Properties and fungal decomposition of iron oxide-associated organic matter

Research output: ThesisDoctoral Thesis (compilation)

Abstract

Soil organic matter (SOM) stores the largest quantity of C in terrestrial ecosystems. Most SOM can be decomposed by microorganisms and released as CO2 into the atmosphere. The remaining fraction of SOM can be resistant against microbial decomposition over centuries to millennia. Changes in the magnitude of this stable SOM pool can have a substantial effect on the atmospheric CO2 concentration and thus the extent of global warming.
In this thesis, the formation properties and persistence of mineral-associated organic matter (MAOM) were investigated in respect to adsorption-desorption properties and enzymatic/fungal availability of iron oxide mineral-associated OM. The effects of environmental factors on these processes were also tentatively evaluated. These studies revealed that MAOM is highly variable in terms of chemical composition, desorption rate and availability to enzymes and fungi. The composition of MAOM depends on the chemical composition of source DOM and the order in which DOM is exposed to mineral surfaces (Paper I). It can be further influenced by the fungal processing of DOM, either via modifications of sizes and chemical structures of DOM, or by the secretion of fungal metabolites (Paper II). Accordingly, factors affecting the fungal processing of DOM, such as the ammonium concentration, also have an impact on the composition of MAOM (Paper III). MAOM could be more dynamic than previously thought, as supported by the findings that the iron oxide mineral-associated proteins can be hydrolysed by a fungal enzyme (Paper IV) and N contained in iron oxide mineral-associated proteins can be assimilated by a common ectomycorrhizal fungus (Paper V). Another novel finding associated with the bioavailability of iron oxide mineral-associated proteins is that the proteolysis of proteins occurs directly at the mineral surfaces without a prior desorption step of the substrate protein (Paper V). This supports the idea that the enzyme-substrate (ES) complexes crucial for proteolysis are formed at the mineral surfaces. Any factor influencing the formation of such ES complexes can have a profound effect on the proteolysis of mineral-associated proteins. As a result, the bioavailability of iron oxide mineral-associated proteins depends on the protein surface coverage, co-adsorption of competitive ligands, and fungal secretion of mineral-surface reactive metabolites (Paper IV and V).

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Subject classification (UKÄ) – MANDATORY

  • Environmental Sciences
Original languageEnglish
QualificationDoctor
Awarding Institution
Supervisors/Assistant supervisor
Award date2019 Dec 18
Print ISBNs978-91-7895-330-1
Electronic ISBNs978-91-7895-331-8
Publication statusPublished - 2019 Nov 11
Publication categoryResearch

Bibliographic note

Defence details Date: 2019-12-18 Time: 10:00 Place: The Blue Hall, The Ecology Building, Sölvegatan 37, Lund External reviewer(s) Name: Keiluweit, Marco Title: Assistant Professor Affiliation: University of Massachusetts Amherst, USA ---

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