Soil microbial responses to fire and interacting global change factors in a California annual grassland

Wildfire in California annual grasslands is an important ecological disturbance and ecosystem control. Regional and global climate changes that affect aboveground biomass will alter fire-related nutrient loading and promote increased frequency and severity of fire in these systems. This can have longterm impacts on soil microbial dynamics and nutrient cycling, particularly in N-limited systems such as annual grasslands. We examined the effects of a lowseverity fire on microbial biomass and specific microbial lipid biomarkers over 3 years following a fire at the Jasper Ridge Global Change Experiment. We also examined the impact of fire on the abundance of ammonia-oxidizing bacteria (AOB), specifically Nitrosospira Cluster 3a ammonia-oxidizers, and nitrification rates 9 months post-fire. Finally, we examined the interactive effects of fire and three other global change factors (N-deposition, precipitation and CO2) on plant biomass and soil microbial communities for three growing seasons after fire. Our results indicate that a low-severity fire is associated with earlier season primary productivity and higher soil-NH4 ? concentrations in the first growing season following fire. Belowground productivity and total microbial biomass were not influenced by fire. Diagnostic microbial lipid biomarkers, including those for Gram-positive bacteria and Gram-negative bacteria, were reduced by fire 9and 21-months post-fire, respectively. All effects of fire were indiscernible by 33-months post-fire, suggesting that above and belowground responses to fire do not persist in the long-term and that these grassland University of Oregon and University of Wisconsin-Madison— institutions where this research took place. Electronic supplementary material The online version of this article (doi:10.1007/s10533-011-9654-3) contains supplementary material, which is available to authorized users. K. M. Docherty Department of Biological Sciences, Western Michigan University, 1903 West Michigan Ave., Kalamazoo, MI 49008-5410, USA K. M. Docherty B. J. M. Bohannan Center for Ecology and Evolutionary Biology (CEEB), University of Oregon, P.O. Box 5289, Eugene, OR 97403, USA T. C. Balser J. L. M. Gutknecht Department of Soil Science, University of WisconsinMadison, 1525 Observatory Drive, Madison, WI 53706, USA T. C. Balser Department of Soil and Water Science, University of Florida, Gainesville, FL 32611, USA J. L. M. Gutknecht (&) Department of Soil Ecology, Helmoltz-Centre for Environmental Research—UFZ, Theodor-Lieser-Strasse 4, 06120 Halle, Germany e-mail: [email protected] 123 Biogeochemistry (2012) 109:63–83 DOI 10.1007/s10533-011-9654-3