Tahira Nawaz

Soil-Plant Relationships in the Arid Saline Desert of Cholistan

The inland vegetation of saline patches in the Cholistan desert faces extreme environmental conditions including predominantly salt stress and limited resource availability. Changes in the salinity gradients may lead to gradual variation in response of individual plant species that ultimately affect community structure and composition. The present study was conducted to determine spatial distribution of individual species along a salinity gradient in the Cholistan desert in relation to their life form and tolerance limits. The results showed variable responses of these species in spatial distribution against the salinity gradient. The plants differed considerably in their tolerance level due to development of differential adaptive strategies under extreme salinities. Excretory species like Aeluropus lagopoides and Sporobolus ioclados dominated the sites with highest salinities along with the leafy succulent Suaeda fruticosa. Stem succulents dominated moderate salinities along with spreading stoloniferous Ochthochloa compressa and tussock grass Cymbopogon jwarancusa. Non-succulent Cressa cretica and tussock grass Lasiurus scindicus were mainly distributed to sites with lower and moderate salinities, while non-succulent plants dominated the lowest salinity site. Of the soil physico-chemical characteristics in the Cholistan desert habitats, salinity may have a direct effect on the life form and survival strategies of occurring plants. Thus, the difference in spatial distribution of individual species along salinity gradients suggested that salinity alone is not a responsible factor to determine community structure, but plant tolerance limits and their life habits are also important.

Structural Features of Some Wheat (Triticum Spp.) Landraces/Cultivars Under Drought and Salt Stress

Seven local landraces of common and durum wheat (Triticum aestivum L. and T. durum L.) from the arid and semi-arid areas of the Sultanate of Oman were examined for specific leaf and stem structural features for water conservation. On the basis of shoot fresh and dry weights (g plant−1), degree of tolerance to drought and salt stresses in these wheat landraces/cultivars can be ranked as S-24 > J-305 > Sarraya > Senain > Cooley > MH-97 > Missani>Hamira > Shwairaa. Modifications related to water conservation were found to be high degree of sclerification, succulence in leaf and stem, low resistance to water conductance in vascular tissue, and pubescence on leaf surface. The salt and drought tolerant cultivar S-24 showed high proportion of chlorenchyma and intensive sclerification in stem structure, and well-developed bulliform cells and dense pubescence on the leaves. These modified features were poorly developed in lesser stress tolerant Omani wheat landraces like Hamira and Shwairaa. Accession Senain also showed stem succulence (solid stem), an important xeromorphic feature. Structural modifications in landrace Missani were found to be increased sclerification in vascular tissue and high number of metaxylem vessels and high proportion of parenchyma in stem, and highly developed bulliform cells in leaf. Overall, the promising anatomical traits in highly stress tolerant landraces/cultivars were chlorenchyma in stem, rigorous sclerification in parenchyma and around vascular tissue, stem and leaf succulence, and enhanced ratio of major conducting tissue.

Modifications in Root and Stem Anatomy for Water Conservation in Some Diverse Blue Panic (Panicum antidotale Retz.) Ecotypes Under Drought Stress

Five ecotypes of Panicum antidotale Retz. adapted to diverse habitats were subjected to drought stress to evaluate their drought tolerance in relation to adaptive anatomical structures. The ecotype from non-stressed habitat had intensive sclerification as well as crystallization in parenchymatous cells, which help prevent water loss. The ecotype from drought-prone habitat had well-developed metaxylem vessel area for better conduction of water and nutrients, and pith area for better storage of water. The ecotype collected from salinity-affected habitat as well as that from saline and waterlogged habitat showed extensive sclerification in the vascular region, which is vital for preventing water loss. The ecotype from a salinity- and drought-prone habitat showed increased metaxylem vessel number and formation of additional metaxylem vessels in the pith region for better conduction, multi-layer exodermis and intensive sclerification for prevention of water loss, and increased parenchymatous region for better storage of water. The most promising anatomical features found in highly drought tolerant ecotypes were increased metaxylem number, multi-layered exodermis, and intensive sclerification in vascular region.

Physiological adaptative characteristics of Imperata cylindrica for salinity tolerance

Two populations of cogongrass [Imperata cylindrica (L.) Raeuschel], one from the saline regions of the Salt Range and the other from the non-saline regions of Faisalabad were assessed for salinity tolerance on the basis of some key morphological and physiological attributes. It was hypothesized that the tolerant population from the Salt Range must have developed some specific structural modifications, which are responsible for its better survival under high salinities. These adaptive components can be effectively used in modern technologies for improving degree of tolerance of other sensitive crops. The population from the Salt Range markedly excelled the Faisalabad population in terms of growth and physiological attributes measured in this study. The Faisalabad population of I. cylindrica was unable to survive at the highest salt level (200 mM NaCl). The tolerance of the Salt Range population to salt stress was found to be related to high accumulation of organic osmotica, particularly total free amino acids and proline as well as Ca2+ in the shoot. The distinctive structural modifications in the Salt Range population were found to be enhanced succulence, well-developed bulliform cells in leaves and smaller stomatal area.

Fourth Order Methods for Finding Multiple as well as Distinct Zeros of Non-linear Equations

In this paper, we point out and analyse six two-step iterative methods for finding multiple as well as distinct zeros of non-linear equations. We prove that the methods for multiple zeros as well as for distinct zeros have fourth order convergence. The methods calculate the multiple as well as distinct zeros with high accuracy. The numerical tests show their better performance in case of algebraic as well as non-algebraic equations.