| Salinity is one of major environmental problem which is limiting the agricultural production. The stress due to salinity is a foremost environmental factor that severely affects the productivity of crop all over the world. Conversely, the output of crop's production is not increasing to match the requirement of food. Overcoming stress due to water deficiency and salts accumulation is a foremost issue in salt affected areas to ensure agricultural sustainability and continues production of food. Therefore, the content of this dissertation based on the research work which was conducted for Brassica napus L. (B. napus) and Orychophragmus violaceus (O. violaceus). The objective were categorize on the basis of salt-tolerance capacity, photosynthesis, stomatal conductance, transpiration, water-use efficiency, water potential, carbonic anhydrase activity,physiological capacitance and leaf tensity of plants. The objective were; 1) to investigate the salt induced effects and afterwards re-watering on physiological characteristics of O. violaceus and B.napus,2) to find out best regime for re-watering based on growth and physiological responses of O. violaceus and B. napus under salt stress subsequently re-watering; 3) to construct a model for prediction of an appropriate regime for dilution of saline water based on electrophysiological characteristics of O. violaceus and B. napus. B. napus and O. violaceus were investigated under growth chamber and greenhouse conditions. The B. napus and O. violaceus were treated in 1st,2nd and 3rd experiments with NaCl, Na2SO4 and mixed treatments as; NaCl (NC1: 2.5, NC2: 5,NC3: 10) g L-1; Na2SO4 (NS1: 2.5, NS2: 5, NS3: 10) g L-1 and mixture of salts (MS1: 2.5 NaCl +10 Na2SO4; MS2: 10 NaCl + 2.5 Na2S04; MS3: 5 NaCl + 5 Na2S04) g L-1 and 0 as control followed by re-watering NC1^0, NS1^0, NC2^1, NS2^1, NC3^2, NS3^2, MS1^0, MS2^0 and MS3^0,respectively. In the salt stress phase, plant height, stem diameter, leaf area, photosynthesis, water potential, physiological capacitance and leaf tensity decreased significantly with increasingly salts concentration under high salt stress levels of single and mixture of salts as NC3, NS3, MS1,MS2 in B.napus and O. violaceus, respectively. In salt stress phase, maximum reduction in net photosynthetic rate was noted 79.54%,80.72%,84.54%,and 74.84% for NC3,NS3,MS1,MS2,respectively, under high concentration levels in B. napus. While, the reduction in net photosynthetic rate in O. violaceus was found 88.55%, 88.92%, 91.20% and 89.36 under NC3,NS3, MS1, MS2, respectively. Photosynthesis activities under slight (NC1, NS1) to moderate stress (NC2, NS2 and MS3) condition were maintained due to stimulation of carbonic anhydrase activity in both B. napus and O. violaceus. However, during salt-stress subsequently re-watering phase, all physiological parameters were maintained and stable but the recoveries were not found under high stress levels. Better effect of re-watering found in plants due to higher WUER under moderate-stress condition, showed the increment in photosynthetic rate per increment of water content. Relatively as compare to other stress levels more recovery in photosynthetic rate was found after re-watering under medium concentration levels, which were 44.94%, 53.45% and 63.04%, respectively in B. napus. While, the recoveries in photosynthetic rate in O. violaceus were found as 55.62%, 65.46% and 50.82% under moderate concentration levels, respectively.Salt-stress subsequently re-watering enhanced the growth of plants. So, dilution of saline water or re-watering of saline water based on growth and physiological properties should be done at moderate level in both species, which was being considering the best zone for threshold tolerance and production of B. napus and O. violaceus under saline condition. Furthermore,a timely and effective measure of water deficiency in plants ensures that damage of growth development is prevented. It can be determined more precisely by constructed a model for dilution point by using their electrophysiological properties. In which, water potential and physiological capacitance of a plant was reflected by water content. The status of water in plants is also be characterized by the plant cell tensity, which reflects the salts resistance of plants.However, salt stress in both species at high concentration affected physiological capacitance and leaf tensity adversely followed the order as NC3^2, NS3^2, MS1^0 and MS2^0, respectively. While in re-watering phase, the increment in leaf tensity under low salt stress treatments (NC1^0 & NS1^0)was found to be highest as 106 cm and 102 cm in O. violaceus, 113 cm and 113 cm inB. napus,respectively. Relatively, more increments of physiological capacitance and leaf tensity were found in O.violaceus under NC2^1,NS2^1 & MS3^0, medium concentration levels,respectively.The increments in leaf tensity under NC2^1, NS2^1 & MS3^0 were found as 101 cm,101 cm,and 102 cm in O. violaceus, 75 cm, 71.7 cm and 70.3 cm in B. napus, respectively. Though, O.violaceus showed better recovery of physiological capacitance and leaf tensity from low to medium concentration levels than B. napus. Subsequently, from the results, best dilution point was 5% - 2.5% for single NaCl and Na2SO4 and 10% - 0.0% for blend of salts. After re-watering,O. violaceus restore its leaf tensity better under medium levels, because the effect of NaCl concentration on leaf tensity (XNC-LT) was 1.66%, which was lower in O. violaceus than the effect of XNC-LT (2.88%) in B. napus, followed same trend by all treatment. Therefore, B. napus and O.violaceus was thought to be the species with single and mixture of salts tolerance adaptability under slight to moderate stress conditions. Hence,the effect of salinity in O.violaceus and B. napus may also be reducing affectively by dilution of saline irrigation based on electrophysiological properties. It would be a better approach to utilize saline water for irrigation instead of applies direct saline water to plant. This study provides new insight in the field of agricultural engineering to plan irrigation scheduling considering the crop ability to salt tolerance and irrigation water use efficiency by apply specific quantity of irrigation calculated based on the salt dilution point. It would be helpful to balance between irrigation amount and optimum crop water consumption in salt affected regions and to utilize saline water in order to safe fresh water resources. |
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