Sap flow of three co-occurring Mediterranean woody species under varying atmospheric and soil water conditions.

Martínez-Vilalta J, Mangirón M, Ogaya R, Sauret M, Serrano L, Peñuelas J, Piñol J (2003) Sap flow of three co-occurring Mediterranean woody species under varying atmospheric and soil water conditions. Tree Physiology 23:747-758.

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.

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

Resum:

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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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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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

Resum:

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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