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| Titel |
Direct impacts of biochar on N2O production during denitrification by a soil microbial community |
| VerfasserIn |
Akanksha Mishra, Johannes Harter, Nikolas Hagemann, Andreas Kappler |
| 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 |
250145659
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| Publikation (Nr.) |
 EGU/EGU2017-9623.pdf |
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| Zusammenfassung |
| Biochar, i.e. biomass heated under O2 limitation to 350-1000∘C (pyrolysis), is suggested as a
beneficial soil amendment to mitigate climate change and to maintain and restore the
fertility of agro-ecosystems. Its stability enables long-term carbon sequestration and
biochar effectively reduces soil-borne N2O emissions. Biochar’s ability to reduce
N2O emissions is well recognized through field and laboratory experiments as well
as meta-analyses. However, the underlying mechanisms remain widely debated.
Microbial nitrogen transformations, especially denitrification, the stepwise reduction
of nitrate/nitrite via NO and N2O to N2, are considered to be a major source of
N2O emissions. Soil microcosm experiments showed lower N2O emissions in the
presence of biochar often correlate with a higher abundance and/or activity of N2O
reducing bacteria in the presence of biochar. However, it is still unknown whether these
shifts in the microbial community and/or activity is cause or effect of reduced N2O
production.
Biochar has the potential to change the physico-chemical environment towards conditions
that favor complete denitrification, i.e. decrease the N2O/(N2O+N2) product ratio.
Specifically, biochar can increase soil pH, reduce the availability of nitrate and increase the
entrapment of gases, including N2O. These effects are known to decrease the N2O/(N2O+N2)
ratio.
In addition to the observed effects in the physio-chemical environment, we hypothesized that
biochar has a direct impact on the soil microbial community. For instance, it has been shown
to provide a suitable habitat to microorganisms, or facilitate electron transfer between
microbe and substrates by acting as an electron shuttle or as a temporary acceptor/donor of
electrons.
To test this hypothesis, our experiment consisted of a microbial community extracted from
soil and cultivated under anoxic conditions. It was introduced as an inoculum into three
different treatments: biochar, quartz (control with a solid) and a solid-free control in the
presence of a well-defined liquid medium. To maintain consistency with respect to
geochemical parameters as well as to exclude any indirect effects of biochar, the
concentration of substrates (nitrate, acetate) and the pH were kept identical in all
three treatments. The biochar used was previously shown to reduce soil-borne N2O
emissions.
The results showed that biochar promoted nitrate reduction coupled to acetate consumption
leading to a faster intermediate accumulation of nitrite compared to the non-biochar
treatments. Additionally, N2O intermediately accumulated in the biochar treatment. Gene
copy numbers from quantitative polymerase chain reaction combined with optical density
measurements suggested that microbes were attached to the biochar surface instead of being
suspended in the liquid. This association of microbial cells with biochar’s surface might
result in expedited consumption of acetate and nitrate. Since similar effects were not
observed in the treatment containing quartz, they were concluded to be specific to
biochar.
These results can be put forth as the first evidence for a direct impact of biochar on microbial
denitrification. Overall, our study highlights the need to take a detailed look at biochar’s
direct effect on the activity of the soil microbial community when designing biochars that
target N2O mitigation. |
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