LIGHT UTILIZATION POTENTIAL OF QUERCUS-PETRAEA, FAGUS-SYLVATICA AND ACER-PSEUDOPLATANUS IN THE YEAR OF ADVANCED PLANTING

Advanced planting of broadleaf species offers a possibility to change species composition in coniferous forests. Despite several growth inve stigation of such plantations, data on their photosynthetic performanc e are lacking. For its investigation, Quercus petraea, Fagus sylvatica and Acer pseudoplatanus were planted from the forest edge up to 35 m inside the closed canopy in one Norway spruce/Scotch pine mixed forest in April 1996. The photosynthetic response to increasing photon flux density was measured on 12 plants from each species three times from J uly to September 1998 (Fig. 2). The evaluation of the porometer data h as shown, that the light compensation point was twice as high for Q. p etraea compared to the other two species (Tab. 2). In relation to the light conditions under the closed canopy, this seems to be the limitin g factor for the survival of Q. petraea plants. The photosynthetic cap acity per unit leaf area decreased in the order Acer pseudoplatanus, F agus sylvatica and Quercus petraea. Both A. pseudoplatanus and Q. petr aea have acclimated their photosynthesis to the prevailing light condi tions (i.e. high efficiency and capacity with increasing light; Fig. 4 and 5). However, Fagus sylvatica, supposed a highly shade tolerant di d not show any acclimation. The planting stress as a possible reason i s discussed. Considering the photosynthetic light utilization, Acer ps dueoplatanus exhibited the best performance and was found optimally su ited for advanced planting below the canopy of existing stands.