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• Experiments are presented that test the relative importance, during ontogeny, of stomatal control and leaf area expansion to optimum seasonal water use in pearl millet (Pennisetum glaucum). These parameters play a key role in the compromise between plant growth and water saving under unpredictable conditions of semiarid environments. • The response of growth and water use of crops to successive 15 d drought periods was measured under field conditions in Niger (West Africa). • From emergence to anthesis, biomass partitioning to stems and panicles depended strongly on leaf area development. Water use was linearly related to green leaf area duration in well watered plots, but was reduced proportionally more than green leaf area in drought-affected plots. The relations of crop growth rate and transpiration efficiency to leaf area depended on ontogenetic changes in biomass partitioning. • In P. glaucum, stomata play a dominant role in reducing crop water use under preanthesis drought, although this control becomes negligible after anthesis because of ontogenetic decline in the range of stomatal conductance. The rate of leaf senescence after anthesis is not drought-dependent.

International audience; Background and Aims: Rooting plasticity is critical for plants exploiting patchy soil-water resources, but empirical evidence remains controversial due to complex root/soil interactions in natural and agricultural environments. We compared cultivated and wild Chenopodium populations from distinct agroecological background to assess their rooting plasticity when exposed to contrasting wet-dry soil profiles in a controlled environment.Methods: Four treatments of increasing dryness were applied during 6 weeks in plants of Chenopodium hircinum, Chenopodium pallidicaule and two ecotypes (wet- and dry-habitat) of Chenopodium quinoa grown in rhizotrons. Root system architecture and growth were sequentially mapped. At the end of the experiment, plant and root morphological traits and dry biomass were measured.Results: Contrary to the other two species, C. quinoa showed accelerated taproot growth in dry soil conditions. The dry-habitat C. quinoa ecotype showed consistently higher plant traits related to longer, coarser, and more numerous root segments which give it a faster taproot growth and sustained root branching at depth in dry soil.Conclusions: High rooting plasticity confers the advantage of fast root elongation and deep soil exploration under soil water deficit. Variation in intrinsic root traits and plastic responses among Chenopodium populations controls their root foraging capacity facing patchy soil-water resources.

History and environment shape crop biodiversity, particularly in areas with vulnerable human communities and ecosystems. Tracing crop biodiversity over time helps understand how rural societies cope with anthropogenic or climatic changes. Exceptionally well preserved ancient DNA of quinoa (Chenopodium quinoa Willd.) from the cold and arid Andes of Argentina has allowed us to track changes and continuities in quinoa diversity over 18 centuries, by coupling genotyping of 157 ancient and modern seeds by 24 SSR markers with cluster and coalescence analyses. Cluster analyses revealed clear population patterns separating modern and ancient quinoas. Coalescence-based analyses revealed that genetic drift within a single population cannot explain genetic differentiation among ancient and modern quinoas. The hypothesis of a genetic bottleneck related to the Spanish Conquest also does not seem to apply at a local scale. Instead, the most likely scenario is the replacement of preexisting quinoa gene pools with new ones of lower genetic diversity. This process occurred at least twice in the last 18 centuries: first, between the 6th and 12th centuries?a time of agricultural intensification well before the Inka and Spanish conquests?and then between the 13th century and today?a period marked by farming marginalization in the late 19th century likely due to a severe multidecadal drought. While these processes of local gene pool replacement do not imply losses of genetic diversity at the metapopulation scale, they support the view that gene pool replacement linked to social and environmental changes can result from opposite agricultural trajectories. Fil: Winkel, Thierry. Université de Montpellier; Fil: Aguirre, María Gabriela. Universidad Nacional de Tucumán; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Laboratorio de Geoarqueología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina Fil: Arizio, Carla Marcela. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación de Recursos Naturales. Instituto de Recursos Biológicos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Aschero, Carlos Alberto. Universidad Nacional de Tucumán; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Estudios Sociales. Universidad Nacional de Tucumán. Instituto Superior de Estudios Sociales; Argentina Fil: Babot, Maria del Pilar. Universidad Nacional de Tucumán; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Estudios Sociales. Universidad Nacional de Tucumán. Instituto Superior de Estudios Sociales; Argentina Fil: Benoit, Laure. Université de Montpellier; Fil: Burgarella, Concetta. Amélioration Génétique Et Adaptation Des Plantes Méditerranéennes Et Tropicales (agap); Fil: Costa Tártara, Sabrina María. Universidad Nacional de Luján; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación de Recursos Naturales. Instituto de Recursos Biológicos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Dubois, Marie-Pierre. Université de Montpellier; Fil: Gay, Laurène. Amélioration Génétique Et Adaptation Des Plantes Méditerranéennes Et Tropicales (agap); Fil: Hocsman, Salomón. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Estudios Sociales. Universidad Nacional de Tucumán. Instituto Superior de Estudios Sociales; Argentina Fil: Jullien, Margaux. Amélioration Génétique Et Adaptation Des Plantes Méditerranéennes Et Tropicales (agap); Fil: Lopez Campeny, Sara Maria Luisa. Universidad Nacional de Tucumán; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Estudios Sociales. Universidad Nacional de Tucumán. Instituto Superior de Estudios Sociales; Argentina Fil: Manifesto, Maria Marcela. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires; Argentina Fil: Navascués, Miguel. Faculte de Medecine Universite Montpellier 1; . Montpellier Supagro; Fil: Oliszewski, Nurit. Universidad Nacional de Tucumán; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Estudios Sociales. Universidad Nacional de Tucumán. Instituto Superior de Estudios Sociales; Argentina Fil: Pintar, Elizabeth Lucia. Austin Community College; Estados Unidos Fil: Zenboudji, Saliha. Université de Montpellier; Fil: Bertero, Hector Daniel. Universidad de Buenos Aires; Argentina Fil: Joffre, Richard. Université de Montpellier

International audience; Agricultural globalization is blamed for destructive impacts on small farms in developing countries. Yet, many local societies are proactive in the face of these changes and show high adaptive capacity. Investigating their transformations with an integrative perspective and enough hindsight may reveal some of the bases of their resilience and adaptive capacity. Using field data and the panarchy concept of resilience theory, we analyzed the territorial and social dynamics of quinoa growers' communities in southern Bolivia over the last four decades, a case study of regime shift in a poverty-stricken rural society which deliberately entered the global food market. Linking the dynamics of the household economy to the territorial and social subsystems over several decades, we gained insights into the interactions that shaped the rise of quinoa production in the region. We found that a vivid tradition of mobility allowing for pluriactivity on-and off-farm, combined with community self-governance, explains how local populations succeeded in articulating individual agency with collective control over their commons of land, seed resources, and social rules. Our vulnerability analysis points to landscape homogenization, social inequity, and increased dependence on external factors as potential sources of unsustainability. We conclude that, to cope with the changes of unprecedented magnitude they are facing, local producers should retain social cohesion and autonomous governance, without giving up on their heritage of mobility and economic redundancy. As regards theory, we identified cross-scale subsystem configurations critical for regime shifts, and confirm the value of panarchy in capturing complex socioecological dynamics.

Reviewing the situation of quinoa production in southern Bolivia, Jacobsen (2011, J. Agron. Crop Sci. 197: 390) argues that the booming export market has a negative effect on the environment and on the home consumption of quinoa, thereby leading to an environmental disaster in the region. In view of the scarcity of scientific knowledge on the rapid social and environmental dynamics in the region, we consider that Jacobsen’s review misrepresents the situation of quinoa production in southern Bolivia. Specifically, we argue that (i) the data presented by Jacobsen (2011, J. Agron. Crop Sci. 197: 390) do not support any drop in quinoa crop yield supposed to reflect soil degradation and (ii) his demonstration regarding home consumption of quinoa is ill-founded from both a nutritional and a cultural point of view. We suggest that the diffusion of the arguments exposed by Jacobsen (2011, J. Agron. Crop Sci. 197: 390), because of their flaws, might have strong negative impacts on those concerned with sustainable food production and fair-trade with developing countries. We conclude that, rather than reinforced agro-technical controls on local farmers, the rising competition in the international quinoa market requires a shift towards an ethical economy and ethical research cooperation with quinoa producers.

Several studies conducted under high input conditions have indicated little susceptibility of pearl millet to water deficit untill early grain filling, because the losses in main shoot production were fully compensated by increased tiller fertility. The present study assessed the impact of water deficits at three development stages : prior to flowering (S30), at the beginning of flowering (S45), and at the end of flowering (S60) in pearl millet grown in experimental conditions similar to Sahelian farming conditions. It included a control irrigation treatment simulating the natural distribution of rainfall throughout the cropping season. Both biomass production and grain yield were severely reduced by S30 and S45, while S60 had no effect. In S30 and S45, the flowering of tillers was delayed or totally inhibited. In both of these treatments, the low number of productive tillers did not compensate for damage to panicle initiation and flowering of the main shoot. All treatments maintained green leaves on the main shoot during the grain filling period, and in S30 leaf growth recovered from mid-season drought. These results illustrate how pearl millet mostly escapes drought by matching its phenology to the mean rainfall distribution in the Sahel. In the case of mid-season drought, some late productive tillers and the maintenance of green leaf biomass of the main shoots limited, but did not overcome, the yield losses. This study stresses the importance of agro-ecological conditions in control treatments, particularly the water regime and crop density, when assessing crop drought resistance. (Résumé d'auteur)

International audience; Frost risk assessment is of critical importance in tropical highlands like the Andes where human activities thrives at altitudes up to 4200 m, and night frost may occur all the year round. In these semi-arid and cold regions with sparse meteorological networks, remote sensing and topographic modeling are of potential interest for understanding how physiography influences the local climate regime. After integrating night land surface temperature from the MODIS satellite, and physiographic descriptors derived from a digital elevation model, we explored how regional and landscape-scale features influence frost occurrence in the southern altiplano of Bolivia. Based on the high correlation between night land surface temperature and minimum air temperature, frost occurrence in early-, middle- and late-summer periods were calculated from satellite observations and mapped at a 1-km resolution over a 45,000 km² area. Physiographic modeling of frost occurrence was then conducted comparing multiple regression (MR) and boosted regression trees (BRT). Physiographic predictors were latitude, elevation, distance from salt lakes, slope steepness, potential insolation, and topographic convergence. Insolation influence on night frost was tested assuming that ground surface warming in the daytime reduces frost occurrence in the next night. Depending on the time period and the calibration domain, BRT models explained 74% to 90% of frost occurrence variation, outperforming the MR method. Inverted BRT models allowed the downscaling of frost occurrence maps at 100-m resolution, illustrating local processes like cold air drainage. Minimum temperature lapse rates showed seasonal variation and mean values higher than those reported for temperate mountains. When applied at regional and subregional scales successively, BRT models revealed prominent effects of elevation, latitude and distance to salt lakes at large scales, whereas slope, topographic convergence and insolation gained influence at local scales. Our results highlight the role of daytime insolation on night frost occurrence at local scale, particularly in the early- and mid-summer periods when solar astronomic forcing is maximum. Seasonal variations and interactions in physiographic effects are also shown. Nested effects of physiographic factors across scales are discussed, as well as potential applications of physiographic modeling to downscale ecological processes in complex terrains. (résumé d'auteur)

International audience; Night radiative frost is a highly limiting factor for agriculture in Andean highlands. Nevertheless, a diversity of crop species was domesticated there, commonly showing high heterogeneity in plant growth at the field level. To examine a possible protective effect of crop canopy heterogeneity against nocturnal radiative frost, a dual approach combining a field experiment and a simplified energy balance model at the leaf level was used. Leaf and air temperatures were registered over an entire quinoa crop cycle in the Andean highlands of Bolivia, comparing two cultivars: Blanca de Yanamuyu, a traditional landrace with high plant height heterogeneity, and Surumi, a more homogeneous selected variety. In both cultivars, inverted air density profiles during calm and clear nights result in air temperature changes up to 4 °C over 1 m height, with minimum air temperature concentrated at the upper part of the canopy. In these conditions, leaf temperature gradients of up to 2.6 °C m-1 develop within the canopy of the traditional landrace, with minimum leaf temperature significantly higher (P < 0.001) in shaded plants of the landrace than in the selected cultivar. A dynamic model of leaf temperature based on canopy parameters and climatic records at screen level adequately simulates leaf temperature differences in the case of a vertically heterogeneous quinoa canopy. A sensitivity analysis of the model reveals that canopy height, leaf area index, and sky cloudiness are most important for the sheltering effect to develop, while air temperature and air humidity play a minor role under typical radiative frost conditions. As for wind velocity, its actual influence remains unclear due to experimental and modelling limitations at low wind speeds. The significance of these results is discussed in terms of the trade-off between stress adaptation and biomass productivity.This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright

Quinoa (Chenopodium quinoa Willd.) is a pseudocereal originated from the Andes important for small farmers' food security as well as for commercial production. Recently, it has been claimed that in Bolivia genetic erosion could result from the marginalization of the crop in the north and from its commercial standardization in the south. The aim of this study was to quantify the hierarchical structure of the genetic variation present in eight quinoa field populations, consisting of cultivated and weedy individuals, representative of the altiplano and interandean valleys of Bolivia. Randomly amplified polymorphic DNA markers show that quinoa has a strong population structure and a high intra-population variation. An effect of geographical structure of the populations was highlighted, due to population isolation, not simply linked to distance but more probably to climatic and orographic barriers present in the studied zone. The population structure is also reinforced by the limited seed exchanges among farmers as revealed by field interviews. This population structure appears related to three major biogeographic zones: the northern and central altiplano, the interandean valley, and the southern Salar. Intrapopulation genetic diversity was higher than that expected for a mainly autogamous species, and higher than that reported in anterior studies based on germ.plasm collections. These results are commented in view of current knowledge on phylogeny and reproductive biology of the species, and their implications regarding genetic resources management are discussed.

International audience; Net photosynthetic rate, radiation use efficiency, chlorophyll (Chl) fluorescence, photochemical reflectance index (PRI), and leaf water potential were measured during a 25

International audience; Measurements of leaf reflectance in two narrow wavelength bands centred around 530 and 570 nm were carried out during withering of two contrasting functional and structural types (annual vs. evergreen): Chenopodium quinoa (Willdenow) and Arbutus unedo (Linnaeus). The photochemical reflectance index PRI = (R530 - R570) / (R530 + R 570) was calculated. The results showed that PRI could be used as a reliable index for a non-destructive and low cost assessment of water stress. However, some limits with the PRI have to be emphasised, e.g. the wilting of leaves during the dry periods. If such limits are under control, PRI could be a way in remote sensing applications.

The effects of pre-flowering drought on millet were studied in two experiments, an on-station, dry-season trial under irrigation and an on-farm trial where drought was induced by natural rainfall regimes (one wet, two dry years). The on-station experimental conditions were adjusted to those of Sahel farms, particularly through low plant density, low soil fertility and an irrigation regime that simulated the natural rainfall pattern. The replanting (5–10%) of missing hills in the on-farm trial increased stand variance significantly, whereas small quantities of applied N reduced it. Grain yield and grain number were equally seriously affected by drought in both experiments; yields were 700–800 kg ha−1 in the control years compared with 200–300 kg ha−1 in drought years. Both experiments showed sub-populations of early-, intermediate- and late-flowering millet plants. Fertile tillers were concentrated in the group of early-flowering plants. Only this group when subjected to moisture stress could secure part of the grain production by delaying, to a maximum of 18 d, the development of fertile tillers beyond the period of stress. Later-flowering plants, mostly uniculm, would be either sterile or unaffected by drought, depending on the exact coincidence of panicle development and drought. Drought did not alter the number of fertile hills per stand, because earlier- or later-flowering plants in the same hill compensated for sterile plants. The period of flowering in a stand was stretched over 40–45 d independently of drought, and this occurred both in the on-station experiment comprising 19 plants per treatment and in the on-farm experiment comprising about 700 hills. Although stand variance was reduced by better crop management and resulted in more fertile hills, more panicles per hill, and taller hills of more uniform height, the spread in flowering period of the millet population tended to be unaffected. Stand variability therefore appeared to be of paramount importance in accounting for drought avoidance.

Under natural conditions, wild and cultivated pearl millet, Pennisetum glaucum (L.) R.Br., exchanged genes for millenia and, nevertheless, maintain high morphological differentiation. Under experimental conditions in the Sahel, hybridization between wild and cultivated pearl millet was measured using isozymic markers and interpreted in relation to the phenology of the plants. Gene flows were asymmetric, engendering 8% of hybrids in the progeny of the wild phenotype, 45% in that of the cultivated phenotype, and 39% in that of the intermediate "shibra" phenotype; these last two phenotypes constitute the sample of cultivated pearl millet. The proportion of hybrids in the progeny of the wild sample was time dependent during the flowering phase of cultivated pearl millet. The proportion of hybrids produced by the cultivated pearl millet was not time dependent. In the seeds produced by the cultivated phenotype along its reproductive phase, the proportion of viable seeds was negatively correlated with the frequency of hybrids. Likewise, the speed of germination of seeds produced by the cultivated or the shibra phenotypes was negatively correlated with the frequency of the hybrids that they contained. The effects of balancing among genetic intermixing, isolation and reproduction barriers, and differential anthropic and natural selection pressures are discussed to better understand the evolution and the maintenance of the polymorphism of Pennisetum glaucum. Key words: pearl millet, wild pearl millet, Pennisetum glaucum, gene flow, domestication, hybrid.

Dans les régions sahéliennes d'Afrique, les formes sauvage et cultivée du mil (#Pennisetum glaucum$ (L.) R. Br.) sont sympatriques et interfertiles, mais demeurent néanmoins distinctes depuis des millénaires. Les barrières à la reproduction ne suffisent pas à expliquer cette situation. Dans le but d'identifier d'autres mécanismes en jeu, la phénologie et l'effort reproductif des deux formes de mil ont été comparés en situation expérimentale au Sahel. La durée de la période de floraison de chaque type était beaucoup plus longue que la durée moyenne de floraison d'un individu. Quand les dernières plantes cultivées finissaient de fleurir, 65% des plantes sauvages étaient encore en train de fleurir et 30% commençaient à le faire. Ces dernières se trouvaient ainsi totalement isolées du flux de gènes de mil cultivé, dans une situation de reproduction endogamique. Les formes sauvage et cultivée du mil se différenciaient également par la répartition de leur investissement dans la biomasse aérienne, à l'exception du nombre de graines produites par plante. Comportement phénologique et effort à la reproduction contribuent au maintien de deux formes distinctes de mil. (Résumé d'auteur)

Studying the water transport in the soil-plant system requires information on the spatio-temporal variability of both subsystems and the ability to assess the impact of the soil heterogeneity and of the biological responses on the coupling between vegetation and its substrate. This study was conducted for 2 years in a vineyard in the Aude Valley, France, by measuring the particle size distribution of the topsoil, the instantaneous isotopic ratios ( 18 O 16 O , 2 H 1 H ) of leaf water, annual shoot biomass production, and interannual persistence of this biomass along a 360 m transect. The resultant spatial series were analysed for their correlations and converted to spectra. Changes in the isotopic ratios along the transect reflect the soil texture gradient, suggesting that the vines root deeper on the gravel layers than elsewhere. This could provide a mechanism for the partial decoupling between soil and vegetation, and thus explain (1) the strong temporal persistence of the vegetation pattern, (2) the low overall correlation between biomass production and soil texture. The spectra show that this correlation concentrates at specific scales which correspond to a minimum variability in the shoot biomass. In this case, therefore, soil texture plays only a minor role in determining the spatial heterogeneity of shoot biomass in grapevine.

International audience; A semi-empirical model of stomatal conductance was used to analyse porometer measurements on different grapevine cultivars under field conditions. Stomatal conductance was expressed as a function of quantum flux density, water vapour deficit, air temperature and leaf water potential. Where possible, the parameters describing the partial functions were estimated from field data and provide physiological insights into the transpiration process. They indicated differential stomatal sensitivity to air humidity in the various cultivars, a characteristic which could be related to their geographical origins.

International audience; A comparative study of soil-plant water relations was conducted on three grapevine cultivars (Vitis vinifera L. cvv. carignane, merlot, shiraz) to investigate their adjustment to short-term and long-term water stress under field conditions. Adjustment was a function of the relative stability of the internal plant water status on diurnal and seasonal scales. On a diurnal scale, stomatal closure in response to water vapour pressure directly contributed to this stability. Indirect evidence suggested an influence of the soil water status on the diurnal stomatal activity. On a seasonal scale, sufficient leaf hydration required high whole-plant hydraulic conductance. This was achieved by either daily stomatal regulation or limitation of leaf area. Physiological adjustment to water stress through stomatal control was well developed in cv. carignane, which originated in a Mediterranean environment. However, cv. shiraz, which was of mesic origin, apparently adjusted to water stress by reducing leaf area. Our study demonstrates the utility of integrating data on stomatal conductance, leaf water potential and whole-plant hydraulic conductance to interpret whole plant adaptation to water stress, and elucidates two mechanisms by which genotypes differentially acclimate to water stress.

International audience; We have tested the following assumption for a spatially complex area of natural vegetation in Southern France. The spectral response of a mixed pixel is a linear combination of the individual responses of its components. The test has been done with HCMM data: each pixel (500m spatial resolution) has been characterized by its components defined as physiognomical vegetation units. Results from the analysis of multitemporal HCMM data indicate that the assumption is verified for albedos and surface temperatures.