Barbeta A., Mejia-Chang M., Ogaya R., Voltas J., Dawson T.E., Penuelas J. (2014) The combined effects of a long-term experimental drought and an extreme drought on the use of plant-water sources in a Mediterranean forest. Global Change Biology. : 0-0.EnllaçDoi: 10.1111/gcb.12785
Vegetation in water-limited ecosystems relies strongly on access to deep water reserves to withstand dry periods. Most of these ecosystems have shallow soils over deep groundwater reserves. Understanding the functioning and functional plasticity of species-specific root systems and the patterns of or differences in the use of water sources under more frequent or intense droughts is therefore necessary to properly predict the responses of seasonally dry ecosystems to future climate. We used stable isotopes to investigate the seasonal patterns of water uptake by a sclerophyll forest on sloped terrain with shallow soils. We assessed the effect of a long-term experimental drought (12 years) and the added impact of an extreme natural drought that produced widespread tree mortality and crown defoliation. The dominant species, Quercus ilex, Arbutus unedo and Phillyrea latifolia, all have dimorphic root systems enabling them to access different water sources in space and time. The plants extracted water mainly from the soil in the cold and wet seasons but increased their use of groundwater during the summer drought. Interestingly, the plants subjected to the long-term experimental drought shifted water uptake toward deeper (10-35 cm) soil layers during the wet season and reduced groundwater uptake in summer, indicating plasticity in the functional distribution of fine roots that dampened the effect of our experimental drought over the long term. An extreme drought in 2011, however, further reduced the contribution of deep soil layers and groundwater to transpiration, which resulted in greater crown defoliation in the drought-affected plants. This study suggests that extreme droughts aggravate moderate but persistent drier conditions (simulated by our manipulation) and may lead to the depletion of water from groundwater reservoirs and weathered bedrock, threatening the preservation of these Mediterranean ecosystems in their current structures and compositions.
Penuelas J., Guenther A., Rapparini F., Llusia J., Filella I., Seco R., Estiarte M., Mejia-Chang M., Ogaya R., Ibanez J., Sardans J., Castano L.M., Turnipseed A., Duhl T., Harley P., Vila J., Estavillo J.M., Menendez S., Facini O., Baraldi R., Geron C., Mak J., Patton E.G., Jiang X., Greenberg J. (2013) Intensive measurements of gas, water, and energy exchange between vegetation and troposphere during the MONTES campaign in a vegetation gradient from short semi-desertic shrublands to tall wet temperate forests in the NW Mediterranean Basin. Atmospheric Environment. 75: 348-364.EnllaçDoi: 10.1016/j.atmosenv.2013.04.032
MONTES ("Woodlands") was a multidisciplinary international field campaign aimed at measuring energy, water and especially gas exchange between vegetation and atmosphere in a gradient from short semi-desertic shrublands to tall wet temperate forests in NE Spain in the North Western Mediterranean Basin (WMB). The measurements were performed at a semidesertic area (Monegros), at a coastal Mediterranean shrubland area (Garraf), at a typical Mediterranean holm oak forest area (Prades) and at a wet temperate beech forest (Montseny) during spring (April 2010) under optimal plant physiological conditions in driest-warmest sites and during summer (July 2010) with drought and heat stresses in the driest-warmest sites and optimal conditions in the wettest-coolest site. The objective of this campaign was to study the differences in gas, water and energy exchange occurring at different vegetation coverages and biomasses. Particular attention was devoted to quantitatively understand the exchange of biogenic volatile organic compounds (BVOCs) because of their biological and environmental effects in the WMB. A wide range of instruments (GC-MS, PTR-MS, meteorological sensors, O3 monitors,. .) and vertical platforms such as masts, tethered balloons and aircraft were used to characterize the gas, water and energy exchange at increasing footprint areas by measuring vertical profiles. In this paper we provide an overview of the MONTES campaign: the objectives, the characterization of the biomass and gas, water and energy exchange in the 4 sites-areas using satellite data, the estimation of isoprene and monoterpene emissions using MEGAN model, the measurements performed and the first results. The isoprene and monoterpene emission rates estimated with MEGAN and emission factors measured at the foliar level for the dominant species ranged from about 0 to 0.2mgm-2h-1 in April. The warmer temperature in July resulted in higher model estimates from about 0 to ca. 1.6mgm-2h-1 for isoprene and ca. 4.5mgm-2h-1 for monoterpenes, depending on the site vegetation and footprint area considered. There were clear daily and seasonal patterns with higher emission rates and mixing ratios at midday and summer relative to early morning and early spring. There was a significant trend in CO2 fixation (from 1 to 10mgCm-2d-1), transpiration (from1-5kgCm-2d-1), and sensible and latent heat from the warmest-driest to the coolest-wettest site. The results showed the strong land-cover-specific influence on emissions of BVOCs, gas, energy and water exchange, and therefore demonstrate the potential for feed-back to atmospheric chemistry and climate. •We present a multidisciplinary biosphere-atmosphere field campaign.•We measured a gradient from semi-desertic shrublands to wet temperate forests.•A wide range of instruments and vertical platforms were used.•Land cover strongly influenced emissions of BVOCs and gas, energy and water exchange.•Vegetation has strong potential for feed-back to atmospheric chemistry and climate. © 2013 Elsevier Ltd.
Peñuelas J, Filella I, Farré G, Owen S, Primante C, Rodrigo A, Martín A, Bosch J, Seco R, Porcar A, Llusià J, Greenberg J, Harley P, Rapparini F, Estiarte M, Mejia-Chang M, Ogaya R, Ibañez J, Sardans J, Turnipseed A, Geron C, Duhl T, Facini O, Baraldi R, Rapparini F, Guenther A (2012) BVOCs in the plant-pollinator market and other applications of ecology to betytyerunderstand BVOC emissions in the environment. BVOCs Gordon Conference, Biogenic Hydrocarbons & the atmosphere. Reaching across scales: from molecule to the globe. Bates College, Maine. June 24-29. Key note invited speaker.
Peñuelas J, Filella I, Estiarte M, Ogaya R, Llusià J, Sardans J, Jump A, Carnicer J, Rico L, Garbulsky M, Coll M, Díaz de Quijano M, Seco R, Rivas-Ubach A, Kefauver S, Barbeta A, Achoategui A, Mejía-Chang M, Gallardo A, Farre G, Fernández M, Terradas J (2012) Ecosystemic and biospheric interactions with carbon cycle. In Carbon dioxide budget: processes and tendencies symposium. Universitat Politècnica de Catalunya, May 23-25.
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