Mountain Scholar :: Browsing by Author "Rhoades, Charles, committee member"

Browsing by Author "Rhoades, Charles, committee member"

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Open Access
Acid mine drainage impacts in the Upper Arkansas River Basin: a study of water quality, treatment efficiency, and predicted longevity
(Colorado State University. Libraries, 2019) Moore, Megan, author; Covino, Tim, advisor; Ross, Matthew, committee member; Wilkins, Mike, committee member; Rhoades, Charles, committee member
Mining activity in the Sugarloaf and Leadville mining districts of Leadville, Colorado has impaired water quality in the Upper Arkansas River Basin. Tributary and main channel waters are often out of compliance with state water quality standards, and stream flora and fauna as well as human use of these waterways is threatened by acid mine drainage. This study aims to describe the impact historical mining activity has had on the waters of the Upper Arkansas River Basin by characterizing water quality, analyzing metal removal efficiency from both active and passive treatment sites in the area, and estimating the time it will take for drainage from mining tunnels to naturally comply with state water quality standards. A comparison of instream dissolved concentrations of cadmium, copper, iron, lead, manganese, and zinc to state water quality standards shows waters of the Upper Arkansas River Basin are often out of compliance with chronic and/or acute standards. This is seen more frequently upstream from treatment sites and higher up in the tributary system than at tributary mouths or in the main channel of the Arkansas River. An examination of metal removal from the Leadville Mine Drainage Tunnel and Yak Tunnel water treatment plants along East Fork and California Gulch shows dissolved metal reduction between 33 and 100 percent compared with 0 to 84 percent at the passive Dinero Wetland Complex along Lake Fork. Finally, an analysis of projected longevity highlights the importance of clean-up plans for future mining projects with estimated impaired water quality continuing upwards of 2000 years at Yak Tunnel.
Open Access
Amendment effects on soil physical properties and restoration of decommissioned forest roads
(Colorado State University. Libraries, 2017) Berlejung, John Michael, author; Fonte, Steven, advisor; Rhoades, Charles, committee member; Paschke, Mark, committee member
Unsealed forest roads, including logging roads and unauthorized roads created by hunters, miners, and recreational users, generate significant harmful effects to local ecosystems and waterways. Rapid restoration of these roads is necessary to prevent erosion, downstream implications for water quality, and a variety of other deleterious ecosystem impacts. Soil amendments, including mulches, composts, and other materials, offer promise to improve soil health, restore soil structure, and support revegetation of these sites. I tested the viability of three locally-sourced soil amendments wood straw mulch, Biosol fertilizer, and biochar alone and in paired combinations to restore soil physical properties important for improved hydrologic function and plant growth. I found that amendment combinations of biochar + mulch and biochar + Biosol significantly reduced soil bulk density when compared to unamended controls. Other factors (aggregate stability, infiltration, sediment production) suggested potential for improvement relative to unamended control plots, but no significant differences between treatments were observed due to high variability within and between sites. Regression analyses revealed that soil physical properties, particularly wet aggregate stability, was significantly correlated with key soil erosion parameters such as infiltration and runoff, suggesting aggregate stability could provide a useful measure of soil restoration success.
Open Access
Biogeochemical implications of beaver-mediated fluvial complexity in river-floodplain meadows
(Colorado State University. Libraries, 2018) Weiss, Tristan N. M., author; Covino, Tim, advisor; Wohl, Ellen, committee member; Rhoades, Charles, committee member; Falkowski, Michael, committee member
Mountain river networks alternate between narrow, transport dominated segments and low gradient wide valley segments that can be important locations for the retention and processing of carbon and nutrients. In North America, beaver (Castor canadensis) engage in dam building that enables the establishment of complex river-floodplain meadows (hereafter "meadows"), characterized by wide riparian corridors, multi-thread channels, and high levels of river-floodplain connectivity. However, in many river-floodplain systems, human land-use and the removal of beaver has led to fluvial simplification characterized by reductions in riparian vegetation and channel incision. We examined differences in hydrology and biogeochemistry among four meadows of varying beaver activity and associated fluvial complexity within Rocky Mountain National Park, USA. We quantified water and dissolved organic carbon (DOC) flux, measured fluorescent dissolved organic matter (DOM) character, and monitored ecosystem metabolism. At complex meadow segments, we observed increased stability across space and through time in patterns of water flux and DOC concentration, export, and character. While DOC dynamics were stable at complex meadow segments, in simplified meadow segments we observed increases in DOC concentration and export, and shifts toward more terrestrially sourced, aromatic, and humic DOM. These results suggest that complex river-floodplain systems facilitate stability in stream flows and maintain water quality with respect to DOC concentration, flux, and form. Conversely, the loss of fluvial complexity in simplified meadow segments can lead to lost hydrologic and biogeochemical stability and make the valley segments more sensitive to future perturbations. Because wide-complex meadow segments can act as key locations of hydrologic retention in mountain stream networks, understanding how fluvial simplification alters water and DOC dynamics may be important for developing targeted restoration strategies for altered mountain headwater systems.
Open Access
Carbon and nitrogen eroded from burned forests in the western U.S.
(Colorado State University. Libraries, 2013) Pierson, Derek, author; Binkley, Daniel, advisor; Rhoades, Charles, committee member; Kelly, Eugene, committee member
Post-wildfire landscapes and downstream aquatic resources are influenced by carbon (C) and nitrogen (N) losses from soil erosion. As opposed to soil erosion, rarely measured losses of sediment C and N may account for a substantial portion of fire impacts. We measured erosion of C and N following eight wildfires for four to six years in the western U.S and compared losses from untreated, burned hillslopes and small catchments with those from adjacent areas that received erosion mitigation treatments. Losses of C, N and sediment were greatest the first two years and declined in subsequent years. Cumulative losses from untreated, burned areas were 16 - 4,700 kg C/ha and 0.7 - 185 kg N/ha over the study period. Across wildfire locations, median sediment C and N concentrations ranged from 0.011 - 0.036 g N/kg and 0.23 - 0.98 g C/kg. Post-fire erosion control treatments reduced C, N and sediment losses by 65-75% compared to untreated areas and generally increased the concentrations of C and N in eroded material. The total C and N lost in post-fire erosion was < 20% of the estimated amount lost from organic and mineral soil layers during combustion and < 5% of the estimated amount remaining in mineral soils after combustion. In general, the N lost with soil erosion is unlikely to impair the productivity of recovering forests, but the eroded N may have consequences on downstream water quality and aquatic habitat.
Open Access
Fire, fungi, flora, and flow: post-fire fungal community assemblages, vegetation establishment, and soil hydrophobicity in forests of the southern Rocky Mountains
(Colorado State University. Libraries, 2023) McNorvell, Michael A., author; Stevens-Rumann, Camille, advisor; Rhoades, Charles, committee member; Remke, Michael, committee member; Wilkins, Michael, committee member
Wildfire is an important ecological driver of ecosystem dynamics in the southern Rocky Mountains at multiple landscape scales, guiding establishment of forest biota both aboveground and below. Size, frequency, and severity of wildfires in coniferous forests across the western United States is increasing at an unprecedented rate. Despite wildfire's significant but disparate influences on forest soils, post-fire research has often focused on aboveground vegetation in isolation from study of belowground soil characteristics and the fire ecology of soil biota. Fungi are vital to forest ecosystems for their functional roles, however, the effects of wildfire on forest-specific fungal communities and how those communities subsequently influence post-fire vegetation communities and soil environments has not been extensively researched in the region over the past several decades. This is a prominent knowledge gap, especially as fungi are highly variable across functional groups, space, and time even in unburned systems. Thus, to build on our understanding of contemporary fire ecology in forested ecosystems of the Southern Rockies, we investigate three wildfires that burned in the state of Colorado during the 2020 fire season and address three research objectives: 1) Examine the influence of forest type and fire severity on post-fire fungal community composition across soil depth and temporal gradients; 2) Determine the effects of post-fire fungal community diversity on forest understory plant diversity and abundance; and 3) Explore relationships between fungal assemblages and observed soil hydrophobicity in burned forested environments. We found that though fire severity and soil depth were the primary influences on quantified fungal diversity, the composition of fungal community assemblages was most heavily influenced by forest type: forests developed fungal communities compositionally unique to one another just two years after fire. Diversity of fungi showed significant influence on aboveground plant diversity and abundance, especially mutualistic fungi (ecto- and arbuscular mycorrhizae) and their respective plant hosts. Finally, significant relationships between fungal diversity and soil hydrophobicity were observed mediated by forest type, fire severity, soil depth, and year post-fire, though these patterns were difficult to surmise and the influence of other important variables may be at play. By more fully understanding how soil fungi interact with aboveground vegetation establishment and belowground soil conditions after wildfire, this research may help inform managers of pathways to better achieve desired post-fire outcomes by leveraging fungal relationships in soil remediation, site preparation, and conservation of post-fire forest ecosystems.
Open Access
Forest soil C and N responses to salvage logging and belowground C inputs in bark beetle infested stands
(Colorado State University. Libraries, 2020) Avera, Bethany N., author; Cotrufo, M. Francesca, advisor; Rhoades, Charles, committee member; Rocca, Monique, committee member; van Diepen, Linda, committee member
Managing forest ecosystems in this era of global change requires a fundamental understanding of forest soil properties and processes. Forest disturbance events are projected to increase in severity and frequency, requiring a better understanding of how post-disturbance management will impact ecological processes such as soil nutrient dynamics and stocks of soil carbon (C). The research in this dissertation focused on areas of widespread mortality in lodgepole pine (Pinus contorta var. latifolia) in northern Colorado due to the most recent outbreak of the endemic mountain pine beetle (MPB; Dendroctonus ponderosae Hopkins). The goal of this research was to examine soil nitrogen (N) stocks, plant N uptake, and changes in forest soil C stocks in soil organic matter (SOM) due to tree mortality and subsequent salvage logging and from different belowground C inputs. To achieve this aim, I compared the three most prevalent management options: 1) uncut beetle-infested lodgepole pine stands and clear-cut salvage logged areas with either 2) post-harvest residue retention or 3) post-harvest residue removal. To determine the impacts of MPB-infestation and salvage logging on ecosystem N stocks and plant N uptake, I implemented an experimental field study by adding 15N-labeled ammonium sulfate to research plots centered over lodgepole pine seedlings. Measuring N stocks and 15N recovery in soil and vegetation pools over two growing seasons highlighted the coupled nature of forest C and N cycling between plant and soil forest ecosystem compartments. The majority of the 15N label was recovered in the soil and was not impacted by the management treatments. In contrast, the N uptake by lodgepole pine seedlings was driven primarily by the amount of C fixation and the patterns of C fixation, in turn, related to other environmental factors modulated by the management treatment, such as available light. An observational field study sought to quantify changes in forest soil C stocks in the bulk soil and SOM fractions and detect any changes in C chemistry as a result of management that may impact C persistence. In the dry, high elevation forests studied, soil C increased with salvage logging likely due to mixing of surface residues and O horizon C into the mineral soil during logging. The distribution of C stocks among the mineral soil fractions and the chemistry of those fractions indicated that root C accumulation in the particulate organic matter (POM, >53 μm) is an important mechanism of soil C accumulation in these forest soils. A mechanistic laboratory incubation evaluated the efficiency of mineral-associated organic matter (MAOM, <53 μm) formation from root and hyphal necromass inputs with different C chemistries. This study showed that rye root necromass with more labile and less structural C than pine roots, was processed most in the 38-day incubation and contributed much more efficiently to the formation of MAOM than did the pine roots. Despite less processing, the arbuscular and ectomycorrhizal fungal necromass both contributed as efficiently as rye roots to MAOM formation. These results indicate that both C chemistry and C/N ratio exert controls on residue processing and MAOM formation. Together, this dissertation work showed that salvage logging stimulated the growth of lodgepole pine seedlings, resulting in increased storage of both C and N in the plant biomass above- and belowground. As this pine root biomass turns over, the root necromass will contribute C to the POM fraction, the largest pool of soil C in this system. The net increase of forest soil C with salvage logging found in this study is notable as it suggests that the MPB-infested lodgepole pine forests of Colorado can be salvage logged with a low risk of significant soil C loss. Additionally, the highest recovery of the N label was in the soil, thus the high soil N recovery with higher soil C supports SOM is a sink of N reducing N losses. Finally, pine seedling colonization by ectomycorrhizal fungi may further aid with nutrient retention and the efficient formation of MAOM during regeneration.
Open Access
Implementing organic amendments to enhance maize yield, soil moisture, and microbial nutrient cycling in temperate agriculture
(Colorado State University. Libraries, 2018) Foster, Erika J., author; Cotrufo, M. Francesca, advisor; Comas, Louise, committee member; Rhoades, Charles, committee member; Wallenstein, Matthew D., committee member
To sustain agricultural production into the future, management should enhance natural biogeochemical cycling within the soil. Strategies to increase yield while reducing chemical fertilizer inputs and irrigation require robust research and development before widespread implementation. Current innovations in crop production use amendments such as manure and biochar charcoal to increase soil organic matter and improve soil structure, water, and nutrient content. Organic amendments also provide substrate and habitat for soil microorganisms that can play a key role cycling nutrients, improving nutrient availability for crops. Additional plant growth promoting bacteria can be incorporated into the soil as inocula to enhance soil nutrient cycling through mechanisms like phosphorus solubilization. Since microbial inoculation is highly effective under drought conditions, this technique pairs well in agricultural systems using limited irrigation to save water, particularly in semi-arid regions where climate change and population growth exacerbate water scarcity. The research in this dissertation examines synergistic techniques to reduce irrigation inputs, while building soil organic matter, and promoting natural microbial function to increase crop available nutrients. The research was conducted on conventional irrigated maize systems at the Agricultural Research Development and Education Center north of Fort Collins, CO. The first field experiment tested a temporally limited irrigation strategy with high application rates of organic amendments (30 Mg ha-1) to increase soil moisture, N and P retention, and enhance soil microbial activity. The experiment used biochar created from bio-energy production. The control plots contained 1.49% total soil carbon, and biochar addition increased total carbon to 2.67%. The biochar also had variable impacts on microbial extracellular enzyme activities, causing a 40% reduction in β-1,4-glucosidase and phosphatase activities, with repercussions for hydrolysis of soil P and cellulose. However, the biochar amendment did not enhance yield. This field experiment also found that the limited irrigation technique reduced water inputs by 30% while maintaining yield. The second experiment of the dissertation determined the mechanism behind the decrease in extracellular enzymatic activities after biochar addition. Through a combination of a Bradford protein assay and a fluorometric assay of potential enzymatic activities, the pine wood biochar adsorbed and reduced both β-glucosidase and acid phosphatase activities by 75-100% relative to a control soil. Though highly variable, depending upon pH, the main factor influencing activity levels was the solid phase. The high temperature biochar had a large surface area within micropores. The substrate can diffuse into the micropores, where it is inaccessible to large enzymes; there is lower catalysis of those substrates, which indicates potentially lower nutrient release in the soil. Finally, to examine the agronomic efficacy of biochar, a second maize field trial was developed also implementing full and limited irrigation. This experiment incorporated an engineered coconut hull biochar, characterized by a neutralized pH, removed toxins from the surface, and homogenized pores. The biochar was banded directly onto the seed row at a low application rate (0.8 Mg ha-1). Additionally, a surface applied plant growth promoting P solubilizing bacterial inoculum was tested alone, and in combination with biochar. To determine the efficacy of these amendments to improve soil nutrient availability and maize yields, the soil nutrient supply, crop nutrient concentration and accumulation, and soil bacterial community composition were measured. The bacterial community data was analyzed using a cutting-edge technique based on Exact Sequence Variants to analyze single nucleotide differences, enhancing comparability with future studies. In this experiment the biochar increased soil available K and S which correlated to crop uptake, shifted the early season microbial community, and increased by 20% over the control (+1.95 Mg ha-1). The inoculum and combination treatments did not impact yield, but in these plots we observed the presence of bacterial families that were added in the original inoculum. Overall this work emphasized the efficacy of precision management strategies with biochar application to enhance yield. This dissertation work underlines the importance of contentiously selecting specific amendment type, application rate and method to achieve either agronomic or environmental benefits. Continued research with synergistic approaches will help to develop best practices within the region to manage agroecosystems for improved resilience.
Open Access
Lodgepole pine regeneration after mountain pine beetle and wildfire: a case study in the High Park Fire, CO
(Colorado State University. Libraries, 2016) Wright, Micah, author; Rocca, Monique, advisor; Rhoades, Charles, committee member; Hoffman, Chad, committee member
The 2012 High Park Fire burned over 35,000 hectares, including 5,000 hectares of lodgepole pine (Pinus contorta) forest that had recently been attacked by mountain pine beetle (MPB, Dendroctonus ponderosae). This sequence of events provided an excellent opportunity to investigate the effects of combined disturbance on lodgepole pine regeneration trajectories. I examined the influence of MPB mortality, high canopy fire severity, site characteristics, and post fire mulching treatments on lodgepole pine recovery at both landscape (∼hectare) and fine (∼cm) spatial scales. At the landscape scale, lodgepole pine seedling densities varied from 240 to 470,000 stems/ha. Seedling densities decreased as MPB mortality and high canopy fire severity increased. At the fine scale, lodgepole pine seedling establishment was positively related to local cone abundance and negatively related to high canopy fire severity. Topographic variables such as aspect and elevation did not have a strong influence on seedling density or establishment at either scale, nor did competition from recovering vegetation have an influence at the fine scale where it was considered. In areas with high canopy fire severity, post-fire straw mulching treatments were positively related to seedling establishment, indicating that mulching treatments may have additional benefits beyond erosion control. My research demonstrates that combinations of pre-fire mountain pine beetle mortality and high canopy fire severity can affect lodgepole pine regeneration, and may drive heterogeneity in the post-fire landscape.
Open Access
Occurrence, distribution, and driving environmental factors of quaking aspen regeneration by seed in the Cameron Peak Fire burn scar
(Colorado State University. Libraries, 2024) Carter, Sarah, author; Hart, Sarah, advisor; Rhoades, Charles, committee member; Rocca, Monique, committee member
As a result of the increasing frequency and severity of wildfires in the mountain west region of North America, greater mortality of montane and subalpine forests has led to changes in forest regeneration patterns and species composition. Increased drought conditions pre- and post-fire due to warming climate and destruction of existing seed have led to loss of historically conifer-dominant forests. This has subsequently opened a niche for post-fire aspen establishment, particularly through seed. The understanding of aspen regeneration by seed is understudied in comparison to the more broadly emphasized vegetative reproduction: a process which is limited spatially by the presence of surviving root networks and a lack of adaptive capacity of clone genetics. In this study, we aimed to (1) quantify the presence and density of post-fire aspen seedling establishment and (2) assess the environmental drivers of post-fire seedling establishment in a recent burn scar in northern Colorado. Two growing seasons following the fire, we conducted field surveys at 38 sites within the Cameron Peak Fire burn scar. We aimed to quantify regeneration of all tree species, including aspen as well as the dominant pre-fire conifers ponderosa pine (Pinus ponderosa), lodgepole pine (Pinus contorta), subalpine fir (Abies lasiocarpa), and Engelmann spruce (Picea engelmannii). Across our study area we found widespread establishment of aspen seedlings, particularly at high elevations, where soil moisture is less limiting. Given the occurrence of aspen seedlings within a site, we found seedlings were most likely to occur in moss seedbeds, near large coarse woody debris, and within microsite concavities, where soil moisture availability is likely higher. Collectively, our findings highlight the importance of moisture availability for the germination and initial survival of aspen seedlings. Further we found occurrence of aspen seedlings far outweighed that of any conifer species. These findings support projected changes in forest composition, species dominance, and range shift following stand replacing fire to favor early successional species such as aspen. The successful dispersal and establishment of aspen seeds in large, high severity burned patches have potential to facilitate the range shift of aspen forests towards higher elevations. These implications become more prevalent as changes in climate increase the risk of high severity fires and loss of seed sources, while decreasing suitability for montane and subalpine forest species to persist and regenerate.
Open Access
Subalpine forest ecosystem responses to long-term nitrogen loading at Loch Vale Watershed, Colorado, USA
(Colorado State University. Libraries, 2020) Weinmann, Tim, author; Boot, Claudia, advisor; Baron, Jill, advisor; Rhoades, Charles, committee member; Covino, Tim, committee member
This thesis presents the results of a long-term N fertilization experiment in the Loch Vale watershed of Rocky Mountain National Park and presents a conceptual model hypothesizing environmental controls on ecosystem responses to N fertilization. The experiment consisted of annual 25 kg N ha-1 application of NH4NO3 fertilizer to three 30 x 30 m subalpine forest plots from 1996 to 2017. Soil, plant, and lysimeter samples were collected over the course of the experiment to address three research goals. First, determine whether increased N input leads simply to increased N output, or whether observable ecosystem effects result. Second, describe changes in the ecosystem responses over time and determine the controls that govern those changes. Third, identify results of the experiment that may generalize to other coniferous forests around the world. The results show that N fertilization causes ecosystem effects in Loch Vale which vary over time and space due to the influence of hypothesized controlling factors such as soil moisture, pH, and plant uptake of N. The results of the Loch Vale experiment suggest that impacts of excess N on boreal forests may include increased plant growth where soil moisture is adequate, but when coupled with drought may lead to increased rates of nitrification, N mineralization, NO3- leaching, and soil acidification.
Open Access
Tracking the impact of wildfire on the soil microbiome across temporal scales
(Colorado State University. Libraries, 2024) Nelson, Amelia Rose, author; Wilkins, Michael J., advisor; Hall, Ed, committee member; Borch, Thomas, committee member; Rhoades, Charles, committee member; Wrighton, Kelly, committee member
As climate change progresses, the western United States is experiencing shifting wildfire behavior to more frequent and severe wildfires. Wildfires reduce soil microbial biomass and alter the soil microbiome community composition, selecting for "pyrophilous" microbial taxa with encoded traits that enable them to persist during wildfire or thrive in the soil thereafter. The soil microbiome is a key player in ecosystem carbon (C) cycling through the mediation of soil organic matter decomposition and stabilization. In addition to post-fire shifts in the soil microbiome, wildfire decreases soil C pools through combustion and alters C quality via fire-induced transformations to aromatic pyrogenic C (PyC). The intricate interplay between wildfire-induced alterations to soil microbiome composition and function, and subsequent ecosystem C cycling, remains poorly understood across different temporal and spatial scales. Leveraging multi-omics data alongside soil chemistry information (e.g., mass spectrometry) can offer insights into how shifting wildfire behavior may influence microbially mediated C cycling in forest ecosystems across the western US. To address this knowledge gap, I developed an extensive multi-omic dataset from burned Colorado subalpine coniferous forest soils collected over time (spanning 1 to 60 years following burning) and disturbance severity (low and high fire severity). This dataset includes 108 metagenomes and 12 metatranscriptomes, resulting in 1651 metagenome-assembled genomes (MAGs) that represent many of the dominant putative pyrophilous taxa previously identified in compositional studies. This dissertation presents the key findings derived from this comprehensive dataset, with the primary goal of addressing how wildfire impacts the soil microbiome with a focus on microbial interactions with soil C. Chapter 1 serves as a comprehensive literature review, providing an overview of prior research relevant to the research presented thereafter. It underscores the timely relevance of this dissertation research by examining how wildfire behavior is shifting globally with climate change and anthropogenic forcing. Given the critical role of forest ecosystems as significant global C sinks, understanding the repercussions of wildfires on ecosystem biogeochemistry is imperative. I broadly summarize previous research regarding severe wildfire impacts to soils and the soil microbiome and focus on existing knowledge gaps regarding the function of the post-wildfire soil microbiome across differing burn severities and time since fire. In Chapter 2, I characterize how burn severity impacts the soil microbiome one year post-fire in Colorado (CO) subalpine coniferous forests using soil samples collected in July 2019 from within the 2018 Ryan and Badger Creek fire burn scars that represent a burn severity gradient (control, low, moderate, and high severity burned soils). I used a suite of tools to understand both the impacts to soil chemistry and the soil microbiome, including Fourier-transform ion cyclotron resonance mass spectrometry (FTICR-MS) to characterize dissolved soil organic matter, 16S rRNA gene and ITS amplicon sequencing for soil microbiome composition, and coupled metagenomics and metatranscriptomics to identify shifts in soil microbial functional potential. The combination of these tools allowed me to characterize the entire soil microbiome, including bacteria, fungi, and viruses. From metagenomic sequencing, I recovered 637 MAGs, 1982 unique DNA and RNA viral populations, and 2 fungal genomes from low and high severity burned soil samples. I broadly found that Actinobacteria dominated the fraction of enriched and active bacterial taxa within high severity surficial soils and exhibited traits (e.g., heat resistance, fast growth, expression of genes for degrading aromatic PyC) that enabled them to survive the soil heating and thrive after the disturbance. Ectomycorrhizal fungi (EMF), key symbionts of coniferous trees and other plant taxa, were depleted in severely burned soils. Lastly, there were abundant viruses targeting dominant Actinobacteria MAGs that likely played important roles in assembly of the post-wildfire soil microbiome and serve as top-down controls of C cycling within the system. Overall, this study served as a holistic and comprehensive snapshot of the post-wildfire soil microbiome at one point in time and laid the foundation for forming hypotheses and guiding the subsequent studies. Building upon the groundwork laid in Chapter 2, Chapter 3 broadly evaluates the relative importance of putative pyrophilous traits identified between one year and 11 years following wildfire. Additionally, I explored the applicability of other proposed conceptual life history strategy frameworks (e.g., Y-A-S framework) in defining post-wildfire soil microbial dynamics. I utilized a series of soil samples collected from a chronosequence of CO wildfire burn scars representing 1, 3, 5, and 11 years following low- and high-severity wildfire. Using genome-resolved metagenomic approaches and combining this newly generated MAG catalog with the MAGs reconstructed from sequencing in Chapter 1 resulted in a total of 825 bacterial MAGs. Again, this dataset was coupled to various soil chemistry datasets, microbial biomass measurements (via PLFA), and marker gene sequencing data. I found that the potential for fast growth was an important bacterial trait driving dominance in the post-wildfire soil microbiome for up to approximately 11 years post-fire. Moreover, I observed that MAGs investing in traits aimed at acquiring diverse resources from the external environment often dominated severely burned soils, aligning with the 'A' strategy outlined in the Y-A-S framework. These insights suggest that microbial trait profiles play a pivotal role in shaping post-wildfire soil microbial successional dynamics. Furthermore, the study marks a significant step towards unraveling how trait-based frameworks can offer valuable insights into post-disturbance microbial ecology. In Chapter 4, the focus shifts to investigating one of the most extreme scenarios that can occur in a terrestrial ecosystem with severe wildfire: a burning-induced aboveground vegetation shift. Pile burning is a common fuel reduction or site preparation practice wherein logging residue is burned on the forest floor and, because of the high soil temperatures often reached during pile burning, can serve as a surrogate for studying impacts to soil caused by severe wildfire. Following clear-cut harvesting, pile burning can lead to the creation of persistence openings dominated by herbaceous plants within successfully regenerating conifer forest. In this study, a paired 60-year chronosequence of burn scar openings and surrounding forests that regenerated after clear-cut harvesting provided a unique opportunity to study soil microbiome changes associated with two distinct ecosystem development trajectories (i.e., burning-induced aboveground vegetation shift, regenerating coniferous forest). The primary objective was to identify whether the belowground soil microbiome exhibited resilience to a disturbance-induced aboveground vegetation shift. I collected soils from the aforementioned chronosequence and interrogated soil microbiome composition (via marker gene sequencing), functional potential (via metagenomics), and function (via laboratory incubations). There were compositional shifts in the soil microbiome that mirrored the ongoing aboveground vegetation shifts, with short-term changes to microbial community composition and C cycling functionality closely resembling a post-wildfire soil microbiome (e.g., PyC degradation). However, over the six-decade chronosequence the soil microbiome composition and function both displayed resilience, converging with that of the surrounding regenerating forest. This final research chapter extended the findings from the previous studies by exploring the longevity of wildfire impact to the soil microbiome in the extreme case of a burning-induced aboveground vegetation shift. The final chapter (Chapter 5) summarizes the key findings of this doctoral research and discusses potential research implications and applications along with future research directions and remaining knowledge gaps. In summary, the aims of this dissertation research were to identify how burn severity influences the soil microbiome composition and function one year post-fire (Chapter 2), assess the longevity of these impacts and the applicability of conceptual traits-based frameworks to the post-fire soil microbiome (Chapter 3), and evaluate the resilience of the belowground soil microbiome to a burning-induced multidecadal aboveground vegetation shift (Chapter 4). This research significantly advances our understanding of the impacts of wildfires on crucial forest ecosystems, with a specific emphasis on ecosystem C cycling.

Browsing by Author "Rhoades, Charles, committee member"

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