THE EFFECT OF PHOTOSYNTHETIC PHOTON FLUX-DENSITY ON DEVELOPMENT OF FROST HARDINESS IN TOP AND ROOTS OF LARIX-LEPTOLEPIS SEEDLINGS

Seedlings of Larix leptolepis were grown in a growth chamber under short day conditions (8 h day) at 4 different photosynthetic photon flux densities (PPFD's). After a period of 8 weeks frost hardiness of the shoot tips and roots, dry matter content, dry weight (dw), content of glucose and starch were determined. The frost hardiness in the shoot tips increased from -15-degrees-C at a PPFD of 55 mumol m-2 s-1 to about -35-degrees-C at 440 mumol m-2 s-1. No effect of PPFD was found on frost hardiness of the roots. A high PPFD results in a high dry matter content. The effect on dry matter content was most pronounced for the shoot tips and less pronounced for the roots. The total dry weight increased for both root and top with increasing PPFD. The height of the plants increased when the PPFD increased up to 220 mumol m-2 s-1.