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Properties and fungal decomposition of iron oxide-associated organic matter

Tian, Zhaomo LU (2019)
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... (More)
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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author
supervisor
opponent
  • Assistant Professor Keiluweit, Marco, University of Massachusetts Amherst, USA
organization
publishing date
type
Thesis
publication status
published
subject
pages
60 pages
defense location
The Blue Hall, The Ecology Building, Sölvegatan 37, Lund
defense date
2019-12-18 10:00:00
ISBN
978-91-7895-331-8
978-91-7895-330-1
language
English
LU publication?
yes
id
47b86e0d-26c0-4584-b50c-32d69cbbc643
date added to LUP
2019-11-12 14:43:00
date last changed
2019-11-20 16:54:42
@phdthesis{47b86e0d-26c0-4584-b50c-32d69cbbc643,
  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. <br/>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).<br/>},
  author       = {Tian, Zhaomo},
  isbn         = {978-91-7895-331-8 },
  language     = {eng},
  month        = {11},
  school       = {Lund University},
  title        = {Properties and fungal decomposition of iron oxide-associated organic matter},
  url          = {https://lup.lub.lu.se/search/ws/files/72073001/PhD_thesis_Zhaomo_Tian.pdf},
  year         = {2019},
}