© 1987 Heron Publishing—Victoria, Canada
Effects of low night temperature and light on chlorophyll fluorescence of field-grown seedlings of Scots pine (Pinus sylvestris L.)
M. Strand (1) and T. Lundmark (2)
1. Department of Plant Physiology, University of Umeå, S-901 87 Umeå, Sweden / 2. Department of Silviculture, Swedish University of Agricultural Sciences, Faculty of Forestry, S-901 83 Umeå, Sweden / Received February 20, 1987
Summary
In vivo chlorophyll fluorescence kinetics was observed in naturally regenerated and planted Scots pine (Pinus sylvestris L.) seedlings growing at two adjacent sites in northern Sweden. Some seedlings were shaded from direct solar radiation and
some were protected from frost at night. Air temperature and solar radiation were monitored. In vivo chlorophyll fluorescence
kinetics of current-year needles was measured at both room temperature and 77 K. On clear days during August, variable fluorescence
of photosystem II of needles from exposed, naturally regenerated seedlings was reduced by night frosts, whereas frost caused
little change in fluorescence of needles from shaded seedlings. Overnight frost-protection reduced the inhibition of photosystem
II by direct sunlight. Recovery from photoinhibitory damage occurred on cloudy days. In September, the decline of variable
fluorescence of photosystem II was more pronounced in unshaded than in shaded seedlings, and coincided with frosts at night.
In addition, the reduction in variable fluorescence was larger for planted seedlings than for naturally regenerated seedlings.
It is suggested that the inhibition of photosystem II activity was caused by an interaction between low temperatures and light.
Natural night frosts are proposed to increase the susceptibility to photoinhibition in the following day(s).
