Christian Messier1, Lluis Coll2, Amélie Poitras-Larivière1, Nicolas Belanger3, and Jacques Brisson4. (1) University of Quebec in Montreal, (2) Centre Tecnològic Forestal de Catalunya, (3) University of Saskatchewan, (4) Université de Montréal
Background/Question/Methods: Living organisms normally compete for both resource and non-resource elements in their struggle for survival. This is true for both plant and animals, but plants, due to their relative immobility, had to develop special strategies. This study assessed the resource and non-resource effects of the presence of fine-roots of competing grasses on the growth, morphology and architecture of fine-roots of 4 tree species varying in successional status: Populus deltoides x P. balsamifera (a hybrid), Betula papyrifera, Acer saccharum and Fraxinus Americana. The first hypothesis tested was that the presence of fine-roots of competing vegetation affects the development of tree fine-roots even when below-ground resource is not limited. The second hypothesis was that early successional/pioneer tree species such as poplar and birch will be more affected by the presence of competing fine-roots than late successional species such as ash and maple. The experiment was conducted in split-containers where half of the roots of tree seedling experienced below-ground competition by grasses and the other half no competition. Results/Conclusions: The study showed the late successional tree species A, saccharum and F. Americana were somewhat affected only by resource competition by grasses, whereas P. deltoides x balsamifera and B. papyrifera were strongly affected by both resource and non-resource competition. Non-resource competition reduced fine-root growth, root branching over root length (a measure of root architecture) and root specific length (a measure of root morphology) of either or both early successional species. These results suggest early successional/pionner tree species may have been selected for root avoidance or segregation and late successional tree species for root tolerance of competition as mechanisms to optimise below-ground resource uptake in their particular environments.
