Plant versus microbial signature in densimetric fractions of Mediterranean forest soils: a study by thermochemolysis gas chromatography mass spectrometry

Clarifying the evidence for microbial‐ and plant‐derived soil organic matter, and the path toward a more quantitative understanding

“…As illustrated by our summary of Ludwig et al (2015) described above, the ratio of short‐to‐long even chain n ‐fatty acids has been applied to estimate the relative contributions of microbes and plants to the lipid pool in SOM. The ratio increases substantially from POM to MAOM, which is interpreted to represent a dominant contribution of microbial lipids to the MAOM fraction (Amelung et al, 2008; Jandl et al, 2004; Ludwig et al, 2015; Rovira & Grasset, 2019). Incubation studies where microbes are the only source of new organic matter corroborate the high potential for microbes to contribute to this lipid pool (Golchin et al, 1996; Kallenbach et al, 2016; Kindler et al, 2009; Olivelli et al, 2020).…”

Impact of Climate on Soil Organic Matter Composition in Soils of Tropical Volcanic Regions Revealed by EGA-MS and Py-GC/MS

“…1,28 Tropical mountainous regions contribute significantly to this storage and are distinguished by considerable variations in climate and soil properties. Studies of SOM dynamics and its controlling factors in tropical environments, where carbon cycles more quickly, are notably limited compared to temperate or boreal regions, 9,17,19,27,29,30 especially for studies characterizing SOM molecular composition. 16,31 Also, tropical volcanic regions offer a unique natural laboratory for simulating a wide array of climatic zones around the world within a relatively small area, thanks to the variation in temperature and precipitation with elevation and rather uniform geological properties.…”

“…Specifically, carboxyl-rich organic matter (OM) compounds bond with mineral surfaces . The origin of OM, be it plant or microbial, discerned from molecular data, also impacts its stability. , Therefore, factors controlling SOM stability are ideally studied on a molecular level …”

“…Tropical forests hold approximately 30% of global SOC stocks, which is higher than the sum of temperate and boreal forests. , Tropical mountainous regions contribute significantly to this storage and are distinguished by considerable variations in climate and soil properties. Studies of SOM dynamics and its controlling factors in tropical environments, where carbon cycles more quickly, are notably limited compared to temperate or boreal regions, ,,,,, especially for studies characterizing SOM molecular composition. , Also, tropical volcanic regions offer a unique natural laboratory for simulating a wide array of climatic zones around the world within a relatively small area, thanks to the variation in temperature and precipitation with elevation and rather uniform geological properties. Meanwhile, in volcanic regions, high-elevation soils contain an abundance of nanocrystalline Al/Fe (e.g., allophane and ferrihydrite) and organo-Al/Fe complexes, collectively referred to as active Al/Fe, , that contribute a large surface area and a dominance of variable charge, whereas low-elevation soils are dominated by more crystalline minerals (e.g., kaolinite).…”

“…7 The origin of OM, be it plant or microbial, discerned from molecular data, also impacts its stability. 8,9 Therefore, factors controlling SOM stability are ideally studied on a molecular level. 5 Diverse analytical methods have been used to analyze SOM composition, from chemical extractions, infrared spectroscopy, and nuclear magnetic resonance to analytical pyrolysis.…”