Lateral and depth variation of loess organic matter overprint related to rhizoliths — Revealed by lipid molecular proxies and X-ray tomography
Lateral and depth variation of loess organic matter overprint related to rhizoliths — Revealed by lipid molecular proxies and X-ray tomography
复制标题
与根岩相关的黄土有机质叠印的横向和深度变化 â 通过脂质分子代理和 X 射线断层扫描揭示
DOI：
10.1016/j.catena.2012.11.011
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发表时间：
2014
期刊：
影响因子：
6.2
通讯作者：
Wiesenberg G.L.B.
中科院分区：
文献类型：
--
作者：
Gocke M;Peth S;Wiesenberg G.L.B.
黄土等陆地沉积物以其古环境意义而闻名。黄土有机碳含量一般很低，但黄土及其有机质被认为是沉积过程中植被和气候的重要陆地档案。然而，LOM信号容易受到其他年龄和起源的OM的污染，而不是同沉积植被，例如沉积后的深根植物。我们假设，根际效应的影响与深根植物的质量，数量和距离前root.The 13米厚的晚更新世黄土-古土壤序列在Nussloch（SW德国）包含根石（钙化根）全新世的深度不同。与碳酸结壳导致保存前根沉积物，根际土允许根的一生中发生的根际过程进行评估。几个水平样带，包括根状石，周围的黄土本文分析了距根际土11 cm范围内的无根黄土和不同深度的无根黄土的碳、烷烃和脂肪酸组成，其中烷烃指标如碳偏好指数（CPI）、平均链长（ACL）、以及n-C27/n-C31和n-C29/n-C31比值表明，根际物质来源于木本植被，而草本植被则是根际物质的来源。几个脂质分子代理，例如短链/长链烷烃，长链烷烃组合物和长链/非常长链FA，表明相当数量的根和根茎微生物OM的掺入。的根际效应，即沉积后叠印的初始LOM在附近的根，不限于前根周围的几毫米，但显着的距离至少为5厘米，可能更多。这一点得到了证实，X射线断层扫描分析，使识别小钙化根仍然和非钙化根通道在前根际，这不能在现场条件下确定。在具有高根际频率的深度间隔中，这需要大部分黄土的侧向覆盖，由于前根际的延伸> 5 cm，在现在地表以下1.95和3.2 m的深度中，黄土可以覆盖整个黄土。（最大值在200 m− 2，深度约2.6 m），这些发现提高了深根植物作为黄土-古土壤序列沉积后显著叠加的潜在来源的重要性。
Terrestrial sediments like loess are well known for their paleoenvironmental significance. Although organic carbon contents are commonly very low, loess and organic matter (LOM) thereof is regarded as important terrestrial archive for vegetation and climate during deposition. However, the LOM signal is prone to contamination by OM of other age and origin than the synsedimentary vegetation, e.g. by postsedimentary deep-rooting plants. We hypothesized that the influence of rhizosphere effects related to deep-rooting plants varies with depth in quality, quantity and distance to the former root.The 13 m thick late Pleistocene loess-paleosol sequence at Nussloch (SW Germany) contains rhizoliths (calcified roots) of Holocene age. With the carbonatic encrustation leading to preservation of former root deposits, rhizoliths allow for assessment of rhizosphere processes that occurred during the root's lifetime. Several horizontal transects comprising rhizoliths, surrounding loess (rhizoloess) up to a distance of 11 cm from rhizoliths, and root-free reference loess from different depth intervals, were analyzed for their carbon (C), alkane and fatty acid (FA) composition.Alkane proxies like carbon preference index (CPI), average chain length (ACL), as well asn-C27/n-C31andn-C29/n-C31ratios indicated grass vegetation as origin of LOM, while rhizoliths derived from woody vegetation. Several lipid molecular proxies, e.g. short chain/long chain alkanes, long chain alkane composition and long chain/very long chain FA, indicated the incorporation of considerable amounts of root and rhizomicrobial OM. The rhizosphere effect, i.e. postsedimentary overprint of initial LOM in the vicinity of roots, was not restricted to few mm around the former root, but notable to distances of at least 5 cm and possibly more. This was confirmed by X-ray tomography analyses enabling identification of small calcified root remains and non-calcified root channels in the former rhizosphere, which could not be identified under field conditions. In depth intervals with high rhizolith frequency, this entailed lateral overprint of large parts of loess, which in depths of 1.95 and 3.2 m below present surface can cover the whole loess due to extension of the former rhizosphere of > 5 cm.Regarding the high rhizolith frequency (maximizing at 200 m− 2at ~ 2.6 m depth) at Nussloch, these findings raise the importance of deep-rooting plants as potential source for significant postsedimentary overprint of loess-paleosol sequences.