Ionic and photosynthetic homeostasis in quinoa challenged by salinity and drought - mechanisms of tolerance

Quinoa (Chenopodium quinoa Willd.) grown under field conditions was exposed to five irrigation water salinities (0, 10, 20, 30 and 40 dS m–1; 4 : 1 NaCl : CaCl2 molar ratio) from flowering, and divided between full irrigation and progressive drought (PD) during seed filling. Quinoa demonstrated homeostatic mechanisms which contributed to quinoa’s extraordinary tolerance. Salinity increased K+ and Na+ uptake by 60 and 100 kg ha–1, respectively, resulting in maintenance of cell turgor by osmotic adjustment, and a 50% increase of the leaf’s fresh weight (FW) : dry weight (DW) ratio and non-significant increase in elasticity enhanced crop water-capacitance. Day respiration (Rd) increased 2.7 times at high salinity but decreased 0.6 times during drought compared with control. Mesophyll conductance (gm) tended to be negatively affected by salinity as the increased succulence (FW : DW) possibly decreased intercellular space and increased cell-wall thickness. However, the increased K+ uptake seemed to alleviate biochemical limitations, as maximum Rubisco carboxylation rate (Vcmax) and photosynthetic electron transport (J) tended to increase under salinity. Overall, salinity and PD restricted stomatal conductance (gs) and photosynthesis (An) moderately, leading to decreased leaf internal to ambient [CO2], increase of intrinsic-water-use-efficiency (An/gs). The saturated electrical conductivity (ECe) resulting in 50% yield was estimated to be 25 dS m–1, reaching no yield at 51.5 dS m–1.