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 related to the water economy of seedlings, the root growth capacity, and the shoot and root nitrogen and non-structural carbohydrate concentration were analysed. Moderate and strongly conditioned seedlings showed a significantly lower minimum transpiration rate than the control and mildly conditioned seedlings. In a subsequent drought cycle after conditioning, these latter treatments exhibited a lower predawn water potential than the moderate and strong conditioning treatments. Drought did not induce any osmotic adjustments or changes in the cell wall elasticity of shoots. Similarly, treatments did not differ in their dehydration tolerance as by the percentage of electrolyte leakage. Mildly and moderately conditioned plants concentrated more nitrogen in shoots and roots respectively. Shoot starch was concentrated more in the moderate and strong conditioning treatments while no differences were observed in roots. Soluble sugars showed the reverse trend, the moderately and strongly conditioned plants exhibiting a higher concentration than control plants in roots but not in shoots. Root growth capacity was significantly reduced in the strongly conditioned plants. ((C) Inra/Elsevier, Paris.).