Beier C., Emmett B.A., Tietema A., Schmidt I.K., Penũelas J., Láng E.K., Duce P., De Angelis P., Gorissen A., Estiarte M., De Dato G.D., Sowerby A., Kröel-Dulay G., Lellei-Kovács E., Kull O., Mand P., Petersen H., Gjelstrup P., Spano D. (2009) Carbon and nitrogen balances for six shrublands across Europe. Global Biogeochemical Cycles. 23: 0-0.EnllaçDoi: 10.1029/2008GB003381
Shrublands constitute significant and important parts of European landscapes providing a large number of important ecosystem services. Biogeochemical cycles in these ecosystems have gained little attention relative to forests and grassland systems, but data on such cycles are required for developing and testing ecosystem models. As climate change progresses, the potential feedback from terrestrial ecosystems to the atmosphere through changes in carbon stocks, carbon sequestration, and general knowledge on biogeochemical cycles becomes increasingly important. Here we present carbon and nitrogen balances of six shrublands along a climatic gradient across the European continent. The aim of the study was to provide a basis for assessing the range and variability in carbon storage in European shrublands. Across the sites the net carbon storage in the systems ranged from 1,163 g C m-2 to 18,546 g C m-2, and the systems ranged from being net sinks (126 g C m -2 a-1) to being net sources (-536 g C m-2 a-1) of carbon with the largest storage and sink of carbon at wet and cold climatic conditions. The soil carbon store dominates the carbon budget at all sites and in particular at the site with a cold and wet climate where soil C constitutes 95% of the total carbon in the ecosystem. Respiration of carbon from the soil organic matter pool dominated the carbon loss at all sites while carbon loss from aboveground litter decomposition appeared less important. Total belowground carbon allocation was more than 5 times aboveground litterfall carbon which is significantly greater than the factor of 2 reported in a global analysis of forest data. Nitrogen storage was also dominated by the soil pools generally showing small losses except when atmospheric N input was high. The study shows that in the future a climate-driven land cover change between grasslands and shrublands in Europe will likely lead to increased ecosystem C where shrublands are promoted and less where grasses are promoted. However, it also emphasizes that if feedbacks on the global carbon cycle are to be predicted it is critically important to quantify and understand belowground carbon allocation and processes as well as soil carbon pools, particularly on wet organic soils, rather than plant functional change as the soil stores dominate the overall budget and fluxes of carbon. Copyright 2009 by the American Geophysical Union.
Prieto P, Peñuelas J, Llusià J, Asensio D, Estiarte M (2009) Effects of long-term experimental night-time warming and drought on photosynthesis, Fv/Fm and stomatal conductance in the dominant species of a Mediterranean shrubland. Acta Physiol Plant doi: 10.1007/s11738-009-0285-4. 31: 729-739.
Lloret F., Peñuelas J., Prieto P., Llorens L., Estiarte M. (2009) Plant community changes induced by experimental climate change: Seedling and adult species composition. Perspectives in Plant Ecology, Evolution and Systematics. 11: 53-63.EnllaçDoi: 10.1016/j.ppees.2008.09.001
Experimental manipulation of climate provides a powerful tool for studying plant community dynamics with respect to current climate change. We experimentally investigated the vegetation dynamics of a Mediterranean shrubland under directional climate change by manipulating rain and temperature at stand level throughout 7 years. We focused on seedling establishment in relation to the between-year variability of drought conditions. We also compared seedling dynamics to changes in the established adult vegetation to assess the coupling between both dynamics. We used multivariate techniques (principal response curves (PRC) and redundancy analysis (RDA)) to explore changes in the whole community, and Generalized Linear Model (GLZM) to analyse the influence of drought on the abundance and survival of the most abundant species. Drought treatment induced significant changes in the species composition of the seedlings, via a differential decrease in the seedling density of most species. No species was particularly favoured in terms of seedling abundance under water-deficit conditions. Warming only explained a low percentage of the variability in seedling species composition. The emergence of seedlings in control plots - which may be considered an estimation of the between-year variability in the conditions for seedling establishment - was a better predictor of seedling emergence in experimental plots than climate manipulation treatments. The PRC analysis of the adults showed dynamics that were different from those recorded for seedlings, and it also showed that drought treatment significantly explained species composition. This result is reinforced by the change in the relative abundance of seedling and adults of the more common species in the drought and warming treatments, supporting the hypothesis that climatic directional change heightens discrepancies between recruitment and the adult performance. The RDA analysis applied to species composition at the end of the experiment failed, however, to attain any statistical significance. The warming treatment did not produce any significant shifts in adult vegetation. In conclusion, directional climate change - particularly drier conditions in Mediterranean shrublands - would result in a change in the recruitment of the plant community. This change in seedling recruitment tends to be different from the dynamics of adults, suggesting that potential adult mortality would not be compensated by actual seedling recruitment, thus enhancing shifts in community composition. © 2008 Rübel Foundation, ETH Zürich.
Llusià J., Penuelas J., Prieto P., Estiarte M. (2009) Net ecosystem exchange and whole plant isoprenoid emissions by a mediterranean shrubland exposed to experimental climate change. Russian Journal of Plant Physiology. 56: 29-37.EnllaçDoi: 10.1134/S1021443709010051
We tested the effect of forecasted soil drought and warming climate conditions for the next decades on emission rates of isoprenoids by mediterranean shrublands. We measured isoprenoid emissions by whole dominant mediterranean woody plants (Erica multiflora L. and Globularia alypum L.) inhabiting the studied shrublands. Monoterpene emissions were detected in both species, but isoprene was emitted only by E. multiflora. Maximum emission rates were found during the hottest periods (except for G. alypum, in which they occurred in autumn), and minimum emission rates in winter in E. multiflora. Terpene emission rates ranged from 0.08 μg/(g dry wt h) in winter in E. multiflora to 8.8 μg/(g dry wt h) in G. alypum in autumn. In E. multiflora, the terpene emission rates decreased in response to soil drought only in summer, but increased in response to warming in spring and autumn. Isoprene emissions ranged from 0.1 μg/(g dry wt h) in spring to 4.4 μg/(g dry wt h) in summer. The effect of the treatments was only detected in autumn when soil drought and warming had a negative effect on isoprene emission rates. These data might improve our knowledge of isoprenoid emissions at the canopy level and in response to climate change, soil drought, or warming. © 2008 MAIK Nauka.
Prieto P., Peñuelas J., Lloret F., Llorens L., Estiarte M. (2009) Experimental drought and warming decrease diversity and slow down post-fire succession in a Mediterranean shrubland. Ecography. 32: 623-636.EnllaçDoi: 10.1111/j.1600-0587.2009.05738.x
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. © 2009 Ecography.
Prieto P., Peñuelas J., Llusià J., Asensio D., Estiarte M. (2009) Effects of experimental warming and drought on biomass accumulation in a Mediterranean shrubland. Plant Ecology. 205: 179-191.EnllaçDoi: 10.1007/s11258-009-9608-1
We studied the effects of experimental warming and drought on the plant biomass of a Mediterranean shrubland. We monitored growth at plant level and biomass accumulation at stand level. The experimentation period stretched over 7 years (1999-2005) and we focused on the two dominant shrub species, Erica multiflora L. and Globularia alypum L. and the tree species Pinus halepensis L. The warming treatment increased shoot elongation in E. multiflora, and the drought treatment reduced shoot elongation in G. alypum. The elongation of P. halepensis remained unaffected under both treatments. The balance between the patterns observed in biomass accumulation for the three studied species in the drought plots (reduction in E. multiflora and P. halepensis and increase in G. alypum) resulted in a trend to reduce 33% the biomass of the drought treatment plots with respect to the untreated plots, which almost doubled their biomass from 1998 to 2005. The results also suggest that under drier conditions larger accumulation of dead biomass may occur at stand level, which combined with higher temperatures, may thus increase fire risk in the Mediterranean area. © Springer Science+Business Media B.V. 2009.
Prieto P., Peñuelas J., Niinemets Ü., Ogaya R., Schmidt I.K., Beier C., Tietema A., Sowerby A., Emmett B.A., Láng E.K., Kröel-Dulay G., Lhotsky B., Cesaraccio C., Pellizzaro G., De Dato G., Sirca C., Estiarte M. (2009) Changes in the onset of spring growth in shrubland species in response to experimental warming along a north-south gradient in Europe. Global Ecology and Biogeography. 18: 473-484.EnllaçDoi: 10.1111/j.1466-8238.2009.00460.x
Aim: To test whether the onset of spring growth in European shrublands is advanced in response to the warmer conditions projected for the next two decades by climate models, and, if there is a change, whether it differs across Europe. Location: The studied sites spanned a broad north-south European gradient with average annual temperatures (8.2-15.6 °C) and precipitation (511-1427 mm). Methods: Bud break'was monitored in eight shrub and grass species in six European sites under control and experimentally warmer conditions generated by automatic roofs covering vegetation during the night. Results: Species responsive to increased temperatures were Vaccinium myrtillus and Empetrum nigrum in Wales, Deschampsia flexuosa in Denmark, Calluna vulgaris in Netherlands, Populus alba in Hungary and Erica multiflora in Spain. Although the acceleration of spring growth was the commonest response to warming treatments, the responses at each site were species specific and year dependent. Under experimental warming 25% of cases exhibited a significantly earlier onset of the growing season and 10% had a significantly delayed onset of vegetative growth. No geographical gradient was detected in the experimental warming effects. However, there was a trend towards a greater dominance of phenological advances with more intense the warming treatments. Above 0.8.°C warming, only advancements were recorded. Main conclusions: Our results show that warmer temperatures projected for the next decades have substantial potential effects on the phenology of the spring growth of dominant species in different European shrublands, with a dominant trend towards advancements the more intense the warming is. However, our study also demonstrates the overall difficulties of applying simple predictive relationships to extrapolate the effects of global change on phenology. Various combinations of environmental factors occur concurrently at different European sites and the interactions between different drivers (e.g. water and chilling) can alter phenology significantly. © 2009 Blackwell Publishing.
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