Hugo Alberto Ruiz

Solute accumulation and distribution during shoot and leaf development in two sorghum genotypes under salt stress

Abstract Seedlings of two forage sorghum genotypes (Sorghum bicolor (L.) Moench) differing in salt tolerance were subjected to 0 and 100 mM NaCl and shoot development, leaf elongation, and organic and inorganic solutes contents in leaves were measured. Salt stress reduced both shoot development and leaf elongation and enhanced leaf senescence and injury. It also led to accumulation of toxic ions (Na+ and Cl−), organic solutes (carbohydrates, amino acids and proline), and reduction of K+ content in leaf blades. Toxic ion accumulation was higher in the basal zone of the leaf blade and occurred during the period of intense leaf growth while organic solutes accumulation, mainly proline, was higher in the apical zone and occurred when the leaves practically had reached their final size. All these changes were more conspicuous in the sensitive than in the tolerant genotype. The latter also retained more toxic ions in leaf sheath tissue than the former. It is suggested that the reduction in shoot development and leaf elongation were related to toxic ion accumulation and depletion of K+ ions in the leaf blades. The accumulation of organic solutes in leaves did not appear to be related to salt tolerance. Proline accumulation appears to be a reaction to salt stress damage and not a plant response associated with salt tolerance.

CONTRIBUTION OF PROLINE AND INORGANIC SOLUTES TO OSMOTIC ADJUSTMENT IN COTTON UNDER SALT STRESS

Physiological responses to salt stress were investigated in two cotton (Gossypium hirsutum L.) cultivars (Pora and Guazuncho) grown hydroponically under various concentrations of NaCl. Dry matter partitioning, plant water relations, mineral composition and proline content were studied. Proline and inorganic solutes were measured to determine their relative contribution to osmotic adjustment. Both leaf water potential (Ψw) and osmotic potential (Ψs)decreased in response to NaCl levels. Although Ψwand Ψs decreased during salt stress, pressure potential Ψp remained between 0.5 to 0.7 MPa in control and all NaCl treatments, even under 200 mol m−3 NaCl. Increased NaCl levels resulted in a significant decrease in root, shoot and leaf growth biomass. Root / shoot ratio increased in response to salt stress. The responses of both cultivars to NaCl stress were similar. Increasing salinity levels increased plant Na+ and Cl−. Potassium level remained stable in the leaves and decreased in the roots with increasing salinity. Salinity decreased Ca2+ and Mg2+ concentrations in leaves but did not affect the root levels of these nutrients. The K/Na selectivity ratio was much greater in the saline treated plants than in the control plants. Osmotic adjustment of roots and leaves was predominantly due to Na+ and Cl− accumulation; the contribution of proline to the osmotic adjustment seemed to be less important in these cotton cultivars.

Plant growth and solute accumulation and distribution in two sorghum genotypes, under NaCl stress

Seedlings of two sorghum (Sorghum bicolor (L.) Moench) genotypes with differential tolerance to salinity were exposed to 0 and 100 mM NaCl, gradually added in increments of 25 mM every 12 hours, in nutrient solution. Seven days after starting the salt treatment the growth of the shoot and root system and the inorganic and organic solutes contents were determined. Salinity reduced the dry matter yield and length of the shoot and root system in both sorghum genotypes, specially in the sensitive one. In general, it was observed an increase in Na + and Cl - transfer to the shoot, in Na + and Cl - accumulation and in the Na + /Cl - ratio but a decrease in the K + and Ca 2+ transfer to shoot and in the K + and Ca 2+ contents in the shoot, always with higher intensity in sensitive genotype. Apparently, the tolerance to high saline concentrations in sorghum seems to be related to the genotype ability to avoid accumulation of harmful levels of Na + and Cl - and, or to maintain adequate levels of K + and Ca 2+ , specially in the shoot. The soluble carbohydrates and amino acids constituted together over 98% of the total organic solutes and showed the greatest absolute increase in concentration during saline stress. Probably, the soluble carbohydrates were the most important organic solutes to contribute to the osmotic adjustment in the leaves and the amino acids in the roots. Under saline stress there was an expressive increase in proline contents, specially in the oldest leaves of sensitive genotype. The proline contents, however, even under salt stress, did not reach the levels of other organic solutes. Contrary to the general acceptance, proline does not seem to have an important role in the mechanism of salt tolerance, at least for these genotypes and under the experimental conditions applied here. ADDITIONAL INDEX TERMS: Salinity, salt stress, salt accumulation, organic solutes accumulation, Sorghum bicolor.

Estimativa do risco de sodificação de solos de Pernambuco pelo uso de águas salinas

An experiment was carried out in permeameters provided with vertical column and constant hydraulic head in order to evaluate sodification risks of soils with contrasting characteristics and treated with solutions of different electrical conductivities (EC) and sodium adsorption ratios (SAR). The treatments consisted of nine soils and eighteen percolating solutions with three EC values (175, 500 and 1,500 μS cm -1 ) and six SAR values (0 to 30 for sandy soils, 0 to 25 for medium textured soils and 0 to 15 for clay textured soils). Initially, the adjustment of the Na:Ca ratio on the cation exchange complex of the soils was performed using solutions with concentration of 50 mmol c L -1 . Later on leaching with solutions of different EC but same SAR was maintained to reach steady state flow, when the permeameters were dismantled and the soil samples removed for chemical analysis. Exchangeable sodium and cation exchange capacity were determined to calculate exchangeable sodium ratio (ESR) and exchangeable sodium percentage (ESP). Equations were adjusted between either ESR or ESP with EC and SAR of the percolating solution, the increment of EC and SAR elevated the soil ESR and the ESP. It may be concluded that the correct assessment of the sodification hazard has to take into consideration the soil properties and the water quality.

Carbono orgânico e Nitrogênio em agregados de um Latossolo Vermelho distrófico sob duas coberturas vegetais

Soil organic matter is constituted by a vast array of compounds that include active and more stable fractions, with different cycling rates. Management practices affect organic carbon and nitrogen contents, organic matter quality, and soil aggregation. The present study aimed to characterize organic carbon and nitrogen in aggregates of a Dystrophic Red Latosol of Minas Gerais State, Brazil, in an area of native vegetation (Cerradao) and another one that has been for 30 years under conventional corn cultivation. Soil samples were collected at depths of 5-10 and 15-20 cm at four different sites. The dried samples were fractioned in the following aggregate classes: diameter 4.75-2.0; 2.0-1.0; 1.0-0.5; 0.5-0.25; 0.25-0.105; and less than 0.105 mm. Total organic carbon (COT), water soluble organic carbon (COS), total nitrogen (NT) and anaerobically-mineralized nitrogen (NMA) were determined for each sample. On average, the COT contents of soil aggregates under conventional tillage were higher, while NT contents were greater in the aggregates of the Cerradao surface layer. The COS and NMA contents, that correspond to more active fractions of organic matter, were significantly higher in aggregates of Cerradao soil. Aggregates of smaller size tended to present higher contents of COT, NT and NMA. Ratios of C/N, COT/COS and NT/NMA were, on average, higher in aggregates of soils under corn. The NT/NMA ratio was significantly higher in the 15-20 cm layer. However, independent of the soil, the lowest NT/NMA ratios were observed in the smallest aggregate classes, indicating the presence of more labile nitrogen forms. Results showed that vegetation cover type and soil management influenced not only the organic carbon and nitrogen contents, but also organic matter quality. Smaller aggregates are not only responsible for a greater stock of organic matter in the soil but also represent important sites of mineralizable nitrogen. The COS, NMA and the ratios of COT/COS and NT/NMA represent valuable indicators to detect alterations in the lability of organic matter due to management.

Condutividade hidráulica de solos de Pernambuco em resposta à condutividade elétrica e RAS da água de irrigação

An experiment was carried out in permeameters provided on vertical soil columns with constant hydraulic head in order to evaluate the hydraulic conductivity of soils with contrasting characteristics, and treated with solutions of different electrical conductivities (EC) and sodium adsorption ratios (SAR). The treatments consisted of nine soils, three EC values (175, 500 and 1.500 mS cm-1) and six SAR values of the irrigation water (0 to 30 for sandy soils, 0 to 25 for medium textured soils, and 0 to 15 for clay textured soils). Initially, an adjustment of the Na:Ca ratio in the cation exchange complex was performed with solutions at concentration of 50 mmolc L-1. The saturated hydraulic conductivity of soil (K0) was measured and the relative hydraulic conductivity (K0R) was determined, considering the maximum average K0 values of each soil as 100%. The K0R values were related to CE and SAR of the treatments, by adjusting the response surfaces. The correlation between K0 and the exchangeable sodium percentage (ESP) showed an inverse relationship between both variables in most of the studied soils. The increment in SAR resulted in the decrease of the K0R. It was not possible to define just one ESP value in order to establish a limit for sodic soils. ESP should be considered together with the EC of the irrigation water, as well as soil properties such as texture and mineralogy.

Osmotic adjustment in roots and leaves of two sorghum genotypes under NaCl stress

Seedlings of two sorghum genotypes [Sorghum bicolor (L.) Moench], one salt tolerant (CSF 20) and the other salt sensitive (CSF 18) were grown in nutrient solution containing 0, 50 and 100 mmol.L-1 NaCl for seven days and the osmotic potential (Ys) and the contribution of organic and inorganic solutes to the Ys were determined in the leaves and roots. Salinity reduced the Ys of the cellular sap of leaves and roots in both genotypes, mainly in the salt sensitive one. The higher decrease in the Ys in the salt sensitive genotype was mostly due to higher accumulation of Na+ and Cl- that probably exceeded the amount needed for the osmotic adjustment. Among the inorganic solutes, K+ contributed the most to the Ys in control unstressed seedlings, but its contribution decreased as salt stress increased, especially in the salt sensitive genotype. Soluble carbohydrates and amino acids were the organic solutes that contributed the most to the leaf and root Ys, respectively. No statistically significant difference in these organic solute contributions to the leaf Ys between genotypes was observed. Their contributions to the root Ys, however, were higher in the salt tolerant genotype, especially at higher NaCl concentration. Proline contribution to leaf and root Ys was quite small in both genotypes and its accumulation was not related to salt tolerance. Our results suggest that the salt tolerant genotype was able to maintain a more adequate osmotic pool in the leaves and roots under salt stress than the salt sensitive genotype.

Deslocamento miscível de cátions básicos provenientes da água residuária de mandioca em colunas de solo

This study aimed to determine the retardation factors and the diffusion-dispersion coefficients of the potassium, sodium, calcium and magnesium ions found in the cassava wastewater, as well as to simulate the resident concentrations in soil columns with 160 cm over a five-hours period. The trials were accomplished under laboratory conditions, by using percolation columns fulfilled with materials from the spodic ortic Quartzarenic Neosol (RQo), typical distrophic Yellow Latosol (LAd) and typical distrophic Yellow Red Latosol (LVAd). The data of the ion concentrations in effluent were analyzed, by using the miscible fluid displacement methodology. The highest values of the retardation factors occurred in the LVAd soil, relative to LAd and RQo soils, pointing out a higher retention of the potassium, sodium, calcium and magnesium ions in the LVAd soil. The values of the diffusive-dispersive coefficients decreased from LVAd toward the RQo soil, whereas the highest value occurred in the RQo soil for the potassium ion and the lowest in the LVAd soil for calcium ion. The simulation of the cassava wastewater application over a five-hours period showed little advance of these ions in the LVAd soil column, comparative to the advance occurred in the RQo and LAd soils, therefore warning about the dangers of the underground water contamination, when applying the cassava wastewater on these two soils.

Dispersão de Latossolos em resposta à utilização de pré-tratamentos na análise textural

The accuracy of particle size analyses depends on a complete dispersion of the soil sample and the maintenance of the stability of the dispersed phase. In some Latosols the dispersion is hindered by microaggregates of high stability. These clay particles are partially detached by chemical and mechanical dispersion and because of their size, account for a systematic overestimation of the silt fraction in the analyzed soil. In order to minimize the amount of pseudo-silt in particle-size analyses of Latosols, an experiment was carried out to test how the efficacy of dispersion was affected by the use of pre-treatments for the removal of cementing agents. The treatments were set up in a factorial arrangement of 7 x 22. Study material were samples of seven Latosols dispersed with NaOH 0.01 mol L-1, with or without pre-treatment for the removal of organic matter and poorly-crystalline Fe and Al oxides. The silt fraction was dispersed again, and clay and silt proportions were determined after the second dispersion. The removal of organic matter and poorly-crystallized Fe and Al oxides increased the clay fraction yield, indicating the breaking up of microaggregates in sizes that correspond to other particle size fractions, especially silt. Pseudo-silt was found in all studied Latosols, in greater amounts in the more oxidic types. Coarse and fine sand fractions also presented clayey microaggregates that are not easily dispersed. After the second dispersion, the silt fraction presented values from 0.199 to 0.537 kg kg-1 of clay. Pre-treatments are recommended to reduce the proportion of pseudo-silt, especially the one used to remove poorly-crystalline Fe and Al oxides.

Fósforo remanescente em argila e silte retirados de Latossolos após pré-tratamentos na análise textural

The presence of highly stable microaggregates can hamper soil dispersion in some Oxisols. These very clayey groupings may be not completely disaggregated by chemical and mechanical dispersion. Due to their size, the silt proportion of the soil is overestimated. A laboratory experiment was conducted to verify the use of the solution equilibrium P (SEP) to evaluate the response to particle size analysis pre-treatments in Oxisols. The treatments were arranged in a 7 x 22 factorial design, in randomized blocks with four replications. The factors were samples of seven Oxisols dispersed with 0.1 mol L-1 NaOH, with and without pre-treatment to remove organic matter (-OM) and poorly crystallized iron oxides (-Ox). SEP was determined in samples of the dispersed clay and silt fractions and in the silt fraction, after a second dispersion with 0.1 mol L-1 NaOH. It was observed that SEP is sensitive enough to identify differences between the treatments applied. This indicates the usefulness of SEP as an auxiliary determination in soil dispersion studies.