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 fo rest regeneration. Effects of water extracts of leaves of E. hermaphro ditum 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. Nitr ogen uptake per unit root length was 3 times faster in mycorrhizal pla nts. The uptake of nitrogen was 92 ng . day-1 per dichotomous tip as c ompared with 22 ng . day-1 per nondichotomous root tip (mycorrhizal pl ants had both dichotomous and nondichotomous tips, whereas uninoculate d plants almost exclusively had nondichotomous tips). A low concentrat ion of extract impaired nitrogen uptake in both mycorrhizal and nonmyc orrhizal 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 red uced to only 0.9 ng. Additions of extract also retarded increases in r oot length and the numbers of root tips, although less markedly, but t he 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 mycorr hizal infection (as indicated by the percentage of dichotomous tips) a nd uptake of nutrients by roots and mycorrhizae were more sensitive to the extract than seed germination and radicle growth, which were demo nstrated to be affected under field conditions.