ALLELOPATHIC EFFECTS BY EMPETRUM-HERMAPHRODITUM ON DEVELOPMENT AND NITROGEN UPTAKE BY ROOTS AND MYCORRHIZAE OF PINUS-SILVESTRIS

Fennoscandian plant communities dominated by the evergreen dwarf shrub Empetrum hermaphroditum Hagerup appear to have negative effects on forest regeneration. Effects of water extracts of leaves of E. hermaphroditum on the development and nitrogen uptake by roots and mycorrhizae (Paxillus involutus Batsch (Fr.)) of Scots pine (Pinus silvestris L.) were studied in a greenhouse experiment. Among seedlings that did not receive E. hermaphroditum extract, mycorrhizal plants grew better than nonmycorrhizal plants and also had a higher shoot to root ratio. Nitrogen uptake per unit root length was 3 times faster in mycorrhizal plants. The uptake of nitrogen was 92 ng . day-1 per dichotomous tip as compared with 22 ng . day-1 per nondichotomous root tip (mycorrhizal plants had both dichotomous and nondichotomous tips, whereas uninoculated plants almost exclusively had nondichotomous tips). A low concentration of extract impaired nitrogen uptake in both mycorrhizal and nonmycorrhizal plants. Uptake per unit root length was reduced to one-third and one-tenth in mycorrhizal and nonmycorrhizal plants, respectively. Calculated per dichotomous tip per day, the uptake of nitrogen was reduced to only 0.9 ng. Additions of extract also retarded increases in root length and the numbers of root tips, although less markedly, but the percentage of dichotomous tips was more strongly reduced. Empetrum hermaphroditum extract also strongly inhibited the growth of Paxillus involutus on modified Melin-Norkrans agar medium. The spread of mycorrhizal infection (as indicated by the percentage of dichotomous tips) and uptake of nutrients by roots and mycorrhizae were more sensitive to the extract than seed germination and radicle growth, which were demonstrated to be affected under field conditions.