Factors Regulating Nitrogen Retention During the Early Stages of Recovery from Fire in Coastal Chaparral Ecosystems
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Fire is a fundamental reorganizing force in chaparral and other Mediterranean-type ecosystems. Postfire nutrient redistribution and cycling are frequently invoked as drivers of ecosystem recovery. The extent to which N is transported from slopes to streams following fire is a function of the balance between the rate at which soil microbes retain and metabolize N into forms that readily dissolve or leach, and how rapidly recovering plants sequester this mobilized N. To better understand how fire impacts this balance, we sampled soil and plant N dynamics in 17 plots distributed across two burned, chaparral-dominated watersheds in Santa Barbara County, California. We measured a variety of ecosystem properties in both burned and unburned plots on a periodic basis for 2 years, including soil water content, pH, soil and plant carbon and nitrogen, extractable inorganic nitrogen, dissolved organic nitrogen, and microbial biomass. In burned plots, nitrification was significantly enhanced relative to rates measured in unburned plots. Ephemeral herbs established quickly following the first postfire rain events. Aboveground plant biomass assimilated N commensurate with soil net mineralization, implying tight N cycling during the early stages of recovery. Microbial biomass N, on the other hand, remained low throughout the study. These findings highlight the importance of herbaceous species in conserving ecosystem nutrients as shrubs gradually recover.
Keywordsdisturbance wildfire xeric ecosystems ash redistribution nitrate leaching mountainous landscapes N-sinks
The authors offer their thanks to John Melack for support and discussions that improved the sampling design and analysis for this study; to Viviane Vincent, Amanda Golay, Sarah Kullbom, Megan Lipps, Daniel Keck, Bailey Smith, Spencer Pritchard, Emma Panish, Brittany Luttrell, Alyssa Raley, and Matt Mass for their field and laboratory assistance; and to Jennifer King and Dad Roux-Michollet for providing laboratory instruments and instruction. The authors also thank the editor and anonymous reviewers for their constructive comments, which helped to improve the manuscript. This study was supported by the NSF RAPID Grant (DEB-0952599), and the Santa Barbara Coastal Long-Term Ecological Research project (OCE-0620276).
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