Browsing by Author "Kurz-Besson, Cathy"
Now showing 1 - 4 of 4
Results Per Page
Sort Options
- Eight years of continuous carbon fluxes measurements in a portuguese eucalypt stand under two main events: drought and fellingPublication . Rodrigues, Abel; Pita, Gabriel; Mateus, João; Kurz-Besson, Cathy; Casquilho, Miguel; Cerasoli, Sofia; Gomes, Alberto; Pereira, João SantosThis paper reports on results from eddy covariance measurements of carbon uptake and evapotranspiration in the eucalypt site of Espirra in Southern Portugal (38◦38 N, 8◦36 W). This site was included in the “Carboeurope” European network and is part of a 300 ha eucalypt forest, with about 1100 trees ha−1, intensively managed as a coppice for pulp production and characterized by a 12-month annual growing period. The climate is of Mediterranean type with a long term (1961–1990) annual average precipitation of 709mm and an annual average air temperature of 15.90 ◦C. During the measurement period (2002–2009) two main events took place, which changed the annual sink pattern of the forest: a drought period of two years (2004–2005) and a tree felling (October and November 2006). We analyzed the daily, seasonal and inter-annual variation of carbon uptake and evapotranspiration, and their relationships with the events and the variability of the main meteorological variables. Before the felling, annual net ecosystem exchange (NEE) increased from −865.56gCm−2 in 2002 to −356.64gCm−2 in 2005 together with a deep decrease in rainfall from 748mm in 2002 to 378.58mm and 396.64mm in 2004 and 2005, respectively. For the same period, seasonal patterns of carbon uptake showed maximum values in April and decreased in July–August. The eucalypt stand recovered its carbon sink ability since June 2007 and had a NEE of −209.01gCm−2 in 2009. After the felling, the carbon uptake occurred from mid-February to mid-October, following an almost opposite pattern than that of the trees in the term of their productive cycle. A quantitative approach using generalized estimating equations (GEEs) was made for the period before the felling to relate monthly NEE and GPP with accumulated photosynthetic active radiation, water vapour pressure and precipitation. In conclusion, our study showed the relevant effects of water stress and anthropogenic interventions in the daily, seasonal and annual patterns of carbon uptake, under a context of good environmental conditions for carbon sequestration.
- Florestas mistas de Sobreiro e Pinheiro-Manso: Conhecimento, desafios e recomendações de gestãoPublication . Correia, Alexandra C.; Barcik, Pedro; Lloberas Lafuente, David; Ramires, Inês; Pinto, Clara; Kurz-Besson, Cathy; Marcelo, Maria da Encarnação; Branco, Manuela; Barreiro, Susana; Botequim, Brigite; Nunes, Leónia; Tomé, Margarida; Costa-e-Silva, Filipe
- Impacto da estrutura e funcionamento do sistema radicular no uso de água pelas árvoresPublication . David, Teresa Soares; Pinto, Clara; Henriques, Manuel; Kurz-Besson, Cathy; Nadezhdina, Nadezhda; Cermak, Jan; Quilhó, Teresa; Paço, Teresa Afonso do; Ferreira, Isabel; Caldeira, M.Conceição; Cohen, S.; Siegwolf, R.; Chaves, M.Manuela; Pereira, João Santos; David, Jorge Soares
- Root functioning, tree water use and hydraulic redistribution in Quercus suber trees: a modeling approach based on root sap flowPublication . David, Teresa S.; Pinto, Clara A.; Nadezhdina, Nadezhda; Kurz-Besson, Cathy; Henriques, Manuel O.; Quilhó, Teresa; Cermak, Jan; Chaves, M.Manuela; Pereira, J.S.; David, J.S.Mediterranean evergreen oaks have to survive a long summer drought. Roots may play a relevant role under these conditions. We studied their structure and function in a mature Quercus suber L. tree in central Portugal. The root system was mapped till the lowest water table level (4.5 m depth). Xylem anatomy was analyzed in a vertical profile belowground. Sap flow was continuously monitored for 1.5 yrs in the stem and roots of this intensively studied tree (heat field deformation method) and in the stem of four trees (Granier method), in relation to environmental variables and predawn leaf water potential. The sources of water uptake were assessed by stable isotope analyses in summer. Results showed a dimorphic root system with a network of superficial roots linked to sinker roots, and a taproot diverting into tangles of deep fine roots submerged for long periods, with parenchyma aerenchyma. Transpiration was not restricted in summer due to root access to groundwater. The isotopic d18O signature of twig xylem water was similar to that of groundwater in the dry season. Two functional types of superficial roots were identified: shallow connected and deep connected roots. A modeling approach was built considering that each superficial root was linked to a sinker, with part of the root deep connected (between the stem and the sinker) and part shallow connected (between the sinker and topsoil). This conceptual framework simulated tree stem sap flow from root sap flow with a high efficiency (R2 = 0.85) in four plot trees. On an annual basis, soil water and groundwater contributions were 69.5% and 30.5% of stem flow, respectively. Annual hydraulic lift and hydraulic descent were 0.9% and 37.0% of stem flow, respectively. The trees maximize the exploitation of the environmental resources by using the topsoil water during most of the year, and groundwater together with hydraulic lift (nutrient supply) in the dry summer. This study shows that a dimorphic root system, with roots reaching groundwater, is an efficient strategy of Q. suber trees to cope with seasonal drought. Knowledge of the functional behavior of Q. suber trees under shallow water table conditions may contribute to the definition of better adapted management practices and to anticipate their responses to climate change