PS 70-157
Long-term nitrogen deposition influences the effects and timing of soil ammonia-oxidizing bacterial responses to fire
Global climate change is a serious and pervasive threat to the biosphere, and has the potential to alter the nutrient cycling and soil microbial communities in many ecological niches. We examined the interactive effects of two climate change factors, nitrogen and fire, on soil ammonia-oxidizing bacterial (AOB) community structure at the Jasper Ridge Global Change Experiment (JRGCE). This experiment is located in a California annual grassland near Palo Alto, CA, which has a distinctive Mediterranean climate. The current work builds on a previous study that examined the effects of a July 2003 fire on AOB community structure at a single nine month post-burn time point. In this study, we examined the proportion of the cluster 3a AOB, which belong to a phylogenetic cluster often associated with high levels of soil ammonium and high nitrification rates. We measured several abiotic soil characteristics, nitrate and ammonium concentrations, and AOB community structure using T-RFLP, immediately, six months, and nine months after the fire.
Results/Conclusions
Unlike previous studies, we found that soil ammonium concentrations in the nitrogen and fire treatments did not differ from the controls, likely due to atypical precipitation patterns during 2011-2012. Two of the three sample dates indicated a trend of increased relative abundance of cluster 3a AOB in the nitrogen fertilized plots relative to the burned and control plots. Our data demonstrate that inter-annual variation plays a large role in determining the response of the soil microbial community to both nitrogen-addition and burning. Further studies which examine the effects of global change on soil microbial diversity and activity in the context of natural environmental variation and disturbance are necessary for an accurate understanding of future global change predictions.
phone 202-833-8773
