Drought-induced photosynthetic inhibition and autumn recovery in two Mediterranean oak species (Quercus ilex and Quercus suber)

Responses of leaf water relations and photosynthesis to summer drought and autumn rewetting were studied in two evergreen Mediterranean oak species, Quercus ilex spp. rotundifolia and Quercus suber. The predawn leaf water potential (ΨlPD), stomatal conductance (gs) and photosynthetic rate (A) at ambient conditions were measured seasonally over a 3-year period. We also measured the photosynthetic response to light and to intercellular CO2 (A/PPFD and A/ Ci response curves) under water stress (summer) and after recovery due to autumn rainfall. Photosynthetic parameters, Vcmax, Jmax and triose phosphate utilization (TPU) rate, were estimated using the Farquhar model. RuBisCo activity, leaf chlorophyll, leaf nitrogen concentration and leaf carbohydrate concentration were also measured. All measurements were performed in the spring leaves of the current year. In both species, the predawn leaf water potential, stomatal conductance and photosynthetic rate peaked in spring, progressively declined throughout the summer and recovered upon autumn rainfall. During the drought period, Q. ilex maintained a higher predawn leaf water potential and stomatal conductance than Q. suber. During this period, we found that photosynthesis was not only limited by stomatal closure, but was also downregulated as a consequence of a decrease in the maximum carboxylation rate (Vcmax) and the light-saturated rate of photosynthetic electron transport (Jmax) in both species. The Vcmax and Jmax increased after the first autumnal rains and this increase was related to RuBisCo activity, leaf nitrogen concentration and chlorophyll concentration. In addition, an increase in the TPU rate and in soluble leaf sugar concentration was observed in this period. The results obtained indicate a high resilience of the photosynthetic apparatus to summer drought as well as good recovery in the following autumn rains of these evergreen oak species

Above-ground phytomass and below-ground biomass production of Salvia verbenaca Linné

Salvia verbenaca L. is a ruderal herbaceous plant, very common in the Mediterranean region. Its flowers are prized for their appearance, and it displays a high degree of adaptability in relation to habitat sites with a paucity of resources. The objective of this study was to obtain data about the production of phytomass and root biomass, with a view to the probable use of this species in urban green spaces. A two-year field experiment was undertaken, comprising four treatments of eight randomly selected plots, four being used in each year. This species was manual seed broadcast at the following densities : 20 000, 15 000, 10 000 and 5 000 viable seeds m2. The production of phytomass and root biomass was assessed through periodic collections, during the seasonal cycle of the species under study. In the first year there appears to have been a tendency for an increase in seed density to cause an increase in phytomass production. In the second year, by which time the plants had settled, when seed density rose from 5 000 to 10 000, a slight increase in phytomass production occurred. However, when the seed density rose from 10 000 to 20 000 seeds m -2, a decrease in phytomass production was observed. Root biomass, in the first year, had minimum value in January and a maximum value in June-July. In the second year, the highest values were observed in May. The relationship between above and below ground biomass, for the first-year experiment, decreased over the cutting dates. However, an inverse behaviour occurred in the second year. Although the values of the phytomass obtained did not reveal statistically significant differences between treatments, when the plants were found already established, they appeared to indicate that densities of seeding between 5 000 and 10 000 m2 could be more advantageous.Salvia verbenaca L. est une herbacée rudérale très commune dans la région méditerranéenne. Ses fleurs sont très prisées pour des raisons esthétiques. Cette espèce présente un degré d’adaptation important pour des habitats pauvres en ressources. L’objectif de cette étude a consisté à analyser la production de la phytomasse et de la biomasse racinaire dans l’optique d’utiliser cette espèce dans les espaces verts des villes. Durant deux ans, une expérience a été réalisée, comprenant quatre traitements avec huit plots aléatoires ; quatre plots étant utilisés chaque année. Les graines ont été semées selon les densités suivantes : 20 000, 15 000, 10 000 et 5 000 graines/ m2. La production de la phytomasse et de la biomasse racinaires a été mesurée suite à des récoltes périodiques pendant la durée du cycle saisonnier. Dans la première année, il semble que l’augmentation de la densité des semis a conduit à un accroissement de la production de phytomasse. Dans la deuxième année, lorsque la plante était déjà installée, l’augmentation de la densité des graines de 5 000 à 10 000 a entraîné une légère croissance de la production de phytomasse. Cependant, lorsque la densité des graines a augmenté de 10 000 à 20 000 graines/ m2, une réduction de la production de phytomasse a été observée. Dans la première année, la biomasse racinaire a présenté une valeur minimum en janvier et une valeur maximum en juin-juillet. Dans la deuxième année, les valeurs les plus hautes ont été observées en mai. La relation entre la phytomasse et la biomasse racinaire, pour la première année, diminue au fil des dates de coupe. Cependant, un phénomène inverse s’est produit au cours de la deuxième année. Bien que les valeurs de la phytomasse n’aient pas révélé de différences significatives entre les traitements, lorsque les plantes sont déjà établies, elles indiquent que les densités de graines comprises entre 5 000 et 10 000/ m2 pourraient être plus avantageuses.Conceição Castro Marcel, Roquete Carlos, Gazarini Luís. Above-ground phytomass and below-ground biomass production of Salvia verbenaca Linné. In: Ecologia mediterranea, tome 28 n°2, 2002. pp. 15-22