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Identifiant CAB : Accession Number: 20113387928 ; National audience; Biomass enjoys special status amongst the sources of renewable energy because it is a source both of energy vectors and of carbonaceous molecules. According to European directives, the contribution of the biomass to the production of energy will triple in the next ten years. Faced with this challenge, it is commonly accepted that the main potential for growth comes from agriculture via dedicated production systems. Research in France on the use of perennial woody plants as crops dedicated to biomass production was conducted by INRA, FCBA and the AILE association several decades ago, in the wake of the first oil shocks. Trials were carried out in intensive forestry using stump sprouting trees: short and very short rotation coppices (SRC and VSRC, respectively). These trials showed that with productive varieties of species such as poplar, willow or eucalyptus grown by rotations of 2 to 7 years depending on the initial planting density, biomass output can reach between 8 and 15 metric tons of dry material per hectare per annum. Based on the results obtained by these three organisations on the basis of several dozen hectares of experimentally grown crops, the influence of a few cropping factors on the productivity of SRCs and VSCRs and the impact of the latter on site fertility were demonstrated. Some data concerning the energy and financial balances for these crops is also presented. Finally, some insight is provided about the role of SRCs and VSCRs in the area of environmental engineering (remediation, phytoextraction). By way of conclusion, a non-exhaustive list of ongoing research projects relating to dedicated systems for producing woody biomass is drawn up. Three main areas are currently apparent: improving the productivity and quality of the products derived from the biomass, acquiring better knowledge of the impact on the physical environment and biodiversity, and defining the criteria that determine their acceptability.; Parmi les sources d’énergies renouvelables, la biomasse bénéficie d’un statut particulier car elle est à la fois source de vecteurs énergétiques et source de molécules carbonées. D’après les directives européennes, la contribution de la biomasse à la production d’énergie triplera d’ici dix ans. Face à ce challenge, il est admis que le principal potentiel de croissance proviendra principalement de l’agriculture via des systèmes de production dédiés. Les recherches conduites en France sur l’utilisation de ligneux pérennes pour des cultures dédiées à la production de biomasse ont été engagées par l’INRA, FCBA et l’association AILE il y a plusieurs décennies, suite aux premiers chocs pétroliers. Des essais ont ainsi été conduits sur une sylviculture intensive d’arbres rejetant de souche : les taillis à courte et à très courte rotation (respectivement TCR et TTCR). Ces essais ont montré qu’avec des variétés productives d’espèces comme le Peuplier, le Saule ou l’Eucalyptus cultivées avec des rotations de 2 à 7 ans selon la densité initiale de plantation, il est possible d’atteindre des productions de biomasse comprises entre 8 et 15 tonnes de matière sèche par hectare et par an. S’appuyant sur des résultats obtenus par les trois organismes cités ci-dessus sur la base de plusieurs dizaines d’hectares d’expérimentations, l’influence de quelques facteurs culturaux sur la productivité des TCR et TTCR et l’impact de ces derniers sur la fertilité des stations sont démontrés. Quelques éléments sur les bilans énergétique et financier de ces cultures sont également présentés. Un éclairage est enfin apporté sur le rôle des TCR et TTCR dans le domaine du génie écologique (remédiation, phytoextraction). En guise de conclusion, une liste non exhaustive de projets de recherche en cours portant sur les systèmes dédiés à la production de biomasse ligneuse est dressée. Sur ce thème, trois axes principaux se dégagent actuellement : améliorer la productivité et la qualité des produits qui en sont issus, mieux connaître les impacts sur le milieu physique et la biodiversité, et cerner les critères de leur acceptabilité.

International audience

International audience; • It is of importance, when comparing physiological responses of leaves to environmental constraints among different genotypes, to take into account any effect related to leaf position and age within the canopy that might interfere with the response to the constraints. • To document such effects, photosynthetic capacity and tolerance to heat and to oxidation were measured on leaves from the top to the bottom of three-month-old single-stem rooted cuttings of Populus deltoides × P. nigra genotypes, ‘Dorskamp’ and ‘Luisa_Avanzo’, thus taking into account a gradient of ages from youngest and still expanding (top) to oldest and fully expanded (bottom) leaves. • All recorded traits were tightly linked to the age of the leaves. Photosynthetic capacity gradually increased during leaf expansion, in parallel with chlorophyll content and relative nitrogen allocation to RuBisCO and to bioenergetics. On the contrary, dark respiration gradually decreased during leaf expansion until a minimum value was reached at maturity. Compared to expanding leaves, young mature leaves were characterized by a lower sensitivity to heat and a higher one to oxidations generated by methyl-viologen. • Leaf characteristics appeared to vary along the stem to a larger extent than between the two genotypes that display largely different productivities in plantations.; •Pour comparer de manière fiable la réponse physiologique de feuilles de différents génotypes aux contraintes abiotiques, il est important de prendre en compte les effets liés à la position et à l’âge des feuilles au sein de la canopée pouvant interférer avec la réponse à la contrainte. •Afin de documenter de tels effets, les capacités photosynthétiques et la tolérance à la chaleur et aux oxydations ont été mesurées sur des feuilles réparties tout le long de la tige de boutures de 3 mois des génotypes de Populus deltoides × P. nigra, ‘Luisa_Avanzo’ et ‘Dorskamp’. •Tous les traits mesurés présentaient une forte variabilité liée à l’âge des feuilles. Les capacités photosynthétiques augmentaient graduellement durant l’expansion foliaire, en parallèle avec les teneurs en chlorophylles et avec l’allocation d’azote à la RuBisCO et au transfert photosynthétique d’électrons. Au contraire, la respiration diminuait graduellement durant l’expansion foliaire jusqu’à ce qu’une valeur minimum soit atteinte à maturité de la feuille. En comparaison avec les feuilles en croissance, les jeunes feuilles matures étaient caractérisées par une tolérance plus grande à la chaleur et plus faible aux oxydations générées par du méthylviologène. •Les caractéristiques foliaires variaient plus le long de la tige qu’entre les deux génotypes, pourtant connus pour leurs différences de niveau de productivité en plantation.

International audience; The quantitative and qualitative estimation of aboveground biomass production is essential for short-rotation forestry. Indirect methods of biomass estimation have been developed based on the establishment of regressions between biomass components and tree dimensions as well as canopy architecture. The difficulty encountered with this method is to know whether, and to what degree, the obtained equations can be used under contrasting environmental conditions and for different genetic backgrounds. In the present study, allometric equations were developed linking tree dry weight (stem, branch and aboveground tree dry weight) with stem circumference, stem height and number of sylleptic branches for five 2-year-old intra- as well as interspecific poplar (Populus) families growing at three contrasting sites in Europe, i.e. Northern Italy, Central France and Southern UK. The multiple regression method was used to find the most precise biomass equation which represents the genetic variation for each family at each site, independently, as well as a common equation involving all families and sites. The two F1 P. deltoides × P. trichocarpa families and the F1 P. alba × P. alba family were the most productive families irrespective of site. However, different patterns in biomass accumulation were observed between these crosses. The F1 P. alba × P. alba family accumulated significantly more biomass in branches than in the stem as compared to both other families. In most cases, different transformations of the dependent variables were needed to improve the linear equations. Stem circumference was superior in predicting tree dry weight, but stem height and number of sylleptic branches were often needed to optimize the equations dependent on family and site. A standardized equation combining the five families and the three sites explained more than 95% of the observed variation for tree dry weight. However, there was a significant family effect, and at the UK site, a severe rust attack could have affected the relationships among the three predictors resulting in a significantly different equation for this site. When the UK site was excluded from the model, no overall site effect was observed. Thus, a single equation might be applied at family level regardless of the environmental conditions when stand density, age and plantation management are comparable.

International audience; Twelve poplar (Populus) genotypes, belonging to different taxa and to the sections Aigeiros and Tacamahaca, were studied during the third growing season of the second rotation of a high density coppice culture. With the objective to highlight the relationships between leaf traits, biomass production and taxon as well as the influence of canopy position, anatomical and morphological leaf characteristics (i.e. thickness of epidermis, of palisade and spongy parenchyma layers, density and length of stomata, leaf area, specific leaf area (SLA) and nitrogen concentration) were examined for mature leaves from all genotypes and at two canopy positions (upper and lower canopy). Above ground biomass production, anatomical traits, stomatal and morphological leaf characteristics varied significantly among genotypes and between canopy positions. The spongy parenchyma layer was thicker than the palisade parenchyma layer for all genotypes and irrespective of canopy position, except for genotypes belonging to the P. deltoides × P. nigra taxon (section Aigeiros). Leaves at the upper canopy position had higher stomatal density and thicker anatomical layers than leaves at the lower canopy position. Leaf area and nitrogen concentration increased from the bottom to the top of the canopy, while SLA decreased. Positive correlations between biomass production and abaxial stomatal density, as well as between biomass production and nitrogen concentration were found. A principal component analysis (PCA) showed that genotypes belonging to the same taxon had similar anatomical characteristics, and genotypes of the same section also showed common leaf characteristics. However, Wolterson (P. nigra) differed in anatomical leaf characteristics from other genotypes belonging to the same section (section Aigeiros). Hybrids between the two sections (Aigeiros × Tacamahaca) expressed leaf characteristics intermediate between both sections, while their biomass production was low.; Douze génotypes de peuplier (Populus), appartenant à différents taxa ainsi qu’aux sections Aigeiros et Tacamahaca, ont été étudiés durant la troisième saison de croissance de la deuxième rotation d’une plantation à forte densité. L’objectif de l’expérience était demettre en évidence les relations entre les caractères foliaires, la production de biomasse et le taxon, ainsi que l’influence de la position des feuilles dans la canopée. Pour ce faire, diverses caractéristiques anatomiques et morphologiques des feuilles (épaisseur des épidermes et des parenchymes palissadique et lacuneux, densité et longueur des stomates, surface foliaire, surface foliaire spécifique (SLA) et teneurs en azote) ont été déterminées pour des feuilles matures de tous les génotypes et à deux hauteurs dans la canopée (haute et basse). La production de biomasse aérienne et les caractères foliaires anatomiques et morphologiques variaient significativement entre génotypes et entre positions dans la canopée. Le parenchyme lacuneux était plus épais que le parenchyme palissadique pour tous les génotypes et quel que soit la hauteur dans la canopée, excepté pour les génotypes appartenant au taxon P. deltoides × P. nigra (section Aigeiros). Les feuilles du sommet de la canopée présentaient des densités de stomates et des épaisseurs de tissus plus importantes que les feuilles de la base de la canopée. La surface des feuilles et leurs teneurs en azote augmentaient de la base vers le sommet de la canopée, tandis que les SLA diminuaient. Des corrélations positives entre la production aérienne de biomasse et la densité de stomates abaxiale ainsi qu’entre la production de biomasse et la teneur en azote foliaire ont été mises en évidence. Une analyse en composantes principales (ACP) a montré que les génotypes appartenant au même taxon présentaient des caractéristiques anatomiques similaires, et que les génotypes de la même section montraient également des caractéristiques foliaires communes. Wolterson (P. nigra) était cependant différent des autres génotypes de la même section (section Aigeiros) en termes de caractères anatomiques. Les hybrides entre les deux sections (Aigeiros × Tacamahaca) présentaient des caractéristiques foliaires intermédiaires entre les sections, alors que leur production de biomasse était faible.

International audience; To test if some leaf parameters are predictors of productivity in a range of Populus deltoides (Bartr.) Marsh. × P. nigra L. clones, we assessed leaf traits and productivity in 2-month-old rooted cuttings from 31 clones growing in 4-l pots in a greenhouse, under conditions of controlled temperature and optimal irrigation. We evaluated four groups of variables describing (1) productivity (total biomass), (2) leaf growth (total leaf number increment and total leaf area increment rate), (3) leaf structure (specific leaf area and nitrogen and carbon contents) and (4) carbon isotope discrimination (∆), which is negatively correlated with time-integrated water-use efficiency. High-yielding clones did not necessarily display high leaf growth rates, but they displayed a larger total leaf area, lower specific leaf area and lower leaf nitrogen concentration than clones with low productivity. Total leaf area was mainly controlled by maximal individual leaf area and total leaf area increment rate (r = 0.51 and 0.56, respectively). Carbon isotope discrimination did not correlate with total biomass, but it was associated with total number of leaves and total leaf area increment rate (r = 0.39 and 0.45, respectively). Therefore, leaf area and specific leaf area were better indicators of productivity than leaf growth traits. The observed independence of ∆ from biomass production provides opportunities for selecting poplar clones combining high productivity and high water-use efficiency.

International audience; Responses to successive drought and re-watering cycles (1–3 cycles) were compared in greenhouse-grown cuttings of Populus × canadensis (Moench) clones, ‘Luisa_ Avanzo’ and ‘Dorskamp.’ Total leaf number increment rate, duration of leaf expansion, total and individual leaf area expansion rates and stomatal conductance were recorded periodically during the experiment. Soil water content (SWC) and predawn leaf water potential (ØWP) were measured four times during each drought cycle. In parallel, relative leaf water content (RWC) and specific leaf area (SLA) were estimated on leaves collected from the top to bottom of each cutting. Under well-watered conditions, ‘Luisa_Avanzo’and ‘Dorskamp’differed in their patterns of leaf area expansion. Although duration of leaf expansion was similar between clones, ‘Luisa_ Avanzo’exhibited higher total leaf number increment rates and individual leaf area increases than ‘Dorskamp.’ As a result, ‘Luisa_Avanzo’ cuttings reached larger individual and total leaf areas than ‘Dorskamp.’‘Dorskamp’leaves had lower SLA than ‘Luisa_Avanzo’ leaves. In response to successive drought cycles, both clones underwent decreases in total leaf number increment rates and in total leaf area expansion rates, but both whole-plant and individual leaf areas were drastically reduced only in ‘Luisa_Avanzo.’ ‘Dorskamp’ maintained a constant leaf area as a result of an increase in the duration of leaf expansion during drought and a significant stimulation of individual leaf area expansion rate and total leaf number increment rate in response to re-watering. Drought caused a greater decrease in SLA in ‘Luisa_Avanzo’ than in ‘Dorskamp.’ Expanded leaves of ‘Dorskamp’ were constitutively dense or thick, or both, whereas leaves of ‘Luisa_Avanzo’ became dense or thick, or both, only in response to drought. In both clones, re-watering caused partial recovery of SLA to control values. Our data confirm previous field and greenhouse observations that ‘Dorskamp’ is more tolerant to successive drought and re-watering cycles than ‘Luisa_Avanzo.’We conclude that this difference is mainly attributable to the plasticity of ‘Dorskamp’ after re-watering, rather than to clonal differences in drought responses.