Anthropogenic N – A global issue examined at regional scale from soils, to fungi, roots and tree rings

¹ Geological Survey of Canada, Lands & Minerals Sector, Natural Resources Canada, 490 de la Couronne, Québec (QC), G1K 9A9, Canada
² Canadian Forest Service, Laurentian Forestry Centre, 1055 du P.E.P.S., P.O. Box 10380, Stn. Sainte-Foy, Québec (QC), G1V 4C7, Canada

^* Corresponding author: martinem.savard@canada.ca

Abstract

Globally increasing anthropogenic airborne emissions of reactive nitrogen (N) generate several environmental issues that require investigating how N accumulation modifies the N cycle. Tree-ring δ¹⁵N series may help understanding past and current perturbations in the forest N cycle. Although several studies have addressed this issue, most of them were of local scale or based on short δ¹⁵N series. The development of this environmental indicator however would benefit from examining, at the regional scale, the relationships of long tree-ring series with soil N biogeochemical processes. Here we explore these links for tree stands of the oil-sands region in northern Alberta, and the coal-fired power plants region in central Alberta, Canada. We characterize the tree-ring δ¹⁵N trends, the N modification rates and bacterial and fungal communities of soil samples collected in the immediate surrounding of the characterized trees. The dataset suggests that specific soil pH, and N-cycling bacterial and fungal communities influence tree-ring δ¹⁵N responses to anthropogenic emissions, correlating either directly or inversely. Overall, tree-ring δ¹⁵N series may record changes in the forest-N cycle, but their interpretation requires understanding key soil biogeochemical processes. «In nature nothing exists alone», Rachel Carson.