Soil Organic N and its role for soil organic matter stability - what's new? Analytical approaches, involved mechanisms and their ecological relevance
The availability of soil organic nitrogen (SON) determines ecosystem fertility and biomass production but also affects litter degradation and thus, the turnover rates of the various soil organic carbon (SOC) pools. The decrease of the C/N ratios during humification indicates that the role of SON in SOC-sequestration is beyond that of only controlling the size of the active cycling entities. As a major constituent of the stabilized SOC pool, it determines its chemical composition and the mechanisms responsible for its increased biochemically resistance. Still, the processes involved in the formation of resistant SON are far from being understood and contradicting models are debated. According to the “ferrous wheel” mechanism, Fe(II) species reduce nitrate to nitrite which reacts with dissolved phenols to aromatic N forms. However, possibly because they are less biochemical recalcitrant than assumed and thus quickly used for biomass production, they were not identified in higher amounts in natural settings, yet. Although increasing evidence point to the importance of peptideous material for SOC stabilization, there is still a paucity of information concerning the involved mechanisms. This material may survive by protective functional groups, by steric hindrance or by physical protection within a hydrophobic network, micelles or aggregates. Continuous recycling within microbial biomass represents an additional explanation. In fire-prone regions, biogenic N is stabilized by its transformation into Black Nitrogen. Newer experiments however are questioning its stability. In the present contribution concepts for SON sequestration are discussed with respect to reported evidences and used methodology, as well as their likelihood and the possible consequences for ecological systems.
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| Format: | comunicación de congreso biblioteca |
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Soil Science Australia
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| Online Access: | http://hdl.handle.net/10261/122805 |
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| Summary: | The availability of soil organic nitrogen (SON) determines ecosystem fertility and biomass production but also affects litter degradation and thus, the turnover rates of the various soil organic carbon (SOC) pools. The decrease of the C/N ratios during humification indicates that the role of SON in SOC-sequestration is beyond that of only controlling the size of the active cycling entities. As a major constituent of the stabilized SOC pool, it determines its chemical composition and the mechanisms responsible for its increased biochemically resistance. Still, the processes involved in the formation of resistant SON are far from being understood and contradicting models are debated. According to the “ferrous wheel” mechanism, Fe(II) species reduce nitrate to nitrite which reacts with dissolved phenols to aromatic N forms. However, possibly because they are less biochemical recalcitrant than assumed and thus quickly used for biomass production, they were not identified in higher amounts in natural settings, yet. Although increasing evidence point to the importance of peptideous material for SOC stabilization, there is still a paucity of information concerning the involved mechanisms. This material may survive by protective functional groups, by steric hindrance or by physical protection within a hydrophobic network, micelles or aggregates. Continuous recycling within microbial biomass represents an additional explanation. In fire-prone regions, biogenic N is stabilized by its transformation into Black Nitrogen. Newer experiments however are questioning its stability. In the present contribution concepts for SON sequestration are discussed with respect to reported evidences and used methodology, as well as their likelihood and the possible consequences for ecological systems. |
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