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 econo- my 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 adjustment or changes in the cell wall elasticity of shoots. Similarly, treatments did not differ in their dehydration tolerance as determined 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 con- trol plants in roots but not in shoots. Root growth capacity was significantly reduced in the strongly conditioned plants. ( © Inra/Elsevier, Paris.) drought resistance / electrolyte leakage / Mediterranean / minimum transpiration / plant quality Rsum -Effet d'un prconditionnement par la scheresse sur les relations hydriques, la capacit de croissance des racines et les concentrations en azote et hydrates de carbone non structuraux de jeunes plants de Pinus halepensis Mill. Des plants de Pinus halepensis gs de 1 an ont t conditionns par application de quatre niveaux de stress hydrique (Tmoin, Faible = -1.2 MPa, Modr = -1.8 MPa et Elev = -2.2 MPa) pendant deux mois. Aprs le prconditionnement, certains paramtres hydriques des plants, la capacit de formation de nouvelles racines et les concentrations en azote, amidon et sucres solubles des parties ariennes et racinaires ont t mesurs. Comparativement aux plants soumis aux conditionnements Tmoin et stress hydrique Faible, ceux condi- tionns par des niveaux de stress hydrique plus forts (traitements Modr et lev) ont prsent i) des taux de transpiration minimale plus faibles (table I), ii) des concentrations en amidon dans les parties ariennes et des sucres solubles dans les racines plus leves (table En revanche, la capacit de croissance de nouvelles racines a t rduite chez les pins prconditionns par un stress hydrique lev (lev) (table