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[hal-02621278] ICOS eddy covariance flux-station site setup: a review
The Integrated Carbon Observation System Re-search Infrastructure aims to provide long-term, continuous observations of sources and sinks of greenhouse gases such as carbon dioxide, methane, nitrous oxide, and water vapour. At ICOS ecosystem stations, the principal technique for measurements of ecosystem-atmosphere exchange of GHGs is the eddy-covariance technique. The establishment and setup of an eddy-covariance tower have to be carefully reasoned to ensure high quality flux measurements being representative of the investigated ecosystem and comparable to measurements at other stations. To fulfill the requirements needed for flux determination with the eddy-covariance technique, variations in GHG concentrations have to be measured at high frequency, simultaneously with the wind velocity, in order to fully capture turbulent fluctuations. This requires the use of high-frequency gas analysers and ultrasonic anemometers. In addition, to analyse flux data with respect to environmental conditions but also to enable corrections in the post-processing procedures, it is necessary to measure additional abiotic variables in close vicinity to the flux measurements. Here we describe the standards the ICOS ecosystem station network has adopted for GHG flux measurements with respect to the setup of instrumentation on towers to maximize measurement precision and accuracy while allowing for flexibility in order to observe specific ecosystem features.
ano.nymous@ccsd.cnrs.fr.invalid (Corinna Rebmann) 26 May 2020
https://hal.inrae.fr/hal-02621278
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[hal-02607385] Difference in shade tolerance drives the mixture effect on oak productivity
1. Assessing how species productivity in mixtures is influenced by species shade tolerance (ST) and phylogeny would be helpful to improve our general understanding of the relationship between tree species diversity and productivity in forests. 2. We investigated the effects of differences in ST and phylogenetic distances (PDs) between pairs of species on the productivity of Quercus petraea growing in 18 mixtures in lowland temperate forests. We calculated the mixture effect as the difference in productivity of Q. petraea in mixed vs. pure stands. Our analyses were based on data from seven annual campaigns of the French National Forest Inventory covering 1,573 plots. 3. The mixture effect on Q. petraea productivity increased when the ST of the companion species decreased. Compared to its productivity in pure stands, Q. petraea productivity in mixed coniferous stands varied from from
ano.nymous@ccsd.cnrs.fr.invalid (Maude Toigo) 16 May 2020
https://hal.inrae.fr/hal-02607385
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[hal-01830947] GIS Coop: networks of silvicultural trials for supporting forest management under changing environment
Context: To understand the dynamics of forest management systems and build adapted growth models for new forestry practices, long-term experiment networks remain more crucial than ever. Aims: Two principles are at the basis of the experimental design of the networks of the Scientific Interest Group Cooperative for data on forest tree and stand growth (GIS Coop): contrasted and extreme silvicultural treatments in diverse pedoclimatic contexts. Methods: Various forest management systems are under study: regular and even-aged stands of Douglas fir, sessile and pedunculate oaks, Maritime and Laricio pines, mixed stands of sessile oak, European silver fir, and Douglas fir combined with other species. Highly contrasted stand density regimes, from open growth to self-thinning, are formalized quantitatively. Results: One hundred and eighty-five sites representing a total of 1206 plots have been set up in the last 20 years, where trees are measured regularly (every 3 to 10 years). The major outputs of these networks for research and management are the calibration/validation of growth and yield models and the drawing up of forest management guides. Conclusion: The GIS Coop adapts its networks so that they can contribute to develop growth models that explicitly integrate pedoclimatic factors and thus also contribute to research on the sustainability of ecosystems under environmental and socio-economic changes.
ano.nymous@ccsd.cnrs.fr.invalid (Ingrid Seynave) 23 Apr 2019
https://agroparistech.hal.science/hal-01830947
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[hal-01918116] Dry-season decline in tree sapflux is correlated with leaf turgor loss point in a tropical rainforest
1. Water availability is a key determinant of forest ecosystem function and tree species distributions. While droughts are increasing in frequency in many ecosystems, including in the tropics, plant responses to water supply vary with species and drought intensity and are therefore difficult to model. Based on physiological first principles, we hypothesized that trees with a lower turgor loss point (pi(tlp)), that is, a more negative leaf water potential at wilting, would maintain water transport for longer into a dry season. 2. We measured sapflux density of 22 mature trees of 10 species during a dry season in an Amazonian rainforest, quantified sapflux decline as soil water content decreased and tested its relationship to tree pi(tlp), size and leaf predawn and midday water potentials measured after the onset of the dry season. 3. The measured trees varied strongly in the response of water use to the seasonal drought, with sapflux at the end of the dry season ranging from 37 to 117% (on average 83 +/- 5 %) of that at the beginning of the dry season. The decline of water transport as soil dried was correlated with tree pi(tlp) (Spearman's rho >= 0.63), but not with tree size or predawn and midday water potentials. Thus, trees with more drought-tolerant leaves better maintained water transport during the seasonal drought. 4. Our study provides an explicit correlation between a trait, measurable at the leaf level, and whole-plant performance under drying conditions. Physiological traits such as pi(tlp) can be used to assess and model higher scale processes in response to drying conditions.
ano.nymous@ccsd.cnrs.fr.invalid (Isabelle Maréchaux) 09 Nov 2018
https://hal.science/hal-01918116
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[hal-01846130] Coordination and trade-offs among hydraulic safety, efficiency and drought avoidance traits in Amazonian rainforest canopy tree species
Predicting responses of tropical forests to climate change-type drought is challenging because of high species diversity. Detailed characterization of tropical tree hydraulic physiology is necessary to evaluate community drought vulnerability and improve model parameterization. Here, we measured xylem hydraulic conductivity (hydraulic efficiency), xylem vulnerability curves (hydraulic safety), sapwood pressure-volume curves (drought avoidance) and wood density on emergent branches of 14 common species of Eastern Amazonian canopy trees in Paracou, French Guiana across species with the densest and lightest wood in the plot. Our objectives were to evaluate relationships among hydraulic traits to identify strategies and test the ability of easy-to-measure traits as proxies for hard-to-measure hydraulic traits. Xylem efficiency was related to capacitance, sapwood water content and turgor loss point, and other drought avoidance traits, but not to xylem safety (P-50). Wood density was correlated (r = -0.57 to -0.97) with sapwood pressure-volume traits, forming an axis of hydraulic strategy variation. In contrast to drier sites where hydraulic safety plays a greater role, tropical trees in this humid tropical site varied along an axis with low wood density, high xylem efficiency and high capacitance at one end of the spectrum, and high wood density and low turgor loss point at the other.
ano.nymous@ccsd.cnrs.fr.invalid (Louis S Santiago) 20 Jul 2018
https://hal.science/hal-01846130
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[hal-02606618] Continental mapping of forest ecosystem functions reveals a high but unrealised potential for forest multifunctionality
Humans require multiple services from ecosystems, but it is largely unknown whether trade-offs between ecosystem functions prevent the realisation of high ecosystem multifunctionality across spatial scales. Here, we combined a comprehensive dataset (28 ecosystem functions measured on 209 forest plots) with a forest inventory dataset (105,316 plots) to extrapolate and map relationships between various ecosystem multifunctionality measures across Europe. These multifunctionality measures reflected different management objectives, related to timber production, climate regulation and biodiversity conservation/recreation. We found that trade-offs among them were rare across Europe, at both local and continental scales. This suggests a high potential for 'win-win' forest management strategies, where overall multifunctionality is maximised. However, across sites, multifunctionality was on average 45.8-49.8% below maximum levels and not necessarily highest in protected areas. Therefore, using one of the most comprehensive assessments so far, our study suggests a high but largely unrealised potential for management to promote multifunctional forests.
ano.nymous@ccsd.cnrs.fr.invalid (P. Fons van Der) 19 Jan 2024
https://hal.inrae.fr/hal-02606618
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[hal-01739286] Comparisons of the performance of δ13C and δ18O of F. sylvatica, P. sylvestris and Q. petraea in the record of past climate variations
Climate reconstructions in temperate Europe have been widely based on oak species. However, other co‐occurring species, largely distributed in Europe, may be used for recording climate variability. In this paper, we documented the inter‐trees and inter‐species variations over 1960‐2007 of oxygen and carbon isotopic compositions in ring cellulose of F. sylvatica, P. sylvestris and Q. petraea co‐occurring in the Fontainebleau forest (France). Our results indicated that large levels of series replication (11 trees on average) were required to generate isotopic mean series representative of the populations. We calculated mean isotopic ratios in pine higher than in the deciduous species, and hypothesized that these contrasts resulted from differences in stomatal conductance, phenology and canopy structure, and, for oxygen, also in water uptake depth and isotopic exchange rate. We found that δ18O and δ13C chronologies were significantly correlated to one another in the three species and responded primarily to air moisture and Tmax, which indicated that stomatal conductance was an important driver of changes in both types of records. We determined that the correlations were strong with the May to July climate variables in F. sylvatica, and with the July and August ones in Q. petraea and P. sylvestris. We showed that the oxygen records were systematically more coherent than those of carbon. This study demonstrated that δ18O, and to a lesser extent δ13C, from the three different species are reliable proxies for reconstructing past hydroclimatic variations in Europe.
ano.nymous@ccsd.cnrs.fr.invalid (Valérie Daux) 20 Mar 2018
https://hal.science/hal-01739286
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[hal-01559409] Sampling and interpolation strategies derived from the analysis of continuous soil CO 2 flux
Soil CO2 flux (Fs) can be measured either manually or automatically. While manual measurements are well suited to capture the spatial variability of Fs, automated measurements are able to capture its temporal variability at fine time scales. The manual method is the most commonly used method to estimate annual carbon budgets. However, such estimates can be biased depending on the measurement frequency, the time at which measurements are made, and the method used to interpolate Fs between two measurements. In this study, we investigated the effects of within-day measurement frequency and of the time of measurement on the estimation of daily Fs. We also investigated the effects on cumulative Fs estimates of weekly and fortnightly sampling frequencies over several months and of the interpolation method used to cumulate Fs. We based our analyses on two complete datasets of automated measurements (one 12-month and one 4-month) recorded in two contrasting ecosystems (a tropical eucalypt plantation and a temperate poplar plantation). Low-frequency time step within a day (every 360 min for the eucalypt and every 180 min for the poplar plantations) was sufficient to capture mean daily Fs accurately. Furthermore, in the tropical site, measurements averaged over any 6h period provided good estimates of the daily flux. By contrast, biases were observed in the temperate site. With one measurement per week, linear interpolation methods provided accurate cumulative fluxes at both sites. However, all interpolation methods failed to produce robust estimates of cumulative Fs in the temperate plantation with one measurement every two weeks. Automated measurements will help to select the best time slot for manual measurements or to correct manual measurements from the apparent deviation between measurements collected during the sampling period and the 24 h-mean CO2 flux. It will also be useful to elaborate empirical equations used to cumulate Fs obtained manually. Combining manual and automated methods will enhance the accuracy of annual soil carbon budgets in forest plantations.
ano.nymous@ccsd.cnrs.fr.invalid (Cécilia Gana) 10 Jul 2017
https://hal.univ-lorraine.fr/hal-01559409
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[hal-02624638] Winter-dormant shoot apical meristem in poplar trees shows environmental epigenetic memory
Trees have a long lifespan and must continually adapt to environmental pressures, notably in the context of climate change. Epigenetic mechanisms are doubtless involved in phenotypic plasticity and in stress memory; however, little evidence of the role of epigenetic processes is available for trees growing in fields. Here, we analyzed the possible involvement of epigenetic mechanisms in the winter-dormant shoot apical meristem of Populus × euramericana clones in memory of the growing conditions faced during the vegetative period. We aimed to estimate the range of genetic and environmentally induced variations in global DNA methylation and to evaluate their correlation with changes in biomass production, identify differentially methylated regions (DMRs), and characterize common DMRs between experiments. We showed that the variations in global DNA methylation between conditions were genotype dependent and correlated with biomass production capacity. Microarray chip analysis allowed detection of DMRs 6 months after the stressful summer period. The 161 DMRs identified as common to three independent experiments most notably targeted abiotic stress and developmental response genes. Results are consistent with a winter-dormant shoot apical meristem epigenetic memory of stressful environmental conditions that occurred during the preceding summer period. This memory may facilitate tree acclimation.
ano.nymous@ccsd.cnrs.fr.invalid (Anne-Laure Le Gac) 26 May 2020
https://hal.inrae.fr/hal-02624638
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[hal-02628253] Changes in the epigenome and transcriptome of the poplar shoot apical meristem in response to water availability affect preferentially hormone pathways.
The adaptive capacity of long-lived organisms such as trees to the predicted climate changes, including severe and successive drought episodes, will depend on the presence of genetic diversity and phenotypic plasticity. Here, the involvement of epigenetic mechanisms in phenotypic plasticity toward soil water availability was examined in Populus×euramericana. This work aimed at characterizing (i) the transcriptome plasticity, (ii) the genome-wide plasticity of DNA methylation, and (iii) the function of genes affected by a drought-rewatering cycle in the shoot apical meristem. Using microarray chips, differentially expressed genes (DEGs) and differentially methylated regions (DMRs) were identified for each water regime. The rewatering condition was associated with the highest variations of both gene expression and DNA methylation. Changes in methylation were observed particularly in the body of expressed genes and to a lesser extent in transposable elements. Together, DEGs and DMRs were significantly enriched in genes related to phytohormone metabolism or signaling pathways. Altogether, shoot apical meristem responses to changes in water availability involved coordinated variations in DNA methylation, as well as in gene expression, with a specific targeting of genes involved in hormone pathways, a factor that may enable phenotypic plasticity.
ano.nymous@ccsd.cnrs.fr.invalid (Clément Lafon-Placette) 27 May 2020
https://hal.inrae.fr/hal-02628253
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[hal-01592230] Ungulates increase forest plant species richness to the benefit of non-forest specialists
Large wild ungulates are a major biotic factor shaping plant communities. They influence species abundance and occurrence directly by herbivory and plant dispersal, or indirectly by modifying plant-plant interactions and through soil disturbance. In forest ecosystems, researchers' attention has been mainly focused on deer overabundance. Far less is known about the effects on understory plant dynamics and diversity of wild ungulates where their abundance is maintained at lower levels to mitigate impacts on tree regeneration. We used vegetation data collected over 10 years on 82 pairs of exclosure (excluding ungulates) and control plots located in a nation-wide forest monitoring network (Renecofor). We report the effects of ungulate exclusion on (i) plant species richness and ecological characteristics, (ii) and cover percentage of herbaceous and shrub layers. We also analyzed the response of these variables along gradients of ungulate abundance, based on hunting statistics, for wild boar (Sus scrofa), red deer (Cervus elaphus) and roe deer (Capreolus capreolus). Outside the exclosures, forest ungulates maintained higher species richness in the herbaceous layer (+15%), while the shrub layer was 17% less rich, and the plant communities became more light-demanding. Inside the exclosures, shrub cover increased, often to the benefit of bramble (Rubus fruticosus agg.). Ungulates tend to favour ruderal, hemerobic, epizoochorous and non-forest species. Among plots, the magnitude of vegetation changes was proportional to deer abundance. We conclude that ungulates, through the control of the shrub layer, indirectly increase herbaceous plant species richness by increasing light reaching the ground. However, this increase is detrimental to the peculiarity of forest plant communities and contributes to a landscape-level biotic homogenization. Even at population density levels considered to be harmless for overall plant species richness, ungulates remain a conservation issue for plant community composition.
ano.nymous@ccsd.cnrs.fr.invalid (Vincent Boulanger) 02 Jul 2018
https://hal.science/hal-01592230
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[hal-01856039] Using Water Stable Isotopes in the Unsaturated Zone to Quantify Recharge in Two Contrasted Infiltration Regimes
A reliable estimate of recharge is needed for the sustainable management of groundwater resources. Water stable isotope (delta O-18 and delta H-2) profiles in the unsaturated zone are frequently used to quantify groundwater recharge based on the seasonality of water isotopic compositions in precipitation. A very simple approach consists of integrating the soil water content between peak values of soil water isotopic composition, typically corresponding to precipitation signatures from warm and cold seasons. When precipitation isotopic compositions are available, a conceptual surface water isotopes budget and lumped parameter dispersion model can be computed. These models were applied on two field sites with similar permeable soils with grass cover but contrasting recharge regimes and seasonality, one in the Paris Basin (France) with continuous recharge from autumn to spring and the other in the St. Lawrence Lowlands (Quebec, Canada) with episodic recharge in fall and after snowmelt. For the two sites, the peak-to-peak method and isotope surface budget led to comparable recharge intensities. At least at the Paris Basin site, evaporation was shown to slightly modify the average unsaturated zone and hence groundwater isotope composition. The proposed parameterization of isotope fractionation due to evaporation allows qualitative estimation of the fraction of evaporation, at least during the recharge seasons. In spite of its simplifications and limitations, the proposed parsimonious model can give estimates of recharge in a variety of sites even if they are not well characterized, as it benefits from the large availability of monthly isotopic compositions in precipitation.
ano.nymous@ccsd.cnrs.fr.invalid (Florent Barbecot) 11 Oct 2018
https://hal.science/hal-01856039v2
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[hal-01803059] Thinning increases tree growth by delaying drought-induced growth cessation in a Mediterranean evergreen oak coppice
The Mediterranean evergreen oak coppices of Southern Europe are increasingly vulnerable to drought because of both the ongoing climate change that increases drought length and intensity, and the lack of forest management that induces a structural aging of the stands. Decreasing stand density through thinning has been widely regarded as a means to improve the resistance of evergreen oak forests to climate change by decreasing the competition for water amongst the remaining stems. Data from a 30-years thinning experiment, that includes a control and four thinning intensity treatments (from 25% to 80% of basal area removed), in a coppiced holm oak (Quercus ilex L.) forest of southern France, was used to quantify the effects of thinning on stem growth. Building on the 'sink limitation' paradigm, which proposes that tree growth is controlled by phenology and climatic constraints and decoupled from carbon assimilation, we investigated if the effect of thinning on stem growth was explained by a delayed drought-induced growth cessation. Using a water balance model, we simulated the date of drought-induced growth cessation, previously found to correspond to the day of the year when water potential drops below a threshold of -1.1 MPa, and used it to predict growth in the different treatments of the thinning experiment. Thinning increased long-term growth at the stem level but decreased the wood biomass at the stand level. Decreasing stem density, and hence the leaf area index, was simulated to delay the date of drought-induced growth cessation. A growth model based on the date of growth cessation explained 85% of the effect of thinning on stem growth over the 30-year period of the study, and 95% for the first five years after thinning. The canopy density for which the effect of thinning is the most beneficial was found to maximize the growth duration without lifting completely the water limitation in summer. Moderate thinning had a sustained beneficial effect on the growth of all stem size classes, whereas stronger thinning intensities increased the size asymmetry of competition and their overall effect dropped faster. Our simple predictive model based on the simulation of the water balance as a function of stand density opens the way to providing management guidelines for the optimization of tree density as a function of water limitation in Mediterranean evergreen woodlands.
ano.nymous@ccsd.cnrs.fr.invalid (Antoine Cabon) 30 May 2018
https://amu.hal.science/hal-01803059
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[hal-01809598] Warmer winters reduce the advance of tree spring phenology induced by warmer springs in the Alps
Mountain regions are particularly susceptible and influenced by the effects of climate change. In the Alps, temperature increased two times faster than in the Northern Hemisphere during the 20th century. As an immediate response in certain tree species, spring phenological phases, such as budburst and flowering, have tended to occur earlier. However, recent studies have shown a slowing down of phenological shifts during the last two decades compared to earlier periods, which might be caused by warmer winters. Indeed, cold temperatures are required to break bud dormancy that occurs in early fall; and dormancy break is a prerequisite for cell elongation to take place in spring when temperature conditions are warm enough. Here we aimed at evaluating the effects of winter warming vs. spring warming on the phonological shift along mountain elevation gradients. We tested the hypothesis that a lack of chilling temperature during winter delayed dormancy release and subsequently spring phonological phases. For this, we used eight years of temperature and phenological records for five tree species (Betula penctula, Fraxinus excelsior, Corylus avellana, Picea abies and Larix deridna) gathered with the citizen science program Phenoclim (www.phenoclim.org) deployed over the French Alps. Our results showed that for similar preseason (i.e. after dormancy break) temperatures, warmer winters significantly delayed budburst and flowering along the elevation gradient (+ 0.9 to + 5.6 days degrees C-1) except for flowering of Corylus and budburst of Picea. For similar cold winter temperatures, warmer preseasons significantly advanced budburst and flowering along the elevation gradient (- 5.3 to -8.4 days degrees C-1). On average, the effect of winter warming was 2.3 times lower than the effect of spring warming. We also showed that warmer winter temperature conditions have a significantly larger effect at lower elevations. As a consequence, the observed delaying effect of winter warming might be beneficial to trees by reducing the risk of exposure to late spring frost on a short term. This could further lead to partial dormancy break at lower elevations before the end of the 21st century, which, in turn, may alter bud development and flowering and so tree fitness.
ano.nymous@ccsd.cnrs.fr.invalid (Daphné Asse) 06 Jun 2018
https://hal.science/hal-01809598
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[hal-01988992] Fir expansion not controlled by moderate densities of large herbivores: a Mediterranean mountain grassland conservation issue
Context Forest expansion following the cessation of grazing is a threat to biodiversity in mountain grasslands that are compo- nents of Mediterranean cultural landscapes. & Aims We hypothesised that ungulates could mitigate tree recruitment, thus conserving mountain grasslands. We tested the efficiency of grazing and browsing by domestic and wild ungulates (sheep, roe and red deer) at inhibiting silver fir (Abies alba Mill.) encroachment in a conservation area, one of the main browsed trees. Methods The fir trees’ age structure was analysed by dendrochronology, and the individual growth patterns and scars were recorded in their tree-ring series. & Results Fir density has increased since the 1960s, simultaneously with the increase in ungulate populations. The scar occur- rences only appeared during the 1970s. Most scars were observed on seedlings and small saplings. The impacts of ungulates are observed on the radial and height growth of trees, mostly on trees < 100 cm, but it did not however result in controlling the recruitment of fir. Conclusion The hypothesis that a moderate density of ungulates might inhibit tree encroachment is therefore rejected, even in the case of a highly palatable species such as silver fir. Ungulates, solely, would not be an appropriate policy for grassland conservation in Mediterranean mountains.
ano.nymous@ccsd.cnrs.fr.invalid (Sandrine Chauchard) 28 Mar 2019
https://univ-lyon1.hal.science/hal-01988992
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[hal-02190815] Phylogenetic patterns and phenotypic profiles of the species of plants and mammals farmed for food
The origins of agriculture were key events in human history, during which people came to depend for their food on small numbers of animal and plant species. However, the biological traits determining which species were domesticated for food provision, and which were not, are unclear. Here, we investigate the phylogenetic distribution of livestock and crops, and compare their phenotypic traits with those of wild species. Our results indicate that phylogenetic clustering is modest for crop species but more intense for livestock. Domesticated species explore a reduced portion of the phenotypic space occupied by their wild counterparts and have particular traits in common. For example, herbaceous crops are globally characterized by traits including high leaf nitrogen concentration and tall canopies, which make them fast-growing species and proficient competitors. Livestock species are relatively large mammals with low basal metabolic rates, which indicate moderate to slow life histories. Our study therefore reveals ecological differences in domestication potential between plants and mammals. Domesticated plants belong to clades with traits that are advantageous in intensively managed high-resource habitats, whereas domesticated mammals are from clades adapted to moderately productive environments. Combining comparative phylogenetic methods with ecologically relevant traits has proven useful to unravel the causes and consequences of domestication.
ano.nymous@ccsd.cnrs.fr.invalid (Rubén Milla) 05 Feb 2024
https://normandie-univ.hal.science/hal-02190815
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[hal-02622472] Response to Editor to the comment by Schipper & Smith to our paper entitled "Continuous soil carbon storage of old permanent pastures in Amazonia
First of all, we recall that the message conveyed in our paper is that Amazonian forest and old tropical pastures act as C sinks by accumulating recurrently (continuously) C in biomass and soil. We do not support the idea that deforestation increases soil C as suggested in the title of Schipper and Smith comment. In our study, pasture C sink was estimated by two independent methods: eddy covariance measurements (Eddy) and a 36-years chronosequence analyzing soil organic C stock to a depth of 100 cm (Chrono). Both methods provide evidence that pastures ≥24 years can restore all or part of C sink of Amazonian forest if sustainable management is applied. Realizing that old pastures accumulate C is crucial in the Amazonian context where pastures are currently replaced by intensive crops (e.g. soybean) inducing a possible loss of this C sink.
ano.nymous@ccsd.cnrs.fr.invalid (Sébastien Fontaine) 26 May 2020
https://hal.inrae.fr/hal-02622472
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[hal-01637751] Anthraco-typology as a key approach to past firewood exploitation and woodland management reconstructions. Dendrological reference dataset modelling with dendro-anthracological tools
Charcoal analysis aims to study different aspects of forest management, techno-economical choices and their specific impact on past landscapes, as well as the impact of climatic events. However, at the present time, charcoal analysis is generally limited to the study of a list of taxa and their relative frequency, as the methods usually employed in dendrochronology to characterize past woodland, based on long tree-ring series, are not suitable for anthracological material. Today, the new challenge for charcoal analysis is thus to develop adapted dendrological tools. In this context, the aim of the ANR DENDRAC project “Development of dendrometrical tools applied to anthracology: study of the interactions between Man, resources and environments” was to characterize modern-day wood stands in accordance with historical woodland practices and convert dendroecological data into parameters adapted to charcoal analysis. The purpose of this study is to define the dendrological features with the help of the anthracological tools without explaining the observed differences between the sampled stands (given the stational variability, age and regeneration modes). The first step consisted in creating dendro-anthracological tools based on morpho-anatomical criteria that help to characterize growth, distinguish heartwood from sapwood and evaluate charcoal-pith distance. The second step involves characterizing three modern-day wood stands (coppice under standard, high forest and young stand formed by a mixture of seeded and coppice trees), defined by their structure, stand density and regeneration modes, using dendrological data measured on fresh wood material and modelled into anthracological data with the dendro-anthracological tools. In this way, anthracological types were defined for each wood stand, forming anthraco-typological models, which area useful for the interpretation of archaeological charcoal assemblages. Finally, an anthracological key is proposed to sort archaeological charcoal fragments in anthraco-groups before data processing.
ano.nymous@ccsd.cnrs.fr.invalid (Alexa Dufraisse) 29 Mar 2018
https://hal.science/hal-01637751
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[hal-01927451] The surface-atmosphere exchange of carbon dioxide in tropical rainforests: Sensitivity to environmental drivers and flux measurement methodology
Tropical rainforests play a central role in the Earth system by regulating climate, maintaining biodiversity, and sequestering carbon. They are under threat by direct anthropogenic impacts like deforestation and the indirect anthropogenic impacts of climate change. A synthesis of the factors that determine the net ecosystem exchange of carbon dioxide (NEE) at the site scale across different forests in the tropical rainforest biome has not been undertaken to date. Here, we study NEE and its components, gross ecosystem productivity (GEP) and ecosystem respiration (RE), across thirteen natural and managed forests within the tropical rainforest biome with 63 total site-years of eddy covariance data. Our results reveal that the five ecosystems with the largest annual gross carbon uptake by photosynthesis (i.e. GEP > 3000 g C m(-2) y(-1)) have the lowest net carbon uptake - or even carbon losses versus other study ecosystems because RE is of a similar magnitude. Sites that provided sub canopy CO2 storage observations had higher average magnitudes of GEP and RE and lower average magnitudes of NEE, highlighting the importance of measurement methodology for understanding carbon dynamics in ecosystems with characteristically tall and dense vegetation. A path analysis revealed that vapor pressure deficit (VPD) played a greater role than soil moisture or air temperature in constraining GEP under light saturated conditions across most study sites, but to differing degrees from -0.31 to -0.87 mu mol CO2 m(-2) s(-1) hPa(-1). Climate projections from 13 general circulation models (CMIP5) under the representative concentration pathway that generates 8.5 W m(-2) of radiative forcing suggest that many current tropical rainforest sites on the lower end of the current temperature range are likely to reach a climate space similar to present-day warmer sites by the year 2050, warmer sites will reach a climate not currently experienced, and all forests are likely to experience higher VPD. Results demonstrate the need to quantify if and how mature tropical trees acclimate to heat and water stress, and to further develop flux-partitioning and gap-filling algorithms for defensible estimates of carbon exchange in tropical rainforests.
ano.nymous@ccsd.cnrs.fr.invalid (Zheng Fu) 19 Nov 2018
https://hal.science/hal-01927451
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[hal-02620150] Cartographie des défoliations du massif forestier du Pays des étangs en Lorraine : Apports potentiels de la télédétection
Depuis le début des années 2000, les chênaies du massif forestier du Pays des étangs en Lorraine, massif essentiellement feuillu, subissent des dépérissements importants, aux causes multiples (insectes défoliateurs, sécheresse et canicule de 2003). La chenille processionnaire du chêne y joue un rôle essentiel en provoquant de nombreuses et importantes défoliations depuis les années 1990. Cette étude exploratoire montre qu’en s’appuyant sur des observations de terrain comme données de référence, une cartographie des défoliations des années 2010 peut être réalisée à partir d’images satellitaires. La méthode s’appuie sur des images à moyenne (MODIS) et haute (Landsat) résolutions spatiales, acquises à plusieurs dates dans l’année, d’une part, et sur une méthode de classification supervisée basée sur les forêts aléatoires d’arbres de décision, d’autre part. Une extrapolation permet d’avoir des indications sur le niveau des défoliations localement. Des améliorations de la méthode sur plusieurs points (meilleure adéquation entre les observations de terrain et les images, utilisation des images satellitaires Sentinel-2, choix des prédicteurs issus des images) sont envisagées afin de l’utiliser pour d’autres forêts subissant également d’importantes défoliations.
ano.nymous@ccsd.cnrs.fr.invalid (Thierry Bélouard) 25 May 2020
https://hal.inrae.fr/hal-02620150
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[hal-02621566] Coupling water and carbon fluxes to constrain estimates of transpiration: the TEA algorithm
Plant transpiration (T), biologically controlled movement of water from soil to atmosphere, currently lacks sufficient estimates in space and time to characterize global ecohydrology. Here we describe the Transpiration Estimation Algorithm (TEA), which uses both the signals of gross primary productivity and evapotranspiration (ET) to estimate temporal patterns of water use efficiency (WUE, i.e., the ratio between gross primary productivity and T) from which T is calculated. The method first isolates periods when T is most likely to dominate ET. Then, a Random Forest Regressor is trained on WUE within the filtered periods and can thus estimate WUE and T at every time step. Performance of the method is validated using terrestrial biosphere model output as synthetic flux data sets, that is, flux data where WUE dynamics are encoded in the model structure and T is known. TEA reproduced temporal patterns of T with modeling efficiencies above 0.8 for all three models: JSBACH, MuSICA, and CASTANEA. Algorithm output is robust to data set noise but shows some sensitivity to sites and model structures with relatively constant evaporation levels, overestimating values of T while still capturing temporal patterns. The ability to capture between-site variability in the fraction of T to total ET varied by model, with root-mean-square error values between algorithm predicted and modeled T/ET ranging from 3% to 15% depending on the model. TEA provides a widely applicable method for estimating WUE while requiring minimal data and/or knowledge on physiology which can complement and inform the current understanding of underlying processes. Plain Language Summary While it is widely known that plants need water to survive, exactly how much water plants in an ecosystem use is hard to quantify. However, many places have been measuring how much total water leaves an ecosystem, both the water plants use directly and the water that simply evaporates from the soil or the surfaces of leaves, using eddy covariance towers. These eddy covariance towers also measure the coming and going of carbon, such as the total amount of carbon taken up by photosynthesis. Here we present the idea that by using the signals from both photosynthesis and total water losses together, we can capture the water signal related to plants, namely, transpiration, using an algorithm called Transpiration Estimation Algorithm (TEA). To verify that TEA is working the way we expect, we test it out using artificial ecosystem simulations where transpiration and photosynthesis come from mathematical models. By thoroughly testing TEA, we have a better idea of how it will work in a real world situation, hopefully opening the door for a better understanding on how much water ecosystems are using and how it might affect our changing planet.
ano.nymous@ccsd.cnrs.fr.invalid (Jacob a. Nelson) 26 May 2020
https://hal.inrae.fr/hal-02621566
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[hal-02628523] Co-occurring woody species have diverse hydraulic strategies and mortality rates during an extreme drought
From 2011 to 2013, Texas experienced its worst drought in recorded history. This event provided a unique natural experiment to assess species-specific responses to extreme drought and mortality of four co-occurring woody species: Quercus fusiformis, Diospyros texana, Prosopis glandulosa, and Juniperus ashei. We examined hypothesized mechanisms that could promote these species' diverse mortality patterns using postdrought measurements on surviving trees coupled to retrospective process modelling. The species exhibited a wide range of gas exchange responses, hydraulic strategies, and mortality rates. Multiple proposed indices of mortality mechanisms were inconsistent with the observed mortality patterns across species, including measures of the degree of iso/anisohydry, photosynthesis, carbohydrate depletion, and hydraulic safety margins. Large losses of spring and summer whole-tree conductance (driven by belowground losses of conductance) and shallower rooting depths were associated with species that exhibited greater mortality. Based on this retrospective analysis, we suggest that species more vulnerable to drought were more likely to have succumbed to hydraulic failure belowground.
ano.nymous@ccsd.cnrs.fr.invalid (Daniel M. Johnson) 27 May 2020
https://hal.inrae.fr/hal-02628523
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[hal-02628568] How does water-stressed corn respond to potassium nutrition? A shoot-root scale approach study under controlled conditions
Potassium (K) is generally considered as being closely linked to plant water dynamics. Consequently, reinforcing K nutrition, which theoretically favors root growth and specific surface, extends leaf lifespan, and regulates stomatal functioning, is often used to tackle water stress. We designed a greenhouse pot-scale device to test these interactions on corn (Zea mays L.), and to analyze their links to plant transpiration. Three levels of K nutrition were combined with two water-supply treatments. Shoot and root development and growth were continuously measured during a 60-day-long experiment. Individual plant transpiration was measured by weighing pots and by calculating water mass balances. The results showed that, although K deficiency symptoms resembled those caused by water shortage, there was no advantage to over-fertilizing water-stressed plants. K failed to decrease either the transpiration per unit leaf surface or to improve water use efficiency. The link between K nutrition and plant transpiration appears solely attributable to the effect of K on leaf area. We conclude that K over-fertilization could ultimately jeopardize crops by enhancing early-stage water transpiration to the detriment of later developmental stages.
ano.nymous@ccsd.cnrs.fr.invalid (Lionel Jordan-Meille) 27 May 2020
https://hal.inrae.fr/hal-02628568
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[hal-02627965] Phenotypic trait variation measured on European genetic trials of Fagus sylvatica L.
We present BeechCOSTe52; a database of European beech (Fagus sylvatica) phenotypic measurements for several traits related to fitness measured in genetic trials planted across Europe. The dataset was compiled and harmonized during the COST-Action E52 (2006-2010), and subsequently cross-validated to ensure consistency of measurement data among trials and provenances. Phenotypic traits (height, diameter at breast height, basal diameter, mortality, phenology of spring bud burst and autumn-leaf discoloration) were recorded in 38 trial sites where 217 provenances covering the entire distribution of European beech were established in two consecutive series (1993/95 and 1996/98). The recorded data refer to 862,095 measurements of the same trees aged from 2 to 15 years old over multiple years. This dataset captures the considerable genetic and phenotypic intra-specific variation present in European beech and should be of interest to researchers from several disciplines including quantitative genetics, ecology, biogeography, macroecology, adaptive management of forests and bioeconomy.
ano.nymous@ccsd.cnrs.fr.invalid (T. Matthew Robson) 26 May 2020
https://hal.inrae.fr/hal-02627965
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[hal-02080264] Land use legacies on forest understory vegetation and soils in the Mediterranean region: Should we use historical maps or in situ land use remnants?
How to move forward if we cannot understand our present from our past? The same applies for the study of ecosystems. Evidence of ecological legacies in temperate post-agricultural forests has been provided on soil physico-chemical properties and understory vegetation richness and composition, which led to distinguish ancient and recent forests. However, no land use legacies dating back more than 50 years have been reported in Mediterranean forests. The definition of ancient and recent forests usually relies on a threshold date, most often provided by historical maps. In France, the Etat-Major map is the most precise, with a relatively high resolution and drawn over the whole country with a standardised method. However, the use of historical maps only for studying land use legacies in forest is questionable in a Mediterranean context characterised by a traditional agro-sylvo-pastoral system. Using a historical ecology approach, our purpose was to examine the legacies of various former land uses on soil and understory vegetation in Mediterranean forests and to compare the relevance of two historical sources: 1860 land use map (map-based PLU) and remnants recorded in the field (in situ PLU remnants). In the Regional Natural Park of Luberon (French Mediterranean area), we inventoried plant communities and analysed soil physico-chemical properties on 100 plots with various past land uses according the Etat-Major map (arable, pasture or forest) and in situ PLU remnants (terrace, stone removal or no remnants). Compared to ancient forest, former arable land hosted more species and had deeper and nutrient-richer soils while former pasture had shallower and nutrient-poorer soils. Similarly, and compared with no remnants, terraces hosted more species and had deeper and nutrient-richer soils whereas stone removal had shallower and nutrient-poorer soils. Understory species composition significantly varied according to map-based PLU and in situ PLU remnants. However, in situ PLU remnants were globally a much better indicator of land use legacies on soil and understory plant composition compared to map-based PLU. We thus confirmed the legacies of past land use on Mediterranean forest soil and understory vegetation. We also stressed that historical ecology should rely on both field evidence and historical maps, particularly in Mediterranean landscapes with a complex history of land uses.
ano.nymous@ccsd.cnrs.fr.invalid (Juliet Abadie) 26 Mar 2019
https://hal.science/hal-02080264
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[hal-02629082] Changes in physicochemical characteristics of a serpentine soil and in root architecture of a hyperaccumulating plant cropped with a legume
Agromining is a new technology that establishes agricultural systems on ultramafic soils in order to produce valuable metal compounds such as nickel (Ni), with the final aim of restoring a soil's agricultural functions. But ultramafic soils are characterized by low fertility levels, and this can limit yields of hyperaccumulators and metal phytoextraction. The objectives of the present work were to test if the association of a hyperaccumulating plant (Alyssum murale) and a Fabaceae (Vicia sativa var. Prontivesa) could induce changes in physicochemical characteristics of a serpentine soil and in root architecture of a hyperaccumulating plant then lead to efficient agromining practices through soil quality improvement. Based on standard agricultural systems, consisting in the association of legumes and another crop such as wheat or rape, a 3-month rhizobox experiment was carried out to study the effect of the co-cropping (Co) or rotation (Ro) of a hyperaccumulating plant (A. murale) with a legume (Vicia sativa) and incorporating legume biomass to soil, in comparison with mineral fertilization (FMo), on the structure and physicochemical properties of an ultramafic soil and on root architecture. All parameters measured (biomass, C and N contents, and Ni taken up) on A. murale conducted in Co showed the highest values followed by FMo and Ro (Co > FMo > Ro), except for root Ni yield for which Ro was better than FMo. The rhizosphere soil of A. murale in co-cropping had larger soil particles size and better aggregate stability than other treatments. Using geostatistics, co-cropped Alyssum showed a greater root surface area spatial distribution. Moreover, co-cropping and rotation induced lower soil diethylene triamine pentaacetic acid-extractable Ni concentrations than other treatments, but higher pH values. A. murale co-cropped with a legume showed a higher biomass production, improved soil physical characteristics, and enhanced Ni phytoextraction. Consequently, legume introduction in Ni-agromining systems could be an innovative strategy to reduce chemical inputs and to improve soil functions.
ano.nymous@ccsd.cnrs.fr.invalid (Ramez Saad) 27 May 2020
https://hal.inrae.fr/hal-02629082
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[hal-01856169] Both gravistimulation onset and removal trigger an increase of cytoplasmic free calcium in statocytes of roots grown in microgravity
Gravity is a permanent environmental signal guiding plant growth and development. Gravity sensing in plants starts with the displacement of starch-filled plastids called statoliths, ultimately leading to auxin redistribution and organ curvature. While the involvement in gravity sensing of several actors such as calcium is known, the effect of statolith displacement on calcium changes remains enigmatic. Microgravity is a unique environmental condition offering the opportunity to decipher this link. In this study, roots of Brassica napus were grown aboard the International Space Station (ISS) either in microgravity or in a centrifuge simulating Earth gravity. The impact of short simulated gravity onset and removal was measured on statolith positioning and intracellular free calcium was assessed using pyroantimonate precipitates as cytosolic calcium markers. Our findings show that a ten-minute onset or removal of gravity induces very low statolith displacement, but which is, nevertheless, associated with an increase of the number of pyroantimonate precipitates. These results highlight that a change in the cytosolic calcium distribution is triggered in absence of a significant statolith displacement.
ano.nymous@ccsd.cnrs.fr.invalid (François Bizet) 09 Aug 2018
https://hal.science/hal-01856169
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[hal-02626073] Liana and tree below-ground water competition-evidence for water resource partitioning during the dry season
To date, reasons for the increase in liana abundance and biomass in the Neotropics are still unclear. One proposed hypothesis suggests that lianas, in comparison with trees, are more adaptable to drought conditions. Moreover, previous studies have assumed that lianas have a deeper root system, which provides access to deeper soil layers, thereby making them less susceptible to drought stress. The dual stable water isotope approach (delta O-18 and d delta H-2) enables below-ground vegetation competition for water to be studied. Based on the occurrence of a natural gradient in soil water isotopic signatures, with enriched signatures in shallow soil relative to deep soil, the origin of vegetation water sources can be derived. Our study was performed on canopy trees and lianas reaching canopy level in tropical forests of French Guiana. Our results show liana xylem water isotopic signatures to be enriched in heavy isotopes in comparison with those from trees, indicating differences in water source depths and a more superficial root activity for lianas during the dry season. This enables them to efficiently capture dry season precipitation. Our study does not support the liana deep root water extraction hypothesis. Additionally, we provide new insights into water competition between tropical canopy lianas and trees. Results suggest that this competition is mitigated during the dry season due to water resource partitioning.
ano.nymous@ccsd.cnrs.fr.invalid (Hannes de Deurwaerder) 26 May 2020
https://hal.inrae.fr/hal-02626073
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[hal-01897771] Biophysical dependences among functional wood traits
Wood properties and especially wood density have been used as functional traits organized along major axes of species life history and strategy. Beyond statistical analyses, a better mechanistic understanding of relationships among wood traits is essential for ecologically relevant interpretation of wood trait variations. A set of theoretical relationships mechanistically linking wood basic density with some other wood traits is derived from cellular material physics. These theoretical models picture basic physical constraints and thus provide null hypotheses for further ecological studies. Analysis is applied to data from two original datasets and several datasets extracted from the literature. Results emphasize the strong physical constraint behind the link between basic density and maximal storable water on the one hand, and elastic modulus on the other hand. Beyond these basic physical constraints, the developed framework reveals physically less expected trends: the amount of free water available for physiological needs increases in less dense wood of fast‐growing species, and the cell wall stiffness decreases with density in temperate hardwoods and is higher in sapling stages in the rainforest understorey where competition for light is associated with high mechanical risk. We emphasize the use of theoretically independent traits derived from models of cellular material physics to investigate the functional variation of wood traits together with their environmental and phylogenetic variations. Although the current study is limited to basic density, green wood lumen saturation and wood specific modulus, we further emphasize the identification of complementary independent wood traits representing other biomechanical functions, nutrient storage, hydraulic conductance and resistance to drought.
ano.nymous@ccsd.cnrs.fr.invalid (Jana Dlouha) 17 Oct 2018
https://hal.science/hal-01897771
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[hal-01897788] Quantifying the motor power of trees
Trees have a motor system to enable upright growth in the field of gravity. This motor function is taken on by reaction wood, a special kind of wood that typically develops in leaning axes and generates mechanical force during its formation, curving up the stem and counteracting the effect of gravity or other mechanical disturbances. Quantifying the mechanical stress induced in wood during maturation is essential to many areas of research ranging from tree architecture to functional genomics. Here, we present a new method for quantifying wood maturation stress. It consists of tilting a tree, tying it to a stake, letting it grow in tilted position, and recording the change in stem curvature that occurs when the stem is released from the stake. A mechanical model is developed to make explicit the link between the change in curvature, maturation strain and morphological traits of the stem section. A parametric study is conducted to analyse how different parameters influence the change in curvature. This method is applied to the estimation of maturation strain in two different datasets. Results show that the method is able to detect genotypic variations in motor power expression. As predicted by the model, we observe that the change in stem curvature is correlated to stem diameter and diameter growth. In contrast, wood maturation strain is independent from these dimensional effects, and is suitable as an intrinsic parameter characterising the magnitude of the plant's gravitropic reaction.
ano.nymous@ccsd.cnrs.fr.invalid (Tancrède Alméras) 17 Oct 2018
https://hal.science/hal-01897788
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[hal-01830867] Assessing the roles of temperature, carbon inputs and airborne pollen as drivers of fructification in European temperate deciduous forests
We aimed at identifying which drivers control the spatio-temporal variability of fruit production in three major European temperate deciduous tree species: Quercus robur, Quercus petraea, and Fagus sylvatica. • We analysed the relations of fruit production with airborne pollen, carbon and water resources and meteorological data in 48 French forests over 14 years (1994-2007). • In oak, acorn production was mainly related to temperature conditions during the pollen emission period, supporting the pollen synchrony hypothesis. In beech, a temperature signal over the two previous years eclipsed the airborne pollen load. • Fruit production in Quercus and Fagus was related to climate drivers, carbon inputs and airborne pollen through strongly non-linear, genus-specific relations. • Quercus and Fagus also differed as regards the secondary growth vs. fructification trade-off. While negative relationships were observed between secondary growth and fruit production in beech, more productive years benefited to both secondary growth and reproductive effort in oak.
ano.nymous@ccsd.cnrs.fr.invalid (François F. Lebourgeois) 05 Jul 2018
https://agroparistech.hal.science/hal-01830867
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[hal-02627725] Systèmes de polyculture-élevage : quels effets des pratiques agricoles sur les teneurs en matières organiques et le fonctionnement microbien du sol ?
Les matières organiques du sol (MOS) sont le pilier de fonctions physiques, chimiques et biologiques des sols. Les micro-organismes du sol sont des acteurs majeurs de la dynamique des MOS. Dans les agroécosystèmes, quel est l’effet de certaines pratiques agricoles sur cette dynamique et sur le fonctionnement microbien des sols ? Six dispositifs expérimentaux (de moyenne à longue durée), situés dans différents contextes pédoclimatiques, ont permis d’étudier les effets, sur la teneur en MOS et sur le fonctionnement microbien du sol, de pratiques agricoles pouvant être mises en œuvre dans les systèmes de polyculture-élevage. Les résultats obtenus montrent que les pratiques agricoles étudiées (apports d’effluents d’élevage, intégration de prairies temporaires, réduction du travail du sol) peuvent augmenter la teneur en MOS et stimuler significativement certaines activités enzymatiques microbiennes intervenant dans la décomposition des MOS. Ainsi, ces pratiques peuvent renforcer la capacité des sols à fournir des éléments minéraux utilisables par les plantes, dans un contexte de limitation des intrants de synthèse dans les systèmes fourragers.
ano.nymous@ccsd.cnrs.fr.invalid (Caroline Petitjean) 26 May 2020
https://hal.inrae.fr/hal-02627725
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[hal-01962145] Anionic exchange membranes, a promising tool to measure distribution of soil nutrients in tropical multispecific plantations
Establishing highly productive forest plantations or crops on poor soils requires appropriate management to ensure sustainable production. The current development of various ecological intensification practices calls for efficient tools to monitor their effects on agro-ecosystems. Ecological intensification such as an association between a N2-fixing tree species and a highly productive species, e.g. an acacia and a eucalypt, is an agro-ecological plantation design that can enhance nutrient cycling and preserve soil fertility in tropical and sub-tropical areas. In this study, Anionic Exchange Membranes (AEM) were used to assess in situ the effect of tree species on the availability and spatial variability of nitrate (N) and phosphorus (P) in pure Acacia mangium (A), pure eucalypt (E) and mixed-species treatments (MA-ME) in a randomized complete block design on a ferralitic arenosol. The results showed that the AEM detected the specific influence of tree species on N and P availability at the stand level as well as interactions between trees in the mixed-species treatment. Moreover, nutrients trapped using AEM were significantly correlated with N and P immobilized in the tree biomass. In the mixed stand, AEM made it possible to understand the specific impact of each tree species on N and P availability reflecting the respective biogeochemical mechanisms at work. This preliminary study showed that AEM are a promising tool that can be used in situ for intensive sampling in multi-local comparisons to highlight the effect of management practices on soil fertility as well as the relationships between vegetation cover and soil.
ano.nymous@ccsd.cnrs.fr.invalid (Edith Le Cadre-Barthélemy) 20 Dec 2018
https://institut-agro-rennes-angers.hal.science/hal-01962145
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[hal-02620604] Gaining a global perspective on Fagaceae genomic diversification and adaptation
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ano.nymous@ccsd.cnrs.fr.invalid (Charles H. Cannon) 26 May 2020
https://hal.inrae.fr/hal-02620604
