『Abstract
Fungi are capable of both nitrification and denitrification and
dominate the microbial biomass in many soils. Recent work suggests
that fungal rather than bacterial pathways dominate N transformation
in desert soils. We evaluated this hypothesis by comparing the
contributions of bacteria and fungi to N2O
production at control and N fertilized sites within a semiarid
grassland in central New Mexico (USA). Soil samples were taken
from the rhizosphere of blue grama (B. gracilus) and the
microbiotic crusts that grow in open areas between the bunch grasses.
Soils incubated at 30% or 70% water holding capacity, were exposed
to one of three biocide treatments (control, cycloheximide or
streptomycin). After 48 h, N2O and CO2 production were quantified along with the activities
of several extracellular enzymes. N2O production
from N fertilized soils was higher than that of control soils
(165 vs. 41 pmol h-1 g-1), was higher for
crust soil than for rhizosphere soil (10 vs, 97 pmol h-1
g-1), and increased with soil water content (16 vs.
60 pmol h-1 g-1). On average, fungicide
(cycloheximide) addition reduced N2O production
by 85% while increasing CO2 production by
69%; bactericide (streptomycin) reduced N2O
by 53% with mixed effects on CO2 production.
N2O production was significantly correlated
with C and N mineralization potential as measured by assays for
glycosidic and proteolytic enzymes, and with extractable nitrate
and ammonium. Our data indicate that fungal nitrifier denitrification
and bacterial autotrophic nitrification dominate N transformation
in this ecosystem and that N2O production is highly sensitive
to soil cover, N deposition and moisture.
Keywords: Nitrous oxide; Fungi; Semiarid grasslands; Sevilleta
LTER; Denitrification; Extracellular enzyme activity』
Introduction
Methods
Site description and sample collection
Soil properties
N2O and CO2 flux
Extracellular enzyme assays
Statistical analyses
Results
Discussion
Acknowledgements
References