Auteurs, date et publication :
Auteurs Béatrice Allard , Michaël Danger , Loïc Ten-Hage , Gérard Lacroix
Publication : Aquatic Sciences
Date : 2025
Volume : 73
Issue : 1
Pages : 113-126
Catégorie(s)
#CNRS #ENS #PLANAQUARésumé
Human activities are enriching many of Earth’s ecosystems with biologically limiting mineral nutrients such as nitrogen (N) and phosphorus (P). In grasslands, this enrichment generally reduces plant diversity and increases productivity. The widely demonstrated positive effect of diversity on productivity suggests a potential negative feedback, whereby nutrient-induced declines in diversity reduce the initial gains in productivity arising from nutrient enrichment. In addition, plant productivity and diversity can be inhibited by accumulations of dead biomass, which may be altered by nutrient enrichment. Over longer timeframes, nutrient addition may increase soil fertility by increasing soil organic matter and nutrient pools. We examined the effects of 5-11 years of nutrient addition at 47 grasslands in twelve countries. Nutrient enrichment increased aboveground live biomass and reduced plant diversity at nearly all sites, and these effects became stronger over time. We did not find evidence that nutrient-induced losses of diversity reduced the positive effects of nutrients on biomass, however nutrient effects on live biomass increased more slowly at sites where litter was also increasing, regardless of plant diversity. This work suggests that short-term experiments may underestimate the long-term nutrient enrichment effects on global, grassland ecosystems.
Auteurs, date et publication :
Auteurs Eric W. Seabloom , Peter B. Adler , Juan Alberti , Lori Biederman , Yvonne M. Buckley , Marc W. Cadotte , Scott L. Collins , Laura Dee , Philip A. Fay , Jennifer Firn , Nicole Hagenah , W. Stanley Harpole , Yann Hautier , Andy Hector , Sarah E. Hobbie , Forest Isbell , Johannes M. H. Knops , Kimberly J. Komatsu , Ramesh Laungani , Andrew MacDougall
Publication : Ecology
Date : 2025
Volume : n/a
Issue : n/a
Catégorie(s)
#CEREEP #CNRS #ENSRésumé
Global changes will modify future nutrient availability with implications for grassland biogeochemistry. Soil organic matter (SOM) is central to grasslands for both provision of nutrients and climate mitigation through carbon (C) storage. While we know that C and nitrogen (N) in SOM can be influenced by greater nutrient availability, we lack understanding of nutrient effects on C and N coupling and stability in soil. Different SOM fractions have different functional relevance and mean residence times, i.e., mineral-associated organic matter (MAOM) has a higher mean residence time than particulate organic matter (POM). By separating effects of nutrient supply on the different SOM fractions, we can better evaluate changes in soil C and N coupling and stability and associated mechanisms. To this end, we studied responses of C and N ratios and distributions across POM and MAOM to 6–10 years of N, phosphorus (P), potassium and micronutrients (K+µ), and combined NPK+µ additions at 11 grassland sites spanning 3 continents and globally relevant environmental gradients in climate, plant growth, soil texture, and nutrient availability. We found addition of N and NPK+µ generally reduced C:N in MAOM and POM. However, at low fertility and at warm, sandy sites, nutrient addition promoted higher MAOM and POM C:N, respectively. Addition of NPK+µ also promoted C storage in POM relative to MAOM, and this was consistent across sites. Our results suggest that addition of macro- and micronutrients consistently decrease SOM stabilization, whereas responses of soil C:N stoichiometry were contingent on SOM fraction and environmental conditions.
Auteurs, date et publication :
Auteurs Katherine S. Rocci , Kaydee S. Barker , Eric W. Seabloom , Elizabeth T. Borer , Sarah E. Hobbie , Jonathan D. Bakker , Andrew S. MacDougall , Rebecca L. McCulley , Joslin L. Moore , Xavier Raynaud , Carly J. Stevens , M. Francesca Cotrufo
Publication : Biogeochemistry
Date : 2022
Volume : 159
Issue : 3
Pages : 353-370
Catégorie(s)
#ANR-Citation #CEREEP #CNRS #ENSAuteurs, date et publication :
Auteurs Baptiste Hulin , Samuel Abiven
Date : 2023
Catégorie(s)
#CNRS #Ecotron IleDeFrance #ENSRésumé
Eutrophication and climate change have increased the frequency of hypoxic conditions in the
hypolimnia of lakes and reservoirs worldwide. Hypoxia can alter zooplankton migration from
vertical to horizontal because zooplankton require oxygen for respiration, and thus may be forced
to littoral refuge during the day. Fish communities can also affect zooplankton migration as well
as zooplankton community composition and size structure. However, the interaction of fish
communities and hypoxia on zooplankton migration has not been studied. We tested the
hypothesis that zooplankton exhibit more extensive (greater magnitude) vertical and horizontal
migration when piscivores are rare than when they are abundant, and also under hypoxic vs. oxic
hypolimnetic conditions. We sampled zooplankton and other environmental variables across six
consecutive days and nights during summer 2019 in a 16-lake experimental system, as part of
AQUACOSM. Half of the artificial lakes received a fertilization treatment with N and P
(eutrophic lakes with hypolimnetic hypoxia), and lakes were manipulated in order to enrich half
of them with European Perch (potentially piscivorous), and to reduce perch individuals in the
other lakes (all lakes had planktivorous Roach). Zooplankton were sampled in the epilimnion and
hypolimnion of the open water habitat and just outside and inside of the vegetated littoral zone.
We will report on the effects of fish communities and dissolved oxygen conditions on
zooplankton density and biomass in littoral vs. pelagic zones, and their diel vertical and
horizontal movements.
Auteurs, date et publication :
Auteurs J. P. Doubek , R. J. Chapina , S. Fiorini , S. K. Goldfarb , G. Lacroix , H. L. Wander , J. D. Stockwell
Date : 2025
Catégorie(s)
#⛔ No DOI found #CNRS #ENS #PLANAQUARésumé
Zooplankton perform daily migrations between pelagic surface waters, where they feed at night, and either deeper waters (diel vertical migration, DVM) or littoral areas (diel horizontal migration, DHM), where they avoid visual predators or damaging ultraviolet radiation during the day. Diel migration patterns can change based on environmental stressors and food web perturbations, and these behavioral changes have implications for ecological processes in lakes. We hypothesized that crustacean DVM decreases and DHM increases in ponds with hypoxic bottom waters and that DVM and DHM are more extensive with higher planktivory by fish. To address our hypotheses, we assessed crustacean and rotifer community composition and daily migration behavior across pelagic and littoral zones of 16 shallow experimental ponds with differing dissolved oxygen concentrations and planktivorous fish densities in August 2019. Community metrics were driven by habitat, with littoral samples containing a higher taxa richness and diversity of crustaceans and rotifers compared to pelagic samples. DVM and DHM behaviors varied widely based on taxonomic groups. Hypoxia and planktivory had minor effects on zooplankton community metrics and migration behaviors. Our findings contribute to the body of knowledge regarding interactive impacts of hypoxia and planktivory on zooplankton communities and behavioral dynamics in shallow ponds.
Auteurs, date et publication :
Auteurs Anna G. Schmidt , Isabel M. Anderson , Rosalie Bruel , Rosaura J. Chapina , Jonathan P. Doubek , Sarah Fiorini , Sadye K. Goldfarb , Gérard Lacroix , Heather L. Wander , Savannah Zigic , Jason D. Stockwell
Publication : Hydrobiologia
Date : 2024
Catégorie(s)
#CNRS #ENS #PLANAQUARésumé
Under higher atmospheric CO2 concentrations, increases in soil moisture and, hence in terrestrial-aquatic carbon transfer are probable. In a coupled terrestrial-aquatic experiment we examined the direct (e.g. through changes in the CO2 water concentration) and indirect (e.g. through changes in the quality and quantity of soil leachates) effects of elevated CO2 on a lake microbial community. The incubation of soils under elevated CO2 resulted in an increase in the volume of leachates and in both chromophoric dissolved organic matter (CDOM) absorption and fluorescence in leachate. When this leachate was added to lake water during a 3-day aquatic incubation, we observed negative direct effects of elevated CO2 on photosynthetic microorganism abundance and a positive, indirect effect on heterotrophic microbial community cell abundances. We also observed a strong, indirect impact on the functional structure of the community with higher metabolic capacities under elevated CO2 along with a significant direct effect on CDOM absorption. All of these changes point to a shift towards heterotrophic processes in the aquatic compartment under higher atmospheric CO2 concentrations.
Auteurs, date et publication :
Auteurs Emma Rochelle-Newall , Audrey Niboyet , Ludwig Jardiller , Sarah Fiorini , Simon Chollet , Mathieu Llavata , Elisa de Santis , Sébastien Barot , Gérard Lacroix
Publication : Aquatic Sciences
Date : 2018
Volume : 80
Issue : 3
Pages : 27
Catégorie(s)
#ANR-Citation #CNRS #Ecotron IleDeFrance #ENSRésumé
Experiments comparing diploids with polyploids and in single grassland sites show that nitrogen and/or phosphorus availability influences plant growth and community composition dependent on genome size; specifically, plants with larger genomes grow faster under nutrient enrichments relative to those with smaller genomes. However, it is unknown if these effects are specific to particular site localities with speciifc plant assemblages, climates, and historical contingencies. To determine the generality of genome size-dependent growth responses to nitrogen and phosphorus fertilization, we combined genome size and species abundance data from 27 coordinated grassland nutrient addition experiments in the Nutrient Network that occur in the Northern Hemisphere across a range of climates and grassland communities. We found that after nitrogen treatment, species with larger genomes generally increased more in cover compared to those with smaller genomes, potentially due to a release from nutrient limitation. Responses were strongest for C3 grasses and in less seasonal, low precipitation environments, indicating that genome size effects on water-use-efficiency modulates genome size–nutrient interactions. Cumulatively, the data suggest that genome size is informative and improves predictions of species’ success in grassland communities.
Auteurs, date et publication :
Auteurs Joseph A. Morton , Carlos Alberto Arnillas , Lori Biedermann , Elizabeth T. Borer , Lars A. Brudvig , Yvonne M. Buckley , Marc W. Cadotte , Kendi Davies , Ian Donohue , Anne Ebeling , Nico Eisenhauer , Catalina Estrada , Sylvia Haider , Yann Hautier , Anke Jentsch , Holly Martinson , Rebecca L. McCulley , Xavier Raynaud , Christiane Roscher , Eric W. Seabloom
Publication : PLOS Biology
Date : 2025
Volume : 22
Issue : 12
Pages : e3002927
Catégorie(s)
#ANR-Citation #CEREEP #CNRS #ENSRésumé
Biochar is the product of intentional pyrolysis of organic feedstocks. It is made under controlled conditions in order to achieve desired physico-chemical characteristics. These characteristics ultimately affect biochar properties as a soil amendment. When biochar is used for carbon storage, an important property is its persistence in soil, often described by the proportion of biochar carbon remaining in soil after a 100 years (Fperm mathrmF_mathrmperm ). We analyzed published data on 1230 biochars to re-evaluate the effect of pyrolysis parameters on biochar characteristics and the possibility to predict Fperm mathrmF_mathrmperm from the maximum temperature reached during pyrolysis (HTT). We showed that biochar ash and nitrogen (N) contents were mostly affected by feedstock type. The oxygen to carbon (O:C) and hydrogen to carbon (H:C) ratios were mostly affected by the extent of pyrolysis (a combination of HTT and pyrolysis duration), except for non (ligno)cellulosic feedstocks (plastic waste, sewage sludge). The volatile matter (VM) content was affected by both feedstock type and the extent of pyrolysis. We demonstrated that HTT is the main driver of H:C – an indicator of persistence – but that it is not measured accurately enough to precisely predict H:C, let alone persistence. We examined the equations to estimate Fperm mathrmF_mathrmperm available in the literature and showed that Fperm mathrmF_mathrmperm calculated from HTT presented little agreement with Fperm mathrmF_mathrmperm calculated from H:C. The sign and magnitude of the bias depended on the equation used to calculate Fperm mathrmF_mathrmperm and the dispersion was usually large. This could lead to improper compensation of carbon emissions and wrong reporting of carbon sinks in national carbon accounting schemes. We recommend not to use HTT as a predictor for persistence and stress the importance to rapidly develop more accurate proxies of biochar C persistence in soil.
Auteurs, date et publication :
Auteurs Johanne Lebrun Thauront , Gerhard Soja , Hans-Peter Schmidt , Samuel Abiven
Publication : GCB Bioenergy
Date : 2025
Volume : 16
Issue : 11
Pages : e13170
Catégorie(s)
#CNRS #Ecotron IleDeFrance #ENSRésumé
Reductions in community evenness can lead to local extinctions as dominant species exclude subordinate species; however, herbivores can prevent competitive exclusion by consuming otherwise dominant plant species, thus increasing evenness. While these predictions logically result from chronic, gradual reductions in evenness, rapid, temporary pulses of dominance may also reduce species richness. Short pulses of dominance can occur as biotic or abiotic conditions temporarily favour one or a few species, manifested as increased temporal variability (the inverse of temporal stability) in community evenness. Here, we tested whether consumers help maintain plant diversity by reducing the temporal variability in community evenness. We tested our hypothesis by reducing herbivore abundance in a detailed study of a developing, tallgrass prairie restoration. To assess the broader implications of the importance of herbivory on community evenness as well as potential mechanisms, we paired this study with a global herbivore reduction experiment. We found that herbivores maintained plant richness in a tallgrass prairie restoration by limiting temporary pulses in dominance by a single species. Dominance by an annual species in a single year was negatively associated with species richness, suggesting that short pulses of dominance may be sufficient to exclude subordinate species. The generality of this site-level relationship was supported by the global experiment in which inter-annual variability in evenness declined in the presence of vertebrate herbivores over timeframes ranging in length from 2 to 5 years, preventing declines in species richness. Furthermore, inter-annual variability of community evenness was also negatively associated with pre-treatment species richness. Synthesis. A loss or reduction of herbivores can destabilize plant communities by allowing brief periods of dominance by one or a few species, potentially triggering a feedback cycle of dominance and extinction. Such cycles may not occur immediately following the loss of herbivores, being delayed until conditions allow temporary periods of dominance by a subset of plant species.
Auteurs, date et publication :
Auteurs Brent Mortensen , Brent Danielson , W. Stanley Harpole , Juan Alberti , Carlos Alberto Arnillas , Lori Biederman , Elizabeth T. Borer , Marc W. Cadotte , John M. Dwyer , Nicole Hagenah , Yann Hautier , Pablo Luis Peri , Eric W. Seabloom
Publication : Journal of Ecology
Date : 2025
Volume : 106
Issue : 1
Pages : 101-112