Effects of a deep container on morpho-functional characteristics and root colonization in Quercus suber L. seedlings for reforestation in Mediterranean climate

Natural recruitment of oaks appears to be declining throughout the northern hemisphere. Summer drought poses a potentially important barrier to oak recruitment in southern California. To evaluate this barrier, we grew evergreen Quercus agrifolia and deciduous Q. lobata from seeds near parental trees. We measured water relations, chlorophyll fluorescence, and gas exchange during these seedlings' fourth and fifth summers and compared them to neighboring adults. Most seedlings had substantially lower values for predawn xylem pressure potential (Ψ(pd)), minimum photosystem II (PSII) quantum efficiency (Φ(PSIIMIN)), maximum quantum efficiency for PSII under dark-adapted leaf conditions (Fv/Fm), and maximum photosynthetic assimilation (Amax), and higher values for maximum nonphotochemical quenching (NPQmax) than did conspecific adults. The high, unvarying Ψ(pd) values of the adults suggest they use perennially available groundwater. Quercus lobata seedlings commonly had lower values for Ψ(pd) than did Q. agrifolia, and values for Ψ(pd) and Φ(PSIIMIN) were significantly related to size in Q. lobata but not in Q. agrifolia. These data suggest important interspecific differences in root architecture. Lower values for Φ(PSIIMIN), Fv/Fm, and higher NPQmax in Q. agrifolia indicate that Q. agrifolia seedlings were usually under more stress than Q. lobata, which typically had higher Amax rates than did Q. agrifolia seedlings. Diurnal photosynthesis curves were quite flat for Q. agrifolia, but they peaked in the morning for Q. lobata. Established seedlings appeared to be under more stress than adults, but this stress did not appear severe enough to cause death. Access to perennially available groundwater may be crucial for the seedling to sapling transition.

https://bsapubs.onlinelibrary.wiley.com/doi/pdf/10.3732/ajb.0800247

A comparative study of oak (Quercus, Fagaceae) seedling physiology during summer drought in southern California.

/pdf/restauracion-en-semiarido-wqg896eel6.pdf

Restauración en semiárido

. We tested how the conditions resulting from alternative management strategies addressed to mitigate abiotic and biotic limitations to plant establishment affect the performance of planted Quercus coccifera seedlings. This species is a xerophytic and heliophillous Mediterranean shrub, of interest for the restoration of abandoned farmland. We hypothesised that release from herb competition by clipping would allow Q. coccifera seedlings to cope more efficiently with water shortage by adjusting their mass allocation pattern. We established three environments of herb competition: absence of competition (AC), reduced competition by clipping (RC), and total competition (TC); and applied two irrigation treatments: low and high irrigation. We measured soil moisture at different depths, above- and below-ground herb biomass, and evaluated seedling responses, such as mortality, growth, biomass allocation, and morphological and physiological features. The TC treatment reduced water availability more than the RC treatment, in agreement with the highest water stress of seedlings under TC conditions. Irrigation increased above- and below-ground herb biomass, whereas clipping reduced herb production. Release of herb competition by clipping increased seedling survivorship by one order of magnitude and resulted in a growth rate comparable to the absence of competition. This growth was mostly related to carbon gain allocated to roots. The competition intensity imposed by treatments was related to a parallel reduction in total plant leaf area, biomass allocated to leaves and shoot:root ratio, and an increase in biomass allocated to roots and leaf mass area. The negative effects of herbs on Q. coccifera seedlings seem the result of competition for both water and light, in contrast with previous research with more mesic Quercus species, for which competition is primarily for water. Clipping of herbs is a feasible technique that greatly improved seedling performance, and thus a valuable alternative to herbicide application, common in native plantations aimed at restoring Mediterranean farmland.

/pdf/clipping-herbaceous-vegetation-improves-early-performance-of-348pgkdjvv.pdf

Clipping herbaceous vegetation improves early performance of planted seedlings of the Mediterranean shrub Quercus coccifera

Le potentiel hydrique est utilise en tant que grandeur thermodynamique qui sfapplique a tous les compartiments du continuum sol-plante-atmosphere et qui reagit la circulation de lfeau entre le sol, les racines, les tiges, les feuilles et lfatmosphere. Il est determine par la methode de la chambre a pression de Scholander ; methode simple et rapide qui donne aussi acces a plusieurs parametres hydriques, decrivant lfetat de lfeau dans la plante, a travers une representation graphique ou courbe-pression-volume (CPV). Cependant, certaines procedures experimentales utilisees lors des mesures peuvent augmenter les risques des erreurs, au niveau des resultats, comme lfutilisation arbitraire dfechantillons de tailles variables. Le but de ce travail est dfetudier lfimpact de la variabilite de la taille des echantillons preleves sur les parametres hydriques et de trouver a la suite des solutions pouvant minimiser les erreurs experimentales induites. De ce fait, 12 CPV par jour ont ete effectuees sur des phyllodes (10}0,5 cm de longueur) et des rameaux de 16}0,5 cm de longueur (avec 5 a 6 phyllodes), de plants dfAcacia cyanlophylla Lindl., preleves a lfaube, sous conditions hydriques non limitantes, temoins, (ƒµb.-0,2 } 0,1 Mpa) ou stressantes (ƒµb = -1,80 } 0,20 Mpa) puis soumis immediatement a saturations (12h, 24h et 48h). Les resultats indiquent qufaussi bien pour les plants temoins que les stresses, la taille de lfechantillon influe significativement leurs parametres hydriques. Le prelevement des rameaux a lfaube, et leurs mises a saturation jusqufa 48h, permettrait dfavoir moins de variations dans le nombre et dans les valeurs des composantes hydriques determines. Mots-cles : taille de lfechantillon, Acacia cyanophylla Lindl., parametres hydriques, courbes pression volume

/pdf/influence-de-la-taille-de-l-echantillon-sur-la-variation-des-1tpes6ucq6.pdf

Influence de la taille de l’échantillon sur la variation des paramètres hydriques déterminés à partir des courbes-pression-volume

Une etude comparative des reponses physiologiques de jeunes plants de chenes sempervirents (chene liege: Quercus suber L. et chene kermes: Q. coccifera L.) et d'un chene caducifolie (chene zeen: Q. faginea Willd) a ete menee en pepiniere a Tunis. Des plants de 6 et 18 mois, eleves en pots, ont ete soumis a une contrainte hydrique par arret d'arrosage pendant deux cycles de dessechement consecutifs d'une duree de deux mois. Nous avons mesure les potentiels hydriques de base et minimum, la perte en eau par rapport a la capacite au champ (transpiration cumulee des plantes), la conductance stomatique et l'assimilation photosynthetique. La biomasse des tiges, des racines, les rapports biomasse tige/racine et la surface foliaire ont ete egalement determines. Le rapport biomasse tige/racine a diminue davantage au cours de la contrainte hydrique chez Q. faginea que chez Q. coccifera. La diminution de la conductance stomatique, liee a la chute du potentiel hydrique foliaire de base, etait plus precoce chez Q. faginea. Les stomates de Q. coccifera sont restes encore partiellement ouverts pour des potentiels de l'ordre de -3MPa. Les reponses de Q. suber etaient intermediaires. La photosynthese nette et la conductance stomatique etaient etroitement correlees et presentaient toutes deux une depression de milieu de journee. Nos resultats indiquent qu'il serait necessaire d'approfondir les etudes ecophysiologiques en fonction de l'age des plants et des feuilles au stade juvenile, pour mieux comprendre le comportement des chenes, notamment ses difficultes de regeneration spontanee

Comparison of the water stress effects on stomatal conductance, photosynthesis and growth of Mediterranean oak seedlings (Quercus suber L., Q. faginea, Q. coccifera) in Tunisia

La conductance stomatique a été suivie chez cinq origines tunisiennes de Caroubier (Ceratonia siliqua L.) soumises ou non à une contrainte hydrique prolongée. L'examen des résultats obtenus montre que les origines Sfax et Béni-Khiar ont fermé plus rapidement leurs stomates après application de la contrainte. Pour toutes les origines, on observe après réhydratation, une réouverture des stomates supérieure à celle des témoins. Au cours d'un deuxième cycle de déshydratation nous avons noté que la conductance stomatique diminue moins fortement qu'au cours du premier, ce qui peut traduire un endurcissement de la feuille et son adaptation à la contrainte.

Modification de la conductance stomatique de diverses origines tunisiennes de caroubier (Ceratonia siliqua L.) soumises a une contrainte hydrique prolongee

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Comparison of the water stress effects on stomatal conductance, photosynthesis and growth of Mediterranean oak seedlings (Quercus suber L., Q. faginea, Q. coccifera) in Tunisia

Modification de la conductance stomatique de diverses origines tunisiennes de caroubier (Ceratonia siliqua L.) soumises a une contrainte hydrique prolongee