RESUMO
Morpho-physiological attributes exhibited in response to drought hardening at the end of the growing season of Eucalyptus globulus Labill under nursery conditions were studied to evaluate the effect of three drought hardening treatments in morpho-physiological traits used as suitable indicators of drought hardiness, such as, plant growth, root growth potential, plant water relationships and survival. Freezing resistance of drought hardened plants was also studied in order to evaluate cross hardening effects in cuttings of Eucalyptus globulus Labill. Drought hardening consisted in induced water stress by watering restriction, until plant stem xylem water potentials (psipd) reached to-0.2, -1.3 and -2.4 MPa. Two water stress-rewatering cycles were applied during 54 days of treatment. The hardening treatments caused a significant reduction in plant height, leaf area, specific leaf area, plant, leaf, stem and root biomass. However, stem diameter was not affected. Root growth potential increased with the exposure to moderate water stress (-1.3 MPa). Drought hardening treatments have not effect on water relationship parameters such as saturation osmotic potential (psipisat), volumetric module of elasticity (e), relative water content (RWCtlp) and osmotic potential (psitlp) at the turgor loss point. Only 1.7 percent and 6 percent of dehydrated dead plants were observed on treatments at -1.3 and -2.4 MPa respectively. Finally, the freezing damage index of leaves (LT50) was not significantly affected by drought hardening treatments. Furthermore, a reduction of 1.1ºC of supercooling capacity was observed at -2.4 MPa. As a conclusion, drought hardening is an important step of plants production programs during the final phase of nursery, because changes in morphological attributes caused by exposure to moderate drought, enable the plants to maintain the balance between transpiration and absorption areas and increase the capacity of plants to generate n...
Assuntos
Secas , Eucalyptus , Efeitos do Clima , Clima Frio/efeitos adversos , Congelamento , Raízes de PlantasRESUMO
Three platinum group elements (Pd, Ir and Rh) both in solution and in pre-reduced form, and also combined with Mg(NO(3))(2) or ascorbic acid, were assessed as possible chemical modifiers on the atomization of As in digest solutions of seafood matrices (clam and fish tissue) by tungsten coil electrothermal atomic absorption spectrometry (TCA-AAS) and compared without a modifier. Of 28 modifier alternatives in study including single form and binary mixtures, and based on maximum pyrolysis temperature without significant As loss and best As absorbance sensitivity during atomization, three modifiers: Rh (0.5microg), Ir (1.0microg) and Rh (0.5microg)+ascorbic acid (0.5microg), at optimum amounts were pre-selected and compared. The definitive modifier (rhodium (0.5microg)) was selected by variance analysis. The mean within-day repeatability was 3% in consecutive measurements (25-300microg l(-1)) (three cycles, each of n=6) and showed good short-term stability of the absorbance measurements. The mean reproducibility was 4% (n=18 in a 3-day period) and the detection limit (3sigma(blank)/slope) was 42pg (n=16). Quantitation was by standard additions to compensate for matrix effects not corrected by the modifier. Three sample digestion procedures were compared in fish and clam tissue samples: microwave acid digestion alone (A) or combined with the addition of 2% (m/v) K(2)S(2)O(8) solution followed either by UV photo-oxidation (B) or re-digestion in a thermal block (C). The accuracy was established by determination of As in certified reference material of dogfish muscle (DORM-2). Procedures B and C showed good recoveries (102% (n=4) and 103% (n=7), respectively), whereas procedure A was not quantitative (85%). The methodology is simple, fast, reliable, of low cost and was applied to the determination of total As in lyophilized samples of clam and fish collected in the Chilean coast.
