carbone (CO2)). Les émissions anthropiques de métaux perturbent les cycles biogéochimiques naturels de ses métaux ce qui a des effets, positifs et négatifs, sur les activités microbiennes qui jouent un rôle important dans la régulation du cycle du carbone, lui-même étant un processus clé dans la rétroaction des changements climatiques. Ces effets restent très difficiles à prédire. Par exemple, les émissions de métaux peuvent stimuler les processus biologiques naturels de production de gaz à effet de serre (GES) (ex. le méthane), amplifiant le phénomène de réchauffement. À l’inverse, les émissions de certains métaux, peu biodisponibles à l’état naturel, peuvent avoir des effets positifs sur la production de biomasse et la séquestration de carbone (contribuant à diminuer les GES). Enfin, les nouvelles technologies de production d’énergie verte, indispensable pour la lutte contre les changements climatiques, utilisent des métaux jusqu’alors peu exploité par l’Homme. L’utilisation de ces métaux constitue une nouvelle source potentielle de contamination qu’il convient de gérer adéquatement

Life in mine tailings: microbial population structure across the bulk soil, rhizosphere, and roots of boreal species colonizing mine tailings in northwestern Québec

Abstract Purpose Mining activities have negative effects on soil characteristics and can result in low pH, high heavy metal content, and limited levels of essential nutrients. A tailings storage area located in northwestern Québec showed natural colonization by plants from the adjacent natural environment. The objective of the study was to determine the main edaphic parameters that structured microbial populations associated with the indigenous woody plants that had naturally colonized the site. Methods Microbial populations were studied in the bulk soil, the rhizosphere, and inside plant roots using Illumina sequencing, ordination analysis (i.e., redundancy analysis (RDA) and principal coordinates analysis (PCoA)), ternary plotting, and statistical analysis (MANOVA). Results The main variables that drove the microbial community patterns were plant species and the tailings pH. Indeed, the main bacterial classes were Gammaproteobacteria and Deltaproteobacteria in both the rhizosphere and root endosphere. Analysis revealed that some dominant operational taxonomic units (e.g., Pseudomonas sp., Acinetobacter sp., and Delftia sp.) were present in increased proportions in roots for each plant species under study. This study also revealed that many of the most abundant fungal genera (e.g., Claussenomyces, Eupenicillium, and Trichoderma) were more abundant in the rhizosphere than in the root endosphere. Conclusions This comprehensive study of the microbial community dynamics in the bulk soil, rhizosphere, and root endosphere of boreal trees and shrubs could be beneficial in facilitating the rehabilitation of disturbed ecosystems

Molybdenum threshold for ecosystem scale alternative vanadium nitrogenase activity in boreal forests

Biological nitrogen fixation (BNF) by microorganisms associated with cryptogamic covers, such as cyanolichens and bryophytes, is a primary source of fixed nitrogen in pristine, high-latitude ecosystems. On land, low molybdenum (Mo) availability has been shown to limit BNF by the most common form of nitrogenase (Nase), which requires Mo in its active site. Vanadium (V) and iron-only Nases have been suggested as viable alternatives to countering Mo limitation of BNF; however, field data supporting this long-standing hypothesis have been lacking. Here, we elucidate the contribution of vanadium nitrogenase (V-Nase) to BNF by cyanolichens across a 600-km latitudinal transect in eastern boreal forests of North America. Widespread V-Nase activity was detected (∼15–50% of total BNF rates), with most of the activity found in the northern part of the transect. We observed a 3-fold increase of V-Nase contribution during the 20-wk growing season. By including the contribution of V-Nase to BNF, estimates of new N input by cyanolichens increase by up to 30%. We find that variability in V-based BNF is strongly related to Mo availability, and we identify a Mo threshold of ∼250 ng·glichen−1 for the onset of V-based BNF. Our results provide compelling ecosystem-scale evidence for the use of the V-Nase as a surrogate enzyme that contributes to BNF when Mo is limiting. Given widespread findings of terrestrial Mo limitation, including the carbon-rich circumboreal belt where global change is most rapid, additional consideration of V-based BNF is required in experimental and modeling studies of terrestrial biogeochemistry

Molybdenum and Phosphorus Interact to Constrain Asymbiotic Nitrogen Fixation in Tropical Forests

Biological di-nitrogen fixation (N2) is the dominant natural source of new nitrogen to land ecosystems. Phosphorus (P) is thought to limit N2 fixation in many tropical soils, yet both molybdenum (Mo) and P are crucial for the nitrogenase reaction (which catalyzes N2 conversion to ammonia) and cell growth. We have limited understanding of how and when fixation is constrained by these nutrients in nature. Here we show in tropical forests of lowland Panama that the limiting element on asymbiotic N2 fixation shifts along a broad landscape gradient in soil P, where Mo limits fixation in P-rich soils while Mo and P co-limit in P-poor soils. In no circumstance did P alone limit fixation. We provide and experimentally test a mechanism that explains how Mo and P can interact to constrain asymbiotic N2 fixation. Fixation is uniformly favored in surface organic soil horizons - a niche characterized by exceedingly low levels of available Mo relative to P. We show that soil organic matter acts to reduce molybdate over phosphate bioavailability, which, in turn, promotes Mo limitation in sites where P is sufficient. Our findings show that asymbiotic N2 fixation is constrained by the relative availability and dynamics of Mo and P in soils. This conceptual framework can explain shifts in limitation status across broad landscape gradients in soil fertility and implies that fixation depends on Mo and P in ways that are more complex than previously thought

Rôle de l'interaction océan-atmosphère dans la variabilité intrasaisonnière de la convection tropicale

PALAISEAU-Polytechnique (914772301) / SudocSudocFranceF

The event-to-event variability of the boreal winter MJO

International audienceDuring boreal winters, perturbations of the convection by the Madden-Julian Oscillation (MJO) peak over three basins distributed in longitude south of the Equator: the eastern Indian Ocean (IO), the south of the Maritime Continent (MC) and the western Pacific Ocean (PO). We use the observed Outgoing Longwave Radiation (OLR) and low-level wind to identify and characterize all wintertime MJO events between 1979 and 2010. There is a large event-to-event variability with some MJO events organized at the planetary-scale having their amplitude well distributed over the 3 basins and some showing only basin-scale organization with a convective perturbation peaking over one or two basins. The average of the MJO amplitude for the three basins shows an intriguing decadal variability consistent for both OLR and low-level wind. The disparity between the 3 basins is dominated by an alternation between MJO amplitude peaking on either the Indian or the Pacific Ocean. This Indo-Pacific alternation, depicted by an Indo-Pacific Index (IPI), is partly related to ENSO. In El Niño conditions, there is not only an extension of the MJO perturbation further east, but also an increase of the MJO perturbation over the western Pacific and a diminution of the MJO perturbation over the eastern Indian Ocean

Adsorption and desorption of Sr-85 and (CS)-C-137 on reference minerals, with and without inorganic and organic surface coatings

Correspondance: [email protected] audienceThe adsorption properties of reference minerals may be considerably modified by the presence of the inorganic and organic coatings that are ubiquitous in soils. It is therefore important to assess the effect of such coatings to evaluate the relevance of adsorption studies on pure minerals. The adsorption of trace amounts of Sr-85 and Cs-137 has been studied in dilute suspensions for various minerals that are common components of soils: quartz, calcium carbonate, kaolinite, montmorillonite and illite. We studied the effect of coatings with either Fe or Al oxide with varying additions of soil-extracted humic or fulvic acid. Both adsorption and desorption were measured and data presented as distribution coefficients, Kd. No adsorption was detected on quartz and it was not possible to coat this surface. Adsorption on calcium carbonate was small and not influenced by coatings. Adsorption of Sr on the three clay minerals was very similar, enhanced by the Al-coating, but not affected by Fe and organic coatings. The presence of organic coatings decreased Cs adsorption on illite. Similar but smaller effects were seen on montmorillonite and kaolinite. Aluminum coating enhanced Cs adsorption on illite, whereas both inorganic coatings caused decreases in adsorption on montmorillonite, and there was no effect on kaolinite. Effects were not additive with mixed, organic-inorganic coatings. Adsorption of both Cs and Sr on all minerals was strongly irreversible, with Kd (desorption) being up to four-times greater than adsorption Kd. The ratio of desorption and adsorption Cs Kd values (an assessment of irreversibility) was inversely related to adsorption Kd. This is consistent with a decreasing contribution of high-affinity adsorption as adsorption increases, but may also reflect the partial loss of organic coatings during desorptio

Intraseasonal Convective Perturbations Related to the Seasonal March of the Indo-Pacific Monsoons

International audienc