About

Carrie Masiello is the W. Maurice Ewing Professor of Biogeochemistry in the Earth, Environmental and Planetary Sciences Department at Rice University. She is also a Professor of Chemistry and Biosciences and serves as the Director of the Sustainability Institute. Her research focuses on developing new tools to understand the processes that control carbon, nitrogen, and water fluxes through the Earth system. Her theoretical work includes creating new methods to measure the physical and chemical properties of the Earth, as well as applying synthetic biology to Earth system questions. Her applied research utilizes these tools to investigate greenhouse gas removal processes, with particular emphasis on water, energy, agriculture, and marine processes. Additionally, her group collaborates with the Baker Institute for Public Policy on carbon market development. Dr. Masiello holds a B.A. in Physics and Mathematics from Earlham College, an M.S. in Environmental Science from the University of North Carolina, Chapel Hill, and a Ph.D. in Earth System Science from the University of California, Irvine. She has been recognized as a Fellow of the Geological Society of America and received the Hamill Innovation Award from Rice University.

Research topics

• Ecology
• Chemistry
• Biology
• Computer Science
• Engineering
• Organic chemistry
• Economics
• Agronomy
• Natural resource economics
• Pharmacology
• Data science
• Environmental science
• Botany
• Computational biology
• Waste management
• Biochemical engineering
• Environmental chemistry
• Nanotechnology

Selected publications

• Changes in Pyrogenic Tracers Over the Last 15,000 Years in the Congo River Catchment Through Multi‐Method Analysis

  Journal of Geophysical Research Biogeosciences · 2025-09-28 · 2 citations

  articleOpen access

  Abstract Black carbon (BC), the most recalcitrant part of the pyrogenic carbon continuum, is formed by the incomplete combustion of biomass and fossil fuels. Methods for detecting BC include the chemical degradation of condensed aromatic compounds into benzenepolycarboxylic acids (BPCA), chemothermal oxidation of organic carbon at 375°C (CTO), 13 C nuclear magnetic resonance combined with a molecular mixing model, thermogravimetry‐differential scanning calorimetry, and the use of polycyclic aromatic hydrocarbons as tracers. However, there is limited knowledge about the comparability of these methods in marine sediments and their suitability as wildfire proxies. Here, we examined a sediment core from the Congo River outflow using a multi‐methodological approach with environmental data and proxies to assess pyrogenic tracers from the Congo River basin over the last 15,000 years and determine commonalities between the methods. Despite differing analytical windows, both dry‐weight and total organic carbon concentrations, and δ 13 C values for most methods showed a congruous trend. Higher BC concentrations and higher δ 13 C values were present during arid periods and lower during humid periods, reflecting changes in vegetation and terrestrial organic matter inputs. For all methods, the sedimentation flux identified significant variations in BC deposition only in the last 1,000 years BP due to anthropogenic land use changes. These findings deepen our understanding of BC in the global carbon cycle and show that BC proxies can reveal distinct transport pathways, with CTO‐BC representing atmospheric deposition and BPCA‐BC and NMR‐BC indicating fluvial inputs to coastal margins, aiding in the reconstruction of past climates and landscapes.

  PublisherDOI

• Effects of matric versus osmotic potential changes on <i>Variovorax beijingensis</i> transcription

  bioRxiv (Cold Spring Harbor Laboratory) · 2025-06-25

  preprintOpen access

  ABSTRACT Soil microbes must continuously adapt to changes in water availability, which dynamically fluctuates with weather and irrigation, and these adaptations are closely linked to soil CO 2 emissions. Soil water potential, which regulates microbe-available water, is controlled by both osmotic and matric potential, which both increase as soils dry. While both parameters can independently increase water potential, the genetic mechanisms underlying microbial responses to both are unknown, with potentially different mechanisms available for soil microbes to respond to these hydrologic parameters. To explore microbial responses to matric versus osmotic potential shifts, we evaluated the growth and transcription of Variovorax beijingensis in soils and liquid cultures of varying water potential. We find this microbe respires in dilute minimal medium (-240 ±104 kPa), in liquid medium supplemented with sucrose (-1323 ±20.8 kPa), and in a pair of matrices that span a similar range of pressures (-183 ±55 and -1393 kPa ±200 kPa). We show that the global gene expression patterns vary significantly across all four conditions, even when the matric potential and osmotic pressure are set to similar values. However, the direction of gene expression changes correlated for 68% of the transcripts arising from an increase in osmotic pressure within liquid medium and an increase in matric potential within the different soils. While a large overlap was observed in the Variovorax transcriptional response to shifts in both osmotic and matric potential, the responses were not identical, with matric potential shifts leading to 2.55-fold more genes exhibiting differential expression. IMPORTANCE It remains hard to establish how changes in soil water properties affect microbial behaviors that regulate soil health, and the energy with which soil water is held is likely a holistic control on at least some of those microbial behaviors. This energy is controlled by parameters associated with soil saltiness (osmotic potential) and texture (matric potential), which both alter bioavailable water by contributing to total soil water potential. To investigate how the global transcriptional profile of a soil microbe changes when the microbe-available water is altered either by changing soil texture or by changing osmolyte concentrations, we varied osmotic and matric potential individually and performed RNA sequencing. We observe differences in the transcriptome across all conditions analyzed. A larger number of genes are differentially expressed as matric potential increases; however, many of the transcripts differentially expressed as osmotic pressure increases covary with those observed as the matrix potential increases.

  PublisherOA PDFDOI

• A roadmap to understanding and anticipating microbial gene transfer in soil communities

  Microbiology and Molecular Biology Reviews · 2025-04-08 · 15 citations

  reviewOpen access

  SUMMARY Engineered microbes are being programmed using synthetic DNA for applications in soil to overcome global challenges related to climate change, energy, food security, and pollution. However, we cannot yet predict gene transfer processes in soil to assess the frequency of unintentional transfer of engineered DNA to environmental microbes when applying synthetic biology technologies at scale. This challenge exists because of the complex and heterogeneous characteristics of soils, which contribute to the fitness and transport of cells and the exchange of genetic material within communities. Here, we describe knowledge gaps about gene transfer across soil microbiomes. We propose strategies to improve our understanding of gene transfer across soil communities, highlight the need to benchmark the performance of biocontainment measures in situ , and discuss responsibly engaging community stakeholders. We highlight opportunities to address knowledge gaps, such as creating a set of soil standards for studying gene transfer across diverse soil types and measuring gene transfer host range across microbiomes using emerging technologies. By comparing gene transfer rates, host range, and persistence of engineered microbes across different soils, we posit that community-scale, environment-specific models can be built that anticipate biotechnology risks. Such studies will enable the design of safer biotechnologies that allow us to realize the benefits of synthetic biology and mitigate risks associated with the release of such technologies.

  PublisherOA PDFDOI

• Environmentally Persistent Free Radicals in Biochar: Environmental Context and Future Research Needs

  Environmental Science & Technology · 2025-06-04 · 26 citations

  reviewSenior authorCorresponding

  Environmentally persistent free radicals (EPFRs) are produced during biochar pyrolysis and, depending on biochar application, can be either detrimental or beneficial. High levels of EPFRs may interfere with cellular metabolism and be toxic, because EPFR-generated reactive oxygen species (e.g., hydroxyl radicals (•OH)) attack organic molecules. However, •OH can be useful in remediating recalcitrant organic contaminants in soils. Understanding the (system-specific) safe range of EPFRs produced by biochars requires knowing both the context of their use and their overall significance in the existing suite of environmental radicals, which has rarely been addressed. Here we place EPFRs in a broader environmental context, showing that biochar can have EPFR concentrations from 108-fold lower to 109-fold higher than EPFRs from other environmental sources, depending on feedstock, production conditions, and degree of environmental aging. We also demonstrate that •OH radical concentrations from biochar EPFRs can be from 104-fold lower to 1017-fold higher than other environmental sources, depending on EPFR type and concentration, reaction time, oxidant concentration, and extent of environmental EPFR persistence. For both EPFR and •OH concentrations, major uncertainties derive from the range of biochar properties and the range of data reporting practices. Controlling feedstock lignin content and pyrolysis conditions are the most immediate options for managing EPFRs. Co-application of compost to provide organics may serve as a postpyrolysis method to quench and reduce biochar EPFRs.

  PublisherDOI

• Assessing Compost Carbon Permanence with Solid-State 13C NMR: Advancing Standards for Climate and Carbon Markets

  ChemRxiv · 2025-11-03

  articleSenior author

  Composted amendments provide an opportunity to sequester organic carbon in soil, contribute to a circular carbon and nutrient economy, reduce landfill waste, and enhance soil health. In some cases, carbon sequestered in soils through compost land applications may be creditable in carbon markets, bringing in revenue to producers as well. One key challenge in the push to incentivize composting through carbon markets is the difficulty in assessing long-term compost carbon permanence accurately, which is critical for pricing compost credits. In this study, we tested a range of commercially available compost samples from Texas and California using standard organic geochemical metrics for organic matter permanence derived from 13C solid-state NMR spectroscopy. The results show variability in compost carbon permanence as assessed by this tool, suggesting that NMR may provide markets with finer resolution information for price setting. One potential uncertainty in NMR assessments of compost carbon permanence is the use of bulking agents in the composting process. Overall, however, 13C solid state NMR offers advantages over traditional California compost maturity tests by enabling standardized maturity indices and more robust quantification of long-term carbon sequestration.

  PublisherDOI

• Assessing Variability in Compost Decomposition using 13C NMR for Carbon Market Integration

  2025-10-29

  articleOpen accessSenior author

  Community composting can significantly reduce CO2 and CH4 emissions in cities, presenting a promising avenue for expanding participation in carbon markets. Traditionally, carbon crediting projects have been tied to land ownership and the land usage preferences of landowners. By integrating sustainability initiatives such as community composting into carbon markets, urban residents can contribute to climate solutions by generating carbon credits and receive financial benefits for their efforts. However, compost production varies widely within the United States because many states lack any standardization as to the feedstock or treatment processes. This lack of consistency in compost production creates issues for carbon credit accreditation. To best understand the value of compost in carbon markets, we have assessed the organic geochemistry of compost via solid-state 13C NMR. Here we find a large range in the degree of decomposition of products marketed in Texas and California as “compost.” This variation has implications for the integrity of compost trading on carbon markets. Inconsistency in decomposition could hinder the scalability and trustworthiness of compost as a carbon credit, making it challenging to establish uniform standards and pricing. Therefore, developing standardized guidelines for compost production and quality assessment is essential for enhancing the reliability and marketability of compost in carbon markets.

  PublisherOA PDFDOI

• Mechanisms of soil carbon preservation illuminated by model mineral-associated organic matter

  bioRxiv (Cold Spring Harbor Laboratory) · 2025-12-13

  preprintOpen access

  Abstract A central control on atmospheric CO 2 is the stabilization of organic carbon in soils. While there are well-described properties associated with stable soil carbon, such as interactions with minerals and conserved chemical features, determining the mechanisms underlying these properties is challenged by soil complexity and heterogeneity. Here we synthesize a naturally complex, tunable model form of mineral-associated organic matter (LabMAOM) to explore mechanisms of stable soil carbon formation and persistence. We show that mineral association and ambient organic matter synergistically stabilize LabMAOM against microbial decomposition. Moreover, different starting compositions of organic matter yield a conserved final LabMAOM chemical composition consistent with natural soils. Our findings open new mechanistic understanding of stable soil carbon and will be of utility to climate modeling and soil health management.

  PublisherDOI

• Beyond the Bench: Contextualizing the Impacts of Char Redox Properties on Biogeochemical Cycling and Microbial Ecosystem Services

  Environmental Science & Technology · 2025-01-07 · 6 citations

  review

  The electrochemical properties of chars have been recently described, positioning chars as active participants in microbial redox processes through functional groups, aromatic structures, redox-active metals, and radicals. While bench-scale studies have advanced mechanistic understanding of char's behavior and potential effects, translating these findings to complex ecosystems remains challenging. This is mainly due to the complexities of microbial communities and the unique properties of various ecosystems. Factors like char aging and patina formation, and environmental parameters including oxygen and moisture availability, pH, and organic matter content can significantly affect char electrochemical properties and microbial interactions. This highlights the need for a broader understanding of char redox processes to predict and effectively manage unintended environmental impacts or enhance beneficial effects. Long-term monitoring of complex systems amended with char is also needed to determine whether char accumulation has long-term redox effects on microbial ecosystem services, including biogeochemical cycling. Predictive understanding of these processes would inform the production of chars to enhance beneficial processes such as increased soil productivity, and provide new opportunities for engineered environmental remediation. Here, we summarize how char redox properties affect well-defined microbial systems and discuss key factors that determine whether the effects of char redox properties are enhanced or attenuated in complex systems. We also identify critical knowledge gaps about chars' role in microbial redox processes that are important for environmental sustainability and postulate that managing char's redox properties, such as electron donating, accepting, or conducting ability, is an emerging opportunity to influence microbial ecosystem services.

  PublisherDOI

• Effects of matric vs osmotic potential changes on <i>Variovorax beijingensis</i> transcription

  mSystems · 2025-10-02 · 1 citations

  articleOpen access

  ABSTRACT Soil water potential, which regulates microbe-available water, is controlled by osmotic and matric potential, which both become more negative as soils dry. While both parameters can independently alter water potential, the genetic mechanisms underlying microbial responses to both are unknown, with potentially different mechanisms available for microbes to respond to these hydrological parameters. To explore microbial responses to matric vs osmotic potential shifts independently, we evaluated the growth and transcription of Variovorax beijingensis in soils and liquid cultures of varying water potential. We found that this microbe respires in dilute minimal medium (−240 ± 104 kPa), in liquid medium containing sucrose (−1,323 ± 21 kPa), and in matrices that span a similar pressure range (−183 ± 55 and −1,393 ± 200 kPa). We show that the global gene expression patterns vary significantly across these four conditions, even when the matric potential and osmotic pressure are set to similar values. However, 68% of the differentially expressed genes (DEGs) observed when transitioning osmotic pressure in liquid medium from −240 to −1,323 kPa were also observed when transitioning matric potential from −183 to −1,393 kPa. As osmotic and matric potential approached the plant wilting point, both presented DEGs implicated in amino acid, betaine, and energy metabolism, as well as plant-growth promotion. While a large overlap was observed in the Variovorax transcriptional response to shifts in both osmotic and matric potential, the responses were not identical, with matric potential shifts leading to 2.55-fold more genes exhibiting differential expression. IMPORTANCE It remains hard to establish how changes in soil water properties affect microbial behaviors that regulate soil health, and the energy with which soil water is held is likely a holistic control on at least some of those microbial behaviors. This energy is controlled by parameters associated with soil salinity (osmotic potential) and texture (matric potential), which both alter bioavailable water by contributing to total soil water potential. To investigate how the transcription of a soil microbe changes when the microbe-available water is altered either by changing soil texture or by changing osmolyte concentrations, we varied osmotic and matric potential individually and performed RNA sequencing. We observe differences in the transcriptome across all conditions analyzed. However, a large set of genes presented similar gene expression changes when osmotic and matric potential approached the plant wilting point, suggesting that these transcriptional changes are independent of the mechanism that alters soil water potential.

  PublisherDOI

• Biochar effects on water availability

  2024-04-12 · 2 citations

  book-chapterSenior author

  Biochar soil application can significantly increase soil water retention and availability. Understanding the biochar-soil interactions that result in soil water improvements and optimizing them will help the biochar community deliver reliable benefits to farmers, ranchers, and urban land managers. This chapter discusses (i) biochar effects on fundamental soil water properties including field capacity, permanent wilting point, plant available water, and microbially available water; (ii) how biochar properties (e.g., biochar intrapore volume, pore size distribution, hydrophobicity, particle size), management practices (e.g., biochar application rate), and soil properties (e.g., soil texture and aggregation) affect biochar performance in improving soil water properties, and (iii) gaps in our knowledge and recommendations for further research to guide us to select and apply biochar with desired properties to increase soil water availability.

  PublisherDOI

Recent grants

• The Effect of Charcoal on Soil Hydrologic Properties Under Natural and Elevated Concentrations

  NSF · $270k · 2010–2015

• The Effects of Land Use Change on the Oxidative Ratio of the Terrestrial Biosphere

  NSF · $400k · 2006–2011

• Early Career: Acquisition of Shared, Basic Biogeochemistry Lab Facilities at Rice University

  NSF · $100k · 2010–2014

• Assessing the Impact of Developing-World Land Use on Riverine Organic Carbon Delivery to the Ocean

  NSF · $389k · 2009–2013

Frequent coauthors

• William C. Hockaday

  Baylor University

  67 shared

• Jonathan J. Silberg

  Rice University

  26 shared

• M. E. Gallagher

  25 shared

• Xiaodong Gao

  22 shared

• Ilenne Del Valle

  17 shared

• T. R. Filley

  17 shared

• Brenda B. Bowen

  University of Utah

  16 shared

• Brandon Dugan

  Colorado School of Mines

  16 shared

Education

• Ph.D., Earth System Science

  University of California Irvine

  1999

• M.S., Chemistry

  University of California Irvine

  1996

• M.S., Environmental Science and Engineering

  University of North Carolina at Chapel Hill

  1993

• B.A., Math, Physics

  Earlham College

  1991

Awards & honors

• Fellow, Geological Society of America (2017)
• Hamill Innovation Award, Rice University/Hamill Foundation (…
• American Fellow, AAUW (2002-2003)