Water-use strategies in two co-occurring Mediterranean evergreen oaks: surviving the summer drought

In the Mediterranean evergreen oakwoodlands of southern Portugal, the main tree species are Quercus ilex ssp. rotundifolia Lam. (holm oak) and Quercus suber L. (cork oak). We studied a savannah-type woodland where these species coexist, with the aim of better understanding the mechanisms of tree adaptation to seasonal drought. In both species, seasonal variations in transpiration and predawn leaf water potential showed a maximum in spring followed by a decline through the rainless summer and a recovery with autumn rainfall. Although the observed decrease in predawn leaf water potential in summer indicates soil water depletion, trees maintained transpiration rates above 0.7 mm day–1 during the summer drought. By that time, more than 70% of the transpired water was being taken from groundwater sources. The daily fluctuations in soil water content suggest that some root uptake of groundwater was mediated through the upper soil layers by hydraulic lift. During the dry season, Q. ilex maintained higher predawn leaf water potentials, canopy conductances and transpiration rates than Q. suber. The higherwater status of Q. ilexwas likely associated with their deeper root systems compared with Q. suber. Whole-tree hydraulic conductance and minimum midday leaf water potential were lower in Q. ilex, indicating that Q. ilex was more tolerant to drought than Q. suber. Overall, Q. ilex seemed to have more effective drought avoidance and drought tolerance mechanisms than Q. suber

Seasonal variation of water uptake of a Quercus suber tree in Central Portugal

Hydraulic redistribution (HR) is the phenomenon where plant roots transfer water between soil horizons of different water potential. When dry soil is a stronger sink for water loss from the plant than transpiration, water absorbed by roots in wetter soil horizons is transferred toward, and exuded into dry soil via flow reversals through the roots. Reverse flow is a good marker of HR and can serve as a useful tool to study it over the long-term. Seasonal variation of water uptake of a Quercus suber tree was studied from late winter through autumn 2003 at Rio Frio near Lisbon, Portugal. Sap flow was measured in five small shallow roots (diameter of 3–4 cm), 1 to 2 m from the tree trunk and in four azimuths and at different xylem depths at the trunk base, using the heat field deformation method (HFD). The pattern of sap flow differed among lateral roots as soil dried with constant positive flow in three roots and reverse flow in two other roots during the night when transpiration ceased. Rain modified the pattern of flow in these two roots by eliminating reverse flow and substantially increasing water uptake for transpiration during the day. The increase in water uptake in three other roots following rain was not so substantial. In addition, the flux in individual roots was correlated to different degrees with the flux at different radial depths and azimuthal directions in trunk xylem. The flow in outer trunk xylem seemed to be mostly consistent with water movement from surface soil horizons, whereas deep roots seemed to supply water to the whole cross-section of sapwood. When water flow substantially decreased in shallow lateral roots and the outer stem xylem during drought, water flow in the inner sapwood was maintained, presumably due to its direct connection to deep roots. Results also suggest the importance of the sap flow sensor placement, in relation to sinker roots, as to whether lateral roots might be found to exhibit reverse flow during drought. This study is consistent with the dimorphic rooting habit of Quercus suber trees in which deep roots access groundwater to supply superficial roots and the whole tree, when shallow soil layers were dry

Mycorrhization of fagaceae forests within mediterranean ecosystems

Mediterranean Fagaceae forests are valuable due to their ecological and socioeconomic aspects. Some profitable plant species, such as Castanea (timber and chestnut), Quercus (timber and cork), and Fagus (timber), encounter in this habitat the excellent edaphoclimatic conditions to develop. All Fagaceae plants are commonly associated to ECM fungal species, which are found in these forests in quite stable communities, mainly enriched in Russulaceae and Telephoraceae species. Currently, the Mediterranean Basin is considered as one of the global biodiversity hotspots, since many of their endemic plant species are not found elsewhere and are now under threat. Due to climate changing and introduction of disease agents, Fagaceae forests are facing an adaptation challenge to both biotic and abiotic threats. Although ECM communities are highly disturbed by climate factors and tree disease incidence, they could play an important role in increasing water availability to the plant and also improving plant tree defense against pathogens. Recent advances, namely, on genomics and transcriptomics, are providing tools for increasing the understanding of Fagaceae mycorrhization process and stress responses to biotic and abiotic stresses. Such studies can provide new information for the implementation of the most adequate management policies for protecting threaten Mediterranean forests.info:eu-repo/semantics/publishedVersio

Variation in cold hardiness and carbohydrate concentration from dormancy induction to bud burst among provenances of three European oak species

International audienc

Relationship between climate and growth of two North African varieties of Pinus pinaster Arn

International audiencePlanting tree species that are well adapted to local ecological conditions guarantees the success and sustainability of forest restoration. The aim of this study was to investigate the acclimation of two varieties of Pinus pinaster (var. renoui from Tunisia and var. maghrebiana from Morocco), to the ecological conditions of the Kroumirie Mountains in northwest of Tunisia. Tree growth performance (diameter at 1.30 m [DBH], ring widths and total height) and climate–growth responses over the period 1970–2013 were evaluated for two varieties. The trees used in this study were from pine variety and provenance trials growing in common garden in Souiniet (21 trees per variety). Significant difference in height growth rate, DBH and ring widths was found between the two varieties. The Maghrebiana variety had the highest survival and mean radial growth rates. The mean sensitivity to climate was the same in two varieties. A significant negative correlation between May precipitation and radial growth was found for var. maghrebiana. Both varieties showed a significant negative correlation between May and June temperatures and radial growth. January–February temperatures had a positive influence on ring width. The Maghrebiana variety appears well acclimatised so it is expected to ensure more successful restoration of Kroumirie Mountains.Planter des essences bien adaptées aux conditions écologiques locales garantit le succès et la durabilité de la restauration des forêts. L'objectif de cette étude était d’évaluer l’acclimatation de deux variétés de Pinus pinaster (var. Renoui de la Tunisie et var. Maghrebiana du Maroc) aux conditions écologiques des montagnes de la Kroumirie au nord‐ouest de la Tunisie. Les performances de croissance des arbres (diamètre à 1,30 m [DBH], largeurs de cernes et hauteur totale) et les réponses climatcroissance sur la période 1970‐2013 ont été évaluées pour les deux variétés. Les arbres utilisés dans cette étude provenaient d'essais de variétés et des provenances de pins poussant dans une plantation comparative à Souiniet (21 arbres par variété). Une différence significative entre les taux de croissance en hauteur, en DBH et des largeurs des cernes a été observée entre les deux variétés. La variété Maghrebiana avait les taux de survie et de croissance radiale les plus élevés. La sensibilité moyenne au climat était la même dans les deux variétés. Une corrélation négative significative entre les précipitations de mai et la croissance radiale a été enregistrée pour maghrebiana var. Les deux variétés ont montré une correlation négative significative entre les températures de mai‐juin et la croissance radiale. Les températures de janvier‐février ont eu une influence positive sur la largeur des cernes. La variété Maghrebiana semble bien acclimatée donc, il est prévu d'assurer une restauration plus réussie des montagnes de la Kroumirie