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Dissolved organic nitrogen (DON) cycling along a temperate forest nitrogen availability gradient.

机译：溶解性有机氮（DON）沿着温带森林的氮可利用量梯度循环。

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摘要

Nitrogen (N) is essential for ecosystem productivity, yet frequently constrains ecosystem primary production. Previously, the majority of research on N cycling has focused on inorganic N biogeochemistry. More recently, research investigating dissolved organic N (DON) has found it also plays a significant role in N biogeochemistry, both as a vector for N loss from terrestrial ecosystems and as a source of plant-available N, which suggests DON is an important component of the terrestrial N cycle.;This dissertation research investigated the role of DON as an N source for temperate trees and as a vector of N loss, using northern hardwood forests of varying tree species composition and soil properties as a basis for study. First, in Chapter 2 I investigated DON uptake by four tree species that commonly occur in either low or high N availability forests. I grew tree seedlings in a greenhouse and labeled them with 15N-enriched amino acids (organic N source), 15N-ammonium, and 15N-nitrate (inorganic N sources). I found that specific uptake rates of amino acid-N were similar across all tree species. However, high N availability species took up NH4+ twice as fast as low N availability species, suggesting amino acid-N was relatively more important to low versus high N availability species. Low N availability species also acquired up to 4 times more total N from amino acids compared to inorganic N sources. These results suggest plant species dominance in a habitat is linked to their ability to use the most available N pool.;Second, in Chapter 3 I investigated dissolved organic matter (DOM) leaching losses from forests that spanned a gradient of N availability and tree species composition. I collected soil solutions for three years with lysimeters and analyzed them for dissolved organic carbon (DOC), dissolved inorganic nitrogen (DIN), and DON composition and fractionated DOC in the solutions into hydrophobic and hydrophilic compounds. I also evaluated the characteristics of soils in the forests. I found that DON losses at 100 cm soil depth were not related to increasing soil N stocks across forests, contrary to my expectations. Surprisingly, DOM losses at this same soil depth demonstrated a unimodal pattern of DOC:DON, with relatively low DOC:DON in DOM losses from low and high N availability forests and relatively high DOC:DON from intermediate N availability forests. These patterns likely resulted from the different source and sink strengths of forest soils for DOM as forest floor composition and soil characteristics changed.;Finally, in Chapter 4 I evaluated how soil characteristics impacted the chemistry of soil waters leaching from soil cores collected from the above forests. I leached 0--10, 0--25, and 0--50 cm deep cores with a common organic matter solution and analyzed the solutions for DOC, DIN, DON, and hydrophobic/hydrophilic fractions. I also measured multiple physical and geochemical characteristics of the soil cores. Soil depth had a stronger impact on DOM chemistry compared to forest differences. DOM concentrations in soil core leachate decreased with soil depth due to the removal of hydrophobic compounds. Noticeably, DON concentrations increased between the input organic matter solution and 10 cm soil depth, which was accompanied by 67-fold increase in the hydrophilic fraction of DON. These results demonstrated that soil has a strong ability to influence the quantity and quality of DOM leaching through forest soils.
机译：氮（N）对于生态系统生产力至关重要，但经常会限制生态系统的初级生产。以前，大多数关于氮循环的研究都集中在无机氮生物地球化学上。最近，研究溶解性有机氮（DON）的研究发现，它在氮生物地球化学中也起着重要作用，既是陆地生态系统中氮损失的载体，又是植物可用氮的来源，这表明DON是重要的组成部分。本论文的研究以不同树种组成和土壤特性的北方硬木森林为基础，研究了DON作为温带树木氮源和氮损失载体的作用。首先，在第2章中，我研究了低氮或高氮可用性森林中常见的四种树种对DON的吸收。我在温室中种植树木幼苗，并用富含15N的氨基酸（有机N来源），15N铵和15N硝酸盐（无机N来源）标记它们。我发现在所有树种中，氨基酸N的特定摄取率均相似。然而，高氮有效性物种吸收NH4 +的速度是低氮有效性物种的两倍，这表明氨基酸N对低氮可用性物种和高氮可用性物种而言相对更为重要。与无机氮源相比，低氮可用性物种从氨基酸中获取的总氮量也多达四倍。这些结果表明，植物物种在栖息地中的优势与它们利用最有效的氮库的能力有关。第二，在第三章中，我研究了跨越氮素可利用量和树木物种梯度的森林中的溶解性有机物（DOM）淋失。组成。我用测渗仪收集了三年的土壤溶液，并分析了它们的溶解有机碳（DOC），溶解无机氮（DIN）和DON组成，并将溶液中的DOC分馏成疏水和亲水化合物。我还评估了森林土壤的特性。我发现，在100厘米土壤深度的DON损失与森林中土壤N储量的增加无关，这与我的预期相反。出乎意料的是，在相同土壤深度下的DOM损失表现出DOC：DON的单峰模式，来自低氮和高氮可用性森林的DOM：DON中的DOC：DON相对较低，而来自中等N可用性森林的DOC：DON相对较高。这些模式可能是由于森林土壤组成和土壤特性发生变化而导致的DOM的不同土壤来源和汇聚强度所致。最后，在第4章中，我评估了土壤特性如何影响从以上收集的土壤核心中浸出的土壤水的化学性质森林。我用常见的有机物溶液浸出了0--10、0--25和0--50 cm深的岩心，并分析了DOC，DIN，DON和疏水/亲水性馏分的溶液。我还测量了土壤核心的多种物理和地球化学特征。与森林差异相比，土壤深度对DOM化学的影响更大。由于去除了疏水性化合物，土壤核心渗滤液中的DOM浓度随土壤深度而降低。值得注意的是，DON的浓度在输入的有机物溶液和10 cm的土壤深度之间增加，同时DON的亲水性分数增加了67倍。这些结果表明，土壤具有很强的能力来影响通过森林土壤淋溶的DOM的数量和质量。

著录项

  • 作者

    Scott, Emily Elizabeth.;

  • 作者单位

    Michigan State University.;

  • 授予单位 Michigan State University.;
  • 学科 Biology Ecology.;Biogeochemistry.
  • 学位 Ph.D.
  • 年度 2012
  • 页码 162 p.
  • 总页数 162
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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