LAUSR

The main objective of this study was to evaluate the influence of leachates from three typical boreal forest ground layers on young tree growth and to explore the linkages between the chemical composition of the leachates, tree growth, the allocation between belowground and aboveground parts, and ectomycorrhizal colonization. An original 6-month greenhouse experiment was set up to investigate (i) the effects of lichen (Cladonia spp.) and feather moss (Pleurozium schreberii [Brid.] Mitt.) leachates on jack pine (Pinus banksiana Lamb.) growth and (ii) the effects of feather moss and Sphagnum spp. leachates on black spruce (Picea mariana [Mill.] B.S.P.) growth. Belowground growth and root allocation was reduced by lichen leachates in 2-year-old pine seedlings, while the impact was significant on both below- and aboveground growth in 6-month-old pine seedlings. A substance having the same migration time as usnic acid was detected in the lichen leachates by high-performance liquid chromatography. Sphagnum spp. and feather moss leachates were not found to have any effect on black spruce seedling growth, despite a higher supply of dissolved inorganic N in the feather moss leachates compared to the leachates of Sphagnum spp. and the control. These results demonstrate that ground layer composition plays a crucial role in shaping the plant community in boreal ecosystems by influencing the chemical composition of the soil solution. They suggest that chemical interference may be another mechanism by which lichens promote the self-perpetuation of open woodlands in the closed-crown boreal forest.