Rodà F, Mayor X, Sabaté S, Diego V (1999) Water and nutrient limitations to primary production. In Rodà F, Retana J, Gracia C, Bellot J (eds) Ecology of Mediterranean evergreen oak forests. Springer, Berlin, pp. 183-194.
Filella I., Peñuelas J. (1999) Altitudinal differences in UV absorbance, UV reflectance and related morphological traits of Quercus ilex and Rhododendron ferrugineum in the Mediterranean region. Plant Ecology. 145: 157-165.LinkDoi: 10.1023/A:1009826803540
We studied the variations in different physiological parameters associated with UV-B radiation defense: UV-B radiation absorbance, UV-visible spectral reflectance, carotenoids concentration, leaf thickness, SLW (specific leaf weigth) and trichome density in Quercus ilex growing at 200 and 1200 m and Rhododendron ferrugineum growing at 2200 m. We examined the role of these parameters as protection mechanisms in an altitudinal gradient of increasing UV radiation in northern Catalonia and in sun and shade leaves. The concentration of UV-B radiation absorbing pigments was 15% higher in sun leaves of Q. ilex at 1200 m than in those from 200 m altitude. Sun leaves of R. ferrugineum presented concentrations three times higher than those of Q. ilex. Reflectance ranged between 5% (in the region 300-400 nm) and 12% (in the region 280-300 nm). The variation of reflectance with altitude followed an inverse trend respect to absorbance in the 280-300 nm region, with higher values the lower the altitude, but in the 300-400 nm region, reflectance of the lower site was the lowest. In both species and altitudes sun leaves presented higher concentrations of UV-B radiation absorbing pigments and UV reflectance than shade leaves. Quercus ilex trees of the higher location presented higher NDPI (Normalized Difference Pigment Reflectance Index) values, indicating higher carotenoids/chlorophyll a ratio. Actual measurements of carotenoid/chlorophyll a ratio confirmed this pattern. The photochemical reflectance index (PRI) presented higher values the higher the location indicating lower photosynthetic radiation-use efficiency. Specific leaf weight (SLW) and leaf thickness were larger in Q. ilex trees of higher location than in those of lower location. In both sites, sun leaves also presented larger SLW values than shade leaves. Adaxial leaf hair density in sun leaves was significantly higher in the lower location. UV absorption and linked morphological traits (SLW, leaf thickness measured in Q. ilex) presented the larger differences among studied plants at different altitudes and seem to be the dominant UV protecting mechanisms.
Lloret F, Verdú M, Flores-Hernández N, Valiente-Banuet A (1999) Fire and resprouting in Mediterranean ecosystems: insights from an external biogeographical region, the Mexican shrubland. American Journal of Botany 86:1655-1661.
Santandreu M, Lloret F (1999) Effects of flowering phenology and habitat on pollen limitation in Erica multiflora L. Canadian Journal of Botany 77:734-743.
Siscart D, Diego V, Lloret F (1999) Acorn ecology. In Rodà F, Retana J, Gracia C, Bellot J (eds) Ecology of Mediterranean evergreen oak forests. Springer, Berlin, pp. 75-87.
Lloret F, Casanovas C, Peñuelas J (1999) Seedling survival of Mediterranean shrubland species in relation to root:shoot ratio, seed size and water and nitrogen use. Functional Ecology 13:210-216.
Canadell J, Djema A, López B, Lloret F, Sabaté S, Siscart D, Gracia C (1999) Structure and dynamics of the root system. In Rodà F, Retana J, Gracia C, Bellot J (eds) Ecology of Mediterranean evergreen oak forests. Springer, Berlin, pp. 47-59.
Habrouk A., Retana J., Espelta J.M. (1999) Role of heat tolerance and cone protection of seeds in the response of three pine species to wildfires. Plant Ecology. 145: 91-99.LinkDoi: 10.1023/A:1009851614885
The post-fire regenerative ability of Pinus halepensis, Pinus nigra and Pinus sylvestris, three of the most important pine species present in the West Mediterranean basin, has been analyzed in the light of seed tolerance to different temperatures and times of exposure, and of seed position during the fire event (seeds inside cones versus free seeds). The combination of different fire intensities and degrees of seed protection allows us to draw different scenarios during the fire event: canopy scenarios (seeds inside cones), surface scenarios (seeds on the ground surface), and soil scenarios (seeds in the top soil layers). There were interspecific differences in the pattern of cone opening under the different heat treatments: cones of P. nigra and P. sylvestris showed similar percentages of opening, but considerably higher than those of P. halepensis. In the three species, seeds inside cones showed higher percentages of germination than those that were free, emphasizing the important role of cones in the protection of pine seeds from high temperatures. The percentage of germination decreased when both the temperature and the time of exposure increased, and there was also a significant species effect: P. halepensis showed higher germination rates than P. nigra, and both were higher than P. sylvestris. The overall scores of seed germination of these three pine species under the conditions tested suggests that their regeneration after fire should come either from the soil bank, or from the canopy bank, but rarely from the ground surface. As the existence of a permanent seed bank in Mediterranean pines is probably limited or nil, pine recruitment after fire appears to be mainly controlled by the existence of a canopy seed bank. The contribution of this canopy bank to the differences in postfire regeneration success of the three pine species is discussed in the light of their seeding phenology and the effects of fire severity on cone opening. The results obtained in this study contribute to explain the successful regeneration of P. halepensis, and the failure of P. nigra and P. sylvestris after fire.
Inclán R., Ribas A., Peñuelas J., Gimeno B.S. (1999) The relative sensitivity of different Mediterranean plant species to ozone exposure. Water, Air, and Soil Pollution. 116: 273-277.LinkDoi: 10.1023/A:1005214005416
An experimental study was performed in open-top chambers to assess the relative O3-sensitivity of the following Mediterranean woody plants: Quercus ilex ssp. ilex, Quercus ilex ssp. ballota, Olea europaea ssp. sylvestris, Ceratonia siliqua and Arbutus unedo. Assessment of O3 'sensitivity' was based on the development of O3-induced visible injury and the extent of the reduction in relative growth rate induced by O3. Two-year-old seedlings were exposed in open-top chambers to charcoal filtered air (CFA), Non-filtered air (NFA) or Non-filtered air supplied with 40 ppb O3 from 09:00 to 18:00 hours (NFA+40). No clear relationships were found between the development of visible injury and effects on plant growth or accumulated biomass. Olea europea ssp. sylvestris and Quercus ilex ssp. ballota appeared to be the most O3-sensitive tree species screened; a ten month exposure to ambient O3 levels (AOT40 = 12.4 ppm.h) caused reductions in height and/or stem growth. Further research is needed to characterise the physiological, biochemical and anatomical characteristics that may underlie the 'sensitivity' of certain Mediterranean species to O3.
Terradas J (1999) Reflexiones para una transición: del estado del bienestar al futuro. En Homenaje a Don Ángel Ramos Fernández (1926-1998). Real Academia de Ciencias Exactas Físicas y Naturales Academia de Ingeniería
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