Research Interests
As a microbial ecologist turned biogeochemist, I am broadly interested in the link between above- and belowground processes. Understanding the connectivity between these two systems is a critical component of our ability to predict the response of ecosystems to global climate change. Through my research, I hope to carve out a niche for myself by pursuing questions that lay at the intersection of the fields of biogeochemistry, microbial ecology, and physiological plant ecology.
As a microbial ecologist turned biogeochemist, I am broadly interested in the link between above- and belowground processes. Understanding the connectivity between these two systems is a critical component of our ability to predict the response of ecosystems to global climate change. Through my research, I hope to carve out a niche for myself by pursuing questions that lay at the intersection of the fields of biogeochemistry, microbial ecology, and physiological plant ecology.
Linking rhizosphere and phyllosphere microbial communities to physiological plant ecology
Recently, I have launched a new line of investigation that seeks to understand the linkage between rhizosphere and phyllosphere microbial communities and physiological plant ecology. As with the human microbiome, we are just now beginning to understand the associations between microbes and their plant hosts. Research in this area is still in its infancy, especially for plants outside of agricultural settings. An example of research that I am interested in pursuing in this area comes from the high elevation spruce-fir forests of North Carolina where fog is a common occurrence. Researchers in the W.K. Smith lab (Wake Forest University) have demonstrated the importance of fog in the water balance of trees in these forests, but I have often wondered if atmospheric nitrogen deposition associated with this fog could provide a nitrogen subsidy to a plant at the leaf-level. A key component of this would be the identification of N-fixing microbes associated with plant leaf tissue, which could be addressed utilizing a combination of culture-dependent and independent (e.g. high-throughput sequencing) techniques. High elevation spruce-fir forests are N limited ecosystems, and demand for N is especially high at the leaf-level. Thus, N-fixing microorganisms associated with the phyllosphere community of a leaf would link N supply to demand. As such, characterization of the plant microbiome could provide additional insight into successful ecophysiological strategies by further elucidating the mechanisms that plants adopt to occupy a niche within a given environment. This project is conducted at Roan Mountain, North Carolina/Tennesse in collaboration with W.K. Smith, Scott Cory, Hannah Schleupner, and S.L. Bräuer.
Recently, I have launched a new line of investigation that seeks to understand the linkage between rhizosphere and phyllosphere microbial communities and physiological plant ecology. As with the human microbiome, we are just now beginning to understand the associations between microbes and their plant hosts. Research in this area is still in its infancy, especially for plants outside of agricultural settings. An example of research that I am interested in pursuing in this area comes from the high elevation spruce-fir forests of North Carolina where fog is a common occurrence. Researchers in the W.K. Smith lab (Wake Forest University) have demonstrated the importance of fog in the water balance of trees in these forests, but I have often wondered if atmospheric nitrogen deposition associated with this fog could provide a nitrogen subsidy to a plant at the leaf-level. A key component of this would be the identification of N-fixing microbes associated with plant leaf tissue, which could be addressed utilizing a combination of culture-dependent and independent (e.g. high-throughput sequencing) techniques. High elevation spruce-fir forests are N limited ecosystems, and demand for N is especially high at the leaf-level. Thus, N-fixing microorganisms associated with the phyllosphere community of a leaf would link N supply to demand. As such, characterization of the plant microbiome could provide additional insight into successful ecophysiological strategies by further elucidating the mechanisms that plants adopt to occupy a niche within a given environment. This project is conducted at Roan Mountain, North Carolina/Tennesse in collaboration with W.K. Smith, Scott Cory, Hannah Schleupner, and S.L. Bräuer.
Plants and Methane: The Role of Vegetation in the Atmospheric Flux of Trace Greenhouse Gases
Methane is the most abundant non-CO2 greenhouse gas in the atmosphere today and has contributed ca. 25% of the total climate forcing over the past 250+ years. The annual flux of methane to the atmosphere is fairly well constrained, estimated ca. 500-600 Tg CH4/yr. Major sources of this flux (both natural and anthropogenic) have been identified, but there is room within this flux estimate to accommodate an additional source/re-evaluation of a known source-strength in the range of 50-100 Tg CH4/yr. Of all the natural sources of methane emissions that have been identified, the contribution of vegetation to the global flux of methane is arguably the least well understood. Prior research has established the roles of 1) live herbaceous and woody vegetation and 2) dead herbaceous vegetation in the atmospheric flux of methane from wetlands. However, the role of dead woody vegetation in the annual flux of methane to the atmosphere from wetlands has not yet been resolved. Because of the substantial role that methane plays as a contributor to global warming, it is essential to gain a better understanding of the sources (and sinks) of this powerful greenhouse gas.
My dissertation research identified standing dead trees as a previously unrecognized pathway for the atmospheric flux of CH4 and CO2 from wetlands. Moving forward, I have continued along this line of investigation to better elucidate the abiotic and biotic controls on the magnitude and direction of fluxes, the mechanisms that induce fluxes from standing dead vegetation, and the importance of this pathway at the landscape level. This last question is particularly relevant as stressors associated with global climate change (i.e. sea level rise, saltwater incursion, and extreme episodic events) are already leading to the conversion of large swaths of coastal forested wetlands to ghost forest landscapes, increasing the spatial footprint of standing dead trees in coastal landscapes and the quantitative importance of this pathway in the annual flux of CH4 and CO2 to the atmosphere.
The primary field site for this study is the Timberlake Observatory for Wetland Restoration (in collaboration with M. Ardón, E. Bernhardt, and A. Helton) in Tyrrell County, North Carolina. My lab has also conducted some recent work at Gull Rock Game Land in Hyde County, North Carolina. Funding for this project has been provided by The Garden Club of America (Wetlands Scholarship), The Wetland Foundation, the Wake Forest University Department of Biology (Vecellio Award for Graduate Student Research), through an American Fellowship from the American Association of University Women, and through a Hollins University Faculty-Student IMPACT Grant.
Methane is the most abundant non-CO2 greenhouse gas in the atmosphere today and has contributed ca. 25% of the total climate forcing over the past 250+ years. The annual flux of methane to the atmosphere is fairly well constrained, estimated ca. 500-600 Tg CH4/yr. Major sources of this flux (both natural and anthropogenic) have been identified, but there is room within this flux estimate to accommodate an additional source/re-evaluation of a known source-strength in the range of 50-100 Tg CH4/yr. Of all the natural sources of methane emissions that have been identified, the contribution of vegetation to the global flux of methane is arguably the least well understood. Prior research has established the roles of 1) live herbaceous and woody vegetation and 2) dead herbaceous vegetation in the atmospheric flux of methane from wetlands. However, the role of dead woody vegetation in the annual flux of methane to the atmosphere from wetlands has not yet been resolved. Because of the substantial role that methane plays as a contributor to global warming, it is essential to gain a better understanding of the sources (and sinks) of this powerful greenhouse gas.
My dissertation research identified standing dead trees as a previously unrecognized pathway for the atmospheric flux of CH4 and CO2 from wetlands. Moving forward, I have continued along this line of investigation to better elucidate the abiotic and biotic controls on the magnitude and direction of fluxes, the mechanisms that induce fluxes from standing dead vegetation, and the importance of this pathway at the landscape level. This last question is particularly relevant as stressors associated with global climate change (i.e. sea level rise, saltwater incursion, and extreme episodic events) are already leading to the conversion of large swaths of coastal forested wetlands to ghost forest landscapes, increasing the spatial footprint of standing dead trees in coastal landscapes and the quantitative importance of this pathway in the annual flux of CH4 and CO2 to the atmosphere.
The primary field site for this study is the Timberlake Observatory for Wetland Restoration (in collaboration with M. Ardón, E. Bernhardt, and A. Helton) in Tyrrell County, North Carolina. My lab has also conducted some recent work at Gull Rock Game Land in Hyde County, North Carolina. Funding for this project has been provided by The Garden Club of America (Wetlands Scholarship), The Wetland Foundation, the Wake Forest University Department of Biology (Vecellio Award for Graduate Student Research), through an American Fellowship from the American Association of University Women, and through a Hollins University Faculty-Student IMPACT Grant.
The Biogeochemical Impacts of Saltwater Incursion on Coastal Freshwater Forested Wetlands
Wetlands provide critical ecosystem services that are becoming increasingly threatened by climate-change related stressors. Of particular issue in the low-lying coastal plains of North Carolina is the threat of saltwater incursion, the landward movement of saline water. Driving forces of incursion events include a variety of natural and anthropogenic-induced factors, most notably sea level rise, drought, and changes in the hydraulic head associated with groundwater depletion. Coastal freshwater systems are disproportionately impacted by incursion events, as changes in water chemistry associated with the influx of seawater impact both above- and belowground processes. As a part of my dissertation work, I examined how changes in soil biogeochemical processes as a result of saltwater incursion impact the ecophysiology of Taxodium distichum (bald cypress), a foundational species in coastal freshwater forested wetlands. As a part of this project, we investigated the sensitivity of this species to incursion events and worked to establish a baseline ecophysiological profile of mature individuals throughout the growing season. This line of research has led me to a new interest in developing the field of restoration ecophysiology, which seeks to understand how traditional techniques from physiological plant ecology can be incorporated within the restoration framework to assist in restoration planning and improve long-term restoration monitoring efforts. The primary field site for this study was the Timberlake Observatory for Wetland Restoration (in collaboration with M. Ardón and E. Bernhardt) in Tyrrell County, North Carolina. Funding for this project was provided by the Wake Forest University Department of Biology (Vecellio Award for Graduate Student Research) and through a North Carolina Sea Grant (NOAA).
Wetlands provide critical ecosystem services that are becoming increasingly threatened by climate-change related stressors. Of particular issue in the low-lying coastal plains of North Carolina is the threat of saltwater incursion, the landward movement of saline water. Driving forces of incursion events include a variety of natural and anthropogenic-induced factors, most notably sea level rise, drought, and changes in the hydraulic head associated with groundwater depletion. Coastal freshwater systems are disproportionately impacted by incursion events, as changes in water chemistry associated with the influx of seawater impact both above- and belowground processes. As a part of my dissertation work, I examined how changes in soil biogeochemical processes as a result of saltwater incursion impact the ecophysiology of Taxodium distichum (bald cypress), a foundational species in coastal freshwater forested wetlands. As a part of this project, we investigated the sensitivity of this species to incursion events and worked to establish a baseline ecophysiological profile of mature individuals throughout the growing season. This line of research has led me to a new interest in developing the field of restoration ecophysiology, which seeks to understand how traditional techniques from physiological plant ecology can be incorporated within the restoration framework to assist in restoration planning and improve long-term restoration monitoring efforts. The primary field site for this study was the Timberlake Observatory for Wetland Restoration (in collaboration with M. Ardón and E. Bernhardt) in Tyrrell County, North Carolina. Funding for this project was provided by the Wake Forest University Department of Biology (Vecellio Award for Graduate Student Research) and through a North Carolina Sea Grant (NOAA).
Geomicrobiology of Ferromanganese Deposits in Caves of the upper Tennessee River Basin
It is widely recognized within the scientific community that the search for extraterrestrial life begins with sound scientific knowledge regarding Earth’s systems that are analogous to Mars, the current focus of NASA’s exobiology program. Insight into the current limits of life on Earth and the biosignatures of the microbial life that inhabit these environments is the keystone in answering fundamental questions concerning the origin, existence, and future of life in the Universe. Caves provide an ideal milieu in which to study these questions as they represent a transition zone from surface to subsurface based ecosystems and contain biogeochemical cycles similar to those hypothesized to occur on Mars.
The southern Appalachians represent one of the most cave-dense terrains in the continental United States: of the 50,000 cave systems known to exist in the United States, ca. 14% occur within the state of Tennessee. Despite the abundance of cave systems in the Appalachians, relatively little is known regarding the organisms that inhabit the subterranean realm therein. My Masters research, in collaboration with S.L. Bräuer and S.K. Carmichael in the Geomicrobiology Research Group at Appalachian State University, represented the first characterization of the geomicrobiology of southern Appalachian cave systems created by the process of carbonic acid speleogenesis. We utilized culture-dependent and independent techniques to characterize ferromanganese (mixed Fe and Mn) deposits in caves of the upper Tennessee River Basin. Our work documented the diversity of Mn(II)-oxidizing organisms that are responsible for the formation of these deposits and provided new insights regarding the biogeochemical impacts of anthropogenic pollution in these subterranean systems. Funding for this project was provided by the Appalachian State University Office of Student Research, the National Science Foundation, and through a North Carolina Space Grant Graduate Research Fellowship (NASA).
It is widely recognized within the scientific community that the search for extraterrestrial life begins with sound scientific knowledge regarding Earth’s systems that are analogous to Mars, the current focus of NASA’s exobiology program. Insight into the current limits of life on Earth and the biosignatures of the microbial life that inhabit these environments is the keystone in answering fundamental questions concerning the origin, existence, and future of life in the Universe. Caves provide an ideal milieu in which to study these questions as they represent a transition zone from surface to subsurface based ecosystems and contain biogeochemical cycles similar to those hypothesized to occur on Mars.
The southern Appalachians represent one of the most cave-dense terrains in the continental United States: of the 50,000 cave systems known to exist in the United States, ca. 14% occur within the state of Tennessee. Despite the abundance of cave systems in the Appalachians, relatively little is known regarding the organisms that inhabit the subterranean realm therein. My Masters research, in collaboration with S.L. Bräuer and S.K. Carmichael in the Geomicrobiology Research Group at Appalachian State University, represented the first characterization of the geomicrobiology of southern Appalachian cave systems created by the process of carbonic acid speleogenesis. We utilized culture-dependent and independent techniques to characterize ferromanganese (mixed Fe and Mn) deposits in caves of the upper Tennessee River Basin. Our work documented the diversity of Mn(II)-oxidizing organisms that are responsible for the formation of these deposits and provided new insights regarding the biogeochemical impacts of anthropogenic pollution in these subterranean systems. Funding for this project was provided by the Appalachian State University Office of Student Research, the National Science Foundation, and through a North Carolina Space Grant Graduate Research Fellowship (NASA).
Cave Microbial Consortia as a Reservoir for the Discovery of Novel Antibiotic Compounds
The recent rise of multi-drug resistant organisms (MDROs), combined with a steady decrease in antibiotic development by pharmaceutical companies over the past several years, has led to a concurrent increase in bioprospecting, the search for novel antibiotic and/or pharmaceutical compounds in the environment. Efforts in this realm often focus on the study of rare and extreme environments, such as caves, due to the relative degree of evolutionary isolation of these systems from surface communities. In collaboration with Amanda Strom, I investigated the diversity of antibiotic production genes in biofilms located within Carter Saltpeter Cave, Carter County, Tennessee. Specifically, we utilized 1) culture-based methods to isolate a diversity of strains of antibiotic-producing fungi and 2) molecular techniques to probe DNA extracted from cave biofilms for the presence of polyketide synthase (pks) genes and β-lactam biosynthesis genes, two suites of antibiotic production genes that are common among microorganisms. Our work was funded by a University Research Council grant from Appalachian State University.
The recent rise of multi-drug resistant organisms (MDROs), combined with a steady decrease in antibiotic development by pharmaceutical companies over the past several years, has led to a concurrent increase in bioprospecting, the search for novel antibiotic and/or pharmaceutical compounds in the environment. Efforts in this realm often focus on the study of rare and extreme environments, such as caves, due to the relative degree of evolutionary isolation of these systems from surface communities. In collaboration with Amanda Strom, I investigated the diversity of antibiotic production genes in biofilms located within Carter Saltpeter Cave, Carter County, Tennessee. Specifically, we utilized 1) culture-based methods to isolate a diversity of strains of antibiotic-producing fungi and 2) molecular techniques to probe DNA extracted from cave biofilms for the presence of polyketide synthase (pks) genes and β-lactam biosynthesis genes, two suites of antibiotic production genes that are common among microorganisms. Our work was funded by a University Research Council grant from Appalachian State University.
Recreational Facilities as Potential Reservoirs for Opportunistic and Human Pathogens
The human microbiome contains many species that are a part of the normal microflora of the skin, respiratory tract, oral cavity, and gastrointestinal tract that are considered to be opportunistic pathogens and could be transmitted from a host to another individual via direct or indirect contact. Recent outbreaks of multi-drug resistant organisms, such as methicillin-resistant Staphylococcus aureus (MRSA) in athletic facilities have increased public awareness of the potential risk of infection associated with the use of equipment at recreational facilities. However, research on the subject of pathogen transmission in recreational facilities has revealed contradictory findings despite the fact that 1) pathogens are known to persist on surfaces for several months and 2) high use surfaces, such as those associated with a gym/athletic facility, are known to be associated with an increase in the risk of transmission. In collaboration with S.L. Bräuer, D.H. Buckley, C. Pepe-Ranney, E. Rabinowitz, A. Strom, D. Vuono, and and S.H. Zinder, we utilized high-throughput sequencing of DNA extracted from swabs of hand-holds on rock climbing walls located in recreational facilities along the eastern seaboard to assess the potential for pathogen transmission in these environments. Results from this study provide some intriguing findings regarding the biogeography of the human microbiome.
The human microbiome contains many species that are a part of the normal microflora of the skin, respiratory tract, oral cavity, and gastrointestinal tract that are considered to be opportunistic pathogens and could be transmitted from a host to another individual via direct or indirect contact. Recent outbreaks of multi-drug resistant organisms, such as methicillin-resistant Staphylococcus aureus (MRSA) in athletic facilities have increased public awareness of the potential risk of infection associated with the use of equipment at recreational facilities. However, research on the subject of pathogen transmission in recreational facilities has revealed contradictory findings despite the fact that 1) pathogens are known to persist on surfaces for several months and 2) high use surfaces, such as those associated with a gym/athletic facility, are known to be associated with an increase in the risk of transmission. In collaboration with S.L. Bräuer, D.H. Buckley, C. Pepe-Ranney, E. Rabinowitz, A. Strom, D. Vuono, and and S.H. Zinder, we utilized high-throughput sequencing of DNA extracted from swabs of hand-holds on rock climbing walls located in recreational facilities along the eastern seaboard to assess the potential for pathogen transmission in these environments. Results from this study provide some intriguing findings regarding the biogeography of the human microbiome.