Submicron structures provide preferential spots for carbon and nitrogen sequestration in soils (original) (raw)

Particulate organic matter as a functional soil component for persistent soil organic carbon

Nature Communications, 2021

The largest terrestrial organic carbon pool, carbon in soils, is regulated by an intricate connection between plant carbon inputs, microbial activity, and the soil matrix. This is manifested by how microorganisms, the key players in transforming plant-derived carbon into soil organic carbon, are controlled by the physical arrangement of organic and inorganic soil particles. Here we conduct an incubation of isotopically labelled litter to study effects of soil structure on the fate of litter-derived organic matter. While microbial activity and fungal growth is enhanced in the coarser-textured soil, we show that occlusion of organic matter into aggregates and formation of organo-mineral associations occur concurrently on fresh litter surfaces regardless of soil structure. These two mechanisms—the two most prominent processes contributing to the persistence of organic matter—occur directly at plant–soil interfaces, where surfaces of litter constitute a nucleus in the build-up of soil c...

Organo-minerals interactions at soils nanoscale - A NanoSIMS approach

It is well documented that conversion of native forest to agricultural land decreases the amount of organic matter in the soil. But the soil organic matter pools may differ in their response to cultivation. Nanometer scale interactions between OM and mineral particles are thought to control the long-term fate of soil organic carbon. To investigate the arrangement of the various soil C compartments at nanoscale in natural aggregates and stabilization mechanisms of soil C, we performed NanoSIMS analysis of native forest soils and cultivated soils adjacent to forest sites. NanoSIMS indentified four types of soil C compartments namely POM (C1), partial decomposed OM (C2), fully decomposed OM (C3) and microbial derived OM (C4) and the spatial distribution of Si, Al, Fe phases within these compartments. Association between SOM and poorly crystallized aluminosilicates could be the major stabilization mechanism in forest soils. In both soils organic matter OM appear mainly as diffuse features co-localized with Al, Si and sometimes Fe-bearing minerals. These associations had no identifiable mineral structure, suggesting the particle size of less than 100 nm. The linking of the spatial distribution of organic and inorganic compounds suggests that POM is gradually incorporated into the mineral matrix. In the forest soils, Al was detected in POM which could delay POM decomposition. We conclude that NanoSIMS is a powerful tool to characterize the organic matter compartments and their spatial distribution with inorganic phases as well as the SOM stabilization mechanisms.

Soil aggregation dynamics and carbon sequestration

The quantity and quality of residues determine the formation and stabilization of aggregate structure for soil organic carbon (SOC) sequestration. Plant roots and residues are the primary organic skeleton to enmesh the inorganic particles together and build macro-and microaggregates while sequestering SOC. There are three major organic binding agents of aggregation: temporary (plant roots, fungal hyphae, and bacterial cells), transient (polysaccharides), and persistent (humic compounds and polymers). Conversion of natural ecosystems into agricultural lands for intensive cultivation severely depletes SOC pools. Magnitude of SOC sequestration in the soil system depends on the residence time of SOC in aggregates. Microaggregates are bound to old organic C, whereas macroaggregates contain younger organic material. Many techniques have been used to assess the SOC distribution in aggregates. Classical methods include SOC determination in aggregate fractions by wet and dry sieving of bulk soil. Isotopic methods including the determination of 13 C and 14 C with mass spectrometry are techniques to quantify the turnover and storage of organic materials in soil aggregates. Other techniques involve the use of computed tomography, X-ray scattering, and X-ray microscopy to examine the internal porosity and inter-aggregate attributes of macro-and microaggregates. Current state-of-knowledge has not unravelled completely the underlying complex processes involved in the sequestration, stability, dynamics, and residence times of SOC in macro-and microaggregates. There is a need to develop a unique conceptual model of aggregate hierarchy.