© 1997 Heron Publishing—Victoria, Canada
Influence of photosynthetic photon flux density on growth and transpiration in seedlings of Fagus sylvatica
N. T. Welander (1) and B. Ottosson (2)
1. Swedish University of Agricultural Sciences, Southern Swedish Forest Research Centre, Box 49, S-230 53 Alnarp, Sweden / 2. Swedish University of Agricultural Sciences, Department of Horticultural Science, Box 55, S-230 53 Alnarp, Sweden / Received August 28, 1995
Summary
Beech seedlings (Fagus sylvatica L.) were grown in various combinations of three photosynthetic photon flux densities (PPFD, 0.7, 7.3 or 14.5 mol m–2 day–1) for two years in a controlled environmental chamber. Dry mass of leaves, stem and roots, leaf area and number of leaves,
and unit leaf rate were affected by both previous-year and current-year PPFD. Number of shoots and length of the main shoot
were affected by previous-year PPFD but not by current-year PPFD. Number of leaves per shoot did not change with PPFD, whereas
leaf dry mass/leaf area ratio was mainly affected by current-year PPFD. During the first 10 days that newly emerged seedlings
were grown at a PPFD of 0.7 or 14.5 mol m–2 day–1, transpiration rate per unit leaf area declined. Thereafter, transpiration increased to a constant new rate. Transpiration
rate per seedling was closely related to leaf area but the relationship changed with time. In two-year-old seedlings grown
at various PPFD combinations of 0.7, 7.3 and 14.5 mol m–2 day–1 during Years 1 and 2, leaf area and transpiration rate per seedling were closely correlated at Weeks 7 and 11 after bud burst.
Weak correlations were found between root dry mass and transpiration rate per seedling. During Year 2, transpiration rate
per leaf area was higher at a particular PPFD in seedlings grown at a previous-year PPFD of 0.7 mol m–2 day–1 than in seedlings grown at a previous-year PPFD of 14.5 mol m–2 day–1. After transfer of two-year-old seedlings at the end of the experiment to a new PPFD (7.3 or 14.5 mol m–2 day–1) for one day, transpiration rates per leaf area, measured at the new PPFD, were correlated with leaf area and root dry mass,
irrespective of former PPFD treatment.
Keywords:
beech, irradiance, seedling morphology, shading.
