Résumé

L'augmentation des émissions anthropiques de CO2 dans l'atmosphère accélère le changement climatique. Les sols contiennent trois fois plus de carbone que l'atmosphère et constituent donc un réservoir d'importance cruciale pour la régulation du climat. Il existe actuellement une réflexion pour stocker le carbone dans les couches profondes du sol, notamment via la rhizodéposition des plantes. Nous avons donc mené une expérience au CEREEP-Ecotron Ile-de-France pour quantifier les apports, et la persistance, du carbone rhizodéposé par les plantes à l'aide d'un marquage continu au 13C-CO2. Pour ce faire, deux variétés de blé aux systèmes racinaires contrastés ont été plantés dans des mésocosmes et cultivés pendant une saison de croissance complète et sous atmosphère enrichie en 13C. Nos objectifs étaient de quantifier le flux de carbone de l'atmosphère vers le sol et de mesurer sa persistance à court terme. Nos résultats suggèrent que la variété ancienne Plantahof rhizodépose une quantité plus élevée de carbone par rapport à la variété récente Nara notamment en profondeur. Cependant, le carbone apporté au sol par ces deux variétés a conduit à des pertes par minéralisation et des priming effects similaires. Ainsi, le bilan total du carbone était plus affecté par la profondeur du sol que les variétés utilisées dans l'étude. Par ailleurs, j'ai étudié, à partir d'une analyse bibliographique, la distribution selon la profondeur des activités enzymatiques hydrolases et oxydoréductases impliquées dans les cycles du carbone, de l'azote et du phosphore en fonction de la profondeur du sol. Les résultats de cette analyse ont montré que les profils d'activité dépendaient très fortement de la façon dont ces activités étaient exprimées, avec des activités qui diminuent avec la profondeur lorsqu'exprimées par masse de sol alors qu'elles sont plutôt stables, voire augmentent, lorsque exprimé par rapport à la biomasse microbienne. Pris dans leur ensemble, ces résultats montrent que la prise en compte du fonctionnement sur l'intégralité de la colonne de sol est indispensable pour comprendre la dynamique du carbone dans les écosystèmes terrestres.

Auteurs, date et publication :

Auteurs Fatima El Mekdad , Naoise Nunan , Xavier Raynaud

Date : 2023

Catégorie(s)

#CNRS #Ecotron IleDeFrance #ENS

Résumé

In the current biodiversity crisis, one of the crucial questions is how quickly plant communities can acclimate to climate warming and longer growing seasons to buffer the impairment of community functioning. Answering this question is pivotal especially for mountain grasslands that experience harsh conditions but provide essential ecosystem services to people. We conducted a reciprocal transplant experiment along an elevation gradient (1,920 m vs. 2,450 m) in the French Alps to test the ability of plant species and communities to acclimate to warming and cooling. For 3 years, we measured weekly the timing of phenological events (e.g. start of flowering or greening) and the length of phenological stages linked to demographic performance (e.g. lengths of flowering or greening periods). We found that warming (and cooling) changed the timing of phenological events strongly enough to result in complete acclimation for graminoids, for communities in early and mid-season, but not at all for forbs. For example, warming resulted in later greening of communities and delayed all phenophases of graminoids. Lengths of phenological stages did not respond strongly enough to climate change to acclimate completely, except for graminoids. For example, warming led to an acclimation lag in the community's yearly productivity and had a strong negative impact on flowering of forbs. Overall, when there was an acclimation failure, responses to cooling were mostly symmetric and confirmed slow acclimation in mountain grasslands. Synthesis. Our study highlights that phenological plasticity cannot prevent disruption of community functioning under climate warming in the short term. The failures to acclimate after 3 years of warming signals that species and communities underperform and are probably at high risk of being replaced by locally better-adapted plants.

Auteurs, date et publication :

Auteurs Billur Bektaş , Wilfried Thuiller , Amelie Saillard , Philippe Choler , Julien Renaud , Marie-Pascale Colace , Raphael Della Vedova , Tamara Münkemüller

Publication : Journal of Ecology

Date : 2025

Volume : 109

Issue : 9

Pages : 3396-3410

Catégorie(s)

#CNRS #Lautaret #UGA

Auteurs, date et publication :

Auteurs Sebastiaan Luyssaert , Mathilde Jammet , Paul C Stoy , Stephan Estel , Julia Pongratz , Eric Ceschia , Galina Churkina , Axel Don , KarlHeinz Erb , Morgan Ferlicoq , Bert Gielen , Thomas Grunwald , Richard A Houghton , Katja Klumpp , Alexander Knohl , Thomas Kolb , Tobias Kuemmerle , Tuomas Laurila , Annalea Lohila , Denis Loustau

Publication : Nature Climate Change

Date : 2025

Volume : 4

Pages : 5

Catégorie(s)

#CNRS #FORET Puechabon

Résumé

Remote sensing is an invaluable tool for tracking decadal-scale changes in vegetation greenness in response to climate and land use changes. While the Landsat archive has been widely used to explore these trends and their spatial and temporal complexity, its inconsistent sampling frequency over time and space raises concerns about its ability to provide reliable estimates of annual vegetation indices such as the annual maximum normalised difference vegetation index (NDVI), commonly used as a proxy of plant productivity. Here we demonstrate for seasonally snow-covered ecosystems, that greening trends derived from annual maximum NDVI can be significantly overestimated because the number of available Landsat observations increases over time, and mostly that the magnitude of the overestimation varies along environmental gradients. Typically, areas with a short growing season and few available observations experience the largest bias in greening trend estimation. We show these conditions are met in late snowmelting habitats in the European Alps, which are known to be particularly sensitive to temperature increases and present conservation challenges. In this critical context, almost 50% of the magnitude of estimated greening can be explained by this bias. Our study calls for greater caution when comparing greening trends magnitudes between habitats with different snow conditions and observations. At a minimum we recommend reporting information on the temporal sampling of the observations, including the number of observations per year, when long-term studies with Landsat observations are undertaken.

Auteurs, date et publication :

Auteurs Arthur Bayle , Simon Gascoin , Logan T. Berner , Philippe Choler

Publication : Ecography

Date : 2025

Volume : 2024

Issue : 12

Pages : e07394

Catégorie(s)

#CNRS #Lautaret #UGA

Résumé

Up to now, the most widely accepted idea of the periglacial environment is that of treeless ecosystems such as the arctic or the alpine tundra, also called the tabula rasa paradigm. However, several palaeoecological studies have recently challenged this idea, that is, treeless environments in periglacial areas where all organisms would have been exterminated near the glacier formed during the Last Glacial Maximum, notably in the Scandinavian mountains. In the Alps, the issue of glacial refugia of trees remains unanswered. Advances in glacier reconstructions show that ice domes did not cover all upper massifs, but glaciers filled valleys. Here, we used fossils of plant and malacofauna from a travertine formation located in a high mountain region to demonstrate that trees (Pinus, Betula) grew with grasses during the Lateglacial-Holocene transition, while the glacier fronts were 200–300 m lower. The geothermal travertine started to accumulate more than 14,500 years ago, but became progressively more meteogene about 11,500 years ago due to a change in groundwater circulation. With trees, land snails (gastropods) associated to woody or open habitats and aquatic mollusc were also present at the onset of the current interglacial, namely the Holocene. The geothermal spring, due to warm water and soil, probably favoured woody glacial ecosystems. This new finding of early tree growth, combined with other scattered proofs of the tree presence before 11,000 years ago in the western Alps, changes our view of the tree distribution in periglacial environments, supporting the notion of tree refugia on nunataks in an ocean of glaciers. Therefore, the tabula rasa paradigm must be revisited because it has important consequences on the global changes, including postglacial plant migrations and biogeochemical cycles.

Auteurs, date et publication :

Auteurs Christopher Carcaillet , Jean-Louis Latil , Sébastien Abou , Adam Ali , Bassam Ghaleb , Frédéric Magnin , Paul Roiron , Serge Aubert

Publication : Global Change Biology

Date : 2025

Volume : 24

Issue : 6

Pages : 2476-2487

Catégorie(s)

#CNRS #Lautaret #UGA

Auteurs, date et publication :

Auteurs Luc Burté , Charles A. Cravotta , Lorine Bethencourt , Julien Farasin , Mathieu Pédrot , Alexis Dufresne , Marie-Françoise Gérard , Catherine Baranger , Tanguy Le Borgne , Luc Aquilina

Publication : Environmental Science & Technology

Date : 2019

Volume : 53

Issue : 10

Pages : 5848-5857

Catégorie(s)

#CNRS #EcoGenO #Université de Rennes

Résumé

Afin de comprendre et prévoir l'évolution de l'écosystème “chênaie pubescente” soumis Le site expérimental de l'Observatoire de Haute-Provence est l'un des trois sites d'expérimentation de la région méditerranéenne française, avec celui de Puéchabon dans l'Hérault et celui de Fontblanche dans les Bouches-du-Rhône. Il s'attache tout particulièrement à mieux comprendre et suivre l'évolution de l'écosystème de la chênaie pubescente soumis au changement climatique.

Auteurs, date et publication :

Auteurs Thierry Gauquelin , Michel Boer , Catherine Fernandez , Nicolas Montes , Mathieu Santonja , Jean-Philippe Orts , Ilja Reiter

Date : 2025

Volume : 32

Pages : 127-132

Catégorie(s)

#CNRS #FORET O3HP

Résumé

Tropospheric ozone is a strong oxidant which affects human health, agricultural yields, and ecosystem functioning. Thus, it is very important to understand what factors determine ozone formation in order to control air pollution. It is well known that isoprene participates in ozone formation. In this study, we assess the potential impact of climate change in the Mediterranean region on ozone concentration, through drought-related increase or decrease in isoprene emissions after 1 (short drought scenario—1 year of 35% annual rain restriction) and 3 (long drought scenario—3 repeated years of 35% annual restriction) years of drought stress. Using an original experimental dataset of Downy oak isoprene emissions for several drought conditions and idealized drought scenarios in a modeling framework, we showed that ozone concentrations follow the same pattern than isoprene emissions. The short drought scenario used an isoprene emission factor (which is the standardized emission rate at 30 °C and 1000 μmol m−2 s−1 of photosynthetically active radiation (PAR)) 83% higher compared with natural drought and, thus, ozone concentrations increased by 5–30 μg m−3 (3–17%). The long drought scenario used an isoprene emission factor 26% lower compared with natural drought, and ozone concentrations accordingly decreased by 1–10 μg m−3 (0.6–6%). Our results showed that ozone concentration is affected by drought intensity and duration through modification of isoprene emissions indicating that drought stress should be implemented in models (predicting the BVOC emissions).

Auteurs, date et publication :

Auteurs Amélie Saunier , Elena Ormeño , Damien Piga , Alexandre Armengaud , Christophe Boissard , Juliette Lathière , Sophie Szopa , Anne-Cyrielle Genard-Zielinski , Catherine Fernandez

Publication : Regional Environmental Change

Date : 2025

Volume : 20

Issue : 4

Pages : 111

Catégorie(s)

#CNRS #FORET Nouragues #FORET O3HP

Résumé

Environmental DNA (eDNA) metabarcoding is a promising tool to estimate aquatic biodiversity. It is based on the capture of DNA from a water sample. The sampled water volume, a crucial aspect for efficient species detection, has been empirically variable (ranging from few centiliters to tens of liters). This results in a high variability of sampling effort across studies, making comparisons difficult and raising uncertainties about the completeness of eDNA inventories. Our aim was to determine the sampling effort (filtered water volume) needed to get optimal inventories of fish assemblages in species-rich tropical streams and rivers using eDNA. Ten DNA replicates were collected in six Guianese sites (3 streams and 3 rivers), resulting in sampling efforts ranging from 17 to 340 liters of water. We show that sampling 34 liters of water detected more than 64% of the expected fish fauna and permitted to distinguish the fauna between sites and between ecosystem types (stream versus rivers). Above 68 liters, the number of detected species per site increased slightly, with a detection rate higher than 71%. Increasing sampling effort up to 340 liters provided little additional information, testifying that filtering 34 to 68 liters is sufficient to inventory most of the fauna in highly diverse tropical aquatic ecosystems.

Auteurs, date et publication :

Auteurs Isabel Cantera , Kévin Cilleros , Alice Valentini , Axel Cerdan , Tony Dejean , Amaia Iribar , Pierre Taberlet , Régis Vigouroux , Sébastien Brosse

Publication : Scientific Reports

Date : 2025

Volume : 9

Issue : 1

Pages : 3085

Catégorie(s)

#CNRS #eDNA

Résumé

Although DNA barcodes-based operational taxonomic units (OTUs) are increasingly used in earthworm research, the relative efficiency of the different methods available to delimit them has not yet been tested on a comprehensive dataset. For this study, we used three datasets containing 651, 2304 and 4773 COI barcodes of earthworms from French Guiana, respectively, to compare five of these methods: two phylogenetic methods—namely Poisson Tree Processes (PTP) and General Mixed Yule Coalescence (GMYC)—and three distance matrix methods—namely Refined Single Linkage (RESL, used for assigning Barcode Index Numbers in the Barcode of Life Data systems), Automatic Barcode Gap Discovery (ABGD), and Assemble Species by Automatic Partitioning (ASAP). We found that phylogenetic approaches are less suitable for delineating OTUs from DNA barcodes in earthworms, especially for large sets of sequences. The computation times are unreasonable, they often fail to converge, and they also show a strong tendency to oversplit species. Among distance-based methods, RESL also has a clear tendency to oversplitting, while ABGD and ASAP are less prone to mismatches and have short computation times. ASAP requires less a priori knowledge for model parameterisation than AGBD, provides efficient graphical outputs, and has a much lower tendency to generate mismatches.

Auteurs, date et publication :

Auteurs Arnaud Goulpeau , Benoit Penel , Marie-Eugénie Maggia , Daniel Fernández Marchán , Dirk Steinke , Mickaël Hedde , Thibaud Decaëns

Publication : Diversity

Date : 2022

Volume : 14

Issue : 10

Pages : 866

Catégorie(s)

#CNRS #FORET Nouragues