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| Titel |
Effects of cryptogamic covers on the global carbon and nitrogen balance as investigated by different approaches |
| VerfasserIn |
Bettina Weber, Philipp Porada, Wolfgang Elbert, Susannah Burrows, Jennifer Caesar, Jörg Steinkamp, Alexandra Tamm, Meinrat O. Andreae, Burkhard Büdel, Axel Kleidon, Ulrich Pöschl |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250095837
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| Publikation (Nr.) |
 EGU/EGU2014-11312.pdf |
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| Zusammenfassung |
| Cryptogamic covers are composed of cyanobacteria, green algae, lichens, bryophytes, fungi
and bacteria in varying proportions. As cryptogamic ground covers, comprising biological
soil and rock crusts they occur on many terrestrial ground surfaces. Cryptogamic plant
covers, containing epiphytic and epiphyllic crusts as well as foliose or fruticose lichens and
bryophytes spread over large portions of terrestrial plant surfaces. Photoautotrophic
organisms within these crusts sequester atmospheric CO2 and many of them include
nitrogen-fixing cyanobacteria, utilizing atmospheric N2 to form ammonium which can be
readily used by vascular plants.
In a large-scale data analysis approach, we compiled all available data on the
physiological properties of cryptogamic covers and developed a model to calculate their
annual nitrogen fixation and net primary production. Here, we obtained a total value of 3.9 Pg
a-1 for the global net uptake of carbon by cryptogamic covers, which corresponds to
approximately 7% of the estimated global net primary production of terrestrial vegetation.
Nitrogen assimilation of cryptogamic covers revealed a global estimate of ~49 Tg a-1,
accounting for as much as about half the estimated total terrestrial biological nitrogen
fixation.
In a second approach, we calculated the global carbon uptake by lichens and bryophytes
by means of a process-based model. In this model, we used gridded climate data
combined with key habitat properties (as e.g. disturbance intervals) to predict the
processes which control net carbon uptake, i.e. photosynthesis, respiration, water
uptake and evaporation. The model relies on equations frequently used in dynamic
vegetation models, which were combined with concepts specific to lichens and
bryophytes. As this model only comprises lichens and bryophytes, the predicted
terrestrial net uptake of 0.34 to 3.3 Gt a-1 is in accordance with our empirically-derived
estimate. Based on this result, we quantified the amount of nitrogen needed by the
organisms to build up biomass. The predicted requirement for nitrogen ranges from
3.5 to 34 Tg a-1, again being in a reasonable range compared to the data analysis
approach.
In experimental field studies (3rd approach), we analyzed the net primary production of
biological soil crusts, i.e. one major group of cryptogamic covers. The microclimatic
conditions (water status, temperature, light intensity) of different types of biological soil
crusts were monitored at 5-minute intervals over a whole year. Conducting a factorial analysis
of CO2 gas exchange of the crusts in the lab, we obtained the net photosynthesis or
respiration rate for all microclimatic conditions encountered in the field. The latter results
were combined with the microclimate data, assigning CO2 gas exchange values to each
microclimate measurement tuple. Integration over the year resulted in an annual carbon
fixation of ~5 g m-2 a-1, being nearly identical to the numbers obtained during the data
analysis approach.
In summary, our three different approaches clearly revealed that cryptogamic covers have
a considerable effect on the global terrestrial C and N cycle, which must not be neglected in
global carbon and nitrogen balances. |
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