Variations in the chemical structure and Carbon-13 natural abundance in water-stable macro- and microaggregates in Haplic Chernozem under the contrasting land use variants

Zinaida Artemyeva; Natalia Danchenko; Yury Kolyagin; Elya Zazovskaya; Boris Kogut

doi:10.1016/j.envres.2022.113701

Variations in the chemical structure and Carbon-13 natural abundance in water-stable macro- and microaggregates in Haplic Chernozem under the contrasting land use variants

Environ Res. 2022 Oct:213:113701. doi: 10.1016/j.envres.2022.113701. Epub 2022 Jun 23.

Authors

Zinaida Artemyeva¹, Natalia Danchenko², Yury Kolyagin³, Elya Zazovskaya⁴, Boris Kogut²

Affiliations

¹ V.V. Dokuchaev Soil Science Institute, Pyzhevskii 7, Bld. 2, Moscow, 119017, Russia. Electronic address: artemyevazs@mail.ru.
² V.V. Dokuchaev Soil Science Institute, Pyzhevskii 7, Bld. 2, Moscow, 119017, Russia.
³ Faculty of Chemistry, Moscow State University, Leninskie Gory, Moscow, 119991, Russia.
⁴ Institute of Geography, Staromonetnyi per. 29, Moscow, 119017, Russia.

PMID: 35752326
DOI: 10.1016/j.envres.2022.113701

Abstract

Water-stable macro- (WSA_ma) and free microaggregates (WSA_mi) were isolated from the 2-1 mm air-dry macroaggregates from the surface horizons of Haplic Chernozem in contrasting variants of land use: the steppe and the bare fallow. The ¹³C NMR data and the ¹³C natural abundance of the Occluded organic matter (OM) (LF_oc) and Clay within WSAs in the steppe obviously indicate a lower degree of microbiological processing of OM within WSA_mi as compared with WSA_ma. This is reflected in lower degrees of decomposition (DI) and aromaticity (ARI) of OM and the C/N ratio, as well as lower ¹³C enrichment. This implies that the "labile" part of OM within WSA_mi (LF_oc and Clay, which are components of microaggregates within water-stable aggregates (mWSAs)) is more physically protected compared to that within WSA_ma. However, the heavier total δ¹³C signature of OM within WSA_mi indicates its greater degree of microbiological processing compared to that within WSA_ma. This seems contrary to the concept of greater physical protection of OM within microaggregates as compared to macroaggregates. It was revealed that the heavier total δ¹³C signature of OM within WSA_mi (greater degree of microbiological processing) is determined by the "oldest" OM located in the inter-aggregate space of WSAs, which is concentrated in the Residue fraction (Res). Due to its quantitative dominance, the Residue fraction is crucial for the total δ¹³C signature of WSAs. Negative changes in the quality of OM under the long-term bare fallow (52-yr) were reflected in a sharp increase in the integral indices of the chemical structure (DI, ARI), as well as the hydrophobicity index (HI) in all studied OM pools. It was accompanied by their ¹³C enrichment in the bare fallow compared to the steppe. Free microaggregates (WSA_mi) are fragments of disintegrated macroaggregates (WSA_ma). We found no evidence of their formation within macroaggregates.

Keywords: (13)С CP/MAS NMR spectroscopy; Carbon cycle; Dynamic light scattering; Soil organic matter; Soil structure; δ(13)C.

MeSH terms

Carbon / chemistry
Carbon Isotopes
Clay
Soil* / chemistry
Water* / analysis

Substances

Carbon Isotopes
Soil
Water
Carbon
Carbon-13
Clay