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

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.