Dominant woody plants alter soil microbial community composition during succession
Belowground assemblages are closely related to the aboveground vegetation and edaphic properties, which are also driven by dominant plants due to direct and indirect influences. However, the effects of dominant woody plants on the belowground organisms along successional gradients remain poorly understood. Plant and soil samples were collected from an initial herbaceous stage (i.e. alpine meadows) and four stages dominated by woody species, beneath and between patches of the dominant woody plants, to assess the effects of dominant woody plants on the succession of microbial communities along a secondary successional gradient. We quantified herbaceous, edaphic, bacterial, and fungal dissimilarities between stages to explore how dominant woody plants affect bacterial and fungal dissimilarities between stages using structural equation modeling. We found that dominant woody plants generally increase the succession of microbial communities in early stages, but decrease it in late stages. Our results further suggest that the herbaceous dissimilarity between stages plays more important roles than the edaphic one in mediating the effect of dominant woody plants on both bacterial and fungal dissimilarities between stages. Our results provide insight into the relative role of direct and indirect influences on microbial dissimilarity between stages and highlight the importance of dominant woody plants in driving microbial succession. As woody encroachment increases in alpine meadows, the dominant woody plants may have strong consequences on the dynamic of microbial communities, thereby affecting ecosystem functioning.
(Global Ecology and Conservation. vol. 31, n° 2351-9894, pp. e01852, 01/11/2021)
CAS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Caractéristiques optiques de la matière organique dissoute dans des eaux usées domestiques
(01/11/2021)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Hg concentrations and stable isotope variations in tropical fish species of a gold-mining-impacted watershed in French Guiana
The aim of the study was to determine if gold-mining activities could impact the mercury (Hg) concentrations and isotopic signatures in freshwater fish consumed by riparian people in French Guiana. Total Hg, MeHg concentrations, and Hg stable isotopes ratios were analyzed in fish muscles from different species belonging to three feeding patterns (herbivorous, periphytophagous, and piscivorous). We compared tributaries impacted by gold-mining activities (Camopi, CR) with a pristine area upstream (Trois-Sauts, TS), along the Oyapock River. We measured δ15N and δ 13C to examine whether Hg patterns are due to differences in trophic level. Differences in δ 15N and δ 13C values between both studied sites were only observed for periphytophagous fish, due to difference of CN baselines, with enriched values at TS. Total Hg concentrations and Hg stable isotope signatures showed that Hg accumulated in fish from both areas has undergone different biogeochemical processes. Δ199Hg variation in fish (−0.5 to 0.2‰) was higher than the ecosystem baseline defined by a Δ199Hg of −0.66‰ in sediments, and suggested limited aqueous photochemical MeHg degradation. Photochemistry-corrected δ202Hg in fish was 0.7‰ higher than the baseline, consistent with biophysical and chemical isotope fractionation in the aquatic environment. While THg concentrations in periphytophagous fish were higher in the gold-mining area, disturbed by inputs of suspended particles, than in TS, the ensemble of Hg isotope shifts in fish is affected by the difference of biotic (methylation/demethylation) and abiotic (photochemistry) processes between both areas and did therefore not allow to resolve the contribution of gold-mining-related liquid Hg(0) in fish tissues. Mercury isotopes of MeHg in fish and lower trophic level organisms can be complementary to light stable isotope tracers.
(Environmental Science and Pollution Research. vol. 28, n° 0944-1344, pp. 60609-60621, 01/11/2021)
GET, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNES, CNRS, UB, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CNRS
On the risk of abrupt changes in the North Atlantic subpolar gyre in CMIP6 models
CMIP5 models have been shown to exhibit rapid cooling events in their projections of the North Atlantic subpolar gyre. Here, we analyze the CMIP6 archive, searching for such rapid cooling events in the new generation of models. Four models out of 35 exhibit such instabilities. The climatic impacts of these events are large on decadal timescales, with a substantial effect on surface temperature over Europe, precipitation pattern in the tropics—most notably the Sahel and Amazon regions—and a possible impact on the mean atmospheric circulation. The mechanisms leading to these events are related to the collapse of deep convection in the subpolar gyre, modifying profoundly the oceanic circulation. Analysis of stratification in the subpolar gyre as compared with observations highlights that the biases of the models explain relatively well the spread in their projections of surface temperature trends: models showing the smallest stratification biases over the recent period also show the weakest warming trends. The models exhibiting abrupt cooling rank among the 11 best models for this stratification indicator, leading to a risk of encountering an abrupt cooling event of up to 36.4%, slightly lower than the 45.5% estimated in CMIP5 models.
(Annals of the New York Academy of Sciences. vol. 1504, n° 0077-8923, pp. 187-201, 01/11/2021)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LOCEAN-VARCLIM, LOCEAN, MNHN, IRD, INSU - CNRS, SU, CNRS, IPSL (FR_636), ENS-PSL, UVSQ, CEA, INSU - CNRS, X, CNES, SU, CNRS, UPCité
Increased risk of near term global warming due to a recent AMOC weakening
Some of the new generation CMIP6 models are characterised by a strong temperature increase in response to increasing greenhouse gases concentration 1. At first glance, these models seem less consistent with the temperature warming observed over the last decades. Here, we investigate this issue through the prism of low-frequency internal variability by comparing with observations an ensemble of 32 historical simulations performed with the IPSL-CM6A-LR model, characterized by a rather large climate sensitivity. We show that members with the smallest rates of global warming over the past 6-7 decades are also those with a large internally-driven weakening of the Atlantic Meridional Overturning Circulation (AMOC). This subset of members also matches several AMOC observational fingerprints, which are in line with such a weakening. This suggests that internal variability from the Atlantic Ocean may have dampened the magnitude of global warming over the historical era. Taking into account this AMOC weakening over the past decades means that it will be harder to avoid crossing the 2°C warming threshold.
(Nature Communications. vol. 12, n° 2041-1723, 20/10/2021)
IPSL (FR_636), ENS-PSL, PSL, UVSQ, CEA, INSU - CNRS, X, IP Paris, CNES, SU, CNRS, UPCité, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LOCEAN-VARCLIM, LOCEAN, MNHN, IRD, INSU - CNRS, SU, CNRS, IPSL (FR_636), ENS-PSL, UVSQ, CEA, INSU - CNRS, X, CNES, SU, CNRS, UPCité, LOCEAN-NEMO R&D, LOCEAN, MNHN, IRD, INSU - CNRS, SU, CNRS, IPSL (FR_636), ENS-PSL, UVSQ, CEA, INSU - CNRS, X, CNES, SU, CNRS, UPCité, LOCEAN, MNHN, IRD, INSU - CNRS, SU, CNRS, IPSL (FR_636), ENS-PSL, PSL, UVSQ, CEA, INSU - CNRS, X, IP Paris, CNES, SU, CNRS, UPCité, LMD, INSU - CNRS, X, IP Paris, ENPC, SU, CNRS, ENS-PSL, PSL, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA
Exploring the use of compound-specific carbon isotopes as a palaeoproductivity proxy off the coast of Adélie Land, East Antarctica
The Antarctic coastal zone is an area of high primary productivity, particularly within coastal polynyas, where large phytoplankton blooms and drawdown of CO2 occur. Reconstruction of historical primary productivity changes and the associated driving factors could provide baseline insights on the role of these areas as sinks for atmospheric CO2 , especially in the context of projected changes in coastal Antarctic sea ice. Here we investigate the potential for using carbon isotopes (δ13C) of fatty acids in marine sediments as a proxy for primary productivity. We use a highly resolved sediment core from off the coast of Adélie Land spanning the last ∼ 400 years and monitor changes in the concentrations and δ13C of fatty acids along with other proxy data from the same core. We discuss the different possible drivers of their variability and argue that C24fatty acid δ13C predominantly reflects phytoplankton productivity in openwater environments, while C18 fatty acid δ13C reflects productivity in the marginal ice zone. These new proxies have implications for better understanding carbon cycle dynamics in the Antarctica coastal zone in future palaeoclimate studies.
(Biogeosciences, n° 1726-4170, pp. 5555-5571, 14/10/2021)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, EPHE, PSL, ULaval, INSU - CNRS, CNRS, LOCEAN-VOG, LOCEAN, MNHN, IRD, INSU - CNRS, SU, CNRS, IPSL (FR_636), ENS-PSL, UVSQ, CEA, INSU - CNRS, X, CNES, SU, CNRS, UPCité
Species stress tolerance and community competitive effects drive differences in species composition between calcareous and siliceous plant communities
Abstract Both chemical and physical properties of soils have been used for two centuries for explaining differences in species composition and diversity between plant communities from calcareous and siliceous soils. Here, we examine the prediction from the ‘physical hypothesis’, which proposes that species from siliceous soils are absent from calcareous soils because of high drought stress, while species from calcareous soils are absent from siliceous soils because of high competition due to higher water availability. This hypothesis therefore predicts a trade‐off between stress tolerance and competitive response that allows calcareous and siliceous species to dominate their respective communities. There has been no attempt to experimentally assess these predictions. We cross‐transplanted with and without neighbours using a removal experiment, two dominant species from calcareous soils (Bromus erectus and Brachypodium sylvaticum) and two species from siliceous soils (Pseudarrhenatherum longifolium and Deschampsia flexuosa) in herbaceous communities from the two soils types. We repeated the experiment 4 years, taking advantage of inter‐annual climatic variability to test the interplay between year quality (dry vs. wet years) and soil types on survival responses with and without neighbours. We quantified species stress tolerances, their competitive responses and the competitive effect of the two community types. In the absence of neighbours, species from siliceous soils had much lower survival than species from calcareous soils during dry years, in particular on calcareous soils. It indicates a lower stress tolerance of siliceous species and a higher level of stress occurring on calcareous soils. Competition strongly reduced the survival of calcareous but not siliceous species, indicating a greater competitive response of the latter and competition was more important on siliceous soils than on calcareous soils during wet years. However, we found that species stress tolerances were more important than competitive effect of neighbours in driving differences in species composition. Synthesis. The contrasting responses found for dominant species from calcareous and siliceous soils support the trade‐off between stress tolerance and competitive response proposed by the physical hypothesis. Our results bring additional evidence that differences in water availability and stress between the two soil types are driving species responses to bedrock types.
(Journal of Ecology. vol. 109, n° 0022-0477, pp. 4132-4142, 10/10/2021)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Campagnes de prélèvements multi-traceurs pour la caractérisation hydro-biogéochimique de la plaine alluviale de la Bassée
La Bassée est un secteur de la plaine alluviale de la Seine situé en amont de Paris, entre les confluences Seine-Aube et Seine-Yonne. Il s’agit d’un territoire caractérisé par la nécessité de concilier des usages différents, mais dont le fonctionnement hydro- biogéochimique complexe reste largement méconnu. Cinq campagnes multi-traceurs ont ainsi été organisées entre 2017 et 2021 afin de mesurer différentes variables biogéochimiques dans les eaux de surface (Seine, Aube, Yonne, gravières, bras morts) et souterraines (nappes des alluvions et de la craie). Ces données ponctuelles permettent d’intégrer les données physiques acquises en continu depuis 2015 par les stations MOLONARI. Les campagnes ont été réalisées en conditions hydrologiques contrastées : deux campagnes en période de hautes eaux (mars 2017 et 2021) et trois en basses eaux (novembre 2017, octobre 2020 et septembre 2021). L’objectif de ce rapport est de présenter les résultats de ces campagnes de manière intégrée et de caractériser le contexte hydrologique et biogéochimique dans lequel s’est déroulée chaque campagne. Ce travail a montré que le critère hydrologique, basé sur le débit en rivière, n’est pas suffisant pour classer les campagnes et interpréter leurs résultats. Un deuxième critère, basé sur la température de l’air, a été proposé pour représenter le potentiel d’activité biologique du système caractéristique de chaque campagne. L’analyse préliminaire des résultats des campagnes a montré que les eaux souterraines dans la Bassée seraient le siège d’une activité de dénitrification permettant l’abattement des nitrates accumulés à l’amont de la plaine
(10/10/2021)
GEOSCIENCES, PSL, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, METIS, UPMC, EPHE, PSL, CNRS, METIS, EPHE, PSL, INSU - CNRS, SU, CNRS, SISYPHE, UPMC, EPHE, PSL, PSL, CNRS, LEESU, ENPC, UPEC UP12, IMPMC, MNHN, SU, CNRS
Pesticide exposure of workers in apple growing in France
Objective Although apple trees are heavily sprayed, few studies have assessed the pesticide exposure of operators and workers in apple orchards. However, these data are crucial for assessing the health impact of such exposures. The aim of this study was to measure pesticide exposure in apple growing according to tasks and body parts. Methods A non-controlled field study was conducted in apple orchards in 4 regions of France during the 2016 and 2017 treatment seasons. Workers’ external contamination and their determinants were assessed over 156 working days corresponding to 30 treatment days, 68 re-entry days and 58 harvesting days. We measured pesticide dermal contamination during each task and made detailed observations of work characteristics throughout the day. Captan and dithianon were used as markers of exposure. Results The median dermal contamination per day was 5.50 mg of captan and 3.33 mg of dithianon for operators, 24.39 mg of captan and 1.84 mg of dithianon for re-entry workers, and 5.82 mg of captan and 0.74 mg of dithianon for harvesters. Thus, workers performing re-entry tasks, especially thinning and anti-hail net opening, presented higher contamination, either equal to or higher than in operators. For these last ones, mixing/loading and equipment cleaning were the most contaminating tasks. Most of the contamination was observed on workers’ hands in all tasks, except for net-opening in which their heads accounted for the most daily contamination. Conclusions This study highlights the importance of taking indirect exposures into account during re-entry work in apple growing.
(International Archives of Occupational and Environmental Health, n° 0340-0131, 09/10/2021)
BPH, UB, INSERM, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LABÉO, ANTICIPE, UNICAEN, NU, CHU Caen Normandie, NU, UNICANCER/CRLC, NU, INSERM, UNICANCER/CRLC, NU, CHU Bordeaux
Towards a better identification of dissolved organic matter from diffuse sources: comparative study between watercourse and soil leachate to search for specific markers
Dissolved organic matter (DOM) is a complex matrix of organic materials obtained from water filtration (typically from 0.7μm). Playing a key role as an interaction between biological and geochemical process, DOM is directly involved in carbon transfer but also in the microbial growth and activities as a source of nutrients and energy. In aquatic environments, DOM can originate from both autochthonous sources such as microorganisms lysis and roots exudates, and allochtonous sources through point discharges (discharges from wastewater treatment plants, storm overflows and industrial discharges) and diffuse discharges (soil leaching and urban runoff). At a scale of a suburban watershed, anthropogenic activities coupled with landuses and occupations increase the diversity of DOM sources. Point sources can readily be identified and sampled unlike diffuse sources. Indeed, during runoffs, the accumulation of inputs, the changes relative to DOM transport as well as biological degradation processes makes it difficult to identify and trace diffuse sources of DOM in water. Thus, better identification of diffuse sources can facilitate the identification of anthropogenic discharges in watercourses. In this context, this study aims to understand the transfer of the DOM fingerprint between the terrestrial and aquatic ecosystem through the identification of reliable and specific physico-chemical and molecular markers from specific diffuse terrigenous sources. In the first stage, water and adjacent soil samples characterized by forest and wine-growing occupations were collected. Then, a leaching simulation and a biodegradation study were carried out on the soil samples. Finally, a multi-analytical approach (UV-Vis spectroscopic analysis, 3D fluorescence, stearic exclusion chromatography and high-resolution mass spectrometry analysis) was applied to water and soil leachate samples to identify and compare specific conservative markers. The spectral signatures obtained from the UV-vis data show an evolution of the quality of soil leachate organic matter as a function of the degradation time which tends towards the signatures of the MOD sampled from the adjacent watercourses. This tendency remains to be confirmed with other optical and molecular data.
(04/10/2021)
RiverLy, INRAE, LPTC, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS