Mineral states and sequestration processes involving soil biogenic components in various soils and desert sands of Inner Mongolia.

Soil biogenic components are subject to continuous sequestration, and export from soils into the surrounding air and water environments. However, the processes involving the stability or lability of their mineral states remain still unclear. To assess these issues, we have measured various biogenic components in a number of agricultural, forest, grassland, and deep soils, as well as desert sands from Inner Mongolia, both in the solid state and liquid extracts. The contents of soil organic carbon (SOC) and soil total nitrogen (STN) were higher in soils than in sands, whilst those of soil total sulfur (STS) and inorganic carbon were higher in sands and deeper soils. The significant positive correlations found between STS and SOC, and STN, and their significant negative correlations with pH and δC-SOC in all soils suggest a pH-dependent sequestration of C, N, and S. The decreased stability of organo-mineral complexes at acidic pH, resulting from the acidification of humic substance (HS) functionalities, leads to a higher availability of nutrients that facilitates the sequestration of soil organic matter (SOM). Conversely, an increase in pH enhances the stability of organo-mineral complexes by promoting negatively charged HS functionalities, which reduces the availability of nutrients and the sequestration of SOM. The δC-SOC enrichment in desert sands (-17.63 to -7.10‰) and its depleted values in soils (-24.9 to -18.8‰) suggest the occurrence of C sequestration in desert, via uptake of enriched atmospheric CO (-8.4‰). The fluorescence spectra of humic substance components and their molecular weights in sands were typically different from those of soils. The predominant relatively low molecular weight (MW) (< 15-25 kDa) of alkali-extracted (complexed state: CS) components and the relatively high MW (> 25 - 15 kDa) of water-extracted (labile state: LS) components of all soils suggest, respectively, their involvement in organo-mineral complexes and for export into the surrounding environment. The quantities of LS and CS soil components differ significantly on dependence of soil characteristics, implying their corresponding lability or stability in soils. These findings will provide useful input for the management of the corresponding soil/sand ecosystems.