Browsing by Author "Gao, Xiaodong"
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Item Agroecosystem modeling of reactive nitrogen emissions from U.S. agricultural soils with carbon amendments(Springer Nature, 2023) Luo, Lina; Cohan, Daniel S.; Masiello, Caroline A.; Lychuk, Taras E.; Gao, XiaodongFertilizer-intensive agriculture is a leading source of reactive nitrogen (Nr) emissions that damage climate, air quality, and human health. Biochar has long been studied as a soil amendment, but its influence on Nr emissions remains insufficiently characterized. More recently, the pyrolysis of light hydrocarbons has been suggested as a source of hydrogen fuel, resulting in a solid zero-valent carbon (ZVC) byproduct whose impact on soil emissions has yet to be tested. We incorporate carbon amendment algorithms into an agroecosystem model to simulate emission changes in the year following the application of biochar or ZVC to the US. fertilized soils. Our simulations predicted that the impacts of biochar amendments on Nr emissions would vary widely (− 17% to + 27% under 5 ton ha−1 applications, − 38% to + 18% under 20 ton ha−1 applications) and depend mostly on how nitrification is affected. Low-dose biochar application (5 ton ha−1) stimulated emissions of all three nitrogen species in 75% of simulated agricultural areas, while high-dose applications (20 ton ha−1) mitigated emissions in 76% of simulated areas. Applying zero-valent carbon at 20 ton ha−1 exhibited similar effects on nitrogen emissions as biochar applications at 5 ton ha−1. Biochar amendments are most likely to mitigate emissions if applied at high rates in acidic soils (pH < 5.84) with low organic carbon (< 55.9 kg C ha−1) and inorganic nitrogen (< 101.5 kg N ha−1) content. Our simulations could inform where the application of carbon amendments would most likely mitigate Nr emissions and their associated adverse impacts.Item Artificial Soils Reveal Individual Factor Controls on Microbial Processes(American Society for Microbiology, 2022) Del Valle, Ilenne; Gao, Xiaodong; Ghezzehei, Teamrat A.; Silberg, Jonathan J.; Masiello, Caroline A.; Bioengineering; Biosciences; Chemical and Biomolecular Engineering; Chemistry; Earth, Environmental and Planetary SciencesSoil matrix properties influence microbial behaviors that underlie nutrient cycling, greenhouse gas production, and soil formation. However, the dynamic and heterogeneous nature of soils makes it challenging to untangle the effects of different matrix properties on microbial behaviors. To address this challenge, we developed a tunable artificial soil recipe and used these materials to study the abiotic mechanisms driving soil microbial growth and communication. When we used standardized matrices with varying textures to culture gas-reporting biosensors, we found that a Gram-negative bacterium (Escherichia coli) grew best in synthetic silt soils, remaining active over a wide range of soil matric potentials, while a Gram-positive bacterium (Bacillus subtilis) preferred sandy soils, sporulating at low water potentials. Soil texture, mineralogy, and alkalinity all attenuated the bioavailability of an acyl-homoserine lactone (AHL) signaling molecule that controls community-level microbial behaviors. Texture controlled the timing of AHL sensing, while AHL bioavailability was decreased ~105-fold by mineralogy and ~103-fold by alkalinity. Finally, we built artificial soils with a range of complexities that converge on the properties of one Mollisol. As artificial soil complexity increased to more closely resemble the Mollisol, microbial behaviors approached those occurring in the natural soil, with the notable exception of organic matter.Item Biochar and Microbial Signaling: Production Conditions Determine Effects on Microbial Communication(American Chemical Society, 2013) Masiello, Caroline A.; Chen, Ye; Gao, Xiaodong; Liu, Shirley; Cheng, Hsiao-Ying; Bennett, Matthew R.; Rudgers, Jennifer A.; Wagner, Daniel S.; Zygourakis, Kyriacos; Silberg, Jonathan J.; Bioengineering; Biosciences; Chemical and Biomolecular Engineering; Earth, Environmental and Planetary SciencesCharcoal has a long soil residence time, which has resulted in its production and use as a carbon sequestration technique (biochar). A range of biological effects can be triggered by soil biochar that can positively and negatively influence carbon storage, such as changing the decomposition rate of organic matter and altering plant biomass production. Sorption of cellular signals has been hypothesized to underlie some of these effects, but it remains unknown whether the binding of biochemical signals occurs, and if so, on time scales relevant to microbial growth and communication. We examined biochar sorption of N-3-oxo-dodecanoyl-L-homoserine lactone, an acyl-homoserine lactone (AHL) intercellular signaling molecule used by many gram-negative soil microbes to regulate gene expression. We show that wood biochars disrupt communication within a growing multicellular system that is made up of sender cells that synthesize AHL and receiver cells that express green fluorescent protein in response to an AHL signal. However, biochar inhibition of AHL-mediated cell–cell communication varied, with the biochar prepared at 700 °C (surface area of 301 m2/g) inhibiting cellular communication 10-fold more than an equivalent mass of biochar prepared at 300 °C (surface area of 3 m2/g). These findings provide the first direct evidence that biochars elicit a range of effects on gene expression dependent on intercellular signaling, implicating the method of biochar preparation as a parameter that could be tuned to regulate microbial-dependent soil processes, like nitrogen fixation and pest attack of root crops.Item Carbon sequestration potential and physicochemical properties differ between wildfire charcoals and slow-pyrolysis biochars(Springer Nature, 2017) Santín, Cristina; Doerr, Stefan H.; Merino, Agustin; Bucheli, Thomas D.; Bryant, Rob; Ascough, Philippa; Gao, Xiaodong; Masiello, Caroline A.Pyrogenic carbon (PyC), produced naturally (wildfire charcoal) and anthropogenically (biochar), is extensively studied due to its importance in several disciplines, including global climate dynamics, agronomy and paleosciences. Charcoal and biochar are commonly used as analogues for each other to infer respective carbon sequestration potentials, production conditions, and environmental roles and fates. The direct comparability of corresponding natural and anthropogenic PyC, however, has never been tested. Here we compared key physicochemical properties (elemental composition, δ13C and PAHs signatures, chemical recalcitrance, density and porosity) and carbon sequestration potentials of PyC materials formed from two identical feedstocks (pine forest floor and wood) under wildfire charring- and slow-pyrolysis conditions. Wildfire charcoals were formed under higher maximum temperatures and oxygen availabilities, but much shorter heating durations than slow-pyrolysis biochars, resulting in differing physicochemical properties. These differences are particularly relevant regarding their respective roles as carbon sinks, as even the wildfire charcoals formed at the highest temperatures had lower carbon sequestration potentials than most slow-pyrolysis biochars. Our results challenge the common notion that natural charcoal and biochar are well suited as proxies for each other, and suggest that biochar’s environmental residence time may be underestimated when based on natural charcoal as a proxy, and vice versa.Item Charcoal Disrupts Soil Microbial Communication through a Combination of Signal Sorption and Hydrolysis(American Chemical Society, 2016) Gao, Xiaodong; Cheng, Hsiao-Ying; Del Valle, Ilenne; Liu, Shirley; Masiello, Caroline A.; Silberg, Jonathan J.; Bioengineering; Biosciences; Earth, Environmental and Planetary SciencesThe presence of charcoal in soil triggers a range of biological effects that are not yet predictable, in part because it interferes with the functioning of chemical signals that microbes release into their environment to communicate. We do not fully understand the mechanisms by which charcoal alters the biologically available concentrations of these intercellular signals. Recently, charcoal has been shown to sorb the signaling molecules that microbes release, rendering them ineffective for intercellular communication. Here, we investigate a second, potentially more important mechanism of interference: signaling-molecule hydrolysis driven by charcoal-induced soil pH changes. We examined the effects of 10 charcoals on the bioavailable concentration of an acyl-homoserine lactone (AHL) used by many Gram-negative bacteria for cell–cell communication. We show that charcoals decrease the level of bioavailable AHL through sorption and pH-dependent hydrolysis of the lactone ring. We then built a quantitative model that predicts the half-lives of different microbial signaling compounds in the presence of charcoals varying in pH and surface area. Our model results suggest that the chemical effects of charcoal on pH-sensitive bacterial AHL signals will be fundamentally distinct from effects on pH-insensitive fungal signals, potentially leading to shifts in microbial community structures.Item Electrothermal mineralization of per- and polyfluoroalkyl substances for soil remediation(Springer Nature, 2024) Cheng, Yi; Deng, Bing; Scotland, Phelecia; Eddy, Lucas; Hassan, Arman; Wang, Bo; Silva, Karla J.; Li, Bowen; Wyss, Kevin M.; Ucak-Astarlioglu, Mine G.; Chen, Jinhang; Liu, Qiming; Si, Tengda; Xu, Shichen; Gao, Xiaodong; JeBailey, Khalil; Jana, Debadrita; Torres, Mark Albert; Wong, Michael S.; Yakobson, Boris I.; Griggs, Christopher; McCary, Matthew A.; Zhao, Yufeng; Tour, James M.Per- and polyfluoroalkyl substances (PFAS) are persistent and bioaccumulative pollutants that can easily accumulate in soil, posing a threat to environment and human health. Current PFAS degradation processes often suffer from low efficiency, high energy and water consumption, or lack of generality. Here, we develop a rapid electrothermal mineralization (REM) process to remediate PFAS-contaminated soil. With environmentally compatible biochar as the conductive additive, the soil temperature increases to >1000 °C within seconds by current pulse input, converting PFAS to calcium fluoride with inherent calcium compounds in soil. This process is applicable for remediating various PFAS contaminants in soil, with high removal efficiencies ( >99%) and mineralization ratios ( >90%). While retaining soil particle size, composition, water infiltration rate, and cation exchange capacity, REM facilitates an increase of exchangeable nutrient supply and arthropod survival in soil, rendering it superior to the time-consuming calcination approach that severely degrades soil properties. REM is scaled up to remediate soil at two kilograms per batch and promising for large-scale, on-site soil remediation. Life-cycle assessment and techno-economic analysis demonstrate REM as an environmentally friendly and economic process, with a significant reduction of energy consumption, greenhouse gas emission, water consumption, and operation cost, when compared to existing soil remediation practices.Item High-temperature electrothermal remediation of multi-pollutants in soil(Springer Nature, 2023) Deng, Bing; Carter, Robert A.; Cheng, Yi; Liu, Yuan; Eddy, Lucas; Wyss, Kevin M.; Ucak-Astarlioglu, Mine G.; Luong, Duy Xuan; Gao, Xiaodong; JeBailey, Khalil; Kittrell, Carter; Xu, Shichen; Jana, Debadrita; Torres, Mark Albert; Braam, Janet; Tour, James M.; NanoCarbon Center and the Rice Advanced Materials Institute; Smalley-Curl InstituteSoil contamination is an environmental issue due to increasing anthropogenic activities. Existing processes for soil remediation suffer from long treatment time and lack generality because of different sources, occurrences, and properties of pollutants. Here, we report a high-temperature electrothermal process for rapid, water-free remediation of multiple pollutants in soil. The temperature of contaminated soil with carbon additives ramps up to 1000 to 3000 °C as needed within seconds via pulsed direct current input, enabling the vaporization of heavy metals like Cd, Hg, Pb, Co, Ni, and Cu, and graphitization of persistent organic pollutants like polycyclic aromatic hydrocarbons. The rapid treatment retains soil mineral constituents while increases infiltration rate and exchangeable nutrient supply, leading to soil fertilization and improved germination rates. We propose strategies for upscaling and field applications. Techno-economic analysis indicates the process holds the potential for being more energy-efficient and cost-effective compared to soil washing or thermal desorption.Item The Apparent Respiratory Quotient of Soils and Tree Stems and the Processes That Control It(Wiley, 2022) Hilman, Boaz; Weiner, Tal; Haran, Tom; Masiello, Caroline A.; Gao, Xiaodong; Angert, AlonThe CO2/O2 fluxes ratio (apparent respiration quotient [ARQ]) measured in soils and plants contains valuable information about the respiratory-substrate stoichiometry and biotic and abiotic non-respiratory processes. We investigated ARQ variability by measurements in soil pore space air, and in headspace air from incubations of bulk-soil and tree stem tissues (both fresh and 24-hr stored tissues) in 10 measurement campaigns over 15 months in a Mediterranean oak forest. Mean (range) ARQ values were: soil air, 0.76 (0.60–0.92); bulk soil, 0.75 (0.53–0.90); fresh stem tissues, 0.39 (0.19–0.70); and stored stem tissues, 0.68 (0.42–1.08). The variability in tree stems was assumed to be controlled by CO2 re-fixation that lowered ARQ from 1.0, the value expected for carbohydrate respiration in plants. We estimate that the values of the stored tissues represent better stem metabolism since the fresh-tissue results contained a signal of wound-response O2 uptake that further lowered ARQ. The mean bulk-soil ARQ (0.75) was considerably lower than expected by soil organic matter (SOM) stoichiometry (0.95). This lower value might represent the stoichiometry of the SOM sub-pool that supports respiration, and/or oxidative depolymerization that increases O2 fluxes. Abiotic O2 uptake was demonstrated to reduce bulk-soil ARQ down to 0.37 and consume Fe2+, but estimated to have small effect under typical respiration rates. Soil-air ARQ was usually higher than bulk-soil ARQ and lower than root ARQ (which, when measured, ranged from 0.73 to 0.96), demonstrating the potential of ARQ to partition the autotrophic and heterotrophic sources of soil respiration. The limitations of this partitioning method are discussed.Item Understanding fragility and engineering activation stability in two-dimensional covalent organic frameworks(Royal Society of Chemistry, 2022) Zhu, Dongyang; Zhang, Jun-Jie; Wu, Xiaowei; Yan, Qianqian; Liu, Fangxin; Zhu, Yifan; Gao, Xiaodong; Rahman, Muhammad M.; Yakobson, Boris I.; Ajayan, Pulickel M.; Verduzco, RafaelThe sensitivity of covalent organic frameworks (COFs) to pore collapse during activation processes is generally termed activation stability, and activation stability is important for achieving and maintaining COF crystallinity and porosity which are relevant to a variety of applications. However, current understanding of COF stability during activation is insufficient, and prior studies have focused primarily on thermal stability or on the activation stability of other porous materials, such as metal–organic frameworks (MOFs). In this work, we demonstrate and implement a versatile experimental approach to quantify activation stability of COFs and use this to establish a number of relationships between their pore size, the type of pore substituents, pore architecture, and structural robustness. Additionally, density functional theory calculations reveal the impact on both inter-and intra-layer interactions, which govern activation stability, and we demonstrate that activation stability can be systematically tuned using a multivariate synthesis approach involving mixtures of functionalized and unfunctionalized COF building blocks. Our findings provide novel fundamental insights into the activation stability of COFs and offer guidance for the design of more robust COFs.