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Les inégalités sociales et territoriales face aux canicules
No full textCe policy brief synthétise les résultats d'une évaluation des inégalités sociales et territoriales face aux fortes chaleurs en France. En exploitant une nouvelle base de données mensuelle couvrant 34 000 communes métropolitaines de 1980 à 2019, l'étude montre que les épisodes de forte chaleur accroissent significativement la mortalité, surtout chez les personnes âgées de plus de 75 ans, avec des effets plus marqués dans les zones urbaines et les communes les plus défavorisées. Depuis la grande canicule de 2003, la mise en place du Plan national canicule a nettement réduit l'impact des fortes chaleurs, mais des inégalités importantes demeurent
Beyond light quantity: Intermittent shading affects growth and yield more than constant shading in rice cultivars
No full textInternational audienceHighlights: • Intermittent shading reduced rice yield and biomass more than constant shading. • Yield losses were mainly due to reduction in tillering, followed by kernel weight. • Incident radiation use efficiency rose under shade, less so with intermittent shading. • Non-linear light response explained lower assimilation with intermittent shade. • Cultivars differed slightly, yet overall responded similarly to intermittent shading.Abstract: Plant responses to shade are often studied under constant light reduction, but rarely under intermittent shading which is frequent in natural environments and multilayered systems such as agrivoltaics and agroforestry. We investigated in controlled environments how a 38 % reduction in daily radiation, applied either continuously or as several intermittent periods per day, affected morphology, phenology, aboveground biomass, yield components, and photosynthetic traits of 14 rice cultivars. Plants were grown under full light with 24 MJ m⁻² day⁻¹ , and both shading treatments received the same daily light integral. On average, continuous shading reduced grain yield by 28 % and aboveground biomass by 27 %, whereas intermittent shading resulted in greater decreases, by 32 % and 31 %, respectively. Yield losses were mainly attributed to reduced tillering and to a lesser extent to 1000-kernel weight. Growth reduction was sub-proportional to light resources, indicating increased incident radiation use efficiency under shading. However, this increase was less pronounced under intermittent shading, chiefly attributable to the curvi-linear response of photosynthesis to light. Furthermore, a decrease in the maximum electron transport rate under intermittent shading conditions suggested reduced photosynthetic capacity as well. Despite substantial variation among cultivars in morphology and photosynthetic parameters under full light, none of these traits predicted differential responses to shading regimes. These findings highlight that diurnal light distribution strongly influences crop performance, beyond the effects of mean light reduction. Consideration of intermittent shading is thus crucial for understanding and modeling plant responses in multilayered systems such as agrivoltaics, intercropping, and agroforestry
Water deficit and salinity stresses modulate growth, physiology, and phytochemical composition of Lavandula coronopifolia Poir. grown in pots under controlled conditions
No full textInternational audienceLavandula coronopifolia Poir. is a medicinal evergreen shrub, wildly distributed in rocky and arid environments. It belongs to the Lamiaceae family, known by the large array of bioactive compounds it contains. Drought and salinity present major threats in arid zones and severely penalize the potential yield of naturally growing desertic plants; however, it may affect the synthesis and accumulation of their metabolites. Few studies have investigated the response of Lavandula species to abiotic stresses and to the best of our knowledge, none have been conducted on L. coronopifolia. Our study aims to investigate various responses of this species to water deficit and salt stress under controlled conditions. Two distinct experiments were conducted in a growth chamber, each lasting one month. The first one focused on water stress, with plants subjected to four water treatments: control (100% field capacity (FC)), moderate water deficit (50% FC), severe water stress (25% FC), and very severe water stress (alternating irrigation to 50% FC for one week followed by cessation of watering for the next week). These treatments were arranged in a randomized complete block design (RCBD) with 3 blocks, each containing 3 replicates per treatment, resulting in 9 replications per treatment. The second experiment investigated the effect of salt stress, where plants were exposed to four NaCl concentrations: 0, 5, 10, and 20 dS/m. This experiment was also conducted using an RCBD, with 4 blocks and 4 replicates per treatment within each block, giving a total of 16 repetitions per treatment. Growth parameters, oxidative stress indicators as well as secondary metabolite content were determined. Results have shown that under both water and salt stress conditions, plant fresh and dry weights decreased significantly. Malondialdehyde levels increased under intense stress in both experiments, indicating enhanced lipid peroxidation. Protein content increased under water stress but showed no change under salt stress. Phenolic and flavonoid contents increased with water stress but decreased with salt stress. Antioxidant activity remained stable under water stress and showed a significant increase with salt stress. These findings enhance our understanding of how plants modulate various traits in response to distinct water and salt stress conditions
A situated proposal for a grounded approach to socio-hydrology
No full textSource Agritrop Cirad (https://agritrop.cirad.fr/616193/)International audienceSocio-hydrology, a range of attempts to better account for 'the social' in hydrological processes, has made significant progress during the Panta Rhei scientific decade of the International Association of Hydrological Sciences. Yet, where socio-hydrological studies continue prioritizing hydrological dynamics in explanations and solutions, critical social science studies continue to remain reluctant to engage in helping solve water problems, especially when this involves quantification. This Special Issue gathers contributions that share the ambition to enhance methodological symmetry between hydrological and social science forms of knowledge-making. Realizing this ambition hinges on (1) revisiting hydrology's epistemological preference for detachment, distance and replicability, replacing it with more modest forms of situated engagement that explicitly (re-)connect socio-hydrological knowledge-making to (always specific and political) places, waters, experiences, people, concerns and actions, and (2) inviting critical social science to leave the comfort of moral high grounds to become engaged in the design and development of practical solutions. This grounding of socio-hydrology takes the form of situated engagement and makes resulting knowledge both more accurate and more actionable, better linking proposed solutions to the transformations towards sustainability and justice that are so urgently needed
Synergistic effect of organic waste products and microbial inocula on iron and zinc biofortification in cowpea [Vigna unguiculata (L.) Walp.]
No full textSource Agritrop Cirad (https://agritrop.cirad.fr/616185/) * Autres projets (id;sigle;titre): AURG-II-2-110-2018;OR4FOOD;(ETH) Organic Residual Products for Biofortified Foods for Africa// 0002010826;;(USA) ASA Reflection and Knowledge//International audienceMicronutrient deficiencies affect over 2 billion people worldwide, with iron (Fe) and zinc (Zn) deficiencies prevalent in Senegal. These deficiencies result from the low Fe and Zn contents in food crop products. This study examined the effects of micronutrient-rich organic waste products (OWPs), in combination with local beneficial microorganisms and mycorrhizal fungi, on Fe and Zn concentrations in cowpea (Vigna unguiculata) grains and haulms. Cowpea trials were conducted over two contrasting consecutive seasons (wet and dry). A factorial block design with four replications was used. The main results showed significant increases in cowpea yield (up to 2.4-fold for grains and 3.2-fold for haulms), Fe concentrations (up to +48% in grains and +259% in haulms), and Zn concentrations (up to +28% in grains and +265% in haulms) with the application of OWP combined with microbial inocula (MIs), compared with those in the control. In addition, the observed effects on the yield and Fe and Zn concentrations depended on the type of OWPs and MIs used. These results validate our initial hypothesis regarding the significant increase in Fe and Zn content in cowpea grains and haulms with the combined application of OWPs, which supply micronutrients, and MIs that facilitate the solubilization and transfer of these micronutrients to the plant. Our findings provide novel insights into the agro-biofortification of cowpeas and can be further developed to guide the selection of OWPs and MIs for use in agroecological biofortification systems
Microplastic impacts on soil and sediment bioturbation: insights from microcosm experiments across diverse ecosystems
No full textInternational audienceEcosystem engineering by bioturbation shapes ecosystems by physically modifying soil and sediment habitats, affecting microbial communities and biogeochemical processes. Although bioturbation is a key process for ecosystem health and functioning, its response to contaminants like microplastics (MPs) remains poorly explored. To address this gap, we conducted three microcosm experiments across terrestrial, freshwater, and marine ecosystems, using three species of ecosystem engineers: Aporrectodea caliginosa (earthworm), Tubifex tubifex (freshwater worm), and Hediste diversicolor (marine worm). Each ecosystem was contaminated by a mixture of polystyrene and polyamide MP fragments and fibers, ranging from 10 to 1000 μm, at two MP concentrations: 0 and 100 mg kg− 1 soil/sediment dry weight. Tracer particles (luminophores) were used to quantify soil/sediment reworking activities of ecosystem engineers. After 21 days of exposure, distinct bioturbation proxies (i.e., maximum penetration depth, surface reworking, particle displacement coefficient, cast production, biodiffusion-like and non-local reworking coefficients) were measured in each microcosm experiment. Our results demonstrated contrasted effects of MPs on bioturbation across ecosystems/ecosystem engineer species. In the terrestrial ecosystem, surface sediment reworking by earthworms remained unaffected by MP contamination although the cast production by A. caliginosa tended to increase (+26 %) with MP contamination. Conversely, in the freshwater ecosystem, the presence of MPs significantly reduced bioturbation activity of tubificid worms, resulting in a nearly fourfold decrease in particle displacement and a substantial reduction in maximum penetration depth of the luminophores. In the marine system, although H. diversicolor maintained effective particle reworking activities with MP contamination, gallery-biodiffusion activity tended to decrease in presence of MPs. Overall, the impact of MP contamination on bioturbation process was context-dependent. It can be hypothesized that the impact of MPs on bioturbation process was dependent on the size of the ecosystem engineering species, with the strongest effect observed on the smallest organism (T. tubifex)
Assessing the non-target effects of herbicides on field margin plant communities after controlling for soil, climate, local context and landscape metrics
No full textInternational audienceHighlights: • We used a national dataset of 500 sites monitored yearly from 2013 to 2018. • We analysed the effects of herbicides on plant margin communities. • Herbicides had a negative effect on richness and nature-value species. • Situations of risk for pesticides drift had a negative effect on margin flora.Abstract: Pesticides are often identified as one of the major causes of biodiversity decline in farmlands. However, our knowledge about this relationship has mostly being inferred from small to landscape-scale studies, or from indirect indicators of agricultural practices at large scales. Here, we used a national network of more than 500 sites monitored yearly from 2013 to 2018 in France to assess the non-target effects of herbicides on field margin plant communities. We used hierarchical generalized linear models to investigate the effects of practices on plant species richness, plant species evenness, proportion of nature-value plants, and proportion of grasses in field margins, while controlling for a large number of possible confounding effects. The intensity of herbicide use had a negative effect on plant species richness, and on the proportion of nature-value plants. In the margin of cereal fields, there was a negative effect of dicotyledon herbicides on richness and a negative effect of grass herbicides on species evenness. We also identified, in some specific crops, a negative effect of non-herbicide treatments on margin flora richness and on the proportion of nature-value plants. The presence of surrounding grasslands had a consistent favourable effect on richness and on the proportion of nature-value plants in field margins. Finally, situations of risk for pesticides drift had a negative effect on margin flora. This study confirms that reducing herbicide use represents a robust lever to maintain the floristic diversity of field margins, which could be combined with strategies reducing the risk of pesticide drift
Access to agricultural lands influences the effects of seasonal drought on early growth and juvenile body mass in a large herbivore
No full textInternational audienceIncreasing rainfall deficits threaten the persistence of terrestrial large herbivores, yet, very few studies have investigated the effects of droughts on populations inhabiting anthropized areas, which dominate European landscapes. We investigated how rainfall deficits (measured using the Standardized Precipitation Index, SPI) and local agricultural land use shaped the early growth of fawns and the body mass that they attained by their first winter in a population of European roe deer (Capreolus capreolus) in southwestern France. Using data on 155 new-born fawns, we found that early growth decreased as local woodland availability increased, irrespective of spring rainfall conditions. In contrast, based on data from 218 GPS-monitored juveniles, aged 8-10 months, we found that local landscape composition and seasonal rainfall deficits had interacting effects on winter body mass. The juveniles were generally heavier with higher proportions of meadows in their predicted home range (mean 0.4 kg +/- 0.2 SE), but this difference disappeared following dry summers (SPI < 1). Juveniles with low access to summer crops (e.g., 5%) were significantly lighter following dry autumns (mean -0.9 kg +/- 0.3 SE), whereas this was not the case for those with higher access to these crops (e.g., 20%). Although populations of large herbivores may respond to harsh climatic conditions by exploiting anthropogenic resources, our results suggest that any compensation effects are strongly dependent on the type of anthropogenic land use and the timing of rainfall deficits, calling for explicitly considering how local climatic conditions and human practices may interact in shaping individual performance and, so, population dynamics
Morphological variation and genetic diversity of breadfruit [Artocarpus altilis (Parkinson) Fosberg] in Vanuatu
No full textInternational audienceBreadfruit, Artocarpus altilis (Parkinson) Fosberg, is a versatile tree crop widely distributed in Oceania and tropical regions. It produces starchy fruits that contribute to food security in Pacific Island countries. In Vanuatu, where it is considered as a secondary food crop, a better understanding of the diversity of this species is a prerequisite for setting up a genetic improvement strategy. A diversity study of 123 accessions collected in 27 villages on eleven islands across Vanuatu and conserved in an ex-situ field gene bank was conducted in 2023–24. Eighteen morphological descriptors of fruits and leaves were utilized and genotyping was performed using 15 single sequence repeat (SSR) markers. The results showed that Vanuatu cultivars exhibit important morphological variation. Most of them (except two) are diploid and seeded. Analysis of SSR profiles revealed four genetic groups and 99 unique multilocus genotypes. Cultivars collected in the northern and north-central regions of Vanuatu appeared to be more genetically diverse than those collected further south. A total of 152 alleles were detected across the 15 loci, with an average number of 10.13 alleles per locus. For comparison, SSR analysis of triploid seedless cultivars from Eastern Polynesia and the Indian Ocean showed that these cultivars, although morphologically different, share a very narrow genetic base and are hardly distinguishable with the set of markers used in this study. These results confirm that Vanuatu is an important centre of breadfruit diversity and that this diversity is dynamic due to the diploid nature of cultivars with a high percentage of seed propagated trees
Cutting date impact on the herbaceous layer in Sahelian rangeland during the wet season
No full textSource Agritrop Cirad (https://agritrop.cirad.fr/615940/)International audienceAnnual herbaceous vegetation is a crucial source of forage for pastoral livestock in the Sahel region. These species grow during the wet season, which coincides with the peak grazing period. Understanding the impact of disturbances on annual herbaceous vegetation is then essential. This study focuses on the temporal aspects of disturbance. In northern Senegal, we established nine different plots and cut them weekly during the wet season and returned to each plot at the end of the season to create a gradient of cutting dates. We measured the plant's phenology, height, dry biomass, and fodder quality. Our results indicated that vegetation growth occurs in three phases: establishment, growth, and flowering. The impact of cutting varied across these phases. Plots cut during the establishment phase exhibited vegetation characteristics similar to those of uncut plots. Plots cut during the growth phase had reduced vegetation height but all individuals completed their growth cycle. Plots cut during the flowering phase had significantly lower biomass at the end of the season and experienced a slight delay in phenological development and increase the quality of the fodder at the end of the season. These findings highlight the importance of cutting timing on vegetation dynamics