Evaluation of 3-hydroxy fatty acids as a pH and temperature proxy in soils from temperate and tropical altitudinal gradients

Abstract

3-OH FAs containing 10 to 18 C and a hydroxyl group in third position are characteristic components of Gram-negative bacteria. These compounds were previously used to detect and quantify Gram-negative bacterial communities in various types of samples, from terrestrial, aquatic and atmospheric environments. The relative abundance of 3-OH FAs in soils was recently shown to vary with mean annual air temperature (MAAT) and pH in soils from Mt. Shennongjia (China). In the current study, the concentrations and abundances of 3-OH FAs were determined in soils from altitudinal transects under tropical and temperate climates-Mt. Rungwe (SW Tanzania) and Mt. Majella (Central Italy), respectively. The aim was to (i) examine and compare the distributions of 3-OH FAs in soils from different climatic zones and to (ii) investigate the potential of 3-OH FAs as temperature and pH proxies. When combined with previously published data, a moderate correlation (R 2 0.62) between the summed iso and anteiso to the total amount of normal 3-OH FAs (RIAN index) and pH is obtained. We show

Development of global temperature and pH calibrations based on bacterial 3-hydroxy fatty acids in soils

“…Nevertheless, the relationships between RAN15 and MAAT along the three mountain transects showed the same slopes but different intercepts (Wang et al, 2016;Huguet et al, 2019), suggesting that regional calibrations may be more adapted to apply RAN15 as a temperature proxy in soils. In contrast, a significant calibration between RAN17 and MAAT could be established using combined data from the three mountain regions (Wang et al, 2016;Huguet et al, 2019).…”

“…Recent studies have unveiled the potential of another family of lipids ̶ 3-hydroxy fatty acids (3-OH FAs) ̶ for temperature and pH reconstructions in terrestrial (Wang et al, 2016(Wang et al, , 2018Huguet et al, 2019) and marine (Yang et al, 2020) settings. 3-OH FAs with 10 to 18 carbon atoms are specifically produced by Gram-negative bacteria and are bound to the lipopolysaccharide (LPS) by ester or amide bonds (Wollenweber and Rietschel, 1990;Wollenweber et al, 1982).…”

“…The analysis of 3-OH FAs in soils showed that the RAN15 and RAN17 indices, defined as the ratio of C15 or C17 anteiso 3-OH FA to normal C15 or C17 3-OH FA, were negatively correlated with MAAT along the three mountains investigated so far: Mts. Shennongjia (China; Wang et al, 2016), Rungwe and Majella ( Tanzania and Italy, respectively;Huguet et al, 2019).…”

“…Even though these results are promising, the linear regressions between pH/MAAT and 3-OH FA indices in terrestrial environments are still based on a rather small dataset (ca. 70 soil samples; Wang et al, 2016;Huguet et al, 2019). The aim of this study was to investigate the applicability of 3-OH FAs as MAAT and pH proxies at the global level using an extended soil dataset and a more developed statistical approach.…”

“…The aim of this study was to investigate the applicability of 3-OH FAs as MAAT and pH proxies at the global level using an extended soil dataset and a more developed statistical approach. 3-OH FA distribution from 54 soils was collected along globally distributed elevational transects (Tibet, Italy, Peruvian Andes and Chile) and was combined with data previously published by Wang et al (2016;Mt Shennongjia, China), Huguet et al (2019;Mt. Rungwe, Tanzania and Mt.…”