Carry-over effects on growth and transpiration in Fagus sylvatica seedlings after drought at various stages of development

In the two experiments carried out, newly emerged F. sylvatica seedlings were grown in pots with sand for 2 years in a controlled environmental chamber. Seedling dry mass, leaf area, and number of leaves decreased because of drought in the previous and in the current year. The decrease in area per leaf was due only to the current-year drought. Drought in both the previous and the current year reduced the number of shoots in the current year. Shoot length was mainly affected by previous-year drought. Current-year seedling transpiration decreased because of drought both in the previous and in the current year. The transpiration rate per unit leaf area was not affected by previous-year drought, whereas an after-effect was found within the growing season. The recovery of transpiration following a drought was up to 20 days. Water-use efficiency was influenced by drought during shoot development. The correlation between integrated transpiration and dry mass increase was high. This study shows that both previous as well as current environmental conditions must be taken into consideration when explaining seedling growth.