© 2005 Heron Publishing—Victoria, Canada
Effects of timing of soil frost thawing on Scots pine
Tapani Repo (1, 2), Tuomo Kalliokoski (1), Timo Domisch (1), Tarja Lehto (3), Hannu Mannerkoski (3), Sirkka Sutinen (1) and Leena Finér (1)
1. The Finnish Forest Research Institute, Joensuu Research Centre, P.O. Box 68, FIN-80101 Joensuu, Finland / 2. Corresponding author (tapani.repo@metla.fi) / 3. University of Joensuu, Faculty of Forestry, 80101 Joensuu, Finland / Received March 18, 2004; accepted November 20, 2004; published online June 1, 2005
Summary
Effects of the timing of soil thawing in the spring on Scots pine (Pinus sylvestris L.) were studied under controlled laboratory conditions. Sixteen 6-year-old saplings were lifted from the field, replanted
in containers and placed in four treatments in controlled environment (CE) chambers with four replicate saplings per chamber.
The saplings were held in the CE chambers during one simulated winter and one simulated growing season. The soil was frozen
to –2 °C during a second simulated winter in the CE chambers, and the soil thawing treatments began at the end of the second
simulated winter. Soil thawing began at various times before (no delay in thawing) and after (delay in thawing) chamber air
conditions were changed from simulated winter to simulated summer. Delayed soil thawing subjected saplings to stress, with
the severity of stress depending on the length of the delay in thawing. If there was no delay or only a short delay in soil
thawing, stress was minor and reversible. A 2-week delay in soil thawing led to death of the saplings. Stress was apparent
as decreases in the variable to maximal chlorophyll fluorescence ratio (Fv/Fm), chlorophyll a/b ratio and needle water potential. In needles of stressed saplings, apoplastic electrical resistance first
decreased and then increased and there were anomalies in the electrical impedance spectra of the stems. Stress from the soil
thawing treatments affected both root and shoot growth.
Keywords:
carbohydrate, chlorophyll, chlorophyll fluorescence, electrical impedance, growth, minirhizotron, phenology, Pinus sylvestris, root, soil freezing, water potential, water stress.
