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| Titel |
Biological soil crusts emit large amounts of NO and HONO affecting the
nitrogen cycle in drylands |
| VerfasserIn |
Alexandra Tamm, Dianming Wu, Nina Ruckteschler, Emilio Rodriguez-Caballero, Jörg Steinkamp, Hannah Meusel, Wolfgang Elbert, Thomas Behrendt, Matthias Sörgel, Yafang Cheng, Paul J. Crutzen  , Hang Su, Ulrich Pöschl, Bettina Weber |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250131978
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| Publikation (Nr.) |
 EGU/EGU2016-12436.pdf |
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| Zusammenfassung |
| Dryland systems currently cover ∼40% of the world´s land surface and are still expanding as
a consequence of human impact and global change. In contrast to that, information on their
role in global biochemical processes is limited, probably induced by the presumption that
their sparse vegetation cover plays a negligible role in global balances. However, spaces
between the sparse shrubs are not bare, but soils are mostly covered by biological soil crusts
(biocrusts). These biocrust communities belong to the oldest life forms, resulting
from an assembly between soil particles and cyanobacteria, lichens, bryophytes,
and algae plus heterotrophic organisms in varying proportions. Depending on the
dominating organism group, cyanobacteria-, lichen-, and bryophyte-dominated
biocrusts are distinguished. Besides their ability to restrict soil erosion they fix
atmospheric carbon and nitrogen, and by doing this they serve as a nutrient source
in strongly depleted dryland ecosystems. In this study we show that a fraction of
the nitrogen fixed by biocrusts is metabolized and subsequently returned to the
atmosphere in the form of nitric oxide (NO) and nitrous acid (HONO). These gases affect
the radical formation and oxidizing capacity within the troposphere, thus being of
particular interest to atmospheric chemistry. Laboratory measurements using dynamic
chamber systems showed that dark cyanobacteria-dominated crusts emitted the
largest amounts of NO and HONO, being ∼20 times higher than trace gas fluxes of
nearby bare soil. We showed that these nitrogen emissions have a biogenic origin, as
emissions of formerly strongly emitting samples almost completely ceased after
sterilization. By combining laboratory, field, and satellite measurement data we
made a best estimate of global annual emissions amounting to ∼1.1 Tg of NO-N
and ∼0.6 Tg of HONO-N from biocrusts. This sum of 1.7 Tg of reactive nitrogen
emissions equals ∼20% of the soil release under natural vegetation according to the
latest IPCC report. In summary, our measurements show that dryland emissions of
nitrogen oxides are largely driven by biocrusts and not by the underlying soil. As
precipitation patterns, which influence biocrust activity, are affected by climate change,
alterations in global nitrogen oxide emissions are to be expected. Thus, the role of
biocrusts in the global cycling of reactive nitrogen needs to be followed and also
implemented in regional and global models of biogeochemistry, air chemistry and climate. |
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