4. Results 28
4.2.2. Parameters obtained from pressure-volume curves
Like the leaf water potentials, the osmotic potentials at saturation (Π0) and incipient plas-molysis (Πp) dropped markedly over the course of the summers of both years of investigation (Fig. 4.2). In 1999, average annualΠ0of the well watered Swedish clone (-1.06 MPa) were sig-nificantly less negative than those of the other genotypes (-1.21 to -1.28 MPa). The droughted plants showed lower values ofΠ0 than the W99/W00-treatments, particularly towards the end of summer, after about two months of drought stress. Only in Bp-Aust.2 this difference never became statistically significant.
Osmotic potentials at the turgor loss point in 1999 were on average 0.81 MPa lower than those at saturation. Annual averages of the well watered Swedish and German trees were slightly more positive than those of the Austrian plants. The Πp values of the
D99/D00-4. Results
Figure 4.2.: Osmotic potentials at saturation and at the turgor loss point (Π0 andΠp) of the four birch clones during the summers of 1999 and 2000. Open circles and dashed lines represent the droughted plants (D99 and D99/D00), filled squares and solid lines the well watered controls (W99 and W99/W00), and crosses and dotted lines the drought-and-recovery treatment in 2000 (D99/W00). Means and stan-dard deviations of 5 leaves from different plants are given. Asterisks indicate significant differences (P ≤0.05) between droughted (D99 and D99/D00) and well watered plants (W99/W00). After the day indicated by the black arrow the volumetric soil water content of the droughted pots was below 3 %.
treatments were markedly more negative than those of the W99/W00-treatments in all geno-types. These differences became particularly significant in mid-August, after a long period of drought but before leaf senescence began.
During the investigated period of 2000, averages of both Π0 and Πp of the well watered
4. Results
Figure 4.3.: Apparent and relative osmotic adjustment of the four birch clones in early August 1999 and 2000. The dark bars (a + c) show the osmotic adjustment at saturation, the lighter ones (b + d) that at the turgor loss point. The left bars of each clone (a + b) show the apparent osmotic adjustment [MPa], which is the absolute difference between the osmotic potentials of the well watered and the droughted plants. The two right bars (c + d) show the relative osmotic adjustment [%], where these differences are given as percentages of the osmotic potentials of the well watered plants.
plants were lower than in 1999. Again, the meanΠ0of the W99/W00 treatments of Bp-Swed.
was more positive than those of the other genotypes. Differences between Πp and Π0 of the well watered plants averaged to 0.67 MPa. As in 1999, osmotic potentials at incipient plas-molysis were more negative in the droughted treatment in 2000 as well, though apart from the values measured on Bp-Swed. in early August 2000, these differences never became statisti-cally significant. Osmotic potentials of the D99/W00-treatments in 2000 did not significantly differ from those of the the W99/W00-treatments.
Differences between osmotic potentials of the droughted and the well watered plants of a given genotype can be termed apparent osmotic adjustment, which can be expressed either as the absolute value, or as a percentage related to the osmotic potentials of the corresponding W99/W00-treatment. Osmotic adjustment of the four genotypes as measured in mid-August of both 1999 and 2000 is shown in Fig. 4.3. Both the absolute and the relative values of osmotic potentials were up to twice as high in the Swedish and the German genotypes (0.38 MPa corresponding to 34 to 36 % forΠ0 and 0.67 to 0.70 MPa corresponding to 36 to 40 % forΠp) than in the two Austrian clones in 1999 (0.18 to 0.26 MPa corresponding to 12 to 19 % for Π0 and 0.03 to 0.22 MPa corresponding to 1 to 9 % forΠp). Osmotic adjustment measured in 2000 was much smaller for all clones, but nevertheless Bp-Swed. and Bp-Germ. osmotically adjusted to a greater extent to the drought stress than the Austrian genotypes in this summer as well.
Moduli of tissue elasticity near full turgor (εmax) of the four birch genotypes as obtained from pressure-volume curves in 1999 are shown in Tab. 4.3. Droughted plants, especially in the genotypes Bp-Aust.1 and Bp-Swed., reached distinctly higherεmaxvalues than the W99/W00-treatments. In 2000, the moduli of elasticity of all clones were higher than in 1999 and showed a marked tendency to higher values towards the end of the summer (Tab. 4.3). Like in 1999,
4. Results
Table 4.3.: Moduli of tissue elasticity near full turgor (εmax[MPa]) of leaves of the four birch clones troughout the growing seasons 1999 and 2000. Means of 4 (3 in June) twigs from different plants are given. Asterisks indicate significant differences (P ≤ 0.05) between droughted (D99/D00) and well watered (W99/W00) plants.
clone treatment June July early August late August 1999
Bp-Aust.1 W99/W00 4.85 4.35 5.08 5.02 D99/D00 4.45 8.57 * 6.93 * 7.29 * Bp-Aust.2 W99/W00 3.95 4.09 5.83 4.85
D99/D00 5.82 * 6.20 7.50 6.66 Bp-Swed. W99/W00 3.80 2.46 2.94 2.95 D99/D00 4.21 3.15 6.07 * 5.19 * Bp-Germ. W99/W00 3.60 4.62 4.29 5.53
D99/D00 4.70 5.15 6.26 6.80
2000
Bp-Aust.1 W99/W00 8.83 7.94 10.49 11.56
D99/W00 9.69 6.96 9.61 10.98
D99/D00 8.89 8.48 12.22 12.52
Bp-Aust.2 W99/W00 4.58 8.41 10.71 10.58
D99/W00 4.05 9.40 10.80 11.37
D99/D00 3.00 9.86 12.73 10.99
Bp-Swed. W99/W00 5.11 7.28 8.05 7.36
D99/W00 3.96 6.26 7.21 7.76
D99/D00 4.25 8.23 10.33 10.42
Bp-Germ. W99/W00 4.48 8.07 8.54 8.68
D99/W00 4.82 7.67 8.59 8.91
D99/D00 4.87 8.57 11.60 11.99
εmaxvalues of both well watered and droughted Swedish trees were the lowest ones, while Bp-Aust.1 obtained the highest values in these treatments. Values ofεmaxwere again consistently higher in droughted plants than in well watered ones in all genotypes, although these differ-ences were not statistically significant. Theεmaxvalues of the drought-and-recovery treatments showed no marked differences from the W99/W00-plants.
Plasticities of osmotic potentials and moduli of elasticity are shown in the appendix in Tab. A.1. In 1999, absolute and relative plasticity with regard toΠ0were highest in Bp-Aust.1, while with regard toΠpthe Swedish and especially the German clone responded more plastic than the Austrian genotypes. Plasticity was generally higher regarding εmax, with Bp-Swed.
reaching the highest values. In 2000, plasticity of all parameters derived from pressure-volume curves was much lower than in 1999, but again Bp-Swed. responded most plastic with regard toεmax.
The moduli of elasticity showed gaussian distributions in both years of investigation, so an analysis of variance could be carried out to evaluate the influences of the individual factors.
Results of this analysis are shown in the appendix in Tab. B.1. In both years the influence of both genotype and treatment on the modulus of elasticity were highly significant.
4. Results