Effects of salt stress on growth and photosynthetic physiological features of Hippophae rhamnoides seedlings

With two-year old seedlings of Hippophea rhamnoides as test materials, the growth, water physiological index, photosynthetic physiological features and chlorophyll content in leaves of two-year-seedlings of Hippophea rhamnoides were studied under 0, 200, 400 and 600 mmol·L-1 NaCl solutions. The results showed that with the increase of NaCl concentration, the fresh weight, dry weight, leaf mass per area (LMA) and leaf total area per plant of H. rhamnoides seedlings declined obviously. Under salt stress, severe water shortage appeared in leaves, the leaf water potential (Ψw) and relative water content (RWC) decreased gradually, while water saturation deficit (WSD) and tissue density (TD) increased gradually. Compared with the control, the content of chlorophyll a (Chl a), chlorophyll b (Chl b), chlorophyll (Chl) and carotenoid (Car) and the chlorophyll a/b (Chl a/Chl b) ratio decreased significantly under salt. When NaCl concentration increased and stress time prolonged, the net photosynthetic rate (Pn), transpiration rate (Tr) and stomatal conductance (Gs) in leaves of H. rhamnoides seedlings declined markedly, and intercellular CO2 concentration (Ci) declined initially and then increased, whereas, water use efficiency (WUE) and stomatal limiting value (Ls) increased initially and then declined. The results indicated that the decline of Pn was mainly caused by stomatal limitations in short term, and by non-stomatal limitations in long run, including physiological metabolic disorder of leaves, photosynthetic capacity decline caused by degradation of the photosynthetic pigment, and so on. Moreover, the higher NaCl concentration, the earlier time changing from stomatal limitations into non-stomatal limitations.