Examining mineral-associated soil organic matter pools through depth in harvested forest soil profiles

Abstract

Mineral-associated organic matter is associated with a suite of soil minerals that can confer stability, resulting in the potential for long-term storage of carbon (C). Not all interactions impart the same level of protection, however; evidence is suggesting that C in certain mineral pools is dynamic and vulnerable to disturbance in the decades following harvesting. The objective of this research was to describe and characterize organic matter-mineral interactions through depth in horizons of soils of contrasting stand age. Sequential selective dissolutions representing increasingly stable mineral-associated organic matter pools from water soluble minerals (deionized water), organo-metal complexes (Na-pyrophosphate), poorly-crystalline minerals (HCl hydroxylamine), and crystalline secondary minerals (Na-dithionite HCl)) were carried out for Ae, Bf and BC horizons sampled from a Young and Mature forest site (35 and 110 years post-harvest) in Mooseland, Nova Scotia, Canada. Sequential selective dissolution extracts were analyzed for C, δ13C, iron (Fe) and aluminum (Al). Organo-metal complexes (OMC) were the largest mineral-associated OM pool in all horizons. This pool dominated the C distribution in B horizons (~60–70% of Bf bulk C), with a minor contribution from poorly-crystalline (PCrys), crystalline (Crys) minerals and water soluble (WS) associations. C in OMC and PCrys pools explained the variation in bulk C in horizons through depth at both sites. Twice as much C in OMC pools was measured at the Mature site compared to the Young site in the Bf horizons, supported by higher C:(Fe+Al) ratios. Isotopic analysis indicated that this extraction procedure isolated distinct mineral-associated OM pools. δ13C signatures of pyrophosphate-extracted OMC pools ranged from -27‰ to -28‰, similar to δ13C of bulk C and to plant-derived humic acids and associated biomass. The water soluble phase (mean δ13C = -29 ‰) was up to 2 ‰ more depleted, whereas the δ13C of Crys pools were more enriched in 13C (-13‰ to -16 ‰) compared to bulk soil. The results from this study suggest that association with minerals does not necessarily confer stability: organo-metal pools dominate in podzol horizons through depth, and contribute most to C storage, but are potentially susceptible to destabilization following the physical changes resulting from forest harvesting disturbance.

Role of biochar in managing the irrigation water requirements of maize plants: the pyramid model signifying the soil hydro-physical and environmental markers

“…This amendment can shift soil biota towards low C turnover bacteria taxa (Zheng et al, 2018) thus, reduces the emissions of greenhouse gases GHGs (Awad et al, 2018). This might take place probably through decreasing the bioavailability of dissolved organic carbon (DOC) via sorption on biochar surfaces (Sheng and Zhu, 2018); and therefore, it persists in soils for long time periods (Singh et al, 2012and Gabriel et al, 2018.…”

Mechanisms of Carbon Sequestration in Highly Organic Ecosystems – Importance of Chemical Ecology

“…From a chemical view, especially the interactions with the mineral phase, particularly iron (Fe) and aluminum (Al) oxides, contribute significantly to the prevention of microbial decomposition and thus stabilize organic C in mineral soils for centuries or millennia . However, as the association with minerals does not necessarily confer stability and ectomycorrhizal fungi living in symbioses with plants may access mineral bound compounds, also this mechanism does not necessary provide long‐term stabilization of organic matter. Overall, potential reactions with minerals do not exclude other stabilization mechanisms, especially not in highly organic soils with low levels of minerals.…”

Networks of Dissolved Organic Matter and Organo-Mineral Associations Stimulate Electron Transfer over Centimeter Distances

“…20−22 OMAs are ubiquitous and can contribute up to 90% to the NOM pool in some soil systems. 23 Given the wide existence of OMAs, a better understanding of their electron transfer properties and interactions with DOM is needed to improve our understanding of the electron flow as well as organic carbon transformation in ecosystems.…”