M Vaz

Publications (4)7.13 Total impact

• Article: Leaf-level responses to light in two co-occurring Quercus (Quercus ilex and Quercus suber): leaf structure, chemical composition and photosynthesis

  M. Vaz, J. Maroco, N. Ribeiro, L. C. Gazarini, J. S. Pereira, M. M. Chaves
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  ABSTRACT: We studied morphological, biochemical and physiological leaf acclimation to incident Photon-Photosynthetic-Flux-Density (PPFD) in Quercus ilex (holm oak) and Quercus suber (cork oak) at Mediterranean evergreen oak woodlands of southern Portugal. Specific leaf area (SLA) decreased exponentially with increasing PPFD in both species. Q. ilex had lower SLA values than Q. suber. Leaf nitrogen, cellulose and lignin concentration (leaf area-based) scaled positively with PPFD. Maximum rate of carboxylation (Vcmax), capacity for maximum photosynthetic electron transport (Jmax), rate of triose-P utilization (VTPU) and the rate of nonphotorespiratory light respiration (Rd) were also positively correlated with PPFD in both Quercus species, when expressed in leaf area but not on leaf mass basis. Q suber showed to have higher photosynthetic potential (Vcmax, Jmaxm and VTPUm) and a higher nitrogen efficient nitrogen use than Q.ilex. Leaf chlorophyll concentration increased with decreasing PPFD, improving apparent quantum use efficiency (Φ) in both Quercus species. We concluded that, in Q.ilex and Q.suber, leaf structural plasticity is a stronger determinant for leaf acclimation to PPFD than biochemical and physiological plasticity. KeywordsLight–Nitrogen–Photosynthesis– Quercus ilex – Quercus suber – SLA
  Agroforestry Systems 04/2012; 82(2):173-181. · 1.38 Impact Factor
• Article: Drought-induced photosynthetic inhibition and autumn recovery in two Mediterranean oak species (Quercus ilex and Quercus suber).

  M Vaz, J S Pereira, L C Gazarini, T S David, J S David, A Rodrigues, J Maroco, M M Chaves
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  ABSTRACT: Responses of leaf water relations and photosynthesis to summer drought and autumn rewetting were studied in two evergreen Mediterranean oak species, Quercus ilex spp. rotundifolia and Quercus suber. The predawn leaf water potential (Ψ(lPD)), stomatal conductance (gs) and photosynthetic rate (A) at ambient conditions were measured seasonally over a 3-year period. We also measured the photosynthetic response to light and to intercellular CO₂ (A/PPFD and A/C(i) response curves) under water stress (summer) and after recovery due to autumn rainfall. Photosynthetic parameters, Vc(max), J(max) and triose phosphate utilization (TPU) rate, were estimated using the Farquhar model. RuBisCo activity, leaf chlorophyll, leaf nitrogen concentration and leaf carbohydrate concentration were also measured. All measurements were performed in the spring leaves of the current year. In both species, the predawn leaf water potential, stomatal conductance and photosynthetic rate peaked in spring, progressively declined throughout the summer and recovered upon autumn rainfall. During the drought period, Q. ilex maintained a higher predawn leaf water potential and stomatal conductance than Q. suber. During this period, we found that photosynthesis was not only limited by stomatal closure, but was also downregulated as a consequence of a decrease in the maximum carboxylation rate (Vc(max)) and the light-saturated rate of photosynthetic electron transport (J(max)) in both species. The Vc(max) and J(max) increased after the first autumnal rains and this increase was related to RuBisCo activity, leaf nitrogen concentration and chlorophyll concentration. In addition, an increase in the TPU rate and in soluble leaf sugar concentration was observed in this period. The results obtained indicate a high resilience of the photosynthetic apparatus to summer drought as well as good recovery in the following autumn rains of these evergreen oak species.
  Tree Physiology 08/2010; 30(8):946-56. · 2.88 Impact Factor
• Source

  Available from: Joao S Pereira

  Article: Water-use strategies in two co-occurring Mediterranean evergreen oaks: surviving the summer drought.

  T S David, M O Henriques, C Kurz-Besson, J Nunes, F Valente, M Vaz, J S Pereira, R Siegwolf, M M Chaves, L C Gazarini, J S David
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  ABSTRACT: In the Mediterranean evergreen oak woodlands of southern Portugal, the main tree species are Quercus ilex ssp. rotundifolia Lam. (holm oak) and Quercus suber L. (cork oak). We studied a savannah-type woodland where these species coexist, with the aim of better understanding the mechanisms of tree adaptation to seasonal drought. In both species, seasonal variations in transpiration and predawn leaf water potential showed a maximum in spring followed by a decline through the rainless summer and a recovery with autumn rainfall. Although the observed decrease in predawn leaf water potential in summer indicates soil water depletion, trees maintained transpiration rates above 0.7 mm day(-1) during the summer drought. By that time, more than 70% of the transpired water was being taken from groundwater sources. The daily fluctuations in soil water content suggest that some root uptake of groundwater was mediated through the upper soil layers by hydraulic lift. During the dry season, Q. ilex maintained higher predawn leaf water potentials, canopy conductances and transpiration rates than Q. suber. The higher water status of Q. ilex was likely associated with their deeper root systems compared with Q. suber. Whole-tree hydraulic conductance and minimum midday leaf water potential were lower in Q. ilex, indicating that Q. ilex was more tolerant to drought than Q. suber. Overall, Q. ilex seemed to have more effective drought avoidance and drought tolerance mechanisms than Q. suber.
  Tree Physiology 07/2007; 27(6):793-803. · 2.88 Impact Factor
• Source

  Available from: Joao S Pereira

  Article: Growth at elevated CO2 leads to down-regulation of photosynthesis and altered response to high temperature in Quercus suber L. seedlings

  T. Faria, D. Wilkins, R T Besford, M Vaz, J S Pereira, M M Chaves
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  ABSTRACT: The effects of growth at elevated CO 2 on the response to high temperatures in terms of carbon assimilation (net photosynthesis, stomatal conductance, amount and activity of Rubisco, and concentrations of total soluble sugars and starch) and of photochemistry (for example, the efficiency of excitation energy captured by open photosystem II reaction centres) were studied in cork oak ( Quercus suber L.). Plants grown in elevated CO 2 (700 ppm) showed a down-regulation of photosynthesis and had lower amounts and activity of Rubisco than plants grown at ambient CO 2 (350 ppm), after 14 months in the greenhouse. At that time plants were subjected to a heat-shock treatment (4 h at 45�C in a chamber with 80% relative humidity and 800–1000 �mol m−2 s−1 photon flux density). Growth in a CO 2 -enriched atmosphere seems to protect cork oak leaves from the short-term effects of high temperature. Elevated CO 2 plants had positive net carbon uptake rates during the heat shock treatment whereas plants grown at ambient CO 2 showed negative rates. Moreover, recovery was faster in high CO 2 -grown plants which, after 30 min at 25�C, exhibited higher net carbon uptake rates and lower decreases in photosynthetic capacity ( A max as well as in the efficiency of excitation energy captured by open photosystem II reaction centres ( F v JF m than plants grown at ambient CO 2 . The stomata of elevated CO 2 plants were also less responsive when exposed to high temperature.