Effect of water stress conditioning on the water relations, root growth capacity, and the nitrogen and non-structural carbohydrate concentration of Pinus halepensis Mill. (Aleppo pine) seedlings

One-year-old Pinus halepensis seedlings were subjected to four water stress conditioning treatments (control, mild= -1.2 MPa, moderate = -1.8 MPa and strong = -2.2 MPa) for 2 months. After conditioning, several parameters rel ated to the water economy of seedlings, the root growth capacity, and the s hoot and root nitrogen and non-structural carbohydrate concentration were a nalysed. Moderate and strongly conditioned seedlings showed a significantly lower minimum transpiration rate than the control and mildly conditioned s eedlings. In a subsequent drought cycle after conditioning, these latter tr eatments exhibited a lower predawn water potential than the moderate and st rong conditioning treatments. Drought did not induce any osmotic adjustment s or changes in the cell wall elasticity of shoots. Similarly, treatments d id not differ in their dehydration tolerance as by the percentage of electr olyte leakage. Mildly and moderately conditioned plants concentrated more n itrogen in shoots and roots respectively. Shoot starch was concentrated mor e in the moderate and strong conditioning treatments while no differences w ere observed in roots. Soluble sugars showed the reverse trend, the moderat ely and strongly conditioned plants exhibiting a higher concentration than control plants in roots but not in shoots. Root growth capacity was signifi cantly reduced in the strongly conditioned plants. ((C) Inra/Elsevier, Pari s.).