RESUMEN
⢠Fire and drought are selective driving forces in Mediterranean plants, and thus their ability to resprout or recruit after these disturbances is of paramount importance. The contrast in regeneration niche between resprouters and seeders, and each group's different root characteristics, suggest that they are subjected to different degrees of environmental stress and, consequently, to different evolutionary forces. ⢠We compared leaf traits, xylem traits related to hydraulic efficiency and vulnerability to cavitation, and the physiological response to an imposed drought between seedlings of resprouters and seedlings of seeders. We used 12 species co-existing in Mediterranean basin ecosystems. ⢠Major differences were found in the xylem architecture and leaf traits, and in the response to drought conditions. Seeders were more efficient at transporting water to leaves but formed, in turn, a safer xylem network. They also presented higher photosynthesis and transpiration rates, and earlier stomatal closure with drought, but good leaf dehydration tolerance. ⢠Seeders and resprouters can be considered two syndromes whose different functional characteristics are related to water availability and drought responses. These characteristics, together with their differences in rooting habits, account for their distinct regeneration niches and, thus, their co-existence.
Asunto(s)
Ecosistema , Fenómenos Fisiológicos de las Plantas , Regeneración/fisiología , Sequías , Región Mediterránea , Fotosíntesis , Estomas de Plantas/fisiología , Transpiración de Plantas/fisiología , Especificidad de la Especie , Agua , Xilema/fisiologíaRESUMEN
Ozone uptake was studied in a pine forest in Tenerife, Canary Islands, an ecotone with strong seasonal changes in climate. Ambient ozone concentration showed a pronounced seasonal course with high concentrations during the dry and warm period and low concentrations during the wet and cold season. Ozone uptake by contrast showed no clear seasonal trend. This is because canopy conductance significantly decreased with soil water availability and vapour pressure deficit. Mean daily ozone uptake averaged 1.9 nmol m(-2) s(-1) during the wet and cold season, and 1.5 nmol m(-2) s(-1) during the warm and dry period. The corresponding daily mean ambient ozone concentrations were 42 and 51 nl l(-1), respectively. Thus we conclude that in Mediterranean type forest ecosystems the flux based approach is more capable for risk assessment than an external, concentration based approach.