Browsing by Author "Pacheco, C.A."
Now showing 1 - 5 of 5
Results Per Page
Sort Options
- Análise de indicadores de desconforto hídrico durante ciclos de stress num olival intensivo no AlentejoPublication . Ferreira, Maria Isabel; Conceição, N.; Pacheco, C.A.; Hausler, M.The identification of a reliable and practical water stress indicator and the corresponding threshold value, for irrigation scheduling, is a classical concern in water management in agriculture. This is not well solved for woody crops, especially those not traditionally irrigated, usually with large roots systems. Aiming to contribute to these studies, we measured water fluxes and some water stress indicators in an olive grove in south Portugal, during successive stress cycles. We report the first preliminary results during a stress cycle in August-September 2011, using sap flow, leaf water potential at predawn, stem diameter variations and soil water content, from which some indicators were derived. From the preliminary information obtained we could not identify a threshold value but very good relationships were found, between the selected automated and not automated variables, useful for farmers and engineering applications. These first encouraging results need confirmation and further analysis
- Biomass allometry and carbon factors for a Mediterranean pine (Pinus pinea L.) in PortugalPublication . Correia, A.A.; Tomé, Margarida; Pacheco, C.A.; Faias, Sónia; Dias, A.C.; Freire, J.; Carvalho, P.O.; Pereira, J.S.Forests play an important role in the global carbon balance because they offset a large portion of the carbon dioxide emitted through human activities. Accurate estimates are necessary for national reporting of greenhouse gas inventories, carbon credit trading and forest carbon management but in Portugal reliable and accessible forest carbon measurement methodologies are still lacking for some species. The objective of this study was to provide forest managers with a comprehensive database of carbon factors and equations that allows estimating stand-level carbon stocks in Pinus pinea L. (P. pinea), regardless of the tree inventory information available. We produced aboveground biomass and stem volume equations, biomass expansion factors (BEF) by component as well as wood basic density (WBD) and component carbon fraction in biomass. A root-to-shoot ratio is also presented using data from trees in which the root system was completely excavated. We harvested 53 trees in centre and south Portugal covering different sizes (6.5 to 56.3 cm), ages (10 to 45 years) and stand densities (20 to 580 trees ha–1). The results indicate that aboveground allometry in P. pinea is not comparable with other pines and varies considerably with stand characteristics, highlighting the need to develop stand-dependent factors and equations for local or regional carbon calculations. BEFaboveground decreases from open (1.33 ± 0.03 Mg m–3) to closed stands (1.07 ± 0.01 Mg m–3) due to a change in biomass allocation pattern from stem to branches. Average WBD was 0.50 ± 0.01 Mg m–3 but varies with tree dimensions and the root-to-shoot ratio found was 0.30 ± 0.03. The carbon fraction was statistically different from the commonly used 0.5 factor for some biomass components. The equations and factors produced allow evaluating carbon stocks in P. pinea stands in Portugal, contributing to a more accurate estimation of carbon sequestered by this forest type.
- Interesse do potencial hídrico foliar de base como indicador da actividade fisiológica da videiraPublication . Lopes, C.M.; Pacheco, C.A.; Vicente-Paulo, J.; Rodrigues, M.L.
- O que fazem as oliveiras de noite ou redistribuição hidráulica num olival de sequeiro no AlentejoPublication . Ferreira, Maria Isabel; Conceição, N.; Pacheco, C.A.; Green, S.Hydraulic redistribution is a mechanism that ensures the survival of superficial roots in dry soil during late summer, as they are submitted during part of the day to a negative flux, coming from roots with access to deep water. This mechanism also enables the plant to continue exploring these upper soil layers, richer in minerals and organic matter and has been observed in many ecosystems, including Montado, in Portugal. A critical question arises: to which extent is the survival of traditional rainfed ecosystems dependent on the water table condition? In order to identify the importance and dynamic of this process in olive groves, a study was conducted in South Portugal using two different, independent methods to follow sap flow in roots. We report the first results obtained with a modified heat pulse method, in a rainfed olive grove. By following roots sap flow from wet spring, 6 months without significant rain and early autumn, we found experimental evidence of hydraulic redistribution from some roots to others
- Seasonal variation of water uptake of a Quercus suber tree in Central PortugalPublication . Nadezhdina, Nadezhda; Ferreira, Maria Isabel; Silva, R.; Pacheco, C.A.Hydraulic redistribution (HR) is the phenomenon where plant roots transfer water between soil horizons of different water potential. When dry soil is a stronger sink for water loss from the plant than transpiration, water absorbed by roots in wetter soil horizons is transferred toward, and exuded into dry soil via flow reversals through the roots. Reverse flow is a good marker of HR and can serve as a useful tool to study it over the long-term. Seasonal variation of water uptake of a Quercus suber tree was studied from late winter through autumn 2003 at Rio Frio near Lisbon, Portugal. Sap flow was measured in five small shallow roots (diameter of 3–4 cm), 1 to 2 m from the tree trunk and in four azimuths and at different xylem depths at the trunk base, using the heat field deformation method (HFD). The pattern of sap flow differed among lateral roots as soil dried with constant positive flow in three roots and reverse flow in two other roots during the night when transpiration ceased. Rain modified the pattern of flow in these two roots by eliminating reverse flow and substantially increasing water uptake for transpiration during the day. The increase in water uptake in three other roots following rain was not so substantial. In addition, the flux in individual roots was correlated to different degrees with the flux at different radial depths and azimuthal directions in trunk xylem. The flow in outer trunk xylem seemed to be mostly consistent with water movement from surface soil horizons, whereas deep roots seemed to supply water to the whole cross-section of sapwood. When water flow substantially decreased in shallow lateral roots and the outer stem xylem during drought, water flow in the inner sapwood was maintained, presumably due to its direct connection to deep roots. Results also suggest the importance of the sap flow sensor placement, in relation to sinker roots, as to whether lateral roots might be found to exhibit reverse flow during drought. This study is consistent with the dimorphic rooting habit of Quercus suber trees in which deep roots access groundwater to supply superficial roots and the whole tree, when shallow soil layers were dry.