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Climate change is expected to increase the frequency of droughts in most tropical regions in the coming decades. A passive phenomenon called hydraulic redistribution (HR) allows some plant species to take up water from deep and wet soil layers and redistribute it in the upper dry layers where other plants and soil biota can benefit from it. In addition, soil fertilization, particularly potassium (K), may also affect drought-adaptive mechanisms and increase water use efficiency (WUE) on poor and acidic tropical soils. The present study aimed at quantifying the role of HR and K fertilization on both wood productivity and WUE for stemwood production (WUEp) of Eucalyptus grandis plantations in Brazil under ambient and reduced (−37%) throughfall conditions. Tree transpiration was measured using trunk sap flow sensors over 21 months, and HR was estimated from the reverse sap flow (RF) observed in shallow roots over 18 months. Tree biomass, hydraulic conductance, soil water storage from surface to the water table (down to 17 m), and leaf photosynthetic capacity were also assessed. Significant HR was detected over the whole year, even during the rainy seasons. Neither potassium fertilization nor throughfall exclusion affected the velocity of water transported by HR, probably because most trees reached water table. Nonetheless, some photosynthetic capacity parameters, including the maximum photosynthetic rate (Amax), increased in treatments with K addition. This higher Amax combined with an increased sapwood area index, was associated with an increase in water uptake by 30 %–50 % and WUEp by 300 % relative to K-deficient trees. We postulate that the increase in WUEp promoted by potassium fertilization was partly driven by an increase in biomass allocation to wood, at the expense of foraging organs (leaves and roots), because K addition alleviated constraints on light and water use. Our results indicate that fertilizing E. grandis plantations with K is beneficial to both wood biomass production and WUEp.

Taro (Colocasia esculenta (L.) Schott) is a substantial staple food in most of the tropical regions. Prolonged exposure to drought impairs crop production worldwide. Tolerant crops have the best capability to cope and avoid drought, through phenotypic flexibility mechanisms. The water use efficiency (WUE) is well known in taro crops, but very scarce information is available relating to their nutrient efficiency (NER) in drought conditions. Our work provided pertinent information about the physiological variation of seven taro accessions subjected to seven months of drought, by recording the differences for nutrient allocation, chlorophyll canopy, biomass loss, and stress intensity. Significant relationships between control and drought treatments on WUE (+85%), total plant biomass (TPB, -26.8%), chlorophyll content index (CCI, +1.8%), and nutrient harvest index (NHI, +0.2%) were detected. Drought led to a generalized loss of TPB as drought avoidance strategy, although distinct phenotypic flexibility was observed through the root:shoot ratio (R:S) and stress index (SI) from the corm and shoot organs. The nutrient allocation from the corms to shoots, with NER increase registered in drought conditions, can be a valuable tool to complement the TPB and WUE productivity traits, to be used in taro breeding programs.

Key Message : Needle anatomic plasticity enables fast-growing maritime pine trees to cope with water limitations by enhancing both water-use efficiency and embolism resistance.Abstract : Maritime pine is a major forest tree grown for wood production in Southern Europe. A breeding program for the selection of fast-growing varieties was established in the 1960s, in France. In the context of climate change, the magnitude of phenotypic plasticity is a key issue for the prediction of putative decreases in productivity in the improved genetic material. We characterized the phenotypic plasticity of anatomical and physiological traits in two families with contrasting growth rates, under different water regimes, at the juvenile stage. An analysis of 38 traits showed that the fastest growing family had the greatest phenotypic plasticity for morphological, anatomic, chemical and physiological traits, enabling it to increase its water use efficiency and embolism resistance in response to water deficit. The observed modifications to the extravascular (proportion of spongy parenchyma in needles) and vascular (xylem in the needles and stem) compartments in response to water constraints were consistent with a higher water use efficiency and greater embolism resistance. The ability to optimize meresis and auxesis according to environmental conditions during needle development could be related to growth performance over time in different environmental conditions. These results suggest that selection for growth in maritime pine leads to the selection of individuals with greater phenotypic plasticity related to higher performances in non-limited conditions.

International audience; The selection of ideotypes combining high biomass production, high water use efficiency (WUE) and adequate wood properties is a major challenge in improving forest trees for industrial plantations. This issue was addressed in a field experiment evaluating 1130 clones of Eucalyptus urophylla * Eucalyptus grandis. Genomic selection using 3303 SNPs and the GBLUP model was carried out at age 55 months to select genitors and clones for stem volume (V55), WUE (using stable carbon isotope composition in stemwood, δ13C as a proxy, transformed into intrinsic WUE, Wi), as well as lignin (KL) and holocellulose (HCEL) contents. The variance components were mainly additive for δ13C(Wi), KL and HCEL, while they were highly non-additive for V55 (the ratio of dominance to additive variance was 130%). The narrow sense heritability was higher for Wi (h2 = 0.704) than for volume and wood traits (

Poplar plantations, widely used for the production of woody biomass, might be at high risk from the climate change-induced increase in the frequency of drought periods. Therefore, selecting improved genotypes, which are highly productive but with a high water use efficiency (WUE), is becoming a major target. The use of automated weighing systems in controlled environments facilitates the estimation of cumulated water loss and whole plant transpiration efficiency (TE). Differences in TE and leaf level intrinsic WUE as well as the contribution of underlying ecophysiological traits were determined in three contrasting P. nigra genotypes. Strong differences in TE among the selected genotypes were congruent with differences in leaf level intrinsic WUE. Our data show that a high total leaf area was overcompensated by a low per leaf area transpiration rate, leading to higher TE in highly productive genotypes originating from cool locations. Nocturnal water loss was relatively low but contributed to variations in TE among genotypes. In response to drought, leaf level WUE increased but not TE, suggesting that carbon losses due to whole plant respiration could offset the drought-induced increase in intrinsic WUE.

International audience; One of the challenges of eco-efficient agriculture is the development of operational farming practices to increase the level of agricultural production, maximize the efficiency of resource use and reduce environmental impacts. Based on the efficiency frontier concept and the decomposition of resource use efficiency, we used a three-quadrant framework allowing to carry a functional analysis of the cropping system. Using a data envelope approach, we established boundary curves which represent the maximum achievable performances (yield, N uptake) when N is the only limiting factor. This framework has been first implemented and tested using published data from 112 agronomic situations of rainfed durum wheat in experimental fields in northern Syria and then further applied on a data set of 245 agronomic situations of durum wheat in farmers’ fields in two grain-producing regions of Tunisia. The results demonstrated the impact of preceding crops: durum wheat following legumes or vegetable showed a higher potential for N uptake but with only a minor effect on its conversion into grains. This positive effect of diversified rotation on potential N uptake by durum wheat is partly of-set by increased N uptake gaps in farmer’s fields indicating a higher effect of other limiting factors.

Key message A genomic segment on maize chromosome 7 influences carbon isotope composition, water use efficiency, and leaf growth sensitivity to drought, possibly by affecting stomatal properties. Abstract Climate change is expected to decrease water availability in many agricultural production areas around the globe. Therefore, plants with improved ability to grow under water deficit are urgently needed. We combined genetic, phenomic, and physiological approaches to understand the relationship between growth, stomatal conductance, water use efficiency, and carbon isotope composition in maize (Zea mays L.). Using near-isogenic lines derived from a maize introgression library, we analysed the effects of a genomic region previously identified as affecting carbon isotope composition. We show stability of trait expression over several years of field trials and demonstrate in the phenotyping platform Phenodyn that the same genomic region also influences the sensitivity of leaf growth to evaporative demand and soil water potential. Our results suggest that the studied genomic region affecting carbon isotope discrimination also harbours quantitative trait loci playing a role in maize drought sensitivity possibly via stomatal behaviour and development. We propose that the observed phenotypes collectively originate from altered stomatal conductance, presumably via abscisic acid. Electronic supplementary material The online version of this article (10.1007/s00122-018-3193-4) contains supplementary material, which is available to authorized users.

Natural selection driven by water availability has resulted in considerable variation for traits associated with drought tolerance and leaf‐level water‐use efficiency (WUE). In Arabidopsis, little is known about the variation of whole‐plant water use (PWU) and whole‐plant WUE (transpiration efficiency). To investigate the genetic basis of PWU, we developed a novel proxy trait by combining flowering time and rosette water use to estimate lifetime PWU. We validated its usefulness for large‐scale screening of mapping populations in a subset of ecotypes. This parameter subsequently facilitated the screening of water use and drought tolerance traits in a recombinant inbred line population derived from two Arabidopsis accessions with distinct water‐use strategies, namely, C24 (low PWU) and Col‐0 (high PWU). Subsequent quantitative trait loci mapping and validation through near‐isogenic lines identified two causal quantitative trait loci, which showed that a combination of weak and nonfunctional alleles of the FRIGIDA (FRI) and FLOWERING LOCUS C (FLC) genes substantially reduced plant water use due to their control of flowering time. Crucially, we observed that reducing flowering time and consequently water use did not penalize reproductive performance, as such water productivity (seed produced per unit of water transpired) improved. Natural polymorphisms of FRI and FLC have previously been elucidated as key determinants of natural variation in intrinsic WUE (δ13C). However, in the genetic backgrounds tested here, drought tolerance traits, stomatal conductance, δ13C. and rosette water use were independent of allelic variation at FRI and FLC, suggesting that flowering is critical in determining lifetime PWU but not always leaf‐level traits., Accelerated flowering time achieved through nonfunctional and weak alleles of flowering time genes FRIGIDA (FRI) and FLOWERING LOCUS C (FLC) reduce water use in Arabidopsis thaliana without detrimentally impacting reproductive output.

There is increasing concern that due to land pressure and the need to maximize income, smallholder coffee farmers are increasingly being forced to cultivate in areas which are considered to be sub-optimal for coffee. Little is known about optimal coffee and tree combinations in these conditions and the degree to which crops and trees compete or are synergistic. In environmental conditions which were sub optimal for coffee cultivation in Nicaragua (1470 mm annual rainfall, 27 °C mean annual temperature and 455 m altitude compared to optima of 2000 mm, 23–24 °C and altitude between 1000 and 1400 m at that latitude, respectively), coffee and shade tree transpiration and soil evaporation were directly and separately measured in agroforestry (AFS) and full sun systems (FS). AFS was found to be a more efficient water user than FS because a greater proportion of rainfall was used by plant transpiration rather than being lost by soil evaporation. Plant transpiration accounted for 83% and 69% of evapotranspiration while soil evaporation represented 17% and 31%, in AFS and FS respectively. In AFS most of the water transpiration was due to coffee (72.5%) and much less by deciduous Tabebuia rosea (19%) and evergreen Simarouba glauca shade trees (8.5%). Furthermore, the study demonstrated the vastly different behaviour in water use by the shade trees. When in leaf, Tabebuia rosea transpired at four to six times the rate of evergreen Simarouba glauca, although crown sizes were similar. Contrasting precipitation between two consecutive years of study demonstrated that competition for water between coffee and shade tree occurred only in a severe dry season when coffee leaf water potential (LWP) reached its lowest values of −2.33 MPa in AFS. It was concluded that in most circumstances there was sufficient water for both coffee and trees, that coffee in AFS was a more efficient user of water than FS coffee, and that evergreen Simarouba glauca was more suitable as coffee shade tree compared to deciduous Tabebuia rosea in the sub optimal environmental condition studied. (Resume d'auteur)

The terrestrial carbon and water cycles are intimately linked: the carbon cycle is driven by photosynthesis, while the water balance is dominated by transpiration, and both fluxes are controlled by plant stomatal conductance. The ratio between these fluxes, the plant water-use efficiency (WUE), is a useful indicator of vegetation function.WUE can be estimated using several techniques, including leaf gas exchange, stable isotope discrimination, and eddy covariance. Here we compare global compilations of data for each of these three techniques.We show that patterns of variation in WUE across plant functional types (PFTs) are not consistent among the three datasets. Key discrepancies include the following: leaf-scale data indicate differences between needleleaf and broadleaf forests, but ecosystem-scale data do not; leaf-scale data indicate differences between C3 and C4 species, whereas at ecosystem scale there is a difference between C3 and C4 crops but not grasslands; and isotope-based estimates of WUE are higher than estimates based on gas exchange for most PFTs.Our study quantifies the uncertainty associated with different methods of measuring WUE, indicates potential for bias when using WUE measures to parameterize or validate models, and indicates key research directions needed to reconcile alternative measures of WUE.

The interactions between hydrological and ecological processes are key issues to improve our predictions of ecosystem responses to increasing droughts. However, predicting the dynamics and the impacts of vegetation water stress remains challenging because of complex ecohydrological feedbacks. The ecohydrological optimality approach proposes that functional adjustments within plant communities may buffer the increase in vegetation water stress despite local water shortage. This study aimed to test whether vegetation water stress may be invariant across contrasting plant communities, reflecting possible optimality processes. We addressed the following question: does a lower soil water storage capacity under the same climate generate greater vegetation water stress over time? We hypothesized that vegetation water stress would be buffered around a low and constant level through the adjustment of vegetation biomass productivity net primary productivity (NPP), evapotranspiration (ET) and/or water-use efficiency (WUE) in relation with local soil water storage capacity. We monitored 12 native plant communities distributed along a gradient of soil water storage capacity (ranging from 20 mm to 120 mm) during five successive years. Net primary productivity, ET, WUE as well as soil water dynamics were assessed and modelled for each plant community throughout the 5 years of study. Vegetation water stress was determined for each plant community as the deviation of between actual ET and their maximum ETm rate achieved under non-limiting conditions. We found that NPP and ET were together proportionally related to local soil water storage capacity across the 5 years of study while WUE did not differ between plant communities. Vegetation water stress was found quite similar for all plant communities whatever the soil water storage capacity. These results suggested that vegetation water stress was strongly buffered by the community-level plant growth rates and total water use along the soil gradient, but not by WUE. Our results suggest that stressful environments rarely exist for plant communities. A dynamic scaling relationship between NPP and ET may underpin the control of vegetation water stress over seasonal and pluriannual time-scales. Such results could contribute to better understanding processes associated with ecohydrological optimality and improve the predictions of vegetation dynamics under increasing droughts. (Resume d'auteur)

International audience; There is increasing interest in rapidly identifying genotypes with improved water use efficiency, exemplified by the development of whole plant phenotyping platforms that automatically measure plant growth and water use. Transpirational responses to atmospheric vapour pressure deficit (VPD) and whole plant water use efficiency (WUE, defined as the accumulation of above ground biomass per unit of water used) were measured in 100 maize (Zea mays L.) genotypes. Using a glasshouse based phenotyping platform with naturally varying VPD (1.5 to 3.8 kPa), a 2-fold variation in WUE was identified in well-watered plants. Regression analysis of transpiration versus VPD under these conditions, and subsequent whole plant gas exchange at imposed VPDs (0.8 to 3.4 kPa) showed identical responses in specific genotypes. Genotype response of transpiration versus VPD fell into two categories: 1) a linear increase in transpiration rate with VPD with low (high WUE) or high (low WUE) transpiration rate at all VPDs, 2) a non-linear response with a pronounced change point at low VPD (high WUE) or high VPD (low WUE). In the latter group, high WUE genotypes required a significantly lower VPD before transpiration was restricted, and had a significantly lower rate of transpiration in response to VPD after this point, when compared to low WUE genotypes. Change point values were significantly positively correlated with stomatal sensitivity to VPD. A change point in stomatal response to VPD may explain why some genotypes show contradictory WUE rankings according to whether they are measured under glasshouse or field conditions. Furthermore, this novel use of a high throughput phenotyping platform successfully reproduced the gas exchange responses of individuals measured in whole plant chambers, accelerating the identification of plants with high WUE.

Highlights • A model scaling stoma behaviour at leaf level is proposed. • The model is tested by reproducing natural variations of light intensity. • Stomatal aperture and photosynthesis decrease as a function of sugar accumulation. • Leaf anatomy influences the rapidity of stomatal conductance. • The model dissects intrinsic water use efficiency into traits of interest., Intrinsic water use efficiency (Wi), the ratio of net CO2 assimilation (A) over stomatal conductance to water vapour (gs), is a complex trait used to assess plant performance. Improving Wi could lead in theory to higher productivity or reduced water usage by the plant, but the physiological traits for improvement and their combined effects on Wi have not been clearly identified. Under fluctuating light intensity, the temporal response of gs is an order of magnitude slower than A, which results in rapid variations in Wi. Compared to traditional approaches, our new model scales stoma behaviour at the leaf level to predict gs and A during a diurnal period, reproducing natural fluctuations of light intensity, in order to dissect Wi into traits of interest. The results confirmed the importance of stomatal density and photosynthetic capacity on Wi but also revealed the importance of incomplete stomatal closure under dark conditions as well as stomatal sensitivity to light intensity. The observed continuous decrease of A and gs over the diurnal period was successfully described by negative feedback of the accumulation of photosynthetic products. Investigation into the impact of leaf anatomy on temporal responses of A, gs and Wi revealed that a high density of stomata produces the most rapid response of gs but may result in lower Wi.

UMR AGAP - équipe AFEF - Architecture et fonctionnement des espèces fruitièresData Availability: The relevant DOIs/accession numbers required to access raw data in Zenodo is: http://dx.doi.org/10.5281/zenodo.35030 (doi: 10.5281/zenodo.35030).; Water use efficiency (WUE) is a quantitative measurement which improvement is a major issue in the context of global warming and restrictions in water availability for agriculture. In this study, we aimed at studying the variation and genetic control of WUE and the respective role of its components (plant biomass and transpiration) in a perennial fruit crop. We explored an INRA apple core collection grown in a phenotyping platform to screen one-year-old scions for their accumulated biomass, transpiration and WUE under optimal growing conditions. Plant biomass was decompose into morphological components related to either growth or organ expansion. For each trait, nine mixed models were evaluated to account for the genetic effect and spatial heterogeneity inside the platform. The Best Linear Unbiased Predictors of genetic values were estimated after model selection. Mean broad-sense heritabilities were calculated from variance estimates. Heritability values indicated that biomass (0.76) and WUE (0.73) were under genetic control. This genetic control was lower in plant transpiration with an heritability of 0.54. Across the collection, biomass accounted for 70% of the WUE variability. A Hierarchical Ascendant Classification of the core collection indicated the existence of six groups of genotypes with contrasting morphology and WUE. Differences between morphotypes were interpreted as resulting from differences in the main processes responsible for plant growth: cell division leading to the generation of new organs and cell elongation leading to organ dimension. Although further studies will be necessary on mature trees with more complex architecture and multiple sinks such as fruits, this study is a first step for improving apple plant material for the use of water.

International audience; Six Populus deltoides Bartr. ex Marsh. × P. nigra L. genotypes were selected to investigate whether stem xylem anatomy correlated with gas exchange rates, water-use efficiency (WUE) and growth performance. Clonal copies of the genotypes were grown in a two-plot common garden test under contrasting water regimes, with one plot maintained irrigated and the other one subjected to moderate summer water deficit. The six genotypes displayed a large range of xylem anatomy, mean vessel and fibre diameter varying from about 40 to 60 μm and from 7.5 to 10.5 μm, respectively. Decreased water availability resulted in a reduced cell size and an important rise in vessel density, but the extent of xylem plasticity was both genotype and trait dependent. Vessel diameter and theoretical xylem-specific hydraulic conductivity correlated positively with stomatal conductance, carbon isotope discrimination and growth performance-related traits and negatively with intrinsic WUE, especially under water deficit conditions. Vessel diameter and vessel density measured under water deficit conditions correlated with the relative losses in biomass production in response to water deprivation; this resulted from the fact that a more plastic xylem structure was generally accompanied by a larger loss in biomass production.

Summary 1. In 2001, Loreau and Hector proposed a method to calculate the effect of biodiversity on ecosystem-level properties that distinguished selection effects (SE) from complementarity effects (CE). The approach was designed and has been widely used for the study of yield in mixed-species situations taking into account the relative abundance of each species in ecosystem-level yield. However, complex functional traits commonly used to integrate ecosystem-level properties that cannot be analysed like yield data because the weighted contribution of each species is not determined by its relative abundance. 2. We adapted the original method by clearly identifying ecologically meaningful weighting coefficients to represent species-specific contributions to ecosystem function. 3. We applied the adapted method of analysis to tree foliar carbon isotope composition in an experimental plantation in order to test the influence of species richness on plot water use efficiency (WUEplot). The appropriate weights for the WUEplot of each species are leaf CO2 assimilation rate. 4. We observed a large range of WUEplot and biodiversity effects among plots. The absence of a significant SE on WUEplot indicated that the overall net biodiversity effect was primarily driven by a CE. The net biodiversity effect and CE were mostly negative, suggesting that interspecific interactions resulted in a decrease in the ratio between carbon acquisition and transpiration at the ecosystem level. 5. The application of the method to complex components of ecosystem functioning provides important new insights into the practical and conceptual aspects of functional biodiversity research.

Throughout the world, huge areas have been occupied by monospecific tree plantations in order to fulfil the increasing demand for industrial wood products. The use of mixed-species plantations has recently been advocated as a potential compromise between maintaining high-volume wood production and conserving other ecosystem services. Yet little is known about the impact of tree species mixture on species- and ecosystem-level carbon accumulation and water use in mixed plantations. We combined data on above-ground biomass, xylem sap flux density, and the carbon and oxygen isotope composition of leaves and needles in a boreal plantation to test whether different levels of species mixture would impact tree- and plot-level biomass production, transpiration and water use efficiency. Data were recorded in 22 20-x-20-m plots (7 for transpiration) randomly allocated to either monocultures or to two-, three-, and five-species mixtures of Scots pine (Pinus sylvestris), Norway spruce (Picea abies), Silver birch (Betula pendula), Common alder (Alms glutinosa) and Siberian larch (Larix sibirica). At tree level, for a given species, we found significant differences among mixtures in transpiration and water use efficiency, though species mixture had no impact on above-ground biomass. At plot level, a large variability in functioning among mixtures was observed, but increasing the number of species in the mixture did not enhance productivity, transpiration or water use efficiency. The presence in mixtures of a high performing species like birch brought about changes in the canopy structure which in turn may have led to changes in micro-environmental conditions. Such changes could have contributed to explain differences in transpiration and water use efficiency among mixtures. We concluded that mixing locally-adapted species under non-limiting soil water conditions did not provide any benefit for ecosystem-level carbon accumulation and water use at this young ontogenic stage, but our study does not preclude that some benefits might arise at older stages. (C) 2013 Elsevier B.V. All rights reserved.

Aims: Genetic variability in grapevine cultivars may influence their strategy to cope with drought through stomatal regulation of transpiration rate. The aim of the present study was to evaluate the stomatal sensitivity of five cultivars (EkigaIna, Grenache. Marselan, Mourvedre. and Syrah) to soil water status and air water vapor pressure deficit (VPD). Methods and results: Leaf gas exchange and canopy light interception efficiency (epsilon(1)) were evaluated through a wide range of predawn leaf water potential (psi(PD)) measurements in a field experiment in Southern France. Additionally. greenhouse experiments were carried out to monitor stomatal response to increasing VPD levels. Ekigaina showed a strong isohydric behavior with the highest decrease in leaf gas exchange in response to soil water stress and VPD. Mourvedre and Grenache showed a similar but relatively less extreme behavior. These three cultivars showed a constant leaf water status during the day through stomatal regulation and a strong decrease in epsilon(1). In contrast, Syrah and Marselan displayed anisohydric behavior as they presented a less sensitive stomatal control. Both cultivars showed fluctuating midday leaf water potential and Marselan was the least affected in tem of c. Conclusion: This study demonstrated that grape cultivars differed in their stomatal response to soil water deficit and VPD. For a given cultivar, a similar stomatal behavior was found in response to both tyro and VPD. Significance and impact of the results: Adaptation to drought and viticulture viability in hot and dry environments could be achieved by identifying and breeding cultivars with drought tolerance traits, Objectifs : La variabilité génétique existante chez les cépages de vigne peut affecter leur stratégie d’adaptation à la sécheresse en régulant la transpiration au travers de la fermeture des stomates. L’objectif du travail a été d’évaluer la sensibilité des stomates de cinq cultivars (Ekigaïna, Grenache, Marselan, Mourvèdre et Syrah) à la disponibilité en eau du sol et au déficit de pression de vapeur (VPD). Méthodes et résultats : Les échanges gazeux des feuilles et l’efficience d’interception du rayonnement (ei) ont été évalués dans une large gamme des valeurs de potentiel hydrique de base (yPD) en conditions de terrain dans le Sud de la France. En outre, une expérimentation complémentaire en serre a été réalisée pour analyser la réponse des stomates face à une augmentation du VPD. L’Ekigaïna a présenté un caractère ioshydrique très marqué avec la plus grande diminution des échanges gazeux en réponse au déficit hydrique du sol et au VPD. Le Mourvèdre et le Grenache ont présenté un comportement similaire bien que moins extrême que l’Ekigaïna. Ces trois cultivars ont montré un potentiel hydrique foliaire constant pendant la journée à cause d’une forte régulation stomatique et une diminution de ei. Par contre, le Syrah et le Marselan, ont montré un comportement anisohydrique avec un control stomatique moins sensible. Les deux cultivars ont présenté une diminution du potentiel hydrique foliaire à midi tandis que le Marselan a été le moins affecté en termes de ei. Conclusions : La présente étude montre que les cultivars présentent des différences dans leur réponse au déficit hydrique du sol et au VPD. Pour un cultivar donné, un comportement stomatique similaire a été observé en réponse au yPD et au VPD. Impacts et signification des résultats : L’adaptation à la sécheresse et la viabilité de la viticulture sur de climats chauds et secs pourrait être atteint par la sélection de cultivars avec de caractères de tolérance.

International audience; Whereas the effects of water and nitrogen (N) on plant Delta C-13 have been reported previously, these factors have scarcely been studied for Delta O-18. Here the combined effect of different water and N regimes on Delta C-13, Delta O-18, gas exchange, water-use efficiency (WUE), and growth of four genotypes of durum wheat [Triticum turgidum L. ssp. durum (Desf.) Husn.] cultured in pots was studied. Water and N supply significantly increased plant growth. However, a reduction in water supply did not lead to a significant decrease in gas exchange parameters, and consequently Delta C-13 was only slightly modified by water input. Conversely, N fertilizer significantly decreased Delta C-13. On the other hand, water supply decreased Delta O-18 values, whereas N did not affect this parameter. Delta O-18 variation was mainly determined by the amount of transpired water throughout plant growth (T-cum), whereas Delta C-13 variation was explained in part by a combination of leaf N and stomatal conductance (g(s)). Even though the four genotypes showed significant differences in cumulative transpiration rates and biomass, this was not translated into significant differences in Delta O-18(s). However, genotypic differences in Delta C-13 were observed. Moreover, similar to 80% of the variation in biomass across growing conditions and genotypes was explained by a combination of both isotopes, with Delta O-18 alone accounting for similar to 50%. This illustrates the usefulness of combining Delta O-18 and Delta C-13 in order to assess differences in plant growth and total transpiration, and also to provide a time-integrated record of the photosynthetic and evaporative performance of the plant during the course of crop growth.

International audience; Genotypic variability for productivity, wateruse efficiency and leaf traits in 33 genotypes selected from an F1 progeny of Populus deltoides Bartr. ex Marsh • Populus trichocarpa L. was explored under optimal and moderate water-deficit conditions. Saplings of the 33 genotypes were grown in a two-plot open field at INRA Orle´ ans (France) and coppiced every year. A moderate water deficit was induced during two successive years on one plot by withholding irrigation, while the second one remained irrigated (control). Stem biomass and leaf structure (e.g., specific leaf area and leaf area) were measured in 2004 and 2005 and functional leaf traits (e.g., carbon isotope discrimination, D) were measured only in 2004. Tolerance to water deficit was estimated at genotype level as the ability to limit losses in biomass production in water deficit versus control trees. Stem biomass, leaf structure and D displayed a significant genotypic variability whatever the irrigation regime. For all traits, genotype ranks remained stable across years for similar irrigation conditions. Carbon isotope discrimination scaled negatively with productivity and leaf nitrogen content in controls. The most productive genotypes were the least tolerant to moderate water deficit. No relationship was evidenced between D and the level of tolerance to water deficit. The relationships between traits evidenced in this collection of P. deltoides • P. trichocarpa F1 genotypes contrast with the ones that were previously detected in a collection of P. deltoides • Populus nigra L. cultivars tested in the same field trial.

International audience; The effects of drought, enhanced UV-B radiation and their combination on plant growth and physiological traits were investigated in a greenhouse experiment in two populations of Populus cathayana Rehder originating from high and low altitude in south-west China.* In both populations, drought significantly decreased biomass accumulation and gas exchange parameters, including net CO2 assimilation rate (A), stomatal conductance (gs), transpiration rate (E) and photosynthetic nitrogen use efficiency (PNUE). However, instantaneous water use efficiency (WUEi), transpiration efficiency (WUET), carbon isotope composition (δ13C) and nitrogen (N) content, as well as the accumulation of soluble protein, UV-absorbing compounds and abscisic acid (ABA) significantly increased in response to drought. On the other hand, cuttings from both populations, when kept under enhanced UV-B radiation, showed very similar changes, as under drought, in all above-mentioned parameters.* Compared with the low altitude population, the high altitude population was more tolerant to drought and enhanced UV-B, as indicated by the higher level of biomass accumulation, gas exchange, water-use efficiency, ABA concentration and UV-absorbing compounds.* After one growing season of exposure to different UV-B levels and watering regimes, the decrease in biomass accumulation and gas exchange, induced by drought, was more pronounced under the combination of UV-B and drought. Significant interactions between drought and UV-B were observed in WUEi, WUET, δ13C, soluble protein, UV-absorbing compounds, ABA and in the leaf and stem N, as well as in the leaf and stem C:N ratio.* Our results showed that UV-B acts as an important signal allowing P. cathayana seedlings to respond to drought and that the combination of drought and UV-B may cause synergistically detrimental effects on plant growth.; Les effets d'une sécheresse, d'une augmentation du rayonnement UV-B et de leur combinaison ont été étudiés sur la croissance et les caractéristiques physiologiques de plants de deux populations de Populus cathayana Rehder originaires de haute et basse altitude dans le sud-ouest de la Chine.* Dans les deux populations, la sécheresse a réduit de manière significative l'accumulation de biomasse et les échanges gazeux foliaires, y compris l'assimilation nette (A) de CO2, la conductance stomatique (gs), la transpiration (E) et l'efficience photosynthétique d'utilisation de l'azote (PNUE). Toutefois, l'efficience instantanée d'utilisation de l'eau (WUEi), l'efficience de transpiration (WUET), la composition isotopique du carbone (δ13C) et le contenu en azote (N), ainsi que l'accumulation de protéines solubles, des composés absorbant les UV et de l'acide abscissique (ABA) ont présenté une augmentation significative en réponse à la sécheresse. D'autre part, des boutures des deux populations, quand elles ont été conservées sous un rayonnement UV-B renforcé, ont montré des changements de tous les paramètres mentionnés ci-dessus, similaires à ceux induits par la sécheresse.* Par rapport à la population de faible altitude, la population de haute altitude, était plus tolérante à la sécheresse et au renforcement du rayonnement UV-B; cela s'est traduit par le niveau plus élevé d'accumulation de biomasse, d'échanges gazeux, de l'efficience d'utilisation de l'eau, de la concentration d'ABA et des composés absorbant les UV.* Après une saison de croissance, la diminution de l'accumulation de biomasse et des échanges gazeux induite par la sécheresse, était plus prononcée dans le cadre de la combinaison du rayonnement UV-B et de la sécheresse. Des interactions significatives entre sécheresse et UV-B ont été observées pour WUEi, WUET, δ13C, les protéines solubles, les composés absorbant les UV, l'ABA et l'azote des feuilles et des tiges, ainsi que pour le rapport C/N des feuilles et des tiges.* Nos résultats ont montré que les UV-B agissent comme un signal important en permettant aux jeunes plants de P. cathayana de faire face à la sécheresse et que la combinaison de la sécheresse et des UV-B peut causer par synergie des effets néfastes pour la croissance des plants.

• We examined the relationships between productivity, leaf traits and carbon isotope discrimination in bulk leaf matter (Δl) and in phloem sap (Δs) from more than 5-year-old trees belonging to Populus deltoides × P. nigra and Populus trichocarpa × P. deltoides; trees were grown in alluvial and non alluvial sites in a commercial poplar plantation. • On both sites, a large genetic variability was evidenced for all variables. The genotypic ranking remained stable between years for all variables, while it differed between sites. Δl scaled positively with Δs and neither Δl nor Δs were correlated with productivity. A significant genotype by site interaction was evident for all variables. The non alluvial site resulted in lower productivity, and in thicker/denser leaves with lower nitrogen and carbon contents. Noteworthy, the genotypic ranking for Δl measured at the alluvial site was similar to that previously established in a glasshouse. • As observed in previous studies from younger trees, there is a potential to select genotypes, combining high productivity and high water-use efficiency, for growth in moderately drought-prone areas., • La productivité, des caractères foliaires et la discrimination isotopique vis-à-vis du carbone de la matière organique des feuilles (Δl) et de la sève élaborée (Δs) ont été étudiés chez Populus deltoides × P. nigra et Populus trichocarpa × P. deltoides à partir d’arbres âgés de plus de cinq ans, cultivés en peupleraie sur des sites alluviaux et non alluviaux. • Des différences génotypiques ont été observées pour toutes les variables. Le classement des génotypes était conservé entre deux années, alors qu’il variait entre sites une année donnée. Δl était corrélé positivement avec Δs et aucun lien n’a été détecté entre Δl ou Δs et productivité. Une interaction significative entre génotype et site a été observée pour toutes les variables. Les arbres du site non alluvial se caractérisaient par une plus faible productivité et des feuilles plus épaisses/denses avec des teneurs en azote et en carbone plus faibles. De façon intéressante, le classement des génotypes pour Δl était maintenu entre les expériences réalisées sur site alluvial et celles précédemment menées en serre. • Toutes expériences confondues, il semble possible de sélectionner des génotypes productifs et efficients afin d’étendre les plantations à des terrains enclins à des sécheresses modérées.

International audience; • Here we tested whether some leaf traits could be used as predictors for productivity in a range of Populus deltoides × P. nigra clones. These traits were assessed in 3-yr-old rooted cuttings from 29 clones growing in an open field trial, in a five randomized complete block design, under optimal irrigation. • Variables were assigned to four groups describing productivity (above-ground biomass, total leaf area), leaf growth (total number of leaves increment rate), leaf structure (area of the largest leaf, specific leaf area, carbon and nitrogen contents), and carbon isotope discrimination in the leaves (∆). • High-yielding clones displayed larger total leaf area and individual leaf area, while no correlation could be detected between productivity and either leaf structure or ∆. By contrast, ∆ was negatively correlated with number of leaves increment rate and leaf N content. • Our study shows that there is a potential to improve water-use efficiency in poplar without necessarily reducing the overall productivity.