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Schlagwörter:
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Zusammenfassung:
Lichens and bryophytes are abundant globally and
they may even form the dominant autotrophs in (sub)polar
ecosystems, in deserts and at high altitudes. Moreover, they
can be found in large amounts as epiphytes in old-growth
forests. Here, we present the first process-based model which
estimates the net carbon uptake by these organisms at the
global scale, thus assessing their significance for biogeochemical
cycles. The model uses gridded climate data and
key properties of the habitat (e.g. disturbance intervals) to
predict processes which control net carbon uptake, namely
photosynthesis, respiration, water uptake and evaporation. It
relies on equations used in many dynamical vegetation models,
which are combined with concepts specific to lichens
and bryophytes, such as poikilohydry or the effect of water
content on CO2 diffusivity. To incorporate the great functional
variation of lichens and bryophytes at the global scale,
the model parameters are characterised by broad ranges of
possible values instead of a single, globally uniform value.
The predicted terrestrial net uptake of 0.34 to 3.3 Gt yr−1 of
carbon and global patterns of productivity are in accordance
with empirically-derived estimates. Considering that the assimilated
carbon can be invested in processes such as weathering or nitrogen fixation, lichens and bryophytes may play a significant role in biogeochemical cycles.
