Soil organic matter turnover depending on land use change: Coupling C/N ratios, δ¹³C, and lignin biomarkers

Abstract

Soil organic carbon (SOC) stocks have been greatly depleted across the globe by conversion of wetlands to croplands, agroforestry, and urban areas. Here, we investigated SOC distribution and turnover in four land use types: a wetland, cropland, forestland, and construction land in the Baiyangdian Wetland, Northern China. The C : N ratios were up to 1.70‐times larger in cropland, forestland, and construction land than in the original wetland because of faster N losses compared to C following wetland conversion. The δ13C values of SOC increased with depth in wetland, and showed an overall depletion compared with the other three land use types. Acid‐to‐Aldehyde ratios of syringyl in wetland were 0.72–1.14‐, 0.72–1.72‐, and 1.18–1.43‐times, and cinnamyl/vanillyl ratios were 0.56–1.05‐, 0.22–0.48‐, and 0.40–0.76‐times those of cropland, forestland, and construction land, which reflects faster lignin decomposition rate in wetlands. The β value was defined by the slope of the linear regression between the logarithm of SOC and δ13SOC values, and decreased from cropland over construction land and forestland to wetland, reflecting the faster SOC turnover with the lower β values. However, SOC content and storage were up to 2.29‐ and 2.07‐times higher in wetlands than in soils of other land use types. The combination of C : N ratios, δ13C, and lignin monomer composition can explain the decrease of β value (corresponding to faster SOC turnover), and can be used as effective proxies to evaluate the sources and turnover of SOC in response to land use changes.

Distribution, sources, and decomposition of soil organic matter along a salinity gradient in estuarine wetlands characterized by C:N ratio, δ13C‐δ15N, and lignin biomarker

“…The sum of VSC phenols is a quantitative measurement of lignin, and positive relationships between lignin and SOC contents were observed for each vegetation type from landward to the seaward (Figure 9a). To a certain extent, the lignin monomer composition could, therefore, well explain the SOC stability and source analysis (Panettieri et al, 2017; Xia, Song, Wang, et al., 2020).…”

“…In addition, CuO oxidation releases p ‐hydroxyl (P; p ‐hydroxybenzaldehyde, p ‐hydroxyacetophenone, and p‐ hydroxybenzoic) and 3,5‐dihydroxybenzoic acid (3,5Bd), a total of 12 monomers phenols. VSC (the sum of vanillyl (V), syringyl (S) and cinnamyl (C) phenols) phenols were summed to represent lignin content in soils, which was normalized to SOC content to represent lignin relative abundance in SOC (Xia, Song, Van Zwieten, et al., 2020; Xia, Song, Wang, et al., 2020).…”

“…Biomarkers take advantage of the unique molecular levels that make up different maternal carriers and the geochemical stability of biochemicals (Liu et al., 2020). Lignin is one of the most recalcitrant C forms derived from plant residues and has been widely used as a biomarker (Xia, Song, Wang, et al., 2020). Lignin consists of a suite of single‐ring phenol compounds, including p ‐hydroxyl (P), vanillyl (V), syringyl (S), and cinnamyl (C).…”

Baseline maps of potentially toxic elements in the soils of Garhwal Himalayas, India: Assessment of their eco‐environmental and human health risks

“…Soil texture, moisture (SM), total soil organic carbon (SOC), and pH were performed according to the respective standard protocols (Walkley & Black, 1934; Xia et al, 2020; Zhong et al, 2019). Samples were air‐dried at 40°C followed by grinding and were then sieved with 100 mesh size.…”

Spartina alterniflora invasion controls organic carbon stocks in coastal marsh and mangrove soils across tropics and subtropics

“…Then, all bombs were flushed with N 2 in the headspace for 10 min and heated at 150℃ for 2.5 h in an oven. The lignin oxidation products were derivatized with N,O‐bis‐(trimethylsilyl) trifluoroacetamide and pyridine at 70°C for 3 h to yield trimethylsilyl derivatives, and were quantified using internal standards (i.e., trans‐Cinnamic acid) on an Agilent 7890B/7010B TQ GC‐MS system (Agilent) using a DB‐5MS column (Xia, Song, Wang, et al, 2020).…”