『Abstract
　In this study, tree-ring concentrations and stable isotope ratios of nitrogen in red spruce trees growing near Quebec（最初のeの頭に´） City (Canada) were used as records of environmental changes for the period between 1880-81 and 2007. On one hand, the trends in nitrogen concentrations of red spruce trees are strongly influenced by the heartwood-sapwood transition zone. Such physiologically-influenced pattern suggests that tree-ring nitrogen concentrations are not representative of soil or air nitrogen variations. On the other hand, the δ¹⁵N trends of the investigated trees do not show any sign of influence from the heartwood-sapwood boundary, meaning that these isotopic values can be representative of environmental conditions. The interannual variations of the δ¹⁵N values were correlated with the total annual precipitation and the measured amounts of regional nitrogen oxide emissions for the 1990-2007 period. The long-term δ¹⁵N values show a decrease of 1.8‰ between 1956-57 and 2007. This decreasing trend is statistically linked to the increasing number of registered cars in the Quebec Province, which produce N emissions characterized by low isotopic values. We suggest that this long-term trend could have been caused by a change to a dominant source of N emissions with low δ¹⁵N values, and/or by the microbiological processes, such as the release of N from mycorrhizal under N-limited environment. Importantly, we demonstrate that this clear isotopic pattern is matching that of other species (pine and beech trees) growing under different ecological conditions, at 260 km from our study site. Therefore, we suggest that nitrogen oxides emitted by car exhausts, themselves linked to the amount of transport-related N deposition at the provincial scale, could have caused the observed trends and have participated to the acidification of soil. This investigation allows suggesting that the δ¹⁵N values of trees have the potential to reflect perturbations of the soil and air nitrogen dynamics caused by anthropogenic N emissions at a large scale.

Keywords: Tree ring; Nitrogen isotopes; Atmospheric pollution; NOx emissions; Picea rubens Sarg』

1. Introduction
2. Materials and methods
　2.1. Study site
　2.2. Air quality at the study site
　2.3. Sample preparation and analyses
　　2.3.1. Sampling of trees and sample preparation
　　2.3.2. Geochemical analyses and data treatment
3. Results
　3.1. Nitrogen concentrations in tree rings
　3.2. Nitrogen isotope ratios in tree rings and soil horizons
4. Discussion
　4.1. Physiological influence on the tree-ring nitrogen concentration series
　4.2. Tree-ring δ¹⁵N series in the Quebec（最初のeの頭に´） site - a record of anthropogenic effects
　4.3. Anthropogenic perturbations of the N cycle - a regional picture
5. Conclusions
acknowledgments
References