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This study investigated the interaction of NaCl-salinity and elevated atmospheric CO2 concentration on gas exchange, leaf pigment composition, and leaf ultrastructure of the potential cash crop halophyte Aster tripolium. The plants were irrigated with five different salinity levels (0, 25, 50, 75, 100% seawater salinity) under ambient and elevated (520 ppm) CO2. Under saline conditions (ambient CO2) stomatal and mesophyll resistance increased, leading to a significant decrease in photosynthesis and water use efficiency (WUE) and to an increase in oxidative stress. The latter was indicated by dilations of the thylakoid membranes and an increase in superoxide dismutase (SOD) activity. Oxidative stress could be counteracted by thicker epidermal cell walls of the leaves, a thicker cuticle, a reduced chlorophyll content, an increase in the chlorophyll a/b ratio and a transient decline of the photosynthetic efficiency. Elevated CO2 led to a significant increase in photosynthesis and WUE. The improved water and energy supply was used to increase the investment in mechanisms reducing water loss and oxidative stress (thicker cell walls and cuticles, a higher chlorophyll and carotenoid content, higher SOD activity), resulting in more intact thylakoids. As these mechanisms can improve survival under salinity, A. tripolium seems to be a promising cash crop halophyte which can help in desalinizing and reclaiming degraded land.

Our study aimed at investigating the influence of elevated atmospheric CO(2) concentration on the salinity tolerance of the cash crop halophyte Aster tripolium L., thereby focussing on protein expression and enzyme activities. The plants were grown in hydroponics using a nutrient solution with or without addition of NaCl (75% seawater salinity), under ambient (380 ppm) and elevated (520 ppm) CO(2). Under ambient CO(2) concentration enhanced expressions and activities of the antioxidant enzymes superoxide dismutase, ascorbate peroxidase, and glutathione-S-transferase in the salt-treatments were recorded as a reaction to oxidative stress. Elevated CO(2) led to significantly higher enzyme expressions and activities in the salt-treatments, so that reactive oxygen species could be detoxified more effectively. Furthermore, the expression of a protective heat shock protein (class 20) increased under salinity and was even further enhanced under elevated CO(2) concentration. Additional energy had to be provided for the mechanisms mentioned above, which was indicated by the increased expression of a beta ATPase subunit and higher v-, p- and f-ATPase activities under salinity. The higher ATPase expression and activities also enable a more efficient ion transport and compartmentation for the maintenance of ion homeostasis. We conclude that elevated CO(2) concentration is able to improve the survival of A. tripolium under salinity because more energy is provided for the synthesis and enhanced activity of enzymes and proteins which enable a more efficient ROS detoxification and ion compartmentation/transport.

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A prerequisite for sustainable saline agriculture of cash crop halophytes in salt affected areas implies exact knowledge of their limits of salinity resistance. Hence, the first part of this study was carried out in pot experiment under greenhouse conditions to evaluate growth and seed yield of C. quinoa Willd. cv. Hualhuas to varying water salinity levels (0, 100, 200, 300, 400 and 500 mM NaCl). The limit of salinity resistance was estimated at 200 mM NaCl (~20 dSm -1 ) based on seed yield production. Depending on the results obtained from pot experiment, field trials were conducted in saline soil location (ECe 17.9 dSm -1 ) and in non-saline soil location (ECe 1.9 dSm -1 ). Seed yield significantly decreased under saline soil by about 61.7% . Beside quantity, soil salinity led to reduce the percentage of moisture, total carbohydrate and total fat contents in seeds. Salinity did not significantly alter the protein content in quinoa seeds. Significant increases in the content of ash and fiber were detected in response to high soil salinity. The high er ash content in seeds under saline conditions was due to the increase of Na + as well as K + , P 3-and Fe ++ concentrations. By contrast, soil salinity led to significant decrease of Ca ++ and Zn ++ contents in seed. Energy dispersive X-ray microanalysis showed that most of Na + in the seeds produced at saline soil was mainly accumulated in the pericarp followed by embryo tissues, while, the interior reserving tissue (perisperm) exhibiting comparatively low concentration. Increasing most of essential minerals, especially Fe, in quino a seeds produced under high saline conditions given quinoa a distinctive value for human consumption. Quinoa can be grown and yielded successfully in salt-affected soils (ECe 17.9 dSm -1 ), where, most if not all of traditional crops cannot grow, although the yield was reduced however, the seed quality was not highly affected.

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