Vulnérabilités liées à l'eau dans les Andes vénézuéliennes : influences des relations sociétés/hydrosystèmes dans le cas de Santa-Cruz-de-Mora

International audienceDes mutations agricoles sont survenues au cours des dernières décennies dans les Andes vénézuéliennes. Cette région autrefois grande productrice de café a vu sa production baisser au profit du maraîchage irrigué et du pastoralisme. Nous avons mené 2 démarches parallèles : la caractérisation des changements d'occupation du sol afin de mettre en perspective le discours des habitants ; et l'analyse des représentations sociales des risques liés à l'eau, restitués plus largement dans les représentations des hydrosystèmes

TRY plant trait database – enhanced coverage and open access

Plant traits - the morphological, anatomical, physiological, biochemical and phenological characteristics of plants - determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait‐based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits - almost complete coverage for ‘plant growth form’. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait–environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives

Maximal Order Codes over Number Fields

We present constructions of codes obtained from maximal orders over number fields. Particular cases include codes from algebraic number fields by Lenstra and Guruswami, codes from units of the ring of integers of number fields, and codes from both additive and multiplicative structures of maximal orders in central simple division algebras. The parameters of interest are the code rate and the minimum Hamming distance. An asymptotic study reveals several families of asymptotically good codes.Accepted versio

Grass strategies and grassland community responses to environmental drivers: a review

Grassland covers about one quarter of the Earth’s land area and is currently estimated to contribute to the livelihoods of over 800 million people. Grassland provides ecosystem goods and services, mainly through the provisioning of milk and meat. Therefore, the proper use of grasslands will be essential for feeding the nine billion people that will inhabit planet Earth by 2050. In the context of a changing climate, we should better understand the interactions of environment, management and grass crop at individual, community and ecosystem levels. Functional ecology focuses on the roles and functions that species play in the community or ecosystem in which they occur. Functional ecology thus aims to understand how plant species adapt to environmental conditions and how management can alter this adaptation. Here, we review the latest advances in plant functional traits research and on species strategies to the main environmental factors occurring in grassland ecosystems: nutrient availability, grazing, cutting and shading. Functional ecology also provides a framework to better understand how species strategies interact with the species composition at the community level. Therefore, the literature on community assembling theories in relation to ecosystem processes most relevant to grassland management and services is also reviewed. Finally, future research questions and some new orientations for grassland experts are offered in order to meet the challenge of maintaining productivity and preservation of these semi-natural environments in the face of global change

Thermo-mechanical characterization of steel-based metal matrix composite reinforced with TiB2 particles using synchrotron X-ray diffraction

International audienceThe thermo-mechanical properties of a ferritic-steel-based metal matrix composite reinforced with titanium diboride (TiB 2) particles were studied using synchrotron X-ray diffraction. The samples were subjected to in situ heat treatment to investigate the effect of the mismatch in the coefficient of thermal expansion between the matrix and reinforcement. In addition, in situ tensile tests were performed to examine the load partitioning in the composite. Load transfer from the ferritic matrix to the TiB 2 particles was observed at the onset of plasticity in the matrix

Impacts of species interactions on grass community productivity under contrasting management regimes.

International audienceProductivity–diversity relationships are routinely described mainly in terms of species richness. However, these relationships can be affected by the functional strategy and physiological plasticity characterizing each species as they respond to environment and management changes. This study, therefore, aimed to analyze species interactions in grass communities presenting the same number of species (n = 6) but different growth strategies, and the impact on community productivity across several forms of field management (two different fertilizer application rates, i.e. 120 and 360 kg N ha-1 year-1, and two cutting frequencies, i.e. 3 and 6 cuts per year). For this purpose, we applied the tripartite partitioning method introduced for the analysis of biodiversity effects (BE). Grass species were cultivated on small plots (4.2 m2) in both mixtures and monocultures. Different management regimes altered both net BE and its component effects: dominance and potential for complementarity. A higher cutting frequency significantly reduced net BE, via a reduction in dominance effect. We found that increased N supply could either increase or decrease complementary effect according to grass mixture composition, i.e. species strategy. Regardless of management intensity, net BE was in general significantly positive especially when including individual species-specific plasticity effects. We conclude that a combination of different grasses has a positive effect on community biomass. Furthermore, both the functional strategy and the functional plasticity of component species play an important role in the intensity of BE. Therefore, biological mechanisms leading to enhanced biomass in sixgrass communities are as effective for productivity as management conditions

Représentations et pratiques autour de la ressource en eau des producteurs maraîchers des Andes vénézuéliennes

Cet article a pour but d’analyser les représentations sociales de l’eau des producteurs maraîchers des hautes vallées andines vénézuéliennes, et cela, dans un contexte où cette ressource constitue un outil essentiel de production agricole. Il s’agit plus particulièrement d’appréhender la manière dont les agriculteurs perçoivent et évaluent l’état actuel de la ressource, et ainsi cerner la justification de leurs comportements et de leurs pratiques agricoles. Dans les années 1960, l’introduction du maraîchage irrigué dans les Andes vénézuéliennes a profondément transformé les rapports à l’eau des sociétés rurales qui ont développé des systèmes d’appropriation et de distribution de la ressource particulièrement efficaces, tant techniquement que socialement. Mais aujourd’hui, les agriculteurs perçoivent des fluctuations de la ressource qu’ils peuvent interpréter comme une conséquence du changement climatique, et/ou comme conséquence de la dynamique agricole en cours. Face à ces phénomènes, de nouvelles pratiques agricoles telles que l’irrigation par micro-aspersion ou encore la préservation des sources d’eau en altitude commencent à émerger.This study aims to analyze social representations for water resource of market gardening producers of the high valleys of Venezuelan Andes, whereas this resource constitutes an essential tool of agricultural production. It proposes more particularly to understand how farmers perceive and assess the current state of the resource and identify the justification of their behaviour and agricultural practices. In the 1960s, the introduction of irrigated gardening in the Venezuelan Andes, has profoundly changed the relationship to water for rural societies who have developed particularly efficient systems of appropriation and distribution of the resource particularly effective, both technically and socially. But, nowadays, the farmers perceive fluctuations in the resource that they can interpret as a consequence of climate change, and/or as a result of actual agricultural dynamics. Faced with this phenomena, new practices such as irrigation by micro-irrigation or the preservation of water sources in altitude begin to emerge

The plasticity of functional traits drives the response of grass species to environmental changes

International audiencePlant functional traits (PFTs) are useful tools to explain species' responses to environmental changes, because their values reflect the strategy whereby adaptation to variations in land use is achieved, resulting in changes in a species' performance. However, the role of PFT plasticity on plant response to environment has barely been explored. This study investigated the relationship between functional shoot traits and their plasticity due to changes in field management. Monocultures of 13 native perennial C-3 grasses were grown in a fully-factorial block design combining species, cutting frequency (i.e. 3 (3C) and 6 (6C) cuts y(-1)) and N supply (i.e. 120 (120N) and 360 (360N) kg ha(-1) y(-1)). In this study, the 3C 360N-treatment provides the optimal growth conditions and consequently allows the characterization of species strategy. Regression analyses were performed between trait values in the 3C 360N-treatments and their respective plasticity to a decrease in N supply, an increase in cutting frequency, or both. Significant regressions were found between trait values in 3C 360N and their plasticity in response to changes in management. We conclude that the ability of species to alter their morphology and/or physiology in response to varying cutting regimes or fertilisation level is both trait - (i.e. strategy indicators) and environment-dependent