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 long-term impacts on soil microbial dynamics and nutrient cycling, particularly in N-limited systems such as annual grasslands. We examined the effects of a low-severity 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 CO 2) 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-NH 4 + 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 9- and 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 communities are resilient to fire disturbance. While N-deposition increased soil NH 4 +, and thus available NH 3, AOB abundance, nitrification rates and Cluster 3a AOB, similar increases in NH 3 in the fire plots did not affect AOB or nitrification. We hypothesize that this difference in response to N-addition involves a mediation of P-limitation as a result of fire, possibly enhanced by increased plant competition and arbuscular mycorrhizal fungi-plant associations after fire.
Bibliographical noteFunding Information:
Acknowledgments The authors would like to thank our many collaborators at the Jasper Ridge Global Change Experiment. Specifically we thank Drs. Chris Field and Nona Chiarello for their work to keep the JRGCE continuing, for allowing our use of the above-ground, below-ground, and litter biomass data, and for their general support of our efforts as collaborators. Dr. Hugh Henry provided feedback on our interpretations of AGB data. We thank Yuka Estrada and Todd Tobeck for coordinating field sampling and sample processing. The Bohannan laboratory and specifically Dr. Sharon Avrahami provided methods and support of this project, as did the Balser laboratory, specifically Dr. Harry Read. We also thank reviewers of the manuscript for many helpful suggestions. Funding for this project was provided by the National Science Foundation (DEB 045-2652) and the NSF Postdoctoral Fellowship Program (Award Number 0805723).
Copyright 2012 Elsevier B.V., All rights reserved.
- Global change
- Soil microbiology