Hugo Rafael Bentzen Santos

Physiological and biochemical responses to drought stress in Barbados cherry

To evaluate physiological genotypic differences between two Barbados cherry genotypes (13- and 14-CPA) under water deficit, initial growth, water relations, and organic solute accumulation were evaluated in an experiment performed using four-month-old seedlings, which were subjected to four water treatments (100, 75, 50, and 25% of field capacity), with five replications. Severe water deficit (25% of field capacity) negatively affected plant height, stem diameter, leaf area, dry matter of the leaves and stem to both genotypes, and root dry matter to genotype 13-CPA. Predawn (Ywpd) and midday leaf water potentials (Ywmd) were reduced in plants grown under 25% of field capacity, only in the genotype 14-CPA. There was not a change in relative water content, even with the reduction in the leaf water potential. Severe water deficit did not induce organic solutes accumulation, instead it reduced carbohydrate content in leaves of genotypes and aminoacids, proline and proteins, in genotype 13-CPA. In the roots accumulation of all organic solutes studied, it was verified genotype 13-CPA under 25% of field capacity, but only carbohydrates increased in plants under 25% of field capacity to 14-CPA. These results suggest two different mechanisms used by Barbados cherry genotypes to maintain the water status. To the 13-CPA one, the accumulation of soluble organic solutes in the roots is the main mechanism used to maintain the tissue hydration. However, the 14-CPA genotype changed the root to shoot ratio in order to avoid desiccation. Despite the mechanism used by both genotypes, a moderate drought stress does not induce significant morphophysiological changes in Barbados cherry.

Efeitos da aplicação de vinhaça sob os atributos físicos do solo coberto com palhiço de cana-de-açúcar

Areas under vinasse application have been associated to favorable physical conditions for root development, aeration, infiltration and water movement in soil profile. This study aimed to evaluate changes on physical attributes of soil under sugarcane straw after vinasse application in two sugarcane growing areas (Area 1 and Area 2) under mechanized management in the state of Paraiba, Brazil. In each area, the samples were collected in the 0-0.20, 0.20-0.40 and 0.40-0.60m layers of the soil, in 36 points, distributed in a 10×10m mesh, one day before and 40 days after vinasse application. The data were submitted to multivariate analysis with repeated measures and geostatistics. The vinasse application decreased soil density and increased total porosity in both Areas and increased organic matter in Area 2. In Area 1 occurred pure nugget effect for the fractions of sand, silt and clay, independent of soil layer. In Area 2, this effect was verified mostly at superficial layers, except for the fraction of clay that presented a moderate degree of spatial dependence.

Pressure-volume (P-V) curves in Atriplex nummularia Lindl. for evaluation of osmotic adjustment and water status under saline conditions

The survival of Atriplex nummularia plants in saline environments is possible mainly due to the presence of salt-accumulating epidermal vesicles. Commonly, destructive methods, such as plant material maceration and subsequent reading in osmometers, are employed in studies on water relations and osmotic adjustment and are inconvenient due to their underestimation of the total water potential inside the cells, which can cause overestimation of an osmotic adjustment that is not present. As a result, methods that preserve leaf structure, such as pressure-volume (P-V) curves, which take into consideration only the salts that compose the symplastic solution, are more adequate. Thus, the main objectives of this study were to evaluate the effect of determination methods of osmotic potential (Ψo) in Atriplex nummularia through destructive and leaf structure-preserving techniques and to determine the water relations of the species under increasing NaCl concentrations. Plants were subjected to daily irrigations, maintaining soil moisture at 80% of field capacity, with solutions of increasing NaCl concentration (0, 0.05, 0.1, 0.2, 0.25 and 0.3 M) for 84 days. Water potential, osmotic potential and osmotic adjustment were determined. In addition, P-V curves were constructed using pressure chambers. Water and osmotic potentials decreased linearly with increasing NaCl concentration in the irrigation solution. The main discrepancies observed were related to the osmotic adjustments determined through maceration and P-V curves. Based on the present research, it was possible to conclude that in studies with species that have salt-accumulating vesicles in the epidermis, such as the plants in the genus Atriplex, constructing P-V curves is more adequate than destructive methods.