Carbon isotopic composition of plant waxes, bulk organics and carbonates from soils of the Serengeti grasslands
Carbon isotopic composition of plant waxes, bulk organics and carbonates from soils of the Serengeti grasslands
复制标题
DOI：
10.1016/j.gca.2021.07.005
复制
发表时间：
2021-07
影响因子：
5
通讯作者：
Dao-lai Zhang;E. Beverly;N. Levin;E. Vidal;Yannick Matia;S. Feakins
中科院分区：
文献类型：
--
作者：
Dao-lai Zhang;E. Beverly;N. Levin;E. Vidal;Yannick Matia;S. Feakins
不同含碳材料（有机和无机）的碳同位素组成通常用于重建热带 C4 草原的分布。然而，目前还没有对现代土壤的研究将大量土壤有机质 (SOM)、土壤碳酸盐 (SC)、植物蜡烷 (alk) 和正烷酸 (acid) 的碳同位素组成 (δ13C) 结合起来，以便对所有四种材料进行比较。在这里，我们研究了坦桑尼亚塞伦盖蒂生态系统中的碳酸盐沉淀草原土壤，使用西北-东南横断面沿线 11 个地点的样本以及每个地点的深度剖面直接比较这四种材料的 δ13C 值。在 9 个地点发现的土壤碳酸盐中，δ13C 结果（δ13CSCmean = 0.5 ‰，1σ = 0.8 ‰，n = 70 个收集的结核）仅表示 C4 草，但 3 个有树木的地点中的 2 个地点不存在土壤碳酸盐。在所有 11 个地点测量了有机物，包括散装 (δ13CSOM−13.1 ± 1.8‰) 和植物蜡生物标志物（例如 δ13C29alk−23.5 ± 3.1、δ13C31alk−22.2 ± 2.0、δ13C33alk−21.9 ± 1.8、 δ13C28酸−19.1±2.1‰、δ13C30酸−21.1±2.6‰和δ13C32酸−20.1±1.7‰）。有机材料中的 δ13C 值记录了采样点 C4 草的优势。大多数地点的地表样本比深层样本的负值更大，反映了近几十年来大气成分和地表输入的变化以及几个世纪以来深度的退化。我们发现每个有机代理之间存在显着相关性，但 δ13C29alkis 对树木输入过度敏感（相对于其他同系物，C29 浓度更高且 13C 消耗更大），而 δ13C31alk、δ13C33alk 和 δ13C32acid 是植被覆盖的稳健记录器。在所有考虑的材料（植物蜡、SOM 和土壤碳酸盐）中，植物蜡烷烃和正烷酸具有最广泛的适用性，可扩展到不含碳酸盐的土壤以及湖泊和海洋沉积档案。
The carbon isotopic composition of different carbon-bearing materials, organic and inorganic, is commonly used to reconstruct distributions of tropical C4grasslands. However, no study of modern soils has yet combined carbon isotopic compositions (δ13C) of bulk soil organic matter (SOM), soil carbonate (SC), plant waxn-alkanes (alk) andn-alkanoic acids (acid) to allow for comparison between all four materials. Here, we studied carbonate-precipitating, grassland soils across the Serengeti ecosystem, Tanzania to directly compare δ13C values of these four materials using samples from 11 sites along a NW–SE transect and depth profiles at each location. Among the soil carbonates found at 9 sites, the δ13C results (δ13CSCmean = 0.5 ‰,1σ = 0.8‰,n= 70 nodules collected), denote C4grasses exclusively, but soil carbonates are absent from two of the three sites with trees. Organics were measured at all 11 sites including bulk (δ13CSOM−13.1 ± 1.8‰) and plant wax biomarkers (e.g., δ13C29alk−23.5 ± 3.1, δ13C31alk−22.2 ± 2.0, δ13C33alk−21.9 ± 1.8, δ13C28acid−19.1 ± 2.1‰, δ13C30acid−21.1 ± 2.6‰, and δ13C32acid−20.1 ± 1.7‰). δ13C values in organic materials record the dominance of C4grasses at the sampled sites. Surface samples are more negative than those at depth at most sites, reflecting changes in atmospheric composition and surficial inputs in recent decades, and degradation at depth over centuries. We found significant correlations between each of the organic proxies, but the δ13C29alkis overly responsive to tree inputs (greater C29concentration and13C-depletion relative to other homologues), whereas the δ13C31alk, δ13C33alkand δ13C32acidare robust recorders of vegetation cover. Of all materials considered (plant wax, SOM and soil carbonates), plant waxn-alkanes andn-alkanoic acids have the broadest applicability, extending to non-carbonate bearing soils, and to lacustrine and marine sedimentary archives.