Abstract Although requiring laborious analytical treatment, tree-ring series of nitrogen isotopes (δ15N) have gained popularity amongst researchers for their potential as environmental indicators as anthropogenic emissions increase globally with potential effects on forest N cycles. Previous studies suggested that tree-ring series correlate with climatic and air quality parameters. However, none discussed the level of replication required for expressing the population signals of specific species of trees. In this investigation, we studied 27 white spruce trees from two sites under distinct environmental conditions to evaluate the appropriate protocol for preparing consistent tree-ring δ15N series. The produced series indicate that high frequency (short-term, 15 years) δ15N trends show coherence between arithmetic means of individual series at replication levels as low as three trees, whereas middle-term pooled trends do not perform as coherently. The low frequency mean trends of individual series obtained for the two sites suggest that local biogeochemical soil conditions modified by anthropogenic emissions modulate the δ15N responses in trees. Hence, we propose that long-term tree-ring δ15N series constitute reliable environmental indicators.

中文翻译：

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单个年轮系列的氮同位素 - 中长期趋势的有效性

摘要 尽管需要费力的分析处理，但随着全球人为排放增加对森林氮循环的潜在影响，树木年轮系列氮同位素 (δ15N) 因其作为环境指标的潜力而受到研究人员的欢迎。先前的研究表明，树轮系列与气候和空气质量参数相关。然而，没有人讨论表达特定树种的种群信号所需的复制水平。在本次调查中，我们在不同环境条件下研究了来自两个地点的 27 棵白云杉树，以评估制备一致年轮 δ15N 系列的适当方案。产生的系列表明高频（短期，15 年）δ15N 趋势表明，在低至三棵树的复制水平上，各个系列的算术平均值之间具有一致性，而中期汇总趋势的表现则不那么一致。两个站点获得的单个序列的低频平均趋势表明，人为排放改变的当地生物地球化学土壤条件调节了树木中的 δ15N 响应。因此，我们建议长期树轮δ15N系列构成可靠的环境指标。