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Vulnerability of soil organic matter to microbial decomposition as a consequence of burning

Abstract

Ecosystem fires are stochastic and anthropogenic phenomena that affect critical soil processes. Nevertheless, environmental managers, policy-makers, and even scientists have often overlooked the induced transformations that fire does to soil organic matter (SOM), which sustains an ecosystem’s overall health. Here, we investigated the effects of simulated fire conditions on bulk SOM, water-extractable organic matter (WEOM), and vulnerability to microbial degradation. Sequential thermal decomposition experiments were carried out to investigate the effect of increasing temperature on C, N, δ13C, and δ15N of bulk SOM and WEOM. A microbial decomposition experiment was also done to determine the effects of burning on SOM degradability. Intermediate-intensity burns caused significant decreases in C and N concentrations in soils, as well as alterations in bulk SOM and WEOM properties. Conversely, the effects of low-intensity burns were less apparent in terms of bulk SOM content and stable C and N isotope composition. However, the results of the microbial decomposition experiment revealed that low-intensity burning resulted in elevated CO2 emission that were significantly correlated with C concentration, δ13C values, and the C/N ratio of WEOM. These results provide evidence that low-intensity burning can have important consequences for soils, altering its organic components and releasing significant amounts of greenhouse gases. Thus, particular focus must be given to managing ecosystem fires and evaluating their impacts, especially because fire is still widely used in agriculture and forest management with frequency projected to increase in the coming years.

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Acknowledgements

This study was funded by the Department of Science and Technology- Philippine Council for Agriculture, Aquatic and Natural Resources Research and Development (DOST-PCAARRD) through the establishment of a new isotope ratio mass spectrometry facility in the Philippine Nuclear Research Institute. G.P. Dicen was also supported by the DOST-Science Education Institute’s Career Incentive Program in the conduct of this research. We thank the International Atomic Energy Agency RAS5084 Project through Mr. Efren J. Sta Maria for allowing us to process some of the samples for use in this research. We also extend our deepest gratitude to our student interns from the Philippine Normal University, Mss. Rianne Joy Maulion and Aishan Joy Israel, who kindly assisted us in some of the analyses in this study. Finally, we thank the anonymous reviewers for reviewing our manuscript in detail and for providing us with invaluable comments that greatly improved the quality of our paper, as well as Dr. Elizabeth Sargent of Georgia Southern University and Dr. Rotacio Gravoso of the Visayas State University for reviewing the final draft of our manuscript.

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Correspondence to Gerald P. Dicen.

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Dicen, G.P., Rallos, R.V., Labides, J.L.R. et al. Vulnerability of soil organic matter to microbial decomposition as a consequence of burning. Biogeochemistry 150, 123–137 (2020). https://doi.org/10.1007/s10533-020-00688-1

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  • DOI: https://doi.org/10.1007/s10533-020-00688-1

Keywords

  • Carbon emission
  • Fire
  • Greenhouse gases
  • Soil organic matter microbial decomposition
  • Stable isotopes
  • Water-extractable organic matter