Branched glycerol dialkyl glycerol tetraether (brGDGT)‐based indices are increasingly used for quantitative mean annual air temperature (MAAT) and soil pH reconstructions. However, large scatter in the relationship between the methylation index of 5‐methyl brGDGTs (MBT′_5ME) and MAAT still exists in arid and/or cold regions, and specific reasons for that offset remain unclear. Here, we present the brGDGT distributions from 18 soil samples along an altitudinal transect spanning a large gradient in MAAT at Mount (Mt.) Tienshan in arid central Asia, which we compare with previously published data from 256 globally distributed soils. Our results indicate that a dramatic increase of brGDGT concentrations occurs at 2,500 m above sea level for the soils from Mt. Tienshan, and a different pattern of brGDGT distributions in response to environmental changes appears below and above this elevation. Soil pH is observed to control the distributions of both 5‐ and 6‐methyl brGDGTs in the soils from Mt. Tienshan and other arid regions. Importantly, we find that the fractional abundances of the 5‐methyl isomers of pentamethylated and hexamethylated brGDGTs (IIa, IIIa) show a distinct negative correlation with soil pH, and the noncyclopentane‐containing tetra‐methylated brGDGT (Ia) is not related to MAAT in arid soils, which can explain the remaining temperature offset of reconstructed MAAT based on the MBT′_5ME index in arid regions. In addition, our data suggest that either the brGDGT‐producing community differs or brGDGT‐producers respond differently to temperature in arid relative to moist soils.

中文翻译：

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土壤pH值在干旱地区主导着5-甲基和6-甲基支链四醚的分布

基于支化甘油二烷基甘油四醚（brGDGT）的指数越来越多地用于定量平均年气温（MAAT）和土壤pH重建。然而，5-甲基brGDGTs（_MBT'5ME），而MAAT仍然存在于干旱和/或寒冷地区，导致这种抵消的具体原因仍不清楚。在这里，我们展示了来自干旱中亚天山山（天山）MAAT上跨越大梯度的高海拔样带的18个土壤样品的brGDGT分布，并将其与之前发表的来自256个全球分布土壤的数据进行了比较。我们的结果表明，在海拔2,500 m处，山上土壤的brGDGT浓度急剧增加。在此海拔之上和之下，出现了天山以及响应环境变化的brGDGT分布的不同模式。观察到土壤的pH值可以控制5t和6t甲基brGDGT在Mt土壤中的分布。天山等干旱地区。重要的，干旱地区的_5ME指数。此外，我们的数据表明，相对于潮湿的土壤，brGDGT的生产社区不同，或者brGDGT的生产商对温度的反应也不同。