 |
| Titel |
Microscale effects on denitrification: does the ability of denitrifying bacteria to reduce N2O depend on their position in the soil matrix? |
| VerfasserIn |
Peter Dörsch, Shahid Nadeem, Åsgeir Almås, Lars R. Bakken |
| Konferenz |
EGU General Assembly 2013
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250079049
|
|
|
|
|
|
| Zusammenfassung |
| Soil is a heterogeneous matrix with a variety of microhabitats which probably select for
organisms with distinct functional traits. The composition and functioning of soil denitrifier
communities (DC) has been studied intensely over the last decades, primarily because of their
role in the emission of N2O from soil. The tacit assumption in such studies is that the soil
microbial community is one “thing”. In the present study, we challenge the concept of DC as
a homogenous entity and suggest a stratification of denitrifier function based on the position
within the soil matrix. We hypothesize that soil contains “inner” and “outer” habitats; the
inner consisting of sites within crevices and cavities of the soil mineral material, structured
organic materials and strong biofilms, the outer consisting of exposed surfaces and
macropores within the soil matrix. We further believe that sequential dispersion/extraction by
density gradient centrifugation (DGC) can be used to crudely separate the organisms
residing in the two habitat types. We operationally define loosely attached cells (LAC)
as those which are liberated from soil particles by moderate dispersion of soils.
LAC were separated from the soil by DGC, and the pellets at the bottom of the
gradients containing bacteria still attached to or embedded in soil material were then
subjected to a stronger dispersion to release the more strongly attached cells (SAC)
which were again separated from the soil by DGC. We hypothesized that SAC
are cells situated deeper in biofilms or other protective structures within the soil
matrix than LAC. We further hypothesized that the two habitats select for different
characteristics regarding the regulation of denitrification. In short, SAC were expected
to express N2O-reductase earlier than LAC, because SAC experience anoxia and
lack of NOx more frequently than LAC. First results from incubations with LAC
and SAC from different soils lend strong support to this hypothesis; in response to
oxygen depletion, both denitrifying communities expressed similar apparent growth
rates, both produced a mixture of NO, N2O and N2, but the relative amount of N2O
produced was much higher for LAC than SAC. This reemphasizes the significance of
soil structure, habitable pore space, predation and bacteria-mineral interactions as
regulating factors for N2O emission in mineral soils and has implications for the
understanding of selection pressures for sustained N2O-reductase activity in soil. |
|
|
|
|
|
|