Salt, nutrient uptake and transport, and ABA of Populus euphratica; a hybrid in response to increasing soil NaCl

The uptake and transport of salt ions (Na+, Cl-), macronutrients (K+, Ca2+, Mg2+) and abscisic acid (ABA) response to increasing soil salinity were ex amined in 2-year-old seedlings of Populus euphratica and a hybrid, P. talas sica Kom x (P. euphratica + Salix alba L.). Leaf burn symptoms appeared in the hybrid after 8 days of exposure to salinity when soil NaCl concentratio n increased to 206 mM, whereas P. euphratica exhibited leaf damage after da y 21 when soil NaCl exceeded 354 mM. Leaf necrosis was the result of excess salt accumulation since the injury followed an abrupt increase of endogeno us salt levels. Compared with the hybrid, P. euphratica exhibited a greater capacity to exclude salt ions from leaves under increasing salinity, espec ially Cl-. Salt treatment altered nutrient balance of the hybrid, leaf K+, Ca2+ and Mg2+ concentrations significantly declined and the same trends wer e observed in roots with the exception of K+. Although K+ levels decreased in salinised P. euphratica, increasing salinity did not affect the levels o f Ca2+ and Mg2+ in leaves, but did increase the uptake of these nutrients w hen salt stress was initiated. NaCl-induced increase of ABA concentration i n xylem sap [ABA] was observed in the two tested genotypes, however xylem [ ABA] increased more rapidly in P. euphratica and a fivefold increase of xyl em [ABA] was recorded after the first day of exposure to salt stress. There fore, we conclude that the increase of Ca2+ uptake may be associated with t he rise of ABA, and thus contributes to membrane integrity maintenance, whi ch enables I! euphratica to regulate uptake and transport of salt ions unde r high levels of external salinity in the longer term.