Different composition and distribution patterns of mineral‐protected versus hydrolyzable lipids in shrubland soils

Abstract

Mineral protection is known as an important mechanism stabilizing soil organic carbon (SOC). However, the composition, sources, and variations of mineral‐protected SOC remain poorly constrained. To fill this knowledge gap, we used hydrofluoric acid to demineralize soil matrix and compared the sources and distribution of mineral‐protected lipids (ML) versus hydrolyzable lipids (HL) of four typical Chinese shrubland soils. ML was found to represent a sizable fraction (9–32%) of total aliphatic lipids (including n‐alkanols; n‐alkanoic acids; α,ω‐alkanedioic acids; hydroxyalkanoic acids; and midchain‐substituted acids) in all soils. Based on carbon chain length and branch positions, microbe‐ and plant‐derived lipids were distinguished. No significant difference was found in the ratio of microbe‐ to plant‐derived lipids in ML versus HL, implying that plant and microbial inputs are equally important for the mineral‐associated soil lipids. However, ML contained a higher proportion of nonspecific lipids, especially at depths. Furthermore, to evaluate key environmental variable(s) controlling the distribution of different lipid components, a multiple stepwise regression analysis was conducted. Notably, ML was mainly affected by SOC‐to‐nitrogen ratio instead of mineralogical properties, implying that the accrual of mineral‐associated soil lipids relies strongly on organic matter properties. Collectively, our findings provide novel insights on sources and accumulation mechanisms of mineral‐protected soil lipids. SOC decomposition and subsequent accretion of degradation products appear to be vital for the sequestration of mineral‐associated soil lipids and warrant better recognition in the investigations of stable soil carbon accumulation mechanisms.

Root carbon interaction with soil minerals is dynamic, leaving a legacy of microbially-derived residues

“…Given the apparent importance of mineral associated lipids observed in our 13 C-NMR results, as well as in the literature 81 , we determined the fingerprint of lipid identity and distribution on our samples. We identified a total of 113 unique lipids.…”

Contrasting Biogeographic Patterns of Bacterial and Archaeal Diversity in the Top- and Subsoils of Temperate Grasslands

“…Soil OC was calculated as total carbon minus inorganic carbon, which was analyzed volumetrically by reaction with hydrochloric acid, as previously described (55). Total phosphorus (TP) was extracted using perchloric acid-sulfuric acid (HClO 4 -H 2 SO 4 ) digestion and measured by a colorimetric method with molybdenum blue (56). Soil pH was measured using a soil-to-water ratio of 1:2.5 (wt/vol).…”

Distribution and Preservation of Root‐ and Shoot‐Derived Carbon Components in Soils Across the Chinese‐Mongolian Grasslands

“…In addition, similar to plant wax lipids (Dai et al, ), soil pH also have a significant negative effect on cutin and suberin concentrations in the alpine soils (Figure ), suggesting an enhanced preservation of lipids at lower pHs likely due to decreased enzyme activities (Nierop et al, ; Sinsabaugh, ) and/or stronger sorption of lipids to mineral surfaces at lower pHs (Feng et al, ). Reactive Fe also has a positive effect on cutin and suberin in the alpine grassland soils (Figure ), indicating enhanced preservation of soil lipids via interaction with mineral matrix (Angst et al, ; Cai et al, ; Lin & Simpson, ). The positive effect of NPP on cutin abundances in the alpine grassland soils corroborates the key role of plant inputs on cutin distribution in this region.…”

“…Helium was used as carrier gas (1.2 ml/min). The mass spectrometer was operated in the electron impact mode at 70 eV ionization energy and scanned from 50 to 650 Daltons (Cai et al, ). Compounds were identified by interpretation of the mass spectrometric fragmentation patterns.…”