关键词:
"Quick check" system
Cash crop halophytes
Gas exchange
NaCl salinity
Nutrients
Salinity tolerance
Spartina townsendii
Water potential
Water relations
摘要:
The aim of this study was to determine the level of salinity tolerance of Spartina townsendii and to study the mechanisms by which this species survives salinity and the specific conditions at the intertidal zone. Therefore, Spartina was irrigated with five different saline levels ranging from nutrient solution (control) to 100% seawater (480 mM NaCl) in a "quick check" system (QCS). The salinity tolerance was measured on the basis of the two parameters maximum yield, and gas exchange. a) The maximum yield of Spartina was reduced by 50% (C50-value) at 480 mM NaCl salinity. b) Gas exchange parameters such as net photosynthesis (μmol * m-2 * s -1), stomatal conductance (mol * m-2 s -1), transpiration (mol * m-2 s-1), and water use efficiency of the photosynthesis (μmol CO2 * mmol-1 H2O) were lowest at 500 mM NaCl-salinity. The strategies employed by Townsend's cordgrass for avoiding salt injury depend on adaptation to low water potential and high Na and Cl concentrations. Spartina has sufficient adjustment mechanisms even at high NaCl salinity suggesting that there was no reason for growth reduction by Water deficit. The low external water potential was balanced e.g. by a decrease of the osmotic potential. Especially Na and Cl were accumulated in high concentrations in the root and shoot. The main defence of Spartina townsendii to elevated salinity regimes is the activation of salt glands. These salt glands are working highly selective and eliminate relatively large quantities of salt by secretion to the leaf surface. However, the salt glands were neither able to balance the high burden especially of Na in the leaf tissues at the high salinity treatment, nor useful in maintaining a constant supply of essential elements such as K, Mg and Ca. The gap between a sufficient nutrient supply and NaCl accumulation grows with increasing salinity and seems to limit the