Water transport in hardened and non-hardened seedlings of Scots pine.

Abstract

The transpiration rates of 20-week-old seedlings of Scots pine preconditioned to short photoperiods and different temperature regimes, were measured. A short photoperiod reduced the transpiration rate in the light by about 10%, whereas a short photoperiod together with low temperature for 3 weeks decreased the rate by 50%. After 6 weeks the transpiration rate was reduced nearly to dark transpira tion rate, indicating that the stomata were almost closed. The results are compared with similar effects caused by water stress and abscisic acid. Additional keywords: Stress, transpiration. Introduction Ecophysiological studies have revealed that two important factors influencing the physiological state of trees in the temperate zones are daylength and temperature (e.g., Kramer, 1936; Heide, 1974). Short photoperiods and low temperature will, for example, induce winter rest and frost hardiness (Weiser, 1970; Christersson, 1978). Changes in water transport and photosynthesis during the year with a decline in the winter season have also been reported (Parker, 1963; Linder, 1977). This investigation was to study the changes of transpiration rate of pine seedlings preconditioned to short photoperiods and different temperatures, to find out which environmental factors are responsible for the decrease in the water trans port during autumn and how they act. Material and methods The plant material consisted of 20-week-old seedlings of Scots pine (Pinus sylvestris L.) grown under conditions described by Andersson et al. (1977). The 20-week-old seedling had a 9 cm long shoot with a fresh weight of 3.5 g. The seedlings were divided into eight groups with five plants in each. The groups were exposed to different daylength and temperature regimes (Table 1). After these precondi tions the transpiration rate of the seven groups of seedlings during dark and light periods were determined in the laboratory. 1 Dept. of Plant Physiology, Botanical Institute, University of G?teborg, Carl Skottsbergs Gata 22, S-413 19 G?teborg, Sweden

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