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The resistance of different genotypes to abiotic stress may be due to genetic effects and/or to phenotypic plasticity allowing them to acclimate to variable conditions. The contribution of one or the other mechanism determines different strategies with implications for the species conservation and adaptive management. In this study, the ecophysiological response to drought of Nothofagus pumilio provenance sites (humid, mesic and xeric) from contrasting precipitation regimes was evaluated in a common garden trial. Seedlings were submitted to progressive drought by withdrawing irrigation (control vs water deficit). Assuming a genetic base determined by selection pressures, populations from more xeric sites are expected to show higher resistance to drought, e. g., higher resistance to xylem cavitation and safety margin, stronger stomatal control and osmotic adjustment. Vulnerability to cavitation curves were performed, and the percentage loss of conductivity (P12, P50, P88 and slope) was obtained. The water potential at turgor loss point (TLP) and the osmotic potential at full turgor (π100) were calculated from pressure–volume curves. The humid site showed a significantly higher P50 value than the mesic and the xeric sites. Pre-dawn water potential differed between the provenances from xeric and mesic conditions under severe water deficit. Natural selection was inferred from the comparison of differentiation at neutral markers and phenotypic traits (FST vs. PST), with signals of adaptive variation (PST > FST) for stomatal density, specific leaf area, TLP, π100 and stomatal conductance. Results suggest a differential adaptive capacity to drought of N. pumilio provenance sites that could be evidencing local adaptation to their home environment.

Microdensity profiles of Douglas-fir's clones and weather data were used to study phenotypic plasticity (dendroplasticity). Within-ring microdensity was interpreted as the variation of tree response to drought constraints during selected growing seasons. An original norm of reaction was obtained by pairing evident points of abrupt changes in tree-ring microdensity profiles and in weather indices. The coefficients of the non-linear models adjusted to the reaction norms were analysed as dendroplasticity variables. Dendroplasticity variables were significantly different between geographical locations, years and clones. Heritability of the dendroplasticity variables ranged from low to high and was similar to heritability values of microdensity variables such as mean ring density (MRD). Coefficients of genetic variation of dendroplasticity variables were intermediate between those of wood density and growth variables. Dendroplasticity variables were phenotypically and genetically related to ring microdensity variables, more strongly to latewood variables. Dendroplasticity provides retrospective, synthetic and easy-to-interpret information about tree response to the variation of the balance between water availability and water demand during the growing season. The proposed model of dendroplasticity is described by a number of parameters that are linked to a biological meaning. Our results suggest that there is a potential for adaptation to drought in Douglas-fir, with two mechanisms involved: at individual level, short-term plastic response during the growing season and, at population level, long-term, between-generation, evolution process.

For a number of years in certain regions of France the Douglas-fir trees (Pseudotsuga menziesii [Mirb.] Franco) have presented symptoms of withering which have been attributed to drought. Our results show that the hydraulic function of the wood plays a part in the resistance of the Douglas-fir to dry conditions. Narrower cellular conduits, and therefore a greater wood density, contribute to the survival of trees confronted with a period of a marked water deficit. This idea is confirmed by the existence of significant relationships between wood density and hydraulic properties of wood in which the raw sap circulates, and also by the relationships found between the ecological preferences of specimens in their area of origin and the density of their wood in regions of France where they have been introduced. Those coming from dry regions have a tendency to develop wood with characteristics similar to that of trees which have survived drought. While the relationship between wood density and survival has been demonstrated, the differences in the nature of this relationship between different sites show that the mechanisms involved are complex and to a large extent still not understood. Le douglas (Pseudotsuga menziesii [Mirb.] Franco) présente depuis quelques années dans certaines régions de France des symptômes de dépérissement que nous attribuons à la sécheresse. Nos résultats montrent que le fonctionnement hydraulique du bois joue un rôle dans la résistance du douglas à la sécheresse: des conduits cellulaires plus étroits, c'est-à-dire une densité plus élevée, favoriseraient la survie d'arbres confrontés à un épisode de déficit en eau marqué. Cette idée est renforcée par l'existence de relations significatives entre densité du bois et propriétés hydrauliques du bois dans lequel circule la sève brute, et par les relations trouvées entre préférences écologiques de provenances dans leur aire d'origine et densité de leur bois dans les régions d'introduction en France: les provenances issues de régions sèches ont tendance à développer un bois possédant des caractéristiques proches de celles des survivants à la sécheresse. Si la relation densité du bois–survie a bien été mise en évidence, des différences entre sites dans la nature de cette relation montrent que les mécanismes impliqués sont complexes et encore largement incompris. Seit einigen Jahren zeigt die Douglasie (Pseudotsuga menziesii [Mirb.] Franco) in verschiedenen Regionen Frankreichs Absterbeerscheinungen, die wir der Trockenheit zuschreiben. Unsere Untersuchungen belegen, dass das Leitsystem des Holzes bei der Resistenz der Douglasie gegenüber Trockenheit eine Rolle spielt: Engere Gefässe, d.h. eine höhere Holzdichte, würden das Überleben der Bäume in Perioden mit ausgeprägtem Wassermangel begünstigen. Diese Idee wird durch signifikante Zusammenhänge zwischen der Holzdichte und den hydraulischen Eigenschaften des Splintholzes sowie durch die gefundenen Beziehungen zwischen den ökologischen Vorlieben der Provenienzen in ihrer Herkunftsregion und der Dichte ihres Holzes in den Regionen Frankreichs, in denen sie eingebracht wurden, belegt: Herkünfte aus trockenen Regionen haben die Tendenz, ein Holz zu entwickeln, das ähnliche Eigenschaften zeigt wie dasjenige von Bäumen, die Trockenperioden überlebten. Die Beziehung Holzdichte–Überleben konnte zwar klar herausgestellt werden, jedoch zeigen die Unterschiede zwischen den Standorten, dass die Wirkungsmechanismen komplex sind und grösstenteils noch nicht verstanden werden. Estación Experimental Agropecuaria Bariloche Fil: Rozenberg, Philippe. INRA. Biologie intégrée pour la valorisation de la diversité des arbres et de la forêt; Francia Fil: Sergent, Anne Sophie. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Bariloche. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Instituto de Investigaciones Forestales y Agropecuarias Bariloche; Argentina Fil: Dalla Salda, Guillermina. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Bariloche. Área de Recursos Forestales. Grupo de Ecología Forestal; Argentina Fil: Martinez Meier, Alejandro. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Bariloche. Área de Recursos Forestales. Grupo de Ecología Forestal; Argentina Fil: Marin, Sara. INRA. Biologie intégrée pour la valorisation de la diversité des arbres et de la forêt; Francia Fil: Ruiz Diaz, Manuela. INRA. Biologie intégrée pour la valorisation de la diversité des arbres et de la forêt; Francia Fil: Bastien, Jean-Charles. INRA. Biologie intégrée pour la valorisation de la diversité des arbres et de la forêt; Francia Fil: Sanchez, Leopoldo. INRA. Biologie intégrée pour la valorisation de la diversité des arbres et de la forêt; Francia Fil: Bréda, Nathalie. INRA. Biologie intégrée pour la valorisation de la diversité des arbres et de la forêt; Francia

Drought response of three Douglas-fir clones (slow, intermediate and fast growing) inhabiting two different climatic regimes in France was examined. We used the hydraulic conductivity and the percent loss of conductivity due to embolism from stems and branches as well as wood microdensity measurements to determine the role of genetics in the control of embolism in this species. Conductivity and tree-ring's microdensity variables (ring width: RW, mean ring density: MRD, minimum ring density: MID and maximum ring density: MAD) were compared in growth rings in all three clones during a typical year (2002) vs. an extremely dry year (2003). A new method was developed in order to assess axial hydraulic specific conductivity (Ks) within tree rings. The results show that branches are more resistant to embolism than stems, and that there are significant differences in embolism resistance among the clones between the two sites. Ks varied between years, sites and clones but the site exerted the most significant effect. Lartimache (more humid site during 2003) trees showed substantially higher Ks than those inhabiting Chassenoix (strongly affected by the 2003 heat and drought wave site). Wood analysis showed a significant year effect for all ring variables and a significant clone effect for all ring variables except for MAD, while the site effect was significant for MRD and MAD. The existence of a genetic control for the study traits indicates that Douglas-fir populations introduced in France may have a selection potential to face extreme climate events like the 2003 heat and drought wave.

The genetic control of tree ring growth in Douglas-fir in response to the drought and heat-wave that occurred in 2003 in Europe was studied with microdensity profiles in three clonal experiments located in three different French regions. The drought and heat-wave significantly affected Douglas-fir wood formation. The Chassenoix site (Northeast of Massif-Central) was more severely affected that the other two: the 2003 year-ring was narrower and less dense than in the other sites and than the previous (2002) and following (2004) year-rings in the same site: ring growth stopped earlier and latewood did not develop completely. The year-rings 2004 and 2002 were very similar in this site. There was a significant genetic control for all ring parameters in the three sites and during the three years. The heritability was highly variable between years and among sites, without any clear pattern in this variability, except in Chassenoix where it was slightly lower in the 2003 year-ring. Variables measuring the response of trees to the 2003 event, i.e., the difference in ring width between 2002 and 2003, or between 2003 and 2004, showed a very variable degree of genetic control, from very low to relatively high. Douglas-fir seemed plastic enough to acclimate to the drought and heat-wave and then to recover during 2004. Furthermore the level of heritability estimated demonstrates that Douglas-fir has an adaptive potential that could be useful for multi-generation long-term response., La réponse du douglas à la canicule de 2003 en France a été étudiée à l'aide de profils microdensitométriques obtenus sur des arbres de 3 tests clonaux situés dans 3 régions différentes. La canicule a significativement affecté la formation du bois du douglas. Les arbres du site de Chassenoix, situé dans le Morvan, ont réagi plus fortement que ceux des 2 autres : le cerne de l'année de la canicule est plus étroit et moins dense que le même cerne dans les 2 autres sites et plus étroit et moins dense que les cernes immédiatement antérieur (2002) et postérieur (2004) dans le même site ; la formation du bois s'est arrêtée plus tôt et le bois final ne s'est pas complètement développé. À Chassenoix, le cerne de l'année 2004 ressemble plus au cerne 2002 qu'au cerne 2003, ce qui traduit une récupération. Nous mettons en évidence un contrôle génétique significatif pour toutes les variables intra-cernes dans les 3 sites, pour les 3 années 2002, 2003 et 2004. Les héritabilités sont très variables entre caractères, sites et années, sans structure particulière, sauf à Chassenoix où ces héritabilités sont légèrement plus faibles durant l'année de la canicule. Des variables décrivant la réponse des arbres entre 2002 et 2003 puis 2003 et 2004 sont très irrégulièrement contrôlées génétiquement, avec des héritabilités allant de 0 à près de 0,5. Le douglas semble avoir été suffisamment plastique pour s'acclimater à la sécheresse et canicule puis pour récupérer en 2004 une croissance proche de celle de 2002. De plus, son potentiel génétique démontré par le niveau d'héritabilité estimé lui donne également une capacité adaptative multi-génération à plus long terme.

Physiological studies have suggested that A. chilensis would survive during drought avoiding water stress through an early stomatal closure. However, there are no studies that have explored other potential mechanisms related to drought resistance or avoidance. The objectives were: (1) to measure hydraulic resistance, vulnerability to cavitation and leaf water relations, and (2) to compare these characteristics between different provenances. Pressure-volume curves demonstrate that A. chilensis has high osmotic potentials at full turgor, high water potentials at turgor loss point, low modulus of elasticity, and did not present elastic or osmotic adjustments after drought. Compared to other gymnosperms, A. chilensis has a high total plant resistance but also a high vulnerability to cavitation. We found no differences between the studied provenances in these variables. Our results confirm that A. chilensis is a drought-avoidance species, and suggest that phenotypic morphological differentiation between populations allows the species to survive throughout its broad distribution., Relations hydriques au niveau de la feuille et du plant chez un conifère de Patagonie Austrocedrus chilensis (D. Don) Pic. Ser. et Bizzarri: implications pour sa capacité à résister à la sécheresse. Des études physiologiques suggèrent que l'Austrocedrus chilensis peut survivre aux périodes de sécheresse évitant le stress hydrique grâce à une fermeture stomatique précoce. Cependant, il n'y a pas d'étude qui eut exploré d'autres mécanismes potentiels liés à la résistance ou à l'évitement de la sécheresse. Les objectifs de ce travail ont été : (1) mesurer la résistance hydraulique, la vulnérabilité à la cavitation et les relations hydriques des feuilles et (2) comparer ces caractéristiques avec celles des populations de différentes provenances. Les courbes pression-volume ont démontré que l'Austrocedrus chilensis possède un potentiel osmotique élevé à pleine turgescence, un potentiel hydrique au point de perte de turgescence, un module d'élasticité bas et qu'il ne présente pas de réglage élastique ou osmotique après la sécheresse. En comparaison avec d'autres gymnospermes, l'Austrocedrus chilensis a une résistance totale élevée mais aussi une importantee vulnérabilité à la cavitation. Nous n'avons pas trouvé de différences significatives entre les provenances étudiées dans ces variables. Nos résultats confirment que l'Austrocedrus chilensis est une espèce qui évite la sécheresse, et ils suggèrent que les changements phénotypiques entre populations permettent à cette espèce de survivre dans sa vaste distribution.

More frequently occurring, drought waves call for a deeper understanding of tree hydraulics and fast and easily applicable methods to measure drought stress. The aim of this study was to establish empirical relationships between the percent loss of hydraulic conductivity (PLC) and the relative water loss (RWL) in woody stem axes with different P50, i.e. the water potential (Ψ) that causes 50% conductivity loss. Branches and saplings of temperate conifer (Picea abies, Larix decidua) and angiosperm species (Acer campestre, Fagus sylvatica, Populus x canescens, Populus tremula, Sorbus torminalis) and trunk wood of mature P. abies trees were analyzed. P50 was calculated from hydraulic measurements following bench top dehydration or air injection. RWL and PLC were fitted by linear, quadratic or cubic equations. Speciesor age-specific RWLs at P50 varied between 10 and 25% and P88, the Ψ that causes 88% conductivity loss, between 18 and 44%. P50 was predicted from the relationship between Ψ and the RWL. The predictive quality for P50 across species was almost 1:1 (r2 =0.99). The approach presented allows thus reliable and fast prediction of PLC from RWL. Branches and saplings with high hydraulic vulnerability tended to have lower RWLs at P50 and at P88. The results are discussed with regard to the different water storage capacities in sapwood and survival strategies under drought stress. Potential applications are screening trees for drought sensitivity and a fast interpretation of diurnal, seasonal or drought induced changes in xylem water content upon their impact on conductivity loss. Estación Experimental Agropecuaria Bariloche Fil: Rosner, Sabine. University of Natural Resources and Life Sciences. Institute of Botany; Austria Fil: Heinzeb, Berthold. Austrian Research Centre for Forest. Department of Forest Genetics; Austria Fil: Savia, Tadeja. University of Natural Resources and Life Sciences; Austria Fil: Dalla Salda, Guillermina. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Bariloche. Área Sistemas Forestales. Grupo de Ecología Forestal; Argentina