wAbstract
@Biological soil crusts (BSCs) are thought to be important in
the fertility of arid lands as gateways for carbon (C) and nitrogen
(N). Studies on the Colorado Plateau have shown that an incomplete
internal N cycle operates in BSCs that results in significant
exports of dissolved organic N, ammonia and nitrate into the bulk
soil through percolating water, thus mechanistically explaining
their role as a N gateway. It is not shown if this pattern is
found in other arid regions. To examine this, we measured rates
of major biogeochemical N-transformations in a variety of BSCs
collected from the Colorado Plateau and the Mojave, Sonoran and
Chihuahuan Deserts. Dinitrogen fixation and aerobic ammonia oxidation
were prominent transformations at all sites. We found anaerobic
ammonia oxidation (anammox) rates to be below the detection limit
in all cases, and at least 50-fold smaller than rates of N2-fixation, making it an irrevalent process for
these BSCs. Heterotrophic denitrification was also of little consequence
for the flow of N, with rates at least an order of magnitude smaller
than those of N2-fixation. Thus we could
confirm that despite the demonstrable differences in microbial
community composition and soil material, BSCs from major biogeographic
regions in arid North America displayed a remarkably consistent
pattern of internal N cycling. The implications for arid land
fertility drawn from previous studies in the Colorado Plateau
appear applicable to BSCs across other arid regions of the Southwestern
United States.
Keywords: Biological soil crust; Desert; Nitrogen; Bacteria; Denitrification;
Ammonia-oxidation; Dinitrogen-fixationx
Introduction
Methods
@Soil sampling and preparation
@Soil geochemical parameters
@Acetylene reduction assay for potential N2
fixation rates
@Ammonium oxidation rates
@Acetylene inhibition assay for potential denitrification rates
@Net Photosynthesis and dark respiration measurements
@Isolation of DNA
@PCR Amplification of 16S rRNA gene
@Denaturing gradient gel electrophoresis
@Sequencing and phylogenic analysis
@Quantification and analysis of GGE fingerprint
@Statistics
Results
@Soil geochemistry
@Microbial community
@Net photosynthesis and dark respiration
@Tracer experiments: absence of anammox and denitrification in
BSCs
@N2-fixation and aerobic ammonia-oxidation
Discussion
Acknowledgments
References