WATER STRESS AND NUTRIENT SOLUTION-MEDIATED CHANGES IN WATER RELATIONS AND AMINO-ACIDS, ORGANIC-ACIDS, AND SUGARS IN XYLEM FLUID OF PRUNUS-SALICINA AND LAGERSTROEMIA-INDICA

The effects and interactions of water stress and nutrient solution on water relations and concentrations of amino acids, organic acids and s ugars in xylem fluid of ''Methley'' plum (Prunus salicina Lindl,) and ''Carolina Beauty'' crape myrtle (Lagerstroemia indica L.) during midd ay were determined. Container-grown plants were irrigated with water o r nutrient solution (i.e., osmolarity = 138 mm) for 15 days, then irri gation was either continued or terminated for the next 5 days. The exp eriments were analyzed as factorial designs for each species separatel y, with the nutrient solution and irrigation status the last 5 days as the main factors. Xylem fluid tension increased approximate to 2- to 3-fold and leaf conductance to water vapor and transpiration mere redu ced approximate to 10-fold by withholding irrigation for both species; plant water relations of L. indica were also influenced by the nutrie nt solution. For both species, the osmolarity of xylem fluid was not a ltered by withholding irrigation, The predominant organic compounds qu antified in both species were amides (i,e., glutamine and asparagine), arginine, and citric and malic acids, Sugars represented a small prop ortion (i,e., generally less than or equal to 1%) of total osmolarity, Irrigation altered the chemical profile of amino acids and organic ac ids to a greater degree than the nutrient solution. Water stress induc ed a 3-fold increase in total organic acids in xylem fluid of both spe cies. The osmolarity and the concentration of most organic compounds i n xylem fluid of P. salicina were not significantly affected by the nu trient solution. Arginine increased markedly in concentration by withh olding irrigation or with the application of nutrient solution fort. i ndica. The concentration of most organic compounds did not vary greatl y in response to variations in soil water or nutrient status. In concl usion, soil water- or nutrient-mediated changes in plant water relatio ns exceeded changes in xylem fluid chemistry.