Biopores and root features as new tools for improving paleoecological understanding of terrestrial sediment-paleosol sequences
Biopores and root features as new tools for improving paleoecological understanding of terrestrial sediment-paleosol sequences
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DOI：
10.1016/j.palaeo.2013.11.010
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发表时间：
2014-01
期刊：
影响因子：
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通讯作者：
M. Gocke;S. Gulyás;U. Hambach;M. Jovanović;G. Kovács;S. Marković;G. Wiesenberg
中科院分区：
文献类型：
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作者：
M. Gocke;S. Gulyás;U. Hambach;M. Jovanović;G. Kovács;S. Marković;G. Wiesenberg
根和根际过程的重要作用在表层土壤中被接受，但在深层土壤（包括土壤母质）中仍有争议。特别是对于黄土和沙丘砂等陆源沉积物，根和根迹大多在剖面描述中被识别，而不是在古环境背景下解释。此外，沉积物沉积和根迹形成的同步性通常被假定。这是挑战部分大的最大生根深度的植物，超过土壤深度，并经常发生的次生碳酸盐和潜在的根起源低于最近的土壤和古土壤的生物孔隙。为了提高陆地沉积物古土壤序列的古环境记录的理解，最近的根和根迹，包括钙化根和根衍生的生物孔隙，在6个土壤，黄土和沙丘砂剖面横跨中欧和东南欧进行了调查。通过X射线显微断层扫描，观察到小的碳酸盐堆积物（直径≤1 mm），通常称为“假菌丝体”，并与根石（钙化根;直径大多为3-20 mm，可能高达100 mm）进行形态学比较，表明前者的根起源，因此需要重新命名为微根石。在水平上对根、生物孔、根状石和微根状石进行定量，得出的最大频率分别为2100 m− 2、4100 m− 2、196 m− 2和12，800 m− 2。考虑到以前的根生长所留下的孔隙体积，这表明它们对沉积物和古土壤的结构性质有重要贡献。根和根迹的深度分布往往分别与土壤和古土壤有关，并且大多数在这些单元内或紧接在这些单元之下显示出最大频率。因此，根迹不一定与周围的沉积物具有相似的年龄，但通常年龄较轻。根迹和周围地层单位之间的时间滞后可以在小的时间段（可能是几十年到几个世纪）之间变化，在微根石的情况下，在更大的根石穿透几个地层单位的情况下，可能是几千年。假设微根石的前根际延伸半径为5 mm，则12，500 m− 2的频率对应于相应深度区间的100%根际面积。这些发现强调了根迹在沉积-古土壤序列中的意义。潜在的时间和空间的不均匀性的根生长，一方面，特别是灌木和乔木植被，并发生在相同的深度间隔不同的年龄和起源的根仍然在另一方面，阻碍了这些与周围的沉积物或古土壤的年代背景的评估。然而，根痕迹在陆地档案提供了宝贵的信息，古植被和古环境条件，如果他们的时间背景是已知的。
The important role of roots and rhizosphere processes is accepted for the top soil, but still under debate for the deep subsoil including soil parent material. Especially for terrestrial sediments like loess and dune sands, roots and root traces are mostly recognized in profile descriptions, but not interpreted in the paleoenvironmental context. Further, synchrony of sediment deposition and root trace formation is commonly assumed. This is challenged by partially large maximum rooting depths of plants, exceeding the soil depth, and by frequent occurrence of secondary carbonates and biopores of potential root origin below recent soil and paleosols. To improve understanding of paleoenvironmental records in terrestrial sediment-paleosol sequences, recent roots and root traces, including calcified roots and root-derived biopores, were investigated in six soil, loess and dune sand profiles across Central and SE Europe. Visualization of small carbonate accumulations (diameter ≤1 mm), frequently called ‘pseudomycelia’, by X-ray microtomographic scanning, and morphologic comparison with rhizoliths (calcified roots; diameter mostly 3–20 mm, up to 100 mm possible) indicate root origin of the former, therefore requiring renaming to microrhizoliths. Quantification of roots, biopores, rhizoliths and microrhizoliths on horizontal levels yielded maximum frequencies of 2100 m− 2, 4100 m− 2, 196 m− 2and 12,800 m− 2, respectively. Considering the pore volume remaining from former root growth this indicates their significant contribution to structural properties of the sediments and paleosols. Depth distribution of roots and root traces was frequently related to soil and paleosols, respectively, and mostly showed maximum frequencies within or immediately below these units. Root traces are therefore not necessarily of similar age like the surrounding sediment, but are typically of younger age. The time lag between root traces and the surrounding stratigraphic unit can vary between small time periods (likely decades to centuries) in case of microrhizoliths and several millenia in case of larger rhizoliths penetrating several stratigraphic units. With assumed radii of former rhizosphere extension of 5 mm for microrhizoliths, a frequency of 12,500 m− 2corresponded to 100% rhizosphere area in the respective depth interval. These findings emphasize the meaning of root traces in sediment–paleosol sequences. Potential temporal and spatial inhomogeneity of root growth on the one hand, especially for shrub and tree vegetation, and occurrence of root remains of different age and origin in identical depth intervals on the other hand, hamper the assessment of the chronologic context of these with the surrounding sediment or paleosol. Nevertheless, root traces in terrestrial archives provide valuable information with respect to paleovegetation and paleoenvironmental conditions, if their chronological context is known.