The influence of shading on growth and morphology in seedlings of Quercus robur L. and Fagus sylvatica L.

Abstract

Growth and morphology in relation to shading was investigated in young seedlings of oak ( Quercus robur L.) and beech ( Fagus sylvatica L.). First-year growth in oak seedlings was compared with first-year growth in beech, a shade-tolerant species. In addition, second-year growth, as influenced by previous and current year light conditions, was investigated in seedlings of oak. The seedlings of oak and beech were grown in various light intensities in a climatic chamber. The photoperiod was 16 h and the day/night temperature 18/14°C. In the first year of growth, oak and beech seedlings were grown in photosynthetic photon flux densities (PPFD) of 0.7, 1.5, 3.0, 7.3, 14.5 and 23.1 mol m −2 day −1, corresponding to about 2, 4, 9, 21, 43 and 70% relative light under field conditions in southern Sweden. In the second year of growth, oak seedlings grown in a previous-year PPFD of 0.7 and 14.5 mol m −2 day −1 were transferred to a current-year PPFD of 0.7, 7.3 and 14.5 mol m −2 day −1. Dry mass of leaves, stem and root in the oak and beech seedlings increased with PPFD. In beech, more dry matter was allocated to the shoot than to the root, whereas the root was more favoured in oak. Unit leaf rate (ULR) increased with PPFD in both species. During the first year, oak showed a higher productivity per leaf area (ULR) than beech. ULR in oak was similar or higher during the second year compared with the first year. Dry mass of dark grown oak seedlings was about 50% of the seedling dry mass achieved at the lowest PPFD. During the second year, the first flush of growth in oak was affected by the previous-year PPFD, and the second flush by the current-year PPFD. First-year seedlings of oak and beech seem to be equally well adapted to low light conditions and it would thus be possible to regenerate oak as well as beech under a dense canopy. However, the present results indicate that oak seedlings may be sensitive to increasing competition for light, as simulated by a transfer to low light level in the second year. Therefore, light intensity should be increased after the first year of seedling growth in regeneration of oak.