Effects of Various Salt–Alkaline Mixed Stresses on the State of Mineral Elements in Nutrient Solutions and the Growth of Alkali Resistant Halophyte Chloris Virgata

Abstract

ABSTRACT Chloris virgata, a naturally alkali-resistant halophyte, was studied. Various salt–alkali conditions with different salinities and pHs were established by mixing sodium chloride (NaCl), sodium bicarbonate (NaHCO3), sodium sulfate (Na2SO4), and sodium carbonate (Na2CO3), in various proportions. The effects of these salt–alkali conditions on the state of mineral elements in nutrient solutions were analyzed using the GEOCHEM-PC program. The relative growth rate (RGR) and tillering rate of stressed C. virgata were determined. The activities of metal ions in nutrient solutions, apart from potassium (K+), decreased with both increased salinity and pH, and high pH resulted in precipitation of metal ions and phosphate. Consequently, the high pH of salt–alkaline mixed stress could cause severe nutrient stress in plants. However, when pH was 6.40–8.74, the effects of pH on RGR and tillering rate were not significant, and the high pH surrounding roots might be resisted by the root cells and prevented from invading the intracellular environment. Only when pH > 8.74 did the harmful action of high pH emerge, and the increased pH induced the severe decreases of RGR and tillering rate at the same salinity. The results indicated that pH adjustment outside the roots might be a key physiological mechanism for C. virgata resisting alkali stress.