JWSS - Journal of Water and Soil Science

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A glasshouse study was conducted to measure the effects of salinity and drought stresses on growth and chemical and biochemical composition of 4 onion cultivars. The cultivars were Dessex, Texas Early Grano (Texas), Dehydrator, and PX492. Salinity treatments included control, 45mM NaCl, 45mM NaCl + 5mM CaCl2 and drought treatments were control (maintaining soil moisture at field capacity) and irrigation when 50% of available water was used. Four weeks after the treatments, the plants were harvested and root and shoot dry weights (RDW, SDW), Na⁺, K⁺, Ca²⁺, total protein, reduced sugars, as well as free proline contents were measured in both roots and shoots.

 Results showed that NaCl and drought treatments significantly reduced SDW and RDW. The Texas cultivar and the Dessex cultivar produced the highest and the lowest amounts of SDW, respectively. NaCl significantly increased Na⁺ uptake but reduced K⁺ uptake in shoots and roots and also reduced Ca²⁺ uptake in roots. NaCl+CaCl₂ significantly alleviated the deleterious effects of NaCl such that SDW significantly increased in two cultivars and increased RDW and the K⁺ contents while causing decreased Na⁺ and sugar contents in shoots and roots of all cultivars. All stresses increased total protein contents of shoots in Texas only but decreased or had no effect on others. Root total protein increased under salinity stress, while drought had no effect. Changes in proline and sugars in both shoots and roots did not follow any particular pattern. Out of the biochemical compositions measured, shoot total protein in plants under the stresses showed a positive significant correlation with SDW, which may be used to screen onion cultivars for drought and salinity stresses.

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Drought stress is one of the most important environmental stresses in reduce of growth and plants production. Determination of resistance mechanisms to environmental stress in plant improvement is very important. In order to , experiment with osmotic potentials of PEG (zero (control), -4, -8 & -12 bar) and alfalfa genotypes was done. The selected alfalfa genotypes namely, Yazdi(tolerant), Nikshahri(moderate) and Ranger(sensitive) were grown in hydroponic culture. After 4 weeks, they were harvested in order to determination of proline accumulation and Ca⁺², K⁺ and Na⁺ concentration. The data showed with increasing of drought stress, proline accumulation were increased, but its rate was different among genotypes and organelles. Concentrations of K⁺, Na⁺ and Ca²⁺ increased with increasing of osmotic stress and there was significant different between genotypes. The K⁺/Na⁺ ratio in the shoots and roots of plant was decreased, when drought stress increased. Morphological and biochemical data showed Yazdi genotype was more tolerant to drought stress in compare with studied genotypes.

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Osmotic adjustment is generally regarded as an important adaptation of wheat to drought. Because it helps to maintain turgor and cell volume, osmotic adjustment is often thought to promote growth, yield, or survival, of plants in dry soils. However, a physiological rationale for such views is lacking. This study was conducted to determine the effect of osmotic adjustment and some of its components on the wheat yield. Ten bread wheat cultivars were grown in pots under different watering levels using a split plot design. During grain filling stage, RWC, leaf sugar content, proline content and osmotic regulation were estimated by sampling flag leaf under normal and stress conditions. Main stem was used for measuring sugar content of different parts of stem. Although there were some differences in osmotic regulation in wheat lines, there were no relationships between yield and osmotic regulation. It was shown that these components probably have a little share in wheat osmotic regulation.

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Heavy metals including cadmium produced as a result of urban, industrial and agricultural activities lead to the water pollution. Also, considering the growing need for silviculture in Iran, it is necessary to conduct a comprehensive research on fast growing and evergreen species of Eucalyptus and their role in heavy metals' absorption. To achieve this goal, Eucalyptus occidentalis seedlings were grown in pots containing silica and irrigated with a mixture of nutrient solution and cadmium chloride in 5, 10 and 15 m M for 10 months. Root and leaf samples were harvested and the amount of cadmium in stem, root and leaf organs was measured. Also, some morphological and physiological characteristics were determined including soluble sugar and praline. The analysis indicated that the cadmium concentrations of 15 mM treatment in the root, leaf and stem were 585, 142 and 87 mg/kg D.W., respectively. Proline content increased with the increase of Cadmium concentration while the content of pigments decreased. The result of this research shows that eucalypt has the potential of cadmium accumulation without any serious damage to its growth. Therefore, the plant can be used to decrease the environmental pollutions.

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In order to assess the effect of drought stress and various levels of potassium on solutes accumulation and chlorophyll of canola and Indian mustard, a field experiment was conducted in a factorial design based on randomized complete block design with three replications including three irrigation regimes (I1=irrigation after 50% depletion of soil water(control),I2 =irrigation after 70% water depletion and I3 =irrigation after 90% water depletion), two species (Hyola 401 hybrid of canola and landrace cultivar of mustard) and three levels of potassium fertilizer (K1=0 ,K2=150 and K3= 250 kg.ha-1 K2SO4 ) at Agricultural and Natural Resources Research Center of Sistan in 2008-2009 cropping season. Water stress increased proline and soluble carbohydrate accumulation in the leaves of Brassica sp. In non stressed condition (control) in different growth stages, proline was lower than water-stressed plants and Leaf proline content decreased significantly after irrigation. Mustard landrace showed higher capability for accumulating assimilates such as proline, soluble carbohydrates and potassium than hybrid Hyola 401. Water stress decreased the amount of chlorophyll a, b and total leaf chlorophyll, but Potassium application caused an increase in the mentioned parameters. The highest content of chlorophyll pigments was observed at flowering stage. Potassium application caused a decrease in proline and an increase in soluble carbohydrates concentration in the leaf under water stress condition. There was a negative correlation between grain yield and proline content and soluble carbohydrates, but grain yield was positively correlated with chlorophyll, a, b. It was concluded that osmotic adjustment can be an important mechanism for Brassica species under water stress conditions and that organic and inorganic compounds such as proline, soluble carbohydrates and potassium play key roles in this regard.