Estiarte M., De Castro M., Espelta J.M. (2007) Effects of resource availability on condensed tannins and nitrogen in two Quercus species differing in leaf life span. Annals of Forest Science. 64: 439-445.LinkDoi: 10.1051/forest:2007021
Seedlings of Quercus ilex and Q. cerrioides, an evergreen and a winter-deciduous oak co-occurring in western-Mediterranean forests, were grown at two light regimes (8 and 36% of photosynthetically active radiation), at two water regimes (500 and 800 mm) and with two nutrient availabilities (standard substrate and 7% increase in soil N). The concentrations of soluble condensed tannins (CT) and nitrogen in the leaves were analyzed to test the phenotypic plasticity of these commonly related parameters in two congeneric species with contrasting leaf habit. Q. ilex contains seven times more CT and a few less N than Q. cerrioides. Light increased CT, whereas neither fertilization nor water had an effect on CT. N concentration was decreased by light, increased by fertilization and not affected by water treatment. Plant growth was increased by light but not affected by fertilization or water treatment. CT were negatively correlated with N concentration. CT of the evergreen species exhibited greater plasticity than the deciduous one as reflected by a steeper negative correlation among nitrogen and CT concentrations in Q. ilex. Given the antiherbivory activity of CT, this implies that in less shaded environments, e.g. canopy aperture by disturbances, leaf tissue quality for herbivores will be much more reduced in Q. ilex than in Q. cerrioides. Higher leaf CT in Q. ilex and its higher plasticity to light availability may explain the higher browsing by sheep in Q. cerrioides than in Q. ilex resprouts, as well as the low recruitment rates of seedlings of the former species, reported in other studies. © INRA, EDP Sciences, 2007.
Estiarte M, Peñuelas J (2007) Conseqüències ecològiques del canvi climàtic. Serra D'Or 571-572: 49-51
Peñuelas J., Estiarte M, Ogaya R, Filella I, Jump A, Garbulsky M, Sardans J., Llusià J, Seco R, Alessio G., Hunt J, Owen S, Asensio D, Prieto P, Ribas A, Carrillo B, Blanch S, Coll M, Kefauer S, Stefanescu C, Lloret F, Terradas J (2007) Climate change effects on Mediterranean forests: from observations to experimentation, from genetics to remote sensing. Afforestation and sustainable forests as means to combat desertification. 16-19 April Jerusalem, Israel, p. 50.
Peñuelas J., Prieto P., Beier C., Cesaraccio C., de Angelis P., de Dato G., Emmett B.A., Estiarte M., Garadnai J., Gorissen A., Láng E.K., Kröel-dulay G., Llorens L., Pellizzaro G., Riis-nielsen T., Schmidt I.K., Sirca C., Sowerby A., Spano D., Tietema A. (2007) Response of plant species richness and primary productivity in shrublands along a north-south gradient in Europe to seven years of experimental warming and drought: Reductions in primary productivity in the heat and drought year of 2003. Global Change Biology. 13: 2563-2581.LinkDoi: 10.1111/j.1365-2486.2007.01464.x
We used a nonintrusive field experiment carried out at six sites - Wales (UK), Denmark (DK), the Netherlands (NL), Hungary (HU), Sardinia (Italy - IT), and Catalonia (Spain -SP) -along a climatic and latitudinal gradient to examine the response of plant species richness and primary productivity to warming and drought in shrubland ecosystems. The warming treatment raised the plot daily temperature by ca. 1 °C, while the drought treatment led to a reduction in soil moisture at the peak of the growing season that ranged from 26% at the SP site to 82% in the NL site. During the 7 years the experiment lasted (1999-2005), we used the pin-point method to measure the species composition of plant communities and plant biomass, litterfall, and shoot growth of the dominant plant species at each site. A significantly lower increase in the number of species pin-pointed per transect was found in the drought plots at the SP site, where the plant community was still in a process of recovering from a forest fire in 1994. No changes in species richness were found at the other sites, which were at a more mature and stable state of succession and, thus less liable to recruitment of new species. The relationship between annual biomass accumulation and temperature of the growing season was positive at the coldest site and negative at the warmest site. The warming treatment tended to increase the aboveground net primary productivity (ANPP) at the northern sites. The relationship between annual biomass accumulation and soil moisture during the growing season was not significant at the wettest sites, but was positive at the driest sites. The drought treatment tended to reduce the ANPP in the NL, HU, IT, and SP sites. The responses to warming were very strongly related to the Gaussen aridity index (stronger responses the lower the aridity), whereas the responses to drought were not. Changes in the annual aboveground biomass accumulation, litterfall, and, thus, the ANPP, mirrored the interannual variation in climate conditions: the most outstanding change was a decrease in biomass accumulation and an increase in litterfall at most sites during the abnormally hot year of 2003. Species richness also tended to decrease in 2003 at all sites except the cold and wet UK site. Species-specific responses to warming were found in shoot growth: at the SP site, Globularia alypum was not affected, while the other dominant species, Erica multiflora, grew 30% more; at the UK site, Calluna vulgaris tended to grow more in the warming plots, while Empetrum nigrum tended to grow less. Drought treatment decreased plant growth in several studied species, although there were some species such as Pinus halepensis at the SP site or C. vulgaris at the UK site that were not affected. The magnitude of responses to warming and drought thus depended greatly on the differences between sites, years, and species and these multiple plant responses may be expected to have consequences at ecosystem and community level. Decreases in biodiversity and the increase in E. multiflora growth at the SP site as a response to warming challenge the assumption that sensitivity to warming may be less well developed at more southerly latitudes; likewise, the fact that one of the studied shrublands presented negative ANPP as a response to the 2003 heat wave also challenges the hypothesis that future climate warming will lead to an enhancement of plant growth and carbon sequestration in temperate ecosystems. Extreme events may thus change the general trend of increased productivity in response to warming in the colder sites. © 2007 Blackwell Publishing Ltd.
Riera P., Peñuelas J., Farreras V., Estiarte M. (2007) Valuation of climate-change effects on Mediterranean shrublands. Ecological Applications. 17: 91-100.LinkDoi: 10.1890/1051-0761(2007)017[0091:VOCEOM]2.0.CO;2
In general, the socioeconomic analysis of natural systems does not enter into the realms of natural science. This paper, however, estimates the human-welfare effects of possible physicochemical and biological impacts of climate change on Mediterranean shrublands over the coming 50 years. The contingent choice method was applied to elicit the trade-offs in perceived values for three climate-sensitive attributes of shrubland (plant cover, fire risk, and soil erosion) and for the costs of programs designed to mitigate changes. Soil erosion was found to be the attribute of shrubland that most concerned the population, followed by fire risk and then plant cover. An increase of 1% in the shrubland area affected by erosion was estimated to cost each person on average 2.9 euros per year in terms of lost welfare, a figure that is equivalent in terms of perceptions of social welfare to an increase of 0.24% in the shrub area burned annually and a decrease of 3.19% in the area of plant cover. These trade-off values may help ecologists, policy makers, and land managers to take social preferences into account. © 2007 by the Ecological Society of America.
Sardans J., Peñuelas J., Estiarte M. (2007) Seasonal patterns of root-surface phosphatase activities in a Mediterranean shrubland. Responses to experimental warming and drought. Biology and Fertility of Soils. 43: 779-786.LinkDoi: 10.1007/s00374-007-0166-1
Mediterranean ecosystems are water limited and the current general circulation Models (GCM) and ecophysiological models forecast a warming and a further increase of drought in the next decades. A stronger water stress can decrease the capacity for nutrient absorption by plants. We conducted a field experiment to simulate forecasted drought and warming in a Mediterranean calcareous shrubland to assess the performance of root-surface phosphatase activities of the dominant shrub Globularia alypum. These enzyme activities were higher in autumn and spring, when the climate conditions were optimal for plant activity, than in summer or winter, when there was either lack of water or cold temperatures. A decrease in soil moisture in drought plots decreased root-surface phosphatase activity (29% in summer and 25% in autumn). The decrease in root-surface phosphatase activity in drought plots coincided with a decrease in P leaf concentrations and P accumulation in aboveground biomass and loss of photosynthetic capacity of some dominant shrub species of this ecosystem, and with a tendency to increase total soil-P. These results suggest that the expected drier conditions in this Mediterranean shrubland in the next decades will slow down the P uptake by plants, thereby, diminishing the P contents in biomass and increasing total P contents in soil in non-available forms and that this can be, in part, attributable to a result of the decrease in root-surface phosphatase activity. © 2007 Springer-Verlag.
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