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Hydrogen and carbon isotopic variations in tree rings and their environmental significance.

机译：树木年轮中氢和碳同位素的变化及其环境意义。

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摘要

Deuterium/hydrogen (deltaD) ratios in trees potentially contain climatic information, and carbon-13/carbon-12 (delta13C) ratios may record plants' response to the increasing atmospheric CO2 concentration. This dissertation reports results of three studies on hydrogen and carbon isotopic systematics of tree rings as tools for climatic reconstruction and global carbon cycle research.;In the first study, I evaluated within-site, between-site and between-species variations of tree rings using Douglas-fir and subalpine fir trees from 5 sites in the Olympic Mountains, Washington, US, which have a wide climatic gradient. I found that between-site variations are significant if the means of two given sites differ by 10‰ or greater, and the means of Douglas-fir and subalpine fir are not significantly different. Significant correlations between the deltaD of tree rings and the annual mean temperature are found for most trees studied, but temperature only explains up to 26% of the deltaD variation in tree rings.;The objective of the second study is to evaluate how water percolation and evaporation in soil affect the fidelity of climatic signal in tree rings. I examined the isotopic compositions of water along plant's water path from precipitation through soil to stem and leaves at a site in Hanover, New Hampshire, US. I demonstrate that water in the soil column is a mixture of winter and summer precipitation with the proportion of winter precipitation increasing with depth. Soil evaporation causes substantial enrichment of deuterium or oxygen-18 in a dry year, but may not in a wet year. The effect of these soil processes on the tree-ring deltaD depends upon the depth from which the plant taps water.;In the third study, I examined change in plants' water use efficiency (W) in response to the increasing CO2 concentration in the atmosphere using the delta13C in two tree forms of the same species (bristlecone pine) with different cambial growth rates at the White Mountains, California, US. I found that W in both tree forms has increased by the similar magnitude over the past 200 years, which indicates that there is no one-to-one relationship between W and cambial growth rate.
机译：树木中的氘/氢（deltaD）比可能包含气候信息，而碳13 /碳12（delta13C）比可能记录植物对大气CO2浓度增加的响应。本论文报告了三项关于年轮氢和碳同位素系统作为气候重建和全球碳循环研究工具的研究结果。在第一项研究中，我评估了年轮的站点内，站点间和物种间变化。使用美国华盛顿州奥林匹克山5个地点的道格拉斯冷杉和亚高山冷杉树，它们的气候梯度很大。我发现，如果两个给定地点的均值相差10‰或更大，则站点间差异就很显着，而道格拉斯冷杉和亚高山冷杉的均值没有显着差异。在大多数研究的树木中，发现树木年轮的deltaD与年平均温度之间存在显着的相关性，但温度最多只能解释树木年轮中deltaD变化的26％.;第二项研究的目的是评估水的渗透和土壤中的水分蒸发会影响树木年轮中气候信号的保真度。我在美国新罕布什尔州汉诺威市的一个地点检查了植物从降水到土壤再到茎叶的水路径中水的同位素组成。我证明土壤柱中的水是冬季和夏季降水的混合物，冬季降水的比例随深度增加。在干燥的一年中，土壤蒸发会导致氘或氧18的大量富集，而在潮湿的一年中可能不会。这些土壤过程对树木年轮ΔD的影响取决于植物自来水的深度。在第三项研究中，我考察了植物水分利用效率（W）随CO2浓度增加而变化的情况。在美国加利福尼亚州怀特山，使用相同物种的两种树型（刚毛松）的delta13C形成大气。我发现，在过去的200年中，两种树的W都以相似的幅度增加，这表明W与冈比亚的增长率之间没有一对一的关系。

著录项

  • 作者

    Tang, Kuilian.;

  • 作者单位

    Dartmouth College.;

  • 授予单位 Dartmouth College.;
  • 学科 Geology.
  • 学位 Ph.D.
  • 年度 2000
  • 页码 113 p.
  • 总页数 113
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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