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...