The effect of grazing by large herbivores on the
microbial community and the ecosystem functions they
provide are relatively unknown in grassland systems. In this
study, the impact of grazing upon the size, composition and
activity of the soil microbial community was measured in
field experiments in two coastal ecosystems: one salt marsh
and one sand dune grassland. Bacterial, fungal and total
microbial biomass were not systematically affected by grazing
across ecosystems, although, within an ecosystem, differences
could be detected. Fungal-to-bacterial ratio did not
differ with grazing for either habitat. Redundancy analysis
showed that soil moisture, bulk density and root biomass
significantly explained the composition of phospholipid fatty
acid (PLFA) markers, dominated by the distinction between
the two grassland habitats, but where the grazing effect could
also be resolved. PLFA markers for Gram-positive bacteria
were more proportionally abundant in un-grazed, and markers
for Gram-negative bacteria in grazed grasslands. Bacterial
growth rate (leucine incorporation) was highest in un-grazed
salt marsh but did not vary with grazing intensity in the sand
dune grassland. We conclude that grazing consistently affects
the composition of the soil microbial community in seminatural
grasslands but that its influence is small (7 % of the
total variation in PLFA composition), compared with differences
between grassland types (89 %). The relatively small
effect of grazing translated to small effects on measurements
of soil microbial functions, including N and C mineralisation.
This study is an early step toward assessing consequences of
land-use change for global nutrient cycles driven by the
microbial community.