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 dSm(-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 nonsignificant increase in elasticity enhanced crop water-capacitance. Dayrespiration (R-d) increased 2.7 times at high salinity but decreased 0.6 times during drought compared with control. Mesophyll conductance (g(m)) 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 (V-cmax) and photosynthetic electron transport (J)tended to increase under salinity. Overall, salinity and PD restricted stomatal conductance (g(s)) and photosynthesis (A(n)) moderately, leading to decreased leaf internal to ambient [CO2], increase of intrinsic-water-use-efficiency (A(n)/g(s)). The saturated electrical conductivity (ECe) resulting in 50% yield was estimated to be 25 dSm(-1), reaching no yield at 51.5 dS m(-1).