Distribution of branched glycerol dialkyl glycerol tetraethers in surface soils of the Qinghai-Tibetan Plateau: implications of brGDGTs-based proxies in cold and dry regions
Distribution of branched glycerol dialkyl glycerol tetraethers in surface soils of the Qinghai-Tibetan Plateau: implications of brGDGTs-based proxies in cold and dry regions
复制标题
青藏高原表层土壤中支链甘油二烷基甘油四醚的分布：基于brGDGTs的代理对寒冷和干旱地区的影响
DOI：
10.5194/bg-12-3141-2015
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发表时间：
2015-01-01
期刊：
影响因子：
4.9
通讯作者：
He, J. -S.
中科院分区：
文献类型：
--
作者：
Ding, S.;Xu, Y.;He, J. -S.
支化甘油二烷基甘油四醚（brGDGT）的甲基化指数（MBT）和环化率（CBT）是重建年平均气温（MAT）和土壤pH值的有用指标。最近，一系列6-甲基brGDGT被鉴定出与5-甲基brGDGT共洗脱。然而，很少有人知道6-甲基brGDGT在青藏高原（QTP），全球气候系统的关键区域。在这里，我们分析了30个表层土壤覆盖大面积的QTP，其中6-甲基brGDGT是最丰富的成分（平均53 +/- 17%的总brGDGT）。6-甲基brGDGT的丰度分数显示出良好的相关性与土壤pH值，而全球MBT '（5 ME）校准高估MAT在QTP。因此，我们提出了包括5-和6-甲基brGDGT的MBT 5/6指数，在QTP中呈现与MAT的强相关性：MAT = -20.14 +39.51 x MBT 5/6（n = 27; r（2）= 0.82; RMSE=1.3 ℃）。另一个指数，即IBT（支链四醚的异构化），基于5-甲基到6-甲基brGDGT的碳骨架异构化，取决于土壤pH：pH = 6.77 -1.56 x IBT（n = 27; r（2）= 0.74; RMSE = 0.32）。我们的研究表明，改变brGDGT的甲基基团的位置可能是另一种机制，一些土壤细菌适应环境pH值的变化，除了众所周知的环化。
The methylation index of branched tetraethers (MBT) and cyclization ratio of branched tetraethers (CBT) based on the distribution of branched glycerol dialkyl glycerol tetraethers (brGDGT) are useful proxies for the reconstruction of mean annual air temperature (MAT) and soil pH. Recently, a series of 6-methyl brGDGTs were identified which were previously co-eluted with 5-methyl brGDGTs. However, little is known about 6-methyl brGDGTs in the Qinghai-Tibetan Plateau (QTP), a critical region of the global climate system. Here, we analyze 30 surface soils covering a large area of the QTP, among which 6-methyl brGDGTs were the most abundant components (average 53 +/- 17% of total brGDGT). The fractional abundance of 6-methyl brGDGTs showed a good correlation with soil pH, while the global MBT'(5ME) calibration overestimates MAT in the QTP. We therefore proposed a MBT5/6 index including both 5- and 6-methyl brGDGTs, presenting a strong correlation with MAT in QTP: MAT = -20.14 + 39.51 x MBT5/6 (n = 27; r(2) = 0.82; RMSE=1.3 degrees C). Another index, namely IBT (isomerization of branched tetraether), based on carbon skeleton isomerization of the 5-methyl to 6-methyl brGDGTs, is dependent on soil pH: pH = 6 .77-1.56 x IBT (n = 27; r(2) = 0.74; RMSE = 0.32). Our study suggests that changing the position of methyl group of brGDGTs may be another mechanism for some soil bacteria to adapt to the ambient pH change in addition to the well-known cyclization.