Cindy De Jonge, Jingjing Guo, Petter Hällberg, Marco Griepentrog, Hamdi Rifai, Andreas Richter, Edson Ramirez, Xinbao Zhang, Rienk H. Smittenberg, Francien Peterse, Pascal Boeckx, Gerd Dercon
Glycerol dialkyl glycerol tetraethers (GDGTs) are microbial membrane-spanning lipids that are produced in a variety of environments. To better understand the potentially confounding effect of soil chemistry on the temperature relationship of branched GDGTs (brGDGTs), isoprenoid GDGTs (isoGDGTs) and GDGT-based proxies MBT’5ME and TEX86, soils from 6 elevation transects (mean annual air temperature 0 – 26 ℃, n = 74) were analyzed. Corroborating earlier work, the MBT’5ME index correlates well with mean annual air temperature in the low pH (pH < 7), non-arid soils under study (r = 0.87, p < 0.001). However, a clear over-estimation of reconstructed temperature in the lowest pH (<3.5) soils is observed, explained by the correlation between brGDGT Ia and free acidity. TEX86 also shows a significant correlation with mean annual air temperature (r = 0.45, p < 0.001), driven by temperature dependent concentration changes of isoGDGTs 3 and cren’. However, an overarching correlation with P/E values dominates concentration changes of all supposed Thaumarchaeotal isoGDGTs lipids (GDGT1-3, cren and cren’), implying a potential impact of soil moisture on TEX86 values. In addition to identifying the impact of these confounding factors on the temperature proxy, GDGT ratios that can be used to constrain changes in soil chemistry, specifically exchangeable Ca2+, sum of basic cations, exchangeable Fe3+ and sum of soil metals are proposed (0.53 < r2 < 0.68), while existing ratios for soil moisture availability are tested for the first time in a dataset of non-arid soils. While the impact of soil chemistry on GDGTs may complicate the interpretation of their temperature proxies, our proposed GDGT ratios can potentially be used to constrain a subset of soil chemistry changes through time. © 2023 The Authors
Geological Institute, Earth Science Department, ETH Zurich, Sonnegstrasse 5, Zurich, 8092, Switzerland; Department of Earth Sciences, Utrecht University, Princetonlaan 8A, CB Utrecht, 3584, Netherlands; Stockholm University, Department of Geological Sciences and Bolin Center for Climate Research, Sweden; Soil Resources, Department of Environmental Systems Science, ETH Zurich, Universitätstrasse 16, Zurich, 8092, Switzerland; Department of Physics, Faculty of Mathematics and Natural Sciences, Universitas Negeri Padang, Indonesia; Centre for Microbiology and Environmental Systems Science, University of Vienna, Djerassiplatz 1, Vienna, 1030, Austria; Universidad Mayor de San Andres Bolivia, La Paz, Bolivia; Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, Chengdu, 610299, China; Now at Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, Switzerland; Isotope Bioscience Laboratory – ISOFYS, Department of Green Chemistry and Technology, Ghent University, Gent, Belgium; Soil and Water Management and Crop Nutrition Laboratory, Joint FAO/IAEA Centre of Nuclear Techniques in Food and Agriculture, Friedensstrasse 1, Seibersdorf, 2444, Austria
