Filella I., Peñuelas J. (2004) Indications of hydraulic lift by Pinus halepensis and its effects on the water relations of neighbour shrubs. Biologia Plantarum. 47: 209-214.EnllaçDoi: 10.1023/B:BIOP.0000022253.08474.fd
We measured the stable deuterium isotopic composition of xylem sap, the shoot predawn and midday water potentials, and the leaf δ13C of Mediterranean shrubs Pistacia lentiscus, Globularia alypum and Rosmarinus officinalis in a south-oriented transect from a large (12 m tall) Aleppo pine tree, Pinus halepensis. We aimed to study the possibility of hydraulic lift from the deep roots of this pine tree to the shallow soil layers and its influence on these neighbour shrubs. These same traits were also studied in several individuals of the shrub Pistacia lentiscus growing with different types of neighbours: just shrubs, a small (3-4 m) pine tree, and the above mentioned large pine tree. The greater the distance from P. halepensis the plants grew, the higher xylem water SD, the lower the soil water content, and, the lower the predawn and midday water potentials were found. These results suggest the existence of an hydraulic lift from deep roots to shallow soil in this big tree. Further indication of this existence is provided by the improved water status of P. lentiscus (higher water potentials and δD, and lower δ13C and, therefore, lower water use efficiencies) when growing close to the big pine in comparison with the same shrub species growing close to small pines or just surrounded by other shrubs. Moreover, all these trends occurred in the dry summer season, but disappeared in the wet spring season.
Filella I., Peñuelas J., Llorens L., Estiarte M. (2004) Reflectance assessment of seasonal and annual changes in biomass and CO2 uptake of a Mediterranean shrubland submitted to experimental warming and drought. Remote Sensing of Environment. 90: 308-318.EnllaçDoi: 10.1016/j.rse.2004.01.010
We aimed to evaluate how the remote sensing vegetation indices NDVI and PRI responded to seasonal and annual changes in an early successional stage Mediterranean coastal shrubland canopy that was submitted to experimental warming and drought simulating predicted climate change for the next decades. These conditions were obtained by using a new non-intrusive methodological approach that increases the temperature and prolongs the drought period by using roofs that automatically cover the vegetation after the sunset or when it rains. On average, warming increased air temperature by 0.7°C and soil temperature by 1.6°C, and the drought treatment reduced soil moisture by 22%. We measured spectral reflectance at the canopy level and at the individual plant level seasonally during 4 years. Shrubland NDVI tracked the community development and activity. In control and warming treatments, NDVI increased with the years while it did not change in the drought treatment. There was a good relationship between NDVI and both community and individual plant biomass. NDVI also decreased in summer seasons when some species dry or decolour. The NDVI of E. multiflora plant individuals was lower in autumn and winter than in the other seasons, likely because of flowering. Shrubland PRI decreased only in winter, similarly to the PRI of the most dominant species, G. alypum. At this community scale, NDVI was better related than PRI to photosynthetic activity, probably because photosynthetic fluxes followed canopy seasonal greening in this complex canopy, which includes brevideciduous, annual and evergreen species and variable morphologies and canopy coverage. PRI followed the seasonal variations in photosynthetic rates in E. multiflora and detected the decreased photosynthetic rates of drought treatment. However, PRI did not track the photosynthetic rates of G. alypum plants which have lower LAIs than E. multiflora. In this community, which is in its early successional stages, NDVI was able to track biomass, and indirectly, CO2 uptake changes, likely because LAI values did not saturate NDVI. Thus, NDVI appears as a valid tool for remote tracking of this community development. PRI was less adequate for photosynthetic assessment of this community especially for its lower LAI canopies. PRI usefulness was also species-dependent and could also be affected by flowering. These results will help to improve the interpretation of remote sensing information on the structure and physiological status of these Mediterranean shrublands, and to gain better insight on ecological and environmental controls on their ecosystem carbon dioxide exchange. They also show the possibility of assessing the impacts of climate change on shrubland communities. © 2004 Elsevier Inc. All rights reserved.
Filella I (2004) Efectes observats del canvi climàtic en els ecosistemes. In Avila A, Terradas J (eds) Aula d'Ecologia. Cicle de conferències 2003. Servei de Publicacions, Universitat Autònoma de Barcelona, Bellaterra, pp. 85-89.
Peñuelas J, Munné-Bosch S, Llusià J, Filella I (2004) Leaf reflectance and photo- and antioxidant protection in field-grown summer-stressed Phillyrea angustifolia. Optical signals of oxidative stress? New Phytologist 162:115-124.
Peñuelas J, Sabaté S, Filella I, Gracia C (2004) Efectos del cambio climático sobre los ecosistemas terrestres: observación, experimentación y simulación. In Valladares F (ed) Ecología del bosque mediterráneo en un mundo cambiante. Ministerio de Medio Ambiente, Madrid, pp. 425-460.
Peñuelas J., Filella I., Zhang X., Llorens L., Ogaya R., Lloret F., Comas P., Estiarte M., Terradas J. (2004) Complex spatiotemporal phenological shifts as a response to rainfall changes. New Phytologist. 161: 837-846.EnllaçDoi: 10.1111/j.1469-8137.2004.01003.x
• Climatic warming produces significant gradual alterations in the timing of life-cycle events, and here we study the phenological effects of rainfall-pattern changes. • We conducted ecosystem field experiments that partially excluded rain and runoff during the growing season in a Mediterranean forest and in a mediterranean shrubland. Studies of time-series of leaf-unfolding, flowering and fruiting over the last 50 yr in central Catalonia were carried out, and greenup onset in the Iberian Peninsula was monitored by satellite images. • Experimental, historical and geographical changes in rainfall produced significant, complex and strongly species-specific, as well as spatially and temporally variable, phenological effects. Among these changes, it was found that in the Iberian Peninsula, greenup onset changes from spring (triggered by rising temperatures) in the northern cool-wet regions to autumn (triggered by the arrival of autumn rainfalls) in the southern warm-dry regions. Even in the mesic Mediterranean central Catalonia (NE of the peninsula) rainfall had a stronger relative influence than temperature on fruiting phenology. • The results show that changes in rainfall and water availability, an important driver of climate change, can cause complex phenological changes with likely far-reaching consequences for ecosystem and biosphere functioning and structure. The seasonal shift in the Iberian Peninsula further highlights this importance and indicates that vegetation may respond to climate change not only with gradual, but also with abrupt temporal and spatial, changes in the timing of greenup onset.
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