Growth Experiments With Seedling of Mountain Birch (Betula pubescens Ehrh.) and Lowland Birch (Betula penula Roth.) Grown at Varying Temperature, Light and Daylength

1991

41 S.

10 Abb., 3 Tab., 38 Lit. Ang.

Unselbständiges Werk

200037925

Seedlings from four mountain birch (Betula pubescens Ehrh.) and one lowland birch (Betula pendula Roth.) population were grown for 6 weeks at varying light intensity, temperature and photoperiod. The growth was followed by subsequent harvesting and non-destructive measurements of leaf and stem growth. In accordance with earlier studies there was a strong latitudinal effect on the critical daylengths for growth. There was also a weaker bur significant effect due to altidude or summer temperature at the habitat. Large differences were also found in growth pattern and compensation mechanisms. Fast growing lowland populations, including lowland birch from southern Norway reacted to low irradiance and high temperatures by increasing their shoot/root ratios and the temperature optimum for shoot elongation vs. leaf growth. In mountain birch from Kevo, northern Finland, on the other hand, plants reacted to increasing temperatures by increasing their net assimilation rates. The shoot/root ratios and leaf area ratios were highest at the earliest stages of growth while maximum net assimilation rates occurred later. This illustrates the high priority in birch for leaf growth. In all populations except northern mountain birch the plants grew better in alternating day and night temperatures than at the corresponding constant temperature.