Passeig ecofisiològic per l'espai i pel temps: l'estudi de les alteracions produïdes pels canvis climàtics i atmosfèrics en l'estructura i el funcionament de les plantes i dels ecosistemes terrestres.

Peñuelas J, Filella I, Estiarte M, Llusià J, Ogaya R, Ribas A, Llorens L, Mangiron M, Munné-Bosch S, Bruna P, Prieto P, Asensio D, Sardans J, Serrano L, Oliveira G, Castells E, Rodà F, Lloret F, Terradas J (2003) Passeig ecofisiològic per l'espai i pel temps: l'estudi de les alteracions produïdes pels canvis climàtics i atmosfèrics en l'estructura i el funcionament de les plantes i dels ecosistemes terrestres. Treballs de la Societat Catalana de Biologia 54:65-84.

Ecophysiological responses of two Mediterranean shrubs, Erica multiflora and Globularia alypum, to experimentally drier and warmer conditions

Llorens L., Peñuelas J., Estiarte M. (2003) Ecophysiological responses of two Mediterranean shrubs, Erica multiflora and Globularia alypum, to experimentally drier and warmer conditions. Physiologia Plantarum. 119: 231-243.
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Doi: 10.1034/j.1399-3054.2003.00174.x

Resum:

A new approach was used to experimentally dry and warm a Mediterranean shrubland. By means of automatically sliding curtains, the drought period was extended by excluding rain over the two growing seasons (spring and autumn), and passive warming was created by avoiding infra-red dissipation at night over the whole year. The aim of the study was to test how a future extended drought period and an increase in temperatures could affect the photosynthetic and water use strategies of two co-occurring Mediterranean shrubs, Erica multiflora and Globularia alypum, which are common species of the dry coastal shrublands. The shoot water potential, leaf gas exchange rates and chlorophyll a fluorescence of plants was monitored seasonally during two years (1999-2001). In addition we measured the photosynthetic response curves to light and CO 2 in autumn 2001 and the foliar N concentration and leaf C and N stable isotopes in summer 1999 and 2000. Droughted plants of both shrub species showed lower shoot water potentials, transpiration rates and stomatal conductances than control plants, although there was a high seasonal variability. Drought treatment reduced significantly the overall leaf net photosynthetic rates of E. multiflora, but not of G. alypum. Droughted plants of E. multiflora also showed lower leaf net photosynthetic rates in response to light and CO2 and lower carboxylation efficiency than controls, but there was no significant effect of drought on its overall photosystem II (PSII) photochemical efficiency. Although warming treatment did not affect the leaf net photosynthetic rates of the two species overall the study, it increased significantly the carboxylation efficiency and leaf net photosynthetic rates of G. alypum plants in response to CO2 levels in autumn 2001. In addition, warming treatment increased the potential photochemical efficiency of PSII (Fv/Fm) of both species (but especially of G. alypum) at predawn or midday and mainly in autumn and winter. Thus, the results suggest that drier conditions might decrease the annual productivity of these Mediterranean shrubs, particularly of E. multiflora, and that future warming could alleviate the present low temperature constraints of the photosynthetic performance of the two studied species, but especially of G. alypum, during the colder seasons. Ultimately, drier and warmer conditions in the near future may change the competitive relationship among these species in such Mediterranean ecosystems.

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Diurnal and seasonal variations in the photosynthetic performance and water relations of two co-occurring Mediterranean shrubs, Erica multiflora and Globularia alypum

Llorens L., Peñuelas J., Filella I. (2003) Diurnal and seasonal variations in the photosynthetic performance and water relations of two co-occurring Mediterranean shrubs, Erica multiflora and Globularia alypum. Physiologia Plantarum. 118: 84-95.
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Doi: 10.1034/j.1399-3054.2003.00101.x

Resum:

Diurnal and seasonal fluctuations in the photosynthetic performance and water relations of two co-occurring Mediterranean shrubs, Erica multiflora and Globularia alypum were monitored throughout two consecutive years at Garraf Natural Park in north-east Spain. Leaf gas exchange rates, chlorophyll fluorescence and shoot water potentials were measured once each season. Leaf nitrogen and carbon concentrations, leaf δ13C and δ15N and specific leaf area (SLA) were also measured once a year (August) on well developed mature leaves. Globularia alypum experienced seasonal fluctuations in their water potential, with the lowest values recorded in summer, whereas E. multiflora did not show significant differences in water potential among seasons. Moreover, lower water potentials were found in G. alypum than in E. multiflora throughout the entire study, suggesting that the latter behaved as a drought-avoiding species, whereas the former tolerated lower water potentials. In both species, maximum leaf gas exchange rates were observed in autumn and secondarily in spring; in contrast, photosynthetic and transpiration rates reached absolute minima in summer. The stronger fluctuations in water potential and leaf gas exchange rates found in G. alypum compared to E. multiflora, suggest that G. alypum is, sensu Levitt (1980), a water spender, whereas E. multiflora is a water conservative. This hypothesis is further supported by a higher integrated water-use efficiency (higher δ13C values) and a higher degree of sclerophylly (lower SLA) in E. multiflora in comparison with G. alypum. Globularia alypum showed higher leaf gas exchange rates and higher predawn potential photochemical efficiency (Fv/Fm) than E. multiflora during most of the study. In spring and autumn, predawn Fv/Fm values were within the optimal range, whereas chronic photoinhibition in summer and winter was detected in both species. However, whereas both species could maintain positive photosynthetic rates in winter, frequent negative values were found in summer, suggesting higher levels of stress during the drought period. These results together with the high correlations that were found between the net photosynthetic rates and several parameters of water availability (accumulated rainfall, soil moisture or midday water potential) provided further evidence of the key role of water availability in the regulation of the photosynthetic rates in these Mediterranean species. Warmer and drier conditions in future decades, as a consequence of climate change, may alter the present, slight competitive advantage of G. alypum and the fitness of both shrub species within semi-arid Mediterranean environments.

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Efectos del cambio climático (sequía y calentamiento) en los procesos del suelo de ecosistemas arbustivos.

Estiarte M, Peñuelas J, Llorens L, Rodà F, Prieto P, Bruna P, Beier C, Schmidt I, Nielsen T, Emmet B, Sowerby A, Tietema A, Gorissen A, Filella I, Llusià J, Lloret F, Terradas J (2003) Efectos del cambio climático (sequía y calentamiento) en los procesos del suelo de ecosistemas arbustivos. In VII Congreso Nacional de la Asociación Española de Ecología Terrestre. AEET-CREAF. Soft Congres, Barcelona, pp. 835-857.

Efectes del canvi climàtic (eixut i escalfament) en una brolla del Garraf: resultats dels projectes Climoor i Vulcan.

Estiarte M, Peñuelas J, Llorens L, Bruna P, Prieto P, Filella I, Llusià J, Lloret F, Rodà F (2003) Efectes del canvi climàtic (eixut i escalfament) en una brolla del Garraf: resultats dels projectes Climoor i Vulcan. In IV Trobada d'Estudiosos del Garraf. Diputació de Barcelona, Barcelona, pp. 65-74.

Photo- and antioxidative protection during summer leaf senescence in Pistacia lentiscus L. grown under mediterranean field conditions

Munné-Bosch S., Peñuelas J. (2003) Photo- and antioxidative protection during summer leaf senescence in Pistacia lentiscus L. grown under mediterranean field conditions. Annals of Botany. 92: 385-391.
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Doi: 10.1093/aob/mcg152

Resum:

Summer leaf senescence in Pistacia lentiscus L. plants serves to remobilize nutrients from the oldest leaves to the youngest ones, and therefore contributes to plant survival during the adverse climatic conditions typical of Mediterranean summers, i.e. water deficit superimposed on high solar radiation and high temperatures. To evaluate the extent of photo- and antioxidative protection during leaf senescence of this species, changes in carotenoids, including xanthophyll cycle pigments, and in the levels of ascorbate and α-tocopherol were measured prior to and during summer leaf senescence in 3-year-old plants grown under Mediterranean field conditions. Although a chlorophyll loss of approx. 20 % was observed during the first stages of leaf senescence, no damage to the photosynthetic apparatus occurred as indicated by constant maximum efficiencies of photosystem II photochemistry. During this period the de-epoxidation state of the xanthophyll cycle, and lutein, neoxanthin and ascorbate levels were kept constant. At the same time β-carotene and α-tocopherol levels increased by approx. 9 and 70 %, respectively, presumably conferring photo- and antioxidative protection to the photosynthetic apparatus. By contrast, during the later stages of leaf senescence, characterized by severe chlorophyll loss, carotenoids were moderately degraded (neoxanthin by approx. 20 %, and both lutein and β-carotene by approx. 35 %), ascorbate decreased by approx. 80 % and α-tocopherol was not detected in senescing leaves. This study demonstrates that mechanisms of photo- and antioxidative protection may play a major role in maintaining chloroplast function during the first stages of leaf senescence, while antioxidant defences are lost during the latest stages of senescence. © 2003 Annals of Botany Company.

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Comparative seasonal gas exchange and chlorophyll fluorescence of two dominant woody species in a Holm Oak Forest

Ogaya R., Peñuelas J. (2003) Comparative seasonal gas exchange and chlorophyll fluorescence of two dominant woody species in a Holm Oak Forest. Flora. 198: 132-141.
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Doi: 10.1078/0367-2530-00085

Resum:

Diurnal courses of net CO2 uptake rate, stomatal conductance (gS), maximum photochemical efficiency of PSII (Fv/Fm) and apparent photosynthetic electron transport rate (ETR) were measured in Quercus ilex and Phillyrea latifolia in a holm oak forest throughout the seasons of the year. These measurements were complemented with response curves of photosynthetic rates to PPFD and CO2 concentrations. P. latifolia was better adapted to drought and warm conditions and showed higher net CO2 uptake, gS and Fv/Fm values than Q. ilex in summer. But in autumn and specially in winter P. latifolia was more sensitive to low temperatures and experienced lower net CO2 uptake, gS, ETR and Fv/Fm values than Q. ilex. The maximum net CO2 uptake values for P. latifolia occurred under summer high temperatures whereas maximum net CO2 uptake values for Q. ilex occurred under winter low temperatures. However, in summer during midday, both species presented null or slightly negative net CO2 uptake rates. Since in the summer season both species experienced similar ETR values, the lower net CO2 uptake values of Q. ilex suggest that Q. ilex presented greater photorespiration rates. During winter, very low Fv/Fm values were found especially for P. latifolia, indicating that maximal photochemical efficiency of PSII is very sensitive to low temperatures. However, they were not accompanied by low net CO2 uptake rates showing that cold photoinhibition determined a potential but not an actual decrease in photosynthetic performance. Under well watered conditions and with high CO2 concentration and saturated PPFD, Q. ilex was able to increase its photosynthetic rates whereas P. latifolia had lower plasticity to make a profit of optimal environmental conditions. These results show different strategies between these two dominant co-occurring species. They also indicate that the warmer and drier conditions expected for the Mediterranean region in the near decades as a result of climate change will favour drought resistant species with lower photosynthetic rates such as P. latifolia in detriment of more mesic species such as Q. ilex.

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Comparative field study of Quercus ilex and Phillyrea latifolia: Photosynthetic response to experimental drought conditions

Ogaya R., Peñuelas J. (2003) Comparative field study of Quercus ilex and Phillyrea latifolia: Photosynthetic response to experimental drought conditions. Environmental and Experimental Botany. 50: 137-148.
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Doi: 10.1016/S0098-8472(03)00019-4

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Quercus ilex and Phillyrea latifolia growing in a holm oak forest in Prades mountains (NE Spain) were subjected to experimental drought conditions. Soil water availability was reduced about 15% by plastic strips and funnels that partially excluded rain throughfall and by ditch exclusion of water runoff. Diurnal courses of maximum photochemical efficiency of PSII (Fv/Fm), apparent photosynthetic electron transport rate (ETR), net photosynthetic rate (A), transpiration rate (E) and water use efficiency (WUE) were measured in sunlit and shade leaves of both species during 2 years. Moreover, the responses of photosynthetic rates to PPFD and CO 2 concentrations were also measured. Q. ilex experienced lower E rates and higher A rates and WUE than P. latifolia throughout the experimental period, but during summer drought these differences disappeared. Q. ilex exhibited a less cold sensitive behavior whereas P. latifolia showed a more heat-drought resistant behavior. Under severe summer drought conditions none of the two species was able to reach a positive carbon gain. Drought treatment produced a slight decrease in Fv/Fm values of Q. ilex plants and a strong decrease in Fv/Fm values of P. latifolia only in winter 2000, when drought stress coincided with cold stress. Drought treatment produced also a slight decrease in ETR values of both species. During midday, A and E rates decreased in drought plots in both species associated to lower photochemical efficiencies. In those drought plots, only P. latifolia was able to increase WUE by reducing transpiration losses during midday. Both species tended to present higher A rates for a given soil humidity in drought than in control plots. However, whereas Q. ilex A rates increased with soil humidity, P. latifolia A rates did not increase above 17% soil humidity, showing no water availability response above such threshold. It is very likely that mesic species such as Q. ilex lose competitive advantage in the drier environment forecasted for next decades than the more xeric P. latifolia. © 2003 Elsevier Science B.V. All rights reserved.

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Effect of drought on diameter increment of Quercus ilex, Phillyrea latifolia, and Arbutus unedo in a holm oak forest of NE Spain

Ogaya R., Peñuelas J., Martínez-Vilalta J., Mangirón M. (2003) Effect of drought on diameter increment of Quercus ilex, Phillyrea latifolia, and Arbutus unedo in a holm oak forest of NE Spain. Forest Ecology and Management. 180: 175-184.
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Doi: 10.1016/S0378-1127(02)00598-4

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The present study was carried out to elucidate the drought growth responses of Quercus ilex L., Phillyrea latifolia L., Arbutus unedo L., and other accompanying woody species of the Mediterranean holm oak forest. We submitted holm oak forest stands in Prades mountains (NE Spain) to a 2-year experimental drought. We reduced soil water availability about 15% by plastic strips and funnels that partially excluded rain throughfall and by ditch interception of water runoff. Mean stem diameter increment showed a great variation depending on the species. A. unedo had larger growth rates than Q. ilex and P. latifolia, but it was also the species that experimented the highest growth reduction in the drought plots (77%), suggesting a higher drought sensitivity than Q. ilex (55%) and P. latifolia (no drought effect). The growth reduction was specially marked in the larger trees. Aboveground stand biomass increment, estimated from stem diameter by allometric relationships, was 1.9 Mg ha-1 per year in the control plots. The 15% reduction in the upper soil moisture produced 42% reduction in this biomass increment. In the drier conditions predicted in this Mediterranean area in the frame of climate change, an important reduction of growth rates can be hence expected, accompanied by a gain of dominance of drought-tolerant species such as P. latifolia in detriment of more mesic species such as Q. ilex. © 2002 Elsevier Science B.V. All rights reserved.

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A global change-induced biome shift in the Montseny mountains (NE Spain)

Penuelas J., Boada M. (2003) A global change-induced biome shift in the Montseny mountains (NE Spain). Global Change Biology. 9: 131-140.
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Doi: 10.1046/j.1365-2486.2003.00566.x

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Shifts in plant species and biome distribution in response to warming have been described in past climate changes. However, reported evidence of such shifts under current climate change is still scarce. By comparing current and 1945 vegetation distribution in the Montseny mountains (Catalonia, NE Spain), we report here a progressive replacement of cold-temperate ecosystems by Mediterranean ecosystems. Beech (Fagus sylvatica) forest has shifted altitudinally upwards by ca. 70 m at the highest altitudes (1600-1700 m). Both the beech forests and the heather (Calluna vulgaris) heathlands are being replaced by holm oak (Quercus ilex) forest at medium altitudes (800-1400 m). This beech replacement has been observed to occur through a progressive isolation and degradation of beech stands. In 'isolated' (small and surrounded by holm oaks) beech stands, beech trees are 30% more defoliated, beech recruitment is 41% lower, and holm oak recruitment is three times higher than in 'continental' (large and continous) beech stands. The progressively warmer conditions, complemented by the land use changes (mainly the cessation of traditional land management) are the apparent causes, providing a paradigmatic example of global change affecting distributions of plant species and biomes.

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