5 research outputs found
The Montado agroforestry system microclimatic specificity in the context of global change
The effects of oak trees on microclimatic
parameters in Quercus rotundifolia Lam. woodland in the
Alentejo, Southern Portugal, are reported. Results show that
oak tree create a marked differentiation in the grass matrix,
between open and undercanopy areas. Compared to open
areas, it presents lower soil moisture beneath the oak canopy,
lower soil temperatures and lower photosynthetically active
radiation (PAR). Soil temperatures outside trees canopy
were generally higher than undercanopy areas, reaching
twice its values during the winter. The decrease of soil water
content is more rapid in areas outside the trees canopy
action, but the replenishment starts early and is faster in
those areas. PAR intercepted by tree canopy is greater than
60%, and affects dramatically herbaceous production.
Different climatic conditions due to the presence of the tree,
associated with greater variability in chemistry environment
undercanopy, if combined with the IPCC forecasts for
Mediterranean region, pose new challenges in the
management of the montado areas
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 herbacĂ©e rudĂ©rale très commune dans la rĂ©gion mĂ©diterranĂ©enne. Ses fleurs sont très prisĂ©es pour des raisons esthĂ©tiques. Cette espèce prĂ©sente un degrĂ© d’adaptation important pour des habitats pauvres en ressources. L’objectif de cette Ă©tude a consistĂ© Ă 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 expĂ©rience a Ă©tĂ© rĂ©alisĂ©e, comprenant quatre traitements avec huit plots alĂ©atoires ; quatre plots Ă©tant utilisĂ©s chaque annĂ©e. Les graines ont Ă©tĂ© semĂ©es selon les densitĂ©s suivantes : 20 000, 15 000, 10 000 et 5 000 graines/ m2. La production de la phytomasse et de la biomasse racinaires a Ă©tĂ© mesurĂ©e suite Ă des rĂ©coltes pĂ©riodiques pendant la durĂ©e du cycle saisonnier. Dans la première annĂ©e, il semble que l’augmentation de la densitĂ© des semis a conduit Ă un accroissement de la production de phytomasse. Dans la deuxième annĂ©e, lorsque la plante Ă©tait dĂ©jĂ installĂ©e, l’augmentation de la densitĂ© des graines de 5 000 Ă 10 000 a entraĂ®nĂ© une lĂ©gère croissance de la production de phytomasse. Cependant, lorsque la densitĂ© des graines a augmentĂ© de 10 000 Ă 20 000 graines/ m2, une rĂ©duction de la production de phytomasse a Ă©tĂ© observĂ©e. Dans la première annĂ©e, la biomasse racinaire a prĂ©sentĂ© une valeur minimum en janvier et une valeur maximum en juin-juillet. Dans la deuxième annĂ©e, les valeurs les plus hautes ont Ă©tĂ© observĂ©es en mai. La relation entre la phytomasse et la biomasse racinaire, pour la première annĂ©e, diminue au fil des dates de coupe. Cependant, un phĂ©nomène inverse s’est produit au cours de la deuxième annĂ©e. Bien que les valeurs de la phytomasse n’aient pas rĂ©vĂ©lĂ© de diffĂ©rences significatives entre les traitements, lorsque les plantes sont dĂ©jĂ Ă©tablies, elles indiquent que les densitĂ©s de graines comprises entre 5 000 et 10 000/ m2 pourraient ĂŞtre plus avantageuses.Conceição Castro Marcel, Roquete Carlos, Gazarini LuĂs. Above-ground phytomass and below-ground biomass production of Salvia verbenaca LinnĂ©. In: Ecologia mediterranea, tome 28 n°2, 2002. pp. 15-22
Microclimatic specificity of a Mediterranean oak woodland (montado) in the context of global change
The effects of oak trees on microclimatic
parameters in Quercus rotundifolia Lam. woodland in the
Alentejo, Southern Portugal, are reported. Results show that
oak tree create a marked differentiation in the grass matrix,
between open and undercanopy areas. Compared to open
areas, it presents lower soil moisture beneath the oak canopy,
lower soil temperatures and lower photosynthetically active
radiation (PAR). Soil temperatures outside trees canopy
were generally higher than undercanopy areas, reaching
twice its values during the winter. The decrease of soil water
content is more rapid in areas outside the trees canopy
action, but the replenishment starts early and is faster in
those areas. PAR intercepted by tree canopy is greater than
60%, and affects dramatically herbaceous production.
Different climatic conditions due to the presence of the tree,
associated with greater variability in chemistry environment
undercanopy, if combined with the IPCC forecasts for
Mediterranean region, pose new challenges in the
management of the montado areas