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| Titel |
Temperature effects on protein depolymerization and amino acid immobilization rates in soils. |
| VerfasserIn |
Lisa Noll, Yuntao Hu, Shasha Zhang, Qing Zheng, Wolfgang Wanek |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250148732
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| Publikation (Nr.) |
 EGU/EGU2017-13013.pdf |
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| Zusammenfassung |
| Increasing N deposition, land use change, elevated atmospheric CO2 concentrations and
global warming have altered soil nitrogen (N) cycling during the last decades. Those changes
affected ecosystem services, such as C and N sequestration in soils, which calls for a better
understanding of soil N transformation processes. The cleavage of macromolecular organic N
by extracellular enzymes maintains an ongoing flow of new bioavailable organic N into biotic
systems and is considered to be the bottle neck of terrestrial N cycling in litter and soils.
Recent studies showed that protein depolymerization is susceptible to changes in C and N
availabilities. Based on general biological observations the temperature sensitivity of
soil organic N processes is expected to depend on whether they are rather enzyme
limited (i.e. Q10=2) or diffusion limited (i.e. Q10= 1.0 – 1.3). However, temperature
sensitivities of protein depolymerization and amino acid immobilization are still
unknown.
We therefore here report short-term temperature effects on organic N transformation rates
in soils differing in physicochemical parameters but not in climate. Soil samples were
collected from two geologically distinct sites close to the LFZ Raumberg-Gumpenstein,
Styria, Austria, each from three different management types (arable land, grassland, forest).
Four replicates of mineral soil were taken from every site and management type. The area
provides a unique opportunity to study geological and management controls in soils without
confounding effects of climate and elevation. The soils differ in several soil chemical
parameters, such as soil pH, base saturation, soil C: N ratio and SOM content as well as
in soil physical parameters, such as soil texture, bulk density and water holding
capacity.
Soils were pre-incubated at 5, 15 and 25˚ C for one day. Protein depolymerization rates
and amino acid immobilization rates were assessed by an isotope pool dilution
assay with 15N labeled amino acids at the three different temperatures. Amino acid
concentrations and at% 15N of amino acids were measured in soil extracts at two
time points by a novel approach based on the conversion of α-amino groups to
N2O and purge-and-trap isotope ratio mass spectrometry. Protein availability was
measured by extraction in solvents of increasing extraction efficiency (water, salt,
metaphosphate, hydroxide), followed by acid hydrolysis to free amino acids and reaction with
orthophthaldialdehyde. Peptidase activity was also measured at 5, 15 and 25˚ C using
fluorescence probes.
We expect that soil texture (clay content) and pH will affect protein sorption and
availability and thereby affect depolymerization rates. Soil C:N ratios may control the N
demand of microorganisms and thus affect enzyme production and amino acid
immobilization rates. Moreover, soil pH is a major control on microbial community
structure and may thereby affect the production of extracellular enzymes involved in
protein and peptide decomposition. Due to the differences in temperature sensitivity
of diffusion and enzymatic processes we expect higher temperature sensitivities
given that protein decomposition is enzyme- rather than substrate-limited. This
study will therefore greatly advance our understanding of major controls of the
soil N cycle and provide highly important data for refining soil N cycle models. |
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