Paleoenvironmental implications of taxonomic variation among δ15N values of chloropigments
Paleoenvironmental implications of taxonomic variation among δ15N values of chloropigments
复制标题
DOI：
10.1016/j.gca.2011.04.024
复制
发表时间：
2011-11-15
影响因子：
5
通讯作者：
Pearson, Ann
中科院分区：
文献类型：
--
作者：
Higgins, Meytal B.;Wolfe-Simon, Felisa;Pearson, Ann
生物量中氮同位素比率的自然变化反映了用于生长的营养源的变化。为了使用光合生物的氯色素的 Delta N-15 值来确定生物量（进而延伸至地表水）的相应 Delta N-15 值，必须限制叶绿素和生物量之间的同位素偏移。在这里，我们检查了各种地质相关类群中的这种偏移，这些类群使用可能近似地球历史不同时期海洋条件的营养源生长。本研究中的浮游植物包括蓝细菌（固氮和非固氮）、真核藻类（红色和绿色）和产氧光合细菌（变形菌），以及来自硫化湖水的环境样本。使用 N-2、NO3- 和 NH4+ 作为氮源培养培养物，并在不同的光照条件和生长条件下进行检查。我们发现原核生物的同位素差异（δ N-15（生物量）- δ N-15（氯色素））具有令人惊讶的高变异性，物种的平均值范围为 -12.2 ppm 到 + 11.7 ppm。我们将这种差异定义为 epsilon(por)，该术语包含成岩卟啉、二氢卟酚以及叶绿素。 epsilon(por) 的负值反映相对于生物量富含 N-15 的氯色素。值得注意的是，这种富集似乎仅发生在蓝藻中。淡水蓝藻物种的 epsilon(por) 平均值为 -9.8 +/- 1.8 ppm，而海洋蓝藻为 -0.9 +/- 1.3 ppm。这些同位素效应在环境上而不是在系统发育上分组，例如。例如，淡水 Chroococcales 的 epsilon(por) 值与淡水 Chroococcales 相似，但与海洋 Chroococcales 不同。我们对真核藻类的 epsilon(por) 测量值（范围 = 千分之 4.7-8.7）与之前关于纯培养物的报告相似。对于所有研究的分类单元，epsilon(por) 的值并不取决于用于生长的氮底物的类型。观察到的 epsilon(por) 环境控制表明，epsilon(por) 值可用于确定沉积记录中真核有机物与蓝藻有机物的埋藏分数。 (C) 2011 Elsevier Ltd. 保留所有权利。
Natural variations in the ratios of nitrogen isotopes in biomass reflect variations in nutrient sources utilized for growth. In order to use delta N-15 values of chloropigments of photosynthetic organisms to determine the corresponding delta N-15 values of biomass - and by extension, surface waters - the isotopic offset between chlorophyll and biomass must be constrained. Here we examine this offset in various geologically-relevant taxa, grown using nutrient sources that may approximate ocean conditions at different times in Earth's history. Phytoplankton in this study include cyanobacteria (diazotrophic and non-diazotrophic), eukaryotic algae (red and green), and anoxygenic photosynthetic bacteria (Proteobacteria), as well as environmental samples from sulfidic lake water. Cultures were grown using N-2, NO3-, and NH4+ as nitrogen sources, and were examined under different light regimes and growth conditions. We find surprisingly high variability in the isotopic difference (delta N-15(biomass) - delta N-15(chloropigment)) for prokaryotes, with average values for species ranging from -12.2 parts per thousand to + 11.7 parts per thousand. We define this difference as epsilon(por), a term that encompasses diagenetic porphyrins and chlorins, as well as chlorophyll. Negative values of epsilon(por) reflect chloropigments that are N-15-enriched relative to biomass. Notably, this enrichment appears to occur only in cyanobacteria. The average value of epsilon(por) for freshwater cyanobacterial species is -9.8 +/- 1.8 parts per thousand, while for marine cyanobacteria it is -0.9 +/- 1.3 parts per thousand. These isotopic effects group environmentally but not phylogenetically, e. g., epsilon(por) values for freshwater Chroococcales resemble those of freshwater Nostocales but differ from those of marine Chroococcales. Our measured values of epsilon(por) for eukaryotic algae (range = 4.7-8.7 parts per thousand) are similar to previous reports for pure cultures. For all taxa studied, values of epsilon(por) do not depend on the type of nitrogen substrate used for growth. The observed environmental control of epsilon(por) suggests that values of epsilon(por) could be useful for determining the fractional burial of eukaryotic vs. cyanobacterial organic matter in the sedimentary record. (C) 2011 Elsevier Ltd. All rights reserved.