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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.


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