Root-associated branched tetraether source microorganisms may reduce estimated paleotemperatures in subsoil
Root-associated branched tetraether source microorganisms may reduce estimated paleotemperatures in subsoil
复制标题
DOI：
10.1016/j.chemgeo.2013.07.017
复制
发表时间：
2013-10
期刊：
影响因子：
3.9
通讯作者：
A. Huguet;M. Gocke;S. Derenne;C. Fosse;G. Wiesenberg
中科院分区：
文献类型：
--
作者：
A. Huguet;M. Gocke;S. Derenne;C. Fosse;G. Wiesenberg
支链甘油二烷基甘油四醚 (GDGT) 是一种高分子量的复杂脂质，最近在土壤中发现，并表明是由仍然未知的细菌产生的。这些化合物的相对分布取决于环境参数，主要是温度和 pH 值。在过去的几年里，越来越多的研究集中在分支 GDGT 作为古气候代理的应用上，但只有少数是在陆地档案中进行的。在本研究中，对钙化和非钙化的活根和死根、周围土壤和沉积物以及远离根的参考材料中的支链 GDGT 进行了分析。样品主要是从肖普隆（匈牙利）附近的两个森林地点的底土中采集的，那里的土壤分别发育于河流沙和黄土沉积物上。与参考材料相比，根部样品和/或根际周围的分支 GDGT 更丰富，这表明分支 GDGT 来源微生物与根表面密切相关。在底土中，基于 GDGT 的前根部和周围沉积物的温度估计值主要低于黄土和沙剖面中参考材料的温度估计值。这可能是由于沉积后掺入了来自以陆地沉积物中的根有机质为食的微生物的支链 GDGT。相比之下，由 GDGT 得出的分支温度似乎不受表土中根系存在的影响，这可能与表土中近期根系的密度远高于底土中的密度有关。这表明根相关微生物的分布更加均匀，尤其是在根部密集的表土中。此外，我们表明样品预处理可能会对支链 GDGT 的丰度和分布产生影响。事实上，用超纯水清洗根部样品可能会导致 GDGT 丰度降低和温度估计值升高，这可能是由于去除了附着在根部表面的颗粒。根部和周围沉积物的脱碳作用对 GDGT 衍生参数的影响有限。综上所述，这些结果表明，从陆地档案中的分支 GDGT 获得的古环境数据可能取决于样品的收集和制备方式，应谨慎解释，特别是在黄土-古土壤序列中，其中钙化根的频率可能局部非常高。
Branched glycerol dialkyl glycerol tetraethers (GDGTs) are complex lipids of high molecular weight, recently discovered in soils and suggested to be produced by still unknown bacteria. The relative distribution of these compounds was shown to depend on environmental parameters, mainly temperature and pH. Over the last years, an increasing number of studies have focused on the application of branched GDGTs as paleoclimate proxies, but only a few were performed in terrestrial archives. In this study, branched GDGTs were analyzed in calcified and non-calcified living and dead roots, in surrounding soil and sediment and in reference material distant from the roots. Samples were mainly collected from subsoil of two forest sites near Sopron (Hungary), where soils developed on fluvial sand and loess deposits, respectively. Branched GDGTs were more abundant in root samples and/or surrounding rhizosphere compared to reference material, suggesting that branched GDGT source microorganisms are closely associated with the root surface. In subsoil, the GDGT-based temperature estimates from former roots and surrounding sediments were mainly lower than those from reference material in both loess and sand profiles. This is likely due to the post-sedimentary incorporation of branched GDGTs deriving from microorganisms that fed on root organic matter in terrestrial sediments. In contrast, branched GDGT-derived temperatures do not seem to be influenced by the presence of roots in topsoil, which may be related to the much higher density of recent roots in topsoil than in subsoil. This argues for a more homogeneous distribution of root-associated microorganisms especially in densely rooted topsoils. In addition, we show that sample pre-treatment may have an effect on the abundance and distribution of branched GDGTs. Indeed, washing root samples with ultrapure water might lead to a decrease in GDGT abundance and an increase in temperature estimates, likely due to the removal of particles adhering to the root surface. Decarbonatization of root and surrounding sediment had only a limited effect on GDGT-derived parameters. Taken together, these results suggest that paleoenvironmental data obtained from branched GDGTs in terrestrial archives might depend on the way the samples were collected and prepared and should be interpreted with caution, especially in loess-paleosol sequences where the frequency of calcified roots can be locally very high.