Study On Salt Tolerance Of Tamarix.spp In Xinjiang

Surpervised by associate Professor Dong Yuzhi&Professor Zhang FusuoThe utilization of halophyte has been proposed as a strategy to expand cultivation onto unfavorable land, however, halophyte mainly have been considered for their tolerance and performance in extremely saline environment, and only a few species have been characterized in terms of their tolerance and physiological responses to salinity .The functional biology underlying salt tolerance in plants is still poorly understood. Tamarix-spp is a perennial recretohalophyte capable of growing under extreme condition, from very dry environments to highly saline soils. To quantify its response to salinity , Tamarix .leptostachys seedlings were exposed to ON 50s 100s 150> 200mM NaCl for 4weeks, in a sand culture and growth, root activity ,and solute accumulation were measured, the presence of NaCl induced a 26.9 % relative decrease in dry weight of Tamarix ramosissima.,and a 173% decrease in dry weight of Tamarix .leptostachys relative to non-salinized controls, these changes were associated with a decrease in relative water content, The solute leakage and proline content were increased in Tamarix arceuthoides. Analysis of ion accumulation revealed that Tamarix .spp accumulated Na* and Cl' as a primary osmoticum in contrast to proline. Generally, Tamarix is a facultative halophyte.The contribution of each of the salt-transporting processes to the NaCl balance of the leaves of the salt-recreting Tamarix was quantitatively investigated. Transpiration rates, xylem sap concentration , shoot salt content ,recretion rates were continuously monitored during three day periods and the salt fluxes in and out of the shoot were calculated . The diurnal excretion pattern ,which gradually decreased toward midday, showed a negative correlation with the daily transpiration pattern, The relative excretion, which is the ratio between the absolute excretion of Na* and the change in its internal content ,was maximal at 50mM NaCl ,and decreased when the concentration of NaCl in the root environment increased ,by contrast ,the absolute excretion increased from 247 to 348 mmol Na+g-1 f.w with increase in the total media salinity from 50 to 200 mM NaCl .respectively .Selectivity of the salt-excretion mechanism is in favor of sodium and against potassium, on the other hand ,potassium has a high affinity for the accumulation systems within the shoots. The results indicated that salt filtration by the roots is by far the most important salt-rejecting mechanism, preventing some 89- 96% of the salt which is carried towards the root surface by the transpiration stream, from entering the shoot .out of the remaining quantity of salts which enter the root xylem and reach the leaves ,only 31-59% is removed by the salt-recreting glands.In conclusion, it is suggested that salt resistance of Tamarix.spp is based upon three different mechanisms: 1) Salt avoidance -where the roots have low permeability to salts, this is by far the most important mechanism .2)Salt tolerance-the capability to preserve normal metabolic activity even in the presence of high intraceliular salt levels.3)Salt evasion -recretion of the penetrating ions, but retention of others .the magnitude of salt recreation in Tamaruuspp does not yield a quantitative solution to the problem of excess accumulation of salt ,Still, recreation may contribute to the mineral balance of T. in a qualitative way ,by changing the ratio between the nutritive ions and the interfering ones. The rejection mechanism at the plant roots and the secrection mechanism at shoots allow the plant to maintain its internal salt content at an approximately constant level despite the great variation in rhizosphere salinity .