Reconstructing C3 and C4 vegetation cover using n-alkane carbon isotope ratios in recent lake sediments from Cameroon, Western Central Africa
Reconstructing C3 and C4 vegetation cover using n-alkane carbon isotope ratios in recent lake sediments from Cameroon, Western Central Africa
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使用中非喀麦隆近期湖泊沉积物中的正烷烃碳同位素比重建 C3 和 C4 植被覆盖
DOI：
10.1016/j.gca.2014.07.004
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发表时间：
2014
影响因子：
5
通讯作者：
Sachse D.
中科院分区：
文献类型：
--
作者：
Garcin Y;Schefuß E;Schwab V. F;Garreta V;Gleixner G;Vincens A;Todou G;Séné O;Onana J.-M;Achoundong G;Sachse D.
热带非洲的树木和灌木在光合作用中使用C 3循环作为碳固定途径，而草和莎草主要使用C 4循环。来自沉积档案的叶蜡脂类，如长链正构烷烃（如n-C 27至n-C 33），继承了代表碳固定途径的碳同位素比值。因此，正构烷烃δ 13 C值常被用来重建过去植被的C3/C4组成，假定C3和C4叶蜡的相对比例反映了C3和C4植物的相对比例。我们比较了现代C3和C4植物的正构烷烃的δ 13 C值与先前公布的最近的湖泊沉积物的值，并提供了一个框架，估计的分数贡献（面积为基础的）C3植被覆盖（fC 3）由这些沉积档案。样本收集在喀麦隆，横跨纬度样带，可容纳广泛的气候带和植被类型，反映在C 3为主的热带雨林逐步向北取代C 4为主的稀树草原。分析的C3植物的特点是显着较高的丰度的n-C29烷烃和显着较低的丰度的n-C33烷烃比C4植物。此外，喀麦隆近期湖泊沉积物中n-C 29和n-C 31烷烃的沉积物δ 13 C值（− 37.4‰至− 26.5‰）通常在C3植物的δ 13 C值范围内，即使来自C4植物占主导地位的集水区植被。在这种情况下，简单的线性混合模型无法准确地重建C3和C4植被覆盖的相对比例时，使用沉积的正构烷烃的δ 13 C值，高估了C3植被的比例，可能是由于植物蜡的生产，保存，运输和/或C3和C4植物之间的沉积的差异。因此，我们测试了一组非线性二元混合模型，使用C3和C4植被作为端员的δ 13 C值。非线性模型包括一个S形函数（正弦平方），它描述了接近最小和最大δ 13 C值时f C3值的微小变化，以及一个双曲线函数，它考虑了上述C3和C4植物之间的差异。模型拟合和不确定性的估计是使用蒙特卡罗算法完成的，可以通过将来的数据添加来改进。与沉积正构烷烃δ 13 C观测值拟合最好的模型要么是双曲线函数，要么是双曲线和正弦平方函数的组合。这种非线性模型可用于将沉积正构烷烃的δ 13 C测量值直接转换为C3植被覆盖的重建。
Trees and shrubs in tropical Africa use the C 3 cycle as a carbon fixation pathway during photosynthesis, while grasses and sedges mostly use the C 4 cycle. Leaf-wax lipids from sedimentary archives such as the long-chain n-alkanes (eg, n-C 27 to n-C 33) inherit carbon isotope ratios that are representative of the carbon fixation pathway. Therefore, n-alkane δ 13 C values are often used to reconstruct past C 3/C 4 composition of vegetation, assuming that the relative proportions of C 3 and C 4 leaf waxes reflect the relative proportions of C 3 and C 4 plants. We have compared the δ 13 C values of n-alkanes from modern C 3 and C 4 plants with previously published values from recent lake sediments and provide a framework for estimating the fractional contribution (areal-based) of C 3 vegetation cover (f C 3) represented by these sedimentary archives. Samples were collected in Cameroon, across a latitudinal transect that accommodates a wide range of climate zones and vegetation types, as reflected in the progressive northward replacement of C 3-dominated rain forest by C 4-dominated savanna. The C 3 plants analysed were characterised by substantially higher abundances of n-C 29 alkanes and by substantially lower abundances of n-C 33 alkanes than the C 4 plants. Furthermore, the sedimentary δ 13 C values of n-C 29 and n-C 31 alkanes from recent lake sediments in Cameroon (− 37.4‰ to− 26.5‰) were generally within the range of δ 13 C values for C 3 plants, even when from sites where C 4 plants dominated the catchment vegetation. In such cases simple linear mixing models fail to accurately reconstruct the relative proportions of C 3 and C 4 vegetation cover when using the δ 13 C values of sedimentary n-alkanes, overestimating the proportion of C 3 vegetation, likely as a consequence of the differences in plant wax production, preservation, transport, and/or deposition between C 3 and C 4 plants. We therefore tested a set of non-linear binary mixing models using δ 13 C values from both C 3 and C 4 vegetation as end-members. The non-linear models included a sigmoid function (sine-squared) that describes small variations in the f C 3 values as the minimum and maximum δ 13 C values are approached, and a hyperbolic function that takes into account the differences between C 3 and C 4 plants discussed above. Model fitting and the estimation of uncertainties were completed using the Monte Carlo algorithm and can be improved by future data addition. Models that provided the best fit with the observed δ 13 C values of sedimentary n-alkanes were either hyperbolic functions or a combination of hyperbolic and sine-squared functions. Such non-linear models may be used to convert δ 13 C measurements on sedimentary n-alkanes directly into reconstructions of C 3 vegetation cover.
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影响因子：
3
作者：
A. Vogts;H. Moossen;F. Rommerskirchen;J. Rullkötter
通讯作者：
A. Vogts;H. Moossen;F. Rommerskirchen;J. Rullkötter
喀麦隆植物地理学研究
DOI：
--
发表时间：
1968
期刊：
影响因子：
--
作者：
R. Letouzey
通讯作者：
R. Letouzey
影响因子：
5
作者：
Garcin, Yannick;Schwab, Valerie F.;Sachse, Dirk
通讯作者：
Sachse, Dirk
过去23000年热带非洲雨带的半球对称性
影响因子：
18.3
作者：
Collins, James A.;Schefuss, Enno;Wefer, Gerold
通讯作者：
Wefer, Gerold
11 个 SIO 站的每月大气 13C/12C 同位素比（1977-2008 年）
DOI：
--
发表时间：
2010
期刊：
影响因子：
--
作者：
R. Keeling;S. Piper;A. Bollenbacher;S. Walker
通讯作者：
S. Walker