Date of Award

Fall 2024

Language

English

Embargo Period

11-25-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

College/School/Department

Department of Environmental and Sustainable Engineering

Program

Environmental and Sustainable Engineering

First Advisor

Rixiang Huang

Committee Members

Rixiang Huang, Yanna Liang, Kyoung-Yeol Kim, Yang Song

Keywords

Fire ash, Macronutrients, Biochar, Extracellular enzymes, Soil organic matter, Enzyme activity

Subject Categories

Environmental Engineering

Abstract

Wildland fire is a main driving force in the Earth system and affects ecosystem properties and processes across spatio-temporal scales. The burning of biomass and production of solid fire residues (conventionally termed fire ash) that are a mixture of completely and incompletely burned materials (inorganic ash and pyrogenic carbon), represent the direct and prominent changes by fires. Cycling of the fire residues is an integral component of elemental cycles and can mediate other biogeochemical processes.

This dissertation aims to fill important knowledge gaps in understanding the disturbance of wildland fires to biogeochemical processes in soils. First, this work characterized and compared the chemical speciation and aqueous dissolution behaviors of macronutrients in fire ash produced across different ecosystems, providing a fundamental dataset and knowledge for exploring the cycling of fire ash. Next, the effects of pyrogenic carbon on soil biogeochemical conditions and processes were explored, through studying its interaction with extracellular enzymes and enzyme substrates, as well as the effects on enzyme activities.

Main findings from this dissertational research include: 1) Variation in macronutrients speciation among wildfire ashes can be attributed to the vegetation composition and elemental stoichiometry of the biomass, as well as fire thermal conditions. This study provides a mechanistic understanding of how fires transform the chemistry of macronutrients and affect macronutrient returning to soils across different ecosystems, which is essential for evaluating the disturbance to ecosystem nutrient cycling by fires; 2) Adsorption of extracellular enzymes onto biochar surfaces is primarily driven by electrostatic interactions, and the extent of adsorption is affected by surface characteristics of the biochar, such as surface chemistry, pore structure, and functional groups; 3) Biochar can change the soil mobility and availability of organophosphates for enzymatic reactions through enzyme and enzyme substrates adsorption. 4) Biochar plays a significant role in modulating soil enzyme activity through direct enzyme and substrates adsorption. The adsorption of extracellular enzymes onto biochar varies with biochar type (feedstock and pyrolysis temperature), which directly influences the degradation of organic matter and nutrient cycling. This study also highlights the importance of proper measurement and interpretation of enzyme activity in systems containing biochar, as conventional enzyme assays may not fully account for biochar's complex role in biochar-substrate-enzyme interactions.

In addition, the research synthesizes current knowledge on the microbial decomposition of biochar, linking soil microbial processes with biochemical transformations. It emphasizes the variations in biochar stability and microbial community responses, contributing to an improved understanding of biochar's role in the global carbon cycle and its environmental stability.

In summary, this dissertation advances the understanding of the effects of fire residues on nutrients speciation and cycling, enzymes and enzymes substrates adsorption, and enzyme activity.

License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.

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