Elevated atmospheric CO2 concentration ameliorates effects of NaCl salinity on photosynthesis and leaf structure of Aster tripolium L.

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

Effect of NaCl salinity on water relations, photosynthesis and chemical composition of Quinoa (Chenopodium quinoa Willd.) as a potential cash crop halophyte

Abstract Despite the large interest in the use of Chenopodium quinoa as a crop on extreme habitats, very little is known about growth response and seed yield under saline conditions. As a prerequisite for its sustainable utilization in salt-affected areas, this study aimed to unravel individual physiological and morphological mechanisms that determine its salt tolerance. Hence, the plants were grown in a hydroponic quick check system with 0, 100, 200, 300, 400, and 500 mM NaCl (equivalent to 0, 20, 40, 60, 80 and 100% seawater salinity). Growth of C. quinoa was slightly stimulated with increasing water salinity, with an optimum at 100 mM NaCl. This was mainly due to enhanced tissue water content and succulence. Higher salinities considerably reduced plant growth, with maximum reduction of 82% observed at 500 mM NaCl. The plants were able to reduce the leaf water potential below the soil water potential. This was associated with substantial decrease in osmotic potential mainly by Na + and Cl -. Interestingly, the plants were able to maintain favorable ion relations in their roots and juvenile leaves, where the metabolic demands are expected to be greatest, even under high NaCl salinity. The net photosynthesis rates were greatly decreased by high salinity, being 28% of initial control values at 500 mM NaCl. Salt-induced photosynthesis inhibition was accompanied with a decrease in transpiration rates but also with improved water use efficiency. Neither osmotic stress nor ion deficiency/toxicity appeared to be determinant for C. quinoa under high saline condition. Salt-induced growth reduction is presumably due to low photosynthate supply as a consequence of impaired photosynthetic capacity. Together, these indicate that C. quinoa is a promising salt-tolerant, in terms of biomass production, and can be grown productively under low to moderate saline condition up to 40% sws