Changes in Osmotic Potential of Douglas-fir (Pseudotsuga menziesii) Seedlings in Relation to Temperature and Photoperiod

1989

S. 413-421

5 Abb., 7 Tab., 33 Lit. Ang.

Unselbständiges Werk

200038959

The influences of temperature and photoperiod on osmotic potential and ful turgor of container-grown Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings, which had completed one growing season, were examined in four experiments. Osmotic potential was measured cryoscopically on expressed sap and also by the pressure volume curve method in experiment 4. in experiment 1, started in January when (Formel) was low, seedlings exposed to 25C for 5 weeks showed an increase in (Formel) of 0.48 MPa compared with seedlings held at 8C, which showed little increase. There were no differences in (Formel) between 8- and 16h photoperiods. In experiment 2, started in September when (Formel) was relatively high, seedlings of interior origin showed decreases in (Formel) at 8C under an 8-h photoperiod (0.55 MPa) and at 25C under a 16-h photoperiod (0.69 MPA). Relatively little decrease in (Formel) occurred in interior seedlings at 8C under a 16-h photoperiod. Coastal seedlings showed no decrease in (Formel) in this experiment. In experiment 3, seedlings were exposed to 1 and 8C under an 8-h photoperiod, but at lower irradiance levels (Formel) than those used in the other experiments (Formel). Starting at values of about -1.9 MPa in October, (Formel) decreased, on overage, for coastal and interior seedlings by 0.76 MPa at 1C and 0.42 MPa at 8C over 6 weeks. Values for coastal seedlings decreased less (0.36 MPa) than those for interior seedlings (0.83 MPa). In experiment 4, seedlings were maintained under ambient conditions outdoors (mean temperatures of 5C day and 3C night), or at 12 or 25C under a 10-h photoperiod, in January and February. After 5 weeks of treatment, (Formel) at 25C was 0.50 MPa, measured cryoscopically, or 0.80 MPa, measured by the pressure-volume method, higher than for seedlings under ambient conditions. At the turgor loss point (Formel), was 1.36 MPa higher at 25C than at ambient temperature. The increase in (Formel) at the beginning of the season and the reduction of (Formel) at the end of the season were therefore dependent on temperature, but an interaction of photoperiod with temperature was observed in September. Index of injury values, calculated from leakage of electrolytes from drought-stressed needles and stems, showed a linear relationship to moisture stress between - 10 and - 2 MPa xylem water potential. In experiment 4, needle and stem index of injury values increased with increase in temperature, as did (Formel values, tending to confirm that information about drought tolerance can be obtained by either method.