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| Titel |
Biological soil crusts (BSC) in the Sahelian zone. Can they impact soil C and N cycles? |
| VerfasserIn |
F. Ehrhardt, I. Bertrand, C. Joulian, C. Valentin, G. Alavoine, O. Malam Issa |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250067219
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| Zusammenfassung |
| Biological soil crusts (BSC) are key component of arid and semiarid ecosystems due to their
ability to incorporate C and N from atmosphere to soil. However, while BSC characteristics
and impact on water cycle or N fixation fluxes in Sahelian zone were studied, the turnover of
the fixed C and N in soils was not studied yet. The aim of this study is to assess the
quantitative impact of BSC on C and N cycles through the contribution of both autotrophic
and heterotrophic microorganisms. Our research is also based on the distinction between the
impact of the abiotic part (underlying physical crust) and that of the biotic part of BSC
(microbial components).
Biological crust and soils were sampled (up to 5 cm depth) in February 2009 at two
locations according a climatic gradient (500 and 700 mm/year) in Western Niger. The
samples were characterised before incubation for their C and N contents, particle size, C
biomass, mineral N, chlorophyll a content and sugar monomers contents. The microbial
diversity of BSC was also determined. C and N fluxes of fixation and mineralization were
measured by incubating BSC at 28 Ë C in dark and light conditions with adapted
moisture.
Higher C and N content and C biomass were found in superficial crust samples compared
to the underlying soil samples. Values obtained on BSC for C ranged from 6.88 to 15.74
g.kg-1 vs 1.10 to 4.14 g.kg-1 within soils. We demonstrated that C fixed under light
conditions by autotrophic biomass from BSC is either assimilated or accumulated under a
polysaccharide form, with C fixation fluxes values ranging from 7.41 to 24.65 μgC.m-2.s-1
in average. These polysaccharides are partly mineralized with a related rate comprised
between 2.95 and 5.83 μgC.m-2.s-1. Therefore, the net C balance is positive, contrary to net
N balance. Indeed, N fixation fluxes measured with an isotopic method, ranged
from 1.32.10-3 to 8.47.10-2 mgN.m-2.h-1, whereas mineralization fluxes were
from 0.47 to 1.01 mgN.m-2.h-1. Carbon cycle was related with the presence of
Proteobacteria and Actinobacteria for the fixation part and rather of Chloroflexi for the
mineralization part. The distribution of both of these species was correlated with BSC fine
particles content. Interestingly, the distribution of Cyanobacteria, the major specie
encountered within BSC (45.3 to 70.9 %) was not related either to C or N fluxes. |
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