Search

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.

Examines the effect of smelter sulfur dioxide emissions. Reduction of photosynthesis; Evaluation of condition during the periods of smelter operation; Relationship between the amplitude of the first-order trends and distance from the smelter.

Globally increasing anthropogenic airborne emissions of reactive nitrogen (N) generateseveral environmental issues that require investigating how N deposition modifies the N cyclein various compartments of the Earth surface. Several natural archives may helpunderstanding the global distribution and impacts of these emissions. In this sense, theisotopic N (δ15N) trends in nitrate from ice cores and total N from North American lakesediments characterized by low primary productivity indicate a general depletion ofδ15N ratios in anthropogenic N accumulated through the last century. Such resultssuggest either complex atmospheric processes changing the signal of deposited N oranthropogenic sources with generally low δ15N signals. What can the tree-ring recordsreveal about this question? Although several studies have attempted to address pastand current perturbations in the forest N cycle due to anthropogenic emissions,most of them were of local scale or based on short series. The development of thisenvironmental indicator however would benefit from examining, at the regional scale, therelationships of long tree-ring series with soil N biogeochemical processes. Here weexplore these links for spruce trees from boreal stands of the oil-sands region innorthern Alberta, and mixed forest stands of the coal-fired power plants region incentral Alberta, Canada. We characterize the tree-ring δ15N trends and intrinsicwater use efficiency (iWUE), the N modification rates and bacterial and fungalcommunities of soil samples directly associated with the selected trees. The tree-ringδ15N series show increasing and decreasing trends with time, independently of thenature and δ15N signals of the sources (coal-fired power plants or oil sands mining).Combined with the soil microbiome results, they suggest that local soil conditions,including specifically soil pH and bacterial and fungal communities, which aremostly responsible for N-cycling in soils, influence tree-ring δ15N responses toanthropogenic emissions. Overall, spruce tree-ring δ15N series may record changes in theforest-N cycle, but their interpretation requires understanding key soil biogeochemicalprocesses. These results support previous suggestions that natural archives do notrecord directly the δ15N signal of anthropogenic N sources (emissions). Equallyimportant, not only atmospheric processes may control the isotopic characteristics ofN cumulating in terrestrial settings, but soil processes may also modify the δ15Nratios of N prior to its accumulation in lake sediments or its assimilation by trees. [ABSTRACT FROM AUTHOR]