Suchergebnisse

5 páginas, 2 figuras. ; During the Cretaceous and early Tertiary, when the climate was warm and the atmospheric CO2 concentration ([CO2]) was at least double that of the present-day, polar forests populated high latitude landmasses. We investigated the density and length of stomata and other epidermal cells of two deciduous and three evergreen "living fossil" tree species representative of these ancient forests. These tree species were grown in a simulated Cretaceous high latitude environment at either ambient (400 ppmv) or elevated (800 ppmv) [CO2] during four years. After 4 years growing at elevated [CO2], the leaf stomatal density and index (percentage of leaf epidermal cells that are stomata) of these plants were similar to those of their counterparts growing at ambient [CO2]. While the CO2 enrichment only modified the stomatal pore length in two of the five studied species, it increased significantly the overall length of the epidermal cells of all the species, reducing their density. These results revealed that leaf epidermal cells of these "living fossil" species were more sensitive than stomata to an experimental doubling of atmospheric CO2 concentration. ; and David J. Beerling for allowing us to participate in the experiment. This study was supported by a European Union Marie Curie postdoctoral fellowship to L.L. (contract N EVK2eCTe2002e50022), by the Spanish Government CGL2006-4025/BOS, CGL2007-64583/BOS and Consolider-Ingenio MONTES CSD2008-00040 projects, the Catalan government SGR2009-458 project, and the Spanish National Research Council CSIC-PIF08-006-3 project. ; Peer reviewed

13 páginas, 6 figuras, 1 tabla. ; This study examined the effects of the combination of UV radiation and water limitation on the leaf photosynthesis, stomatal conductance, and terpene emissions of four Mediterranean species. 1-year-old seedlings of these Mediterranean species [Daphne gnidium L., Pistacia lentiscus L., Ilex aquifolium L. and Laurus nobilis L.] were grown under one of three UV treatments (without UV, with UVA, or with UVA ? UVB) and two watering regimes (high and low water supply). In general, UV treatments did not affect significantly leaf photosynthesis or stomatal conductance, although UVA and UVB radiation in September led to a reduction in leaf stomatal conductance in D. gnidium. Leaf photosynthesis rates did not differ significantly between the two watering treatments, even though, in three of the species, leaf stomatal conductance was significantly higher among the well-watered plants. The effects of UV on terpene emissions were species-specific; D. gnidium had the highest terpene emission rates when grown under UVA ? UVB radiation, which was also true for L. nobilis in September. Overall, UV treatments did not have a significant effect on total terpene emission rates in I. aquifolium, but UVB and UVA in July and September, respectively, reduced emission rates in P. lentiscus. A limited water supply reduced the terpene emission rates in D. gnidium, increased emissions in L. nobilis, and did not affect the emission rates in the other two species. ; Grants from the Spanish Government (CGL2006-04025/BOS, CGL2007-64583/BOS, and CGC2010- 17172), Consolider-Ingenio Montes (CSD2008-00040), and the Catalan government (SGR2009-458) supported the research. ; Peer reviewed

14 páginas, 12 figuras, 2 tablas. ; Plant community recovery (species richness, diversity and composition) of a post-fire Mediterranean shrubland was monitored over a seven year period (1998 2005) under experimental drought and warming that simulated the environmental conditions forecast for this area in the coming decades. Species richness and Shannon's index were positively correlated with accumulated precipitation in the growing season and both variables were negatively affected by reduced water availability in drought plots. The relative abundance of the different species in both treatments was linearly correlated with their relative abundance in control plots. Moreover, we found species-specific responses to treatments. Drought and warming treatment reduced the competitive ability of the obligate seeder tree Pinus halepensis against native resprouter shrubs and consequently, the transformation from shrub to pine tree dominated vegetation was slowed down. Conversely, the water use strategy of Globularia alypum may allow this species to maintain a dominant position in drought plots. Therefore, future drier and warmer conditions in Mediterranean areas may severely affect plant community recovery after a disturbance, due to the existence of both abundance-dependent and species-specific responses that may change inter-specific competitive relationships. ; This research was funded by EU under the projects CLIMOOR (Contract ENV4-CT97-0694) and VULCAN (Contract EVK2- CT-2000-00094) and we also received financial help from the Spanish Government (grants CGL2006-04025/BOS and Consolider MONTES CSD2008-00040), the Catalan Government (grant SGR2005-00312), the European project ALARM (Contract 506675), and the Fundacio´n Banco Bilbao Vizcaya 2004 grant. ; Peer reviewed

15 páginas, 3 tablas, 8 figuras. ; Polar forests populated high-latitude landmasses during the Cretaceous and early Paleogene when the climate was warm and the atmospheric CO2 concentration ([CO2 ]) was at least double that of the present-day. We investigated emission rates and composition of monoterpenes in relation to photoinhibition and photoprotection of two evergreen and three deciduous ''living fossil'' tree species representative of these ancient forests, after growth in a simulated Cretaceous polar (75 N) environment at either ambient (400 ppm) or elevated (800 ppm) [CO2 ] for four years. Total monoterpene emission rates peaked during the polar summer, when prolonged periods of 24 h light would have been conducive to enhancing the formation and chemical lifetime of ozone, and hence its radiative forcing. During most of the growing season, a-pinene was the main compound emitted, although the magnitude and chemical speciation of emissions was highly species specific. Growth at elevated [CO2 ] changed the composition of monoterpene emissions in evergreen and deciduous species, but only altered total leafscale emission rates of the deciduous species. The continuous daylight (photon flux: 300– 400 mmol PAR m 2 s 1 ) of the simulated polar summer (14.5 weeks) did not result in leaf photoinhibition or increased photoprotection via the xanthophyll cycle. Nevertheless, species with high a-pinene emission rates showed also high values of photochemical efficiency at ambient [CO2], suggesting a possible function of this monoterpene in protecting the photosynthetic apparatus. We suggest that high monoterpene emissions from forests during the long polar summers may constitute a regional high-latitude climatic feedback through alteration of tropospheric composition, and secondary organic aerosol formation. These biotic effects may be important to represent in Earth system models of ancient ''greenhouse'' climates. ; This study was supported by a European Union Marie Curie postdoctoral fellowship to L.L. (contract EVK2 –CT – 2002 – 50022) and by the Spanish Government REN2006 – 4025/BOS and the Catalan Government SGR2005 – 00312 projects. ; Peer reviewed