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Expanding our understanding of nitrogen dynamics after fire: how severe fire and aridity reduce ecosystem nitrogen retention

Maxwell Strain, Mary Brady, Erin Hanan

Abstract

Background Fires release large pulses of nitrogen (N), which can be taken up by recovering plants and microbes or exported to streams, where it can threaten water quality. Aims The amount of N exported depends on the balance between N mineralization and rates of N uptake after fire. Burn severity and soil moisture interact to drive these rates, but their effects can be difficult to predict. Methods To understand how soil moisture and burn severity influence postfire N cycling and retention in a dryland watershed, we quantified changes in plant biomass, plant N content, soil microbial biomass, inorganic N pools, and net N mineralization for two years after fire. We compared sites that were unburned with those that burned at moderate or high severity, capturing variation in soil moisture within each severity category. Key Results Severe fire limited N uptake by plants. Dry conditions after fire limited both plant and microbial N uptake. Implications When fire is severe or when soils are relatively dry after fire, recovering plants and microbes are less likely to take up postfire N and therefore, are more susceptible to N export.

WF23191  Accepted 26 July 2024

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