Soil chemistry, temperature and bacterial community composition drive brGDGT distributions along a subarctic elevation gradient

Production of diverse brGDGTs by Acidobacterium Solibacter usitatus in response to temperature, pH, and O2 provides a culturing perspective on brGDGT proxies and biosynthesis

“…In contrast to its limited effect on brGDGT cyclization, pH in S. usitatus cultures did significantly modulate brGDGT methylation at lower temperatures. The observed decrease in MBT′ 5Me values in response to increased pH is consistent with the effects of soil pH on brGDGT methylation recently observed in subarctic soils (Halffman et al, 2022 ). We note, however, that the absence of 6‐ and 7‐methyl isomers and near absence of doubly cyclized brGDGTs in S. usitatus limits our ability to draw direct comparisons with environmental samples through other pH‐related indices.…”

“…Reported temperatures for environmental samples were standardized where possible by Raberg et al ( 2022a , 2022b ) but are necessarily++ different for some sample types (e.g., water temperature for lacustrine SPM versus air temperature for bone). To further supplement the dataset presented by Raberg et al ( 2022b ), we compiled soils published with in situ soil temperature data (recorded using temperature loggers at 2–10 cm depth) from Wang et al ( 2020 ), Pérez‐Angel et al ( 2020 ), De Jonge et al, 2019 , Sigurdsson et al ( 2016 ), Wang and Liu ( 2021 ), and Halffman et al ( 2022 ). We used mean monthly temperatures, either calculated from hourly measurements (De Jonge et al 2019 ; Sigurdsson et al 2016 ; May 8, 2013, to May 7, 2015), provided through personal communication (H. Wang and W. Liu, September 3, 2020; Wang et al 2020 ), or reported (Pérez‐Angel et al, 2020 ), to calculate in situ mean annual temperature (MAT), mean temperature of months above freezing (MAF), mean summer (June, July, and August) temperature (JJA), and temperature of the warmest month (WMT).…”

Microclimate, an important part of ecology and biogeography

“…In some cases, microclimate data did improve ecological models (forest plants, see Haesen, Lenoir, et al., 2023; and tundra plants see Kemppinen et al., 2021), yet, one approach is not necessarily transferable to other organisms (Lembrechts, Lenoir, et al., 2019). For instance, decade‐long gridded air temperature data did outperform short‐term soil temperature data in distribution models of bacterial membrane lipids with long‐term stability in the soil (Halffman et al., 2022), as patterns that form over decades or centuries do not relate to short‐term microclimatic fluctuations. These examples highlight that methods, including microclimate data and tools, should always be hypothesis‐driven and justified by ecological and biogeographical theory.…”

Branched glycerol dialkyl glycerol tetraether (brGDGT) distributions influenced by bacterial community composition in various vegetation soils on the Tibetan Plateau

“…Similarly, noncyclic pentamethylated brGDGT IIa were also found in higher abundance in southern Tibetan soils (Bai et al, 2018), inner Mongolia (Guo et al, 2022), and the Chinese Tianshan Mountains (Duan et al, 2020). This suggests that the spatial variation in the relative abundance of brGDGTs is not only linked to temperature or pH, but could result from changes in the bacterial community that are responding to other environmental factors or niche partitioning due to differences in vegetation, for example, pH, oxygen limitation, and cation exchange capacity (Halamka et al, 2021;Halffman et al, 2022). The low relative abundance of IIIa in our samples (Fig.…”

“…The Worldclim2 dataset interpolates monthly temperature data compiled from globally distributed weather stations to a 30 arc-second spatial resolution across a temporal range from 1970-2000 (Fick and Hijmans, 2017). The mean annual soil temperatures were gained from global gridded soil temperature maps according to Lembrechts et al (2022), which used over 8500 time series of soil temperatures measured in situ across the world and a machine learning approach to model predictor variables of the soil and air temperature offset, and finally interpolate soil temperatures (Lembrechts et al, 2022).…”