Response of soil microbial activity to grazing, nitrogen deposition, and exotic cover in a serpentine grassland
Esch, E.;D. Hernández;J. Pasari;R.G. Kantor and P. Selmants. 2013.
Abstract
Background and aims Exotic species, nitrogen (N)
deposition, and grazing are major drivers of change
in grasslands. However little is known about the inter-
active effects of these factors on below-ground micro-
bial communities.
Methods We simulated realistic N deposition increases
with low-level fertilization and manipulated grazing
with fencing in a split-plot experiment in California's
largest serpentine grassland. We also monitored grazing intensity using camera traps and measured total
available N to assess grazing and nutrient enrich-
ment effects on microbial extracellular enzyme
activity (EEA), microbial N mineralization, and
respiration rates in soil.
Results Continuous measures of grazing intensity and
N availability showed that increased grazing and N
were correlated with increased microbial activity and
were stronger predictors than the categorical grazing
and fertilization measures. Exotic cover was also gen-
erally correlated with increased microbial activity
resulting from exotic-driven nutrient cycling altera-
tions. Seasonal effects, on abiotic factors and plant
phenology, were also an important factor in EEA with
lower activity occurring at peak plant biomass.
Conclusions In combination with previous studies from
this serpentine grassland, our results suggest that graz-
ing intensity and soil N availability may affect the soil
microbial community indirectly via effects on exotic
cover and associated changes in nutrient cycling while
grazing directly impacts soil community function.
Key Words
California . Cattle . Extracellular enzyme activity . Fertilization . Festuca perennis . Invasive species
