Intraseasonal variation in the δ15N signature of taiga trees and shrubs

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Abstract
We examined the stable isotope ratios of nitrogen from six dominant taiga species over three distinct phenological periods during the growing season. Temporal changes in the isotopic signature varied among species, but were not consistent within a given growth form. Despite large variation between nitrogen concentrations in new, mature, and senescent foliage, the seasonal fluctuations in δ15N were small with the exception of aspen, a tree species growing on the most fertile sites. In the absence of strong within-season variation in isotope signature, we conclude that this parameter reasonably well integrates the plant-nitrogen relations over the growing season for most species, with the caveat that this parameter may show significant temporal variation in species from high-nitrogen environments. We found a significant, positive relationship between nitrogen concentration and δ15N values in mature and newly flushed foliage, suggesting that plant enrichment in δ15N is associated with increased soil nitrogen turnover.

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