Delayed soil thawing affects root and shoot functioning and growth in Scots pine
Tapani Repo (1), Tarja Lehto (2) and Leena Finér (1)
1. The Finnish Forest Research Institute, Joensuu Research Unit, P.O. Box 68, FI-80101 Joensuu, Finland / 2. Corresponding author () / 3. University of Joensuu, Faculty of Forest Sciences, P.O. Box 111, FI-80101 Joensuu, Finland / Received July 27, 2007; accepted May 28, 2008; published online August 1, 2008
Summary
In boreal regions, soil can remain frozen after the start of the growing season. We compared relationships between root characteristics
and water relations in Scots pine (Pinus sylvestris L.) saplings subjected to soil frost treatments before and during the first week of the growing period in a controlled environment
experiment. Delayed soil thawing delayed the onset of sap flow or totally blocked it if soil thawing lagged the start of the
growing period by 7 days. This effect was reflected in the electrical impedance of needles and trunks and in the relative
electrolyte leakage of needles. Prolonged soil frost reduced or completely inhibited root growth. In unfrozen soil, limited
trunk sap flow was observed despite unfavorable aboveground growing conditions (low temperature, low irradiance, short photoperiod).
Following the earliest soil thaw, sap flow varied during the growing season, depending on light and temperature conditions,
phenological stage of the plant and the amount of live needles in the canopy. The results suggest that delayed soil thawing
can reduce tree growth, and if prolonged, it can be lethal.
