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| Titel |
Identification and quantification of nitrogen cycling processes in cryptogamic covers |
| VerfasserIn |
Bettina Weber, Dianming Wu, Katharina Lenhart, Alexandra Tamm, Nina Ruckteschler, Emilio Rodriguez-Caballero, Wolfgang Elbert, Susannah Burrows, Tim Clough, Jörg Steinkamp, Hannah Meusel, Thomas Behrendt, Burkhard Büdel, Meinrat O. Andreae, Matthias Sörgel, Yafang Cheng, Paul Crutzen  , Frank Keppler, Hang Su, Ulrich Pöschl |
| 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 |
250129579
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| Publikation (Nr.) |
 EGU/EGU2016-9712.pdf |
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| Zusammenfassung |
| Cryptogamic covers (CC) comprise communities of photoautotrophic cyanobacteria,
lichens, algae, and bryophytes together with heterotrophic bacteria, microfungi, and
archaea in varying proportions. Depending on their habitat, cryptogamic rock covers,
cryptogamic plant covers, and cryptogamic soil covers are distinguished. The latter
comprise biological soil crusts (biocrusts), which globally occur under dryland
conditions. In a first assessment of their global role, we quantified that CC fix ∼49 Tg of
nitrogen (N) per year (Elbert et al., 2013), corresponding to ∼1/2 of the maximum
terrestrial biological N fixation determined in the latest IPCC report. The fixed
N is used for biomass formation and partially leached into the ground, where it
can be taken up by plants or transformed into N oxides, being emitted into the
atmosphere.
We show that biocrusts release nitric oxide (NO) and nitrous acid (HONO), which are key
species in the global cycling of nitrogen and in the production of ozone and hydroxyl
radicals, regulating the oxidizing power and self-cleaning capacity of the atmosphere. Based
on laboratory, field and satellite measurement data, we obtained a best estimate of 1.1 Tg a−1
of NO-N and 0.6 Tg a−1 of HONO-N being globally emitted by biocrusts, corresponding to
∼20% of the global nitrogen oxide emissions from soils under natural vegetation (Weber et
al., 2015). During full wetting and drying cycles, emissions peaked at low water contents
suggesting NO- and HONO-formation under aerobic conditions during nitrification. Other
measurements revealed that cryptogamic organisms release nitrous oxide (N2O),
a greenhouse gas of crucial importance for climate change. The emission rates
varied with temperature, humidity, and N deposition, but divided by respiratory CO2
emission they formed an almost constant ratio, which allowed upscaling on the
global scale. We estimated annual N2O emissions of 0.3 – 0.6 Tg by cryptogams,
accounting for 4-9% of the global N2O budget from natural terrestrial sources (Lenhart et
al., 2015). 15N isotope labeling experiments revealed that nitrate (NO3−) was a
precursor of N2O, suggesting that N2O may be formed during denitrification. Thus,
our experiments revealed that CC play a prominent role in different steps of the N
cycle, being relevant in terrestrial biogeochemistry, atmospheric chemistry and air
quality.
Literature
Elbert W, Weber B, Burrows S, Steinkamp J, Büdel B, Andreae MO, Pöschl U (2012)
Contribution of cryptogamic covers to the global cycles of carbon and nitrogen. Nature
Geosciences 5: 459-462.
Lenhart K, Weber B, Elbert W, Steinkamp J, Clough T, Crutzen P, Pöschl U, Keppler F
(2015) Nitrous oxide and methane emissions from cryptogamic covers. Global Change
Biology 21(10): 3889-3900.
Weber B, Wu D, Tamm A, Ruckteschler N, Rodríguez-Caballero E, Steinkamp J, Meusel
H, Elbert W, Behrendt T, Sörgel M, Cheng Y, Crutzen P, Su H, Pöschl U (2015) Biological
soil crusts accelerate the nitrogen cycle through large NO and HONO emissions in
drylands. Proceedings of the National Academy of Sciences 112(50): 15384-15389. |
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