Search NASA⌕ Search

SEARCH · Search NASA

Results for “biogeochemistry”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Microbial Ecology of Permafrost Soils: Populations, Processes, and Perspectives

Permafrost microbial research has flourished in the past decades, due in part to improvements in sampling and molecular techniques, but also the increased focus on the permafrost greenhouse gas feedback to climate change and other ecological processes in high latitude and alpine permafrost soils. Permafrost microorganisms are adapted to these extreme environments and remain active at low temperatures and when resources are limited. They are also an important component of global elemental cycles as they regulate organic matter turnover and greenhouse gas production, particularly as permafrost thaws. Here we review the permafrost microbiology literature coupled with an exploration of its historical aspects, with a particular focus on a new understanding advanced by molecular biology techniques. We further identify knowledge gaps and ways forward to improve our understanding of microbial contributions to ecosystem biogeochemistry of permafrost-affected systems.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

NanoSIP: NanoSIMS Applications for Microbial Biology

High-resolution imaging with secondary ion mass spectrometry (nanoSIMS) has become a standard method in systems biology and environmental biogeochemistry and is broadly used to decipher ecophysiological traits of environmental microorganisms, metabolic processes in plant and animal tissues, and cross-kingdom symbioses. When combined with stable isotope-labeling—an approach we refer to as nanoSIP—nanoSIMS imaging offers a distinctive means to quantify net assimilation rates and stoichiometry of individual cell-sized particles in both low- and high-complexity environments. While the majority of nanoSIP studies in environmental and microbial biology have focused on nitrogen and carbon metabolism (using 15 N and 13 C tracers), multiple advances have pushed the capabilities of this approach in the past decade. The development of a high-brightness oxygen ion source has enabled high-resolution metal analyses that are easier to perform, allowing quantification of metal distribution in cells and environmental particles. New preparation methods, tools for automated data extraction from large data sets, and analytical approaches that push the limits of sensitivity and spatial resolution have allowed for more robust characterization of populations ranging from marine archaea to fungi and viruses. Further, NanoSIMS studies continue to be enhanced by correlation with orthogonal imaging and ‘omics approaches; when linked to molecular visualization methods, such as in situ hybridization and antibody labeling, these techniques enable in situ function to be linked to microbial identity and gene expression. Here we present an updated description of the primary materials, methods, and calculations used for nanoSIP, with an emphasis on recent advances in nanoSIMS applications, key methodological steps, and potential pitfalls.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2023

Breaking the Ice: A Review of Phages in Polar Ecosystems

Bacteriophages, or phages, are viruses that infect and replicate within bacterial hosts, playing a significant role in regulating microbial populations and ecosystem dynamics. However, phages from extreme environments such as polar regions remain relatively understudied due to challenges such as restricted ecosystem access and low biomass. In this study, understanding the diversity, structure, and functions of polar phages is crucial for advancing our knowledge of the microbial ecology and biogeochemistry of these environments. In this review, we will explore the current state of knowledge on phages from the Arctic and Antarctic, focusing on insights gained from -omic studies, phage isolation, and virus-like particle abundance data. Metagenomic studies of polar environments have revealed a high diversity of phages with unique genetic characteristics, providing insights into their evolutionary and ecological roles. Phage isolation studies have identified novel phage–host interactions and contributed to the discovery of new phage species. Virus-like particle abundance and lysis rate data, on the other hand, have highlighted the importance of phages in regulating bacterial populations and nutrient cycling in polar environments. Overall, this review aims to provide a comprehensive overview of the current state of knowledge about polar phages, and by synthesizing these different sources of information, we can better understand the diversity, dynamics, and functions of polar phages in the context of ongoing climate change, which will help to predict how polar ecosystems and residing phages may respond to future environmental perturbations.

09 BIOMASS FUELS↗
DOE OSTI2021

Metal Removal by a Free Surface Constructed Wetland and Prediction of Metal Bioavailability and Toxicity with Diffusive Gradients in Thin Films (DGT) and Biotic Ligand Model (BLM)

The H-02 constructed wetland is a free water surface wetland to remove copper (Cu) and zinc (Zn) from the industrial wastewater. In this study, we evaluated the performance of the wetland from 2018 to 2019 and coupled the diffusive gradients in thin films (DGTs) and biotic ligand model (BLM) to explore metal speciation and bioavailability in wetland waters. Surface water samples were collected and piston DGTs were deployed in different sites of the wetland. The H-02 wetland functioned well during the sampling period with high removal efficiencies (Cu: 73.8 ± 1.2% and Zn: 75.2 ± 16.0%). In our study, with the assumption that the combination of BLM predicted inorganic metals species, BLM Cu(II) and BLM Zn(II), were the bioavailable and toxic species, DGT-Cu did not correlate to BLM Cu(II) (P = 0.47), but DGT-Zn positively correlated to BLM Zn(II) (R 2 = 0.35, P < 0.001). Compared to the modeling results of BLM, DGT-indicated labile and/or bioavailable Cu included not only free Cu ions and inorganic Cu complexes but also a high percentage of Cu-labile organic matter complexes. DGT-indicated Zn included free Zn ion, inorganic Zn, and only a low percentage of Zn-labile organic matter complexes. Our findings illustrated the appropriate use of passive sampling techniques and geological modeling when biomonitoring could be substituted. Furthermore, the close monitoring of metal concentrations, speciation, and bioavailability helps us understand metal biogeochemistry and metal removal processes and ensure the long-term sustainability of the constructed wetland.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Soil Particulate Organic Matter is Related to Ericoid Mycorrhizal Shrubs, not Ectomycorrhizal Trees, in a Temperate Forest

Mycorrhizal associations are key drivers of soil biogeochemistry, but previous studies have focused almost exclusively on ectomycorrhizal (EcM) and arbuscular mycorrhizal (AM) associations. Ericoid mycorrhizal (ErM) shrubs frequently occur in forest understories and are expanding in response to disturbance, but are rarely considered in biogeochemical frameworks. We investigated the relationships of understory ErM shrubs and overstory trees on carbon (C) and nitrogen (N) in soil organic matter fractions in a southern Appalachian temperate forest. We sampled the 0–10 cm mineral soil layer from 43 plots at the Coweeta Hydrologic Laboratory, across gradients in overstory EcM dominance and understory ErM shrub biomass. Soil C:N ratios increased with both increasing EcM dominance and increasing ErM shrub biomass. However, total particulate organic matter (POM) C, and the proportion of C and N held in POM increased with increasing ErM shrub biomass, but not with increasing EcM dominance. In contrast, mineral-associated organic matter (MAOM) C and N were negatively associated with EcM dominance, but were not related to ErM shrubs. Our findings suggest that ErM shrubs facilitate POM formation while AM trees promote MAOM formation. Because ErM shrub biomass represents a small fraction of total forest biomass, our work provides evidence that ErM shrubs have an outsized effect on soil organic matter, which advocates for their inclusion in mechanistic studies and biogeochemical frameworks.

Bonilla, Kayla A. [University of Georgia, Athens, ↗
DOE OSTI2021

Quantifying microbial control of soil organic matter dynamics at macrosystem scales

Soil organic matter (SOM) stocks, decomposition and persistence are largely the product of controls that act locally. Yet the controls are shaped and interact at multiple spatiotemporal scales, from which macrosystem patterns in SOM emerge. Theory on SOM turnover recognizes the resulting spatial and temporal conditionality in the effect sizes of controls that play out across macrosystems, and couples them through evolutionary and community assembly processes. For example, climate history shapes plant functional traits, which in turn interact with contemporary climate to influence SOM dynamics. Selection and assembly also shape the functional traits of soil decomposer communities, but it is less clear how in turn these traits influence temporal macrosystem patterns in SOM turnover. Here, we review evidence that establishes the expectation that selection and assembly should generate decomposer communities across macrosystems that have distinct functional effects on SOM dynamics. Representation of this knowledge in soil biogeochemical models affects the magnitude and direction of projected SOM responses under global change. Yet there is high uncertainty and low confidence in these projections. To address these issues, we make the case that a coordinated set of empirical practices are required which necessitate (1) greater use of statistical approaches in biogeochemistry that are suited to causative inference; (2) long-term, macrosystem-scale, observational and experimental networks to reveal conditionality in effect sizes, and embedded correlation, in controls on SOM turnover; and (3) use of multiple measurement grains to capture local- and macroscale variation in controls and outcomes, to avoid obscuring causative understanding through data aggregation. Here, when employed together, along with process-based models to synthesize knowledge and guide further empirical work, we believe these practices will rapidly advance understanding of microbial controls on SOM and improve carbon cycle projections that guide policies on climate adaptation and mitigation.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Linking soil biodiversity and ecosystem function in a Neotropical savanna

Conserving the remaining savanna ecosystems in the Brazilian savanna (Cerrado) — a global biodiversity hotspot that stores carbon and provides water to a large portion of South America — requires understanding the ecological processes maintaining their function. Nutrient cycling supports savanna function via plant litter production and decomposition by soil fauna, releasing nutrients for plant and soil organism uptake. Soil biodiversity and biogeochemistry linkages with litter dynamics in Neotropical savannas under a changing climate are poorly understood. Here, in this study, we combined two years of rainfall seasonality, leaf and wood litter production and decomposition with soil epigeic fauna abundance — the number of ground-surface dwelling invertebrates collected through pitfall traps — taxa richness, Shannon's diversity and Pielou's evenness, and 16 soil biogeochemical variables measured in 12 plots of preserved savanna. Rainfall seasonality modulated the mean soil epigeic fauna diversity and evenness across all plots, which were highest in the rainy season, in contrast to litterfall rates, which peaked in the dry season. In the dry season (April to September), the Formicidae family was the most abundant with 50% of all individuals, while in the rainy season (October to March), the Isoptera order was the most abundant with approximately 39% of individuals. Wood litter decomposition grouped with annual Hemiptera abundance, co-varying with soil epigeic fauna diversity and evenness per plot and against soil fertility variables. Leaf litter decomposition co-varied with the total epigeic fauna abundance and soil pH. We speculate that the specific need to decompose wood litter may be associated with a greater need for diversity than an abundance of soil epigeic fauna. Our work highlights the role of rainfall seasonality on soil biodiversity and physicochemistry, which is also tightly linked with litter production and decomposition. This study advances our understanding of the mechanisms governing nutrient cycling in savanna ecosystems on nutrient-impoverished soils, with implications for achieving sustainable conservation and restoration goals.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2026

Response of soil nutrient pools and microbiomes to recurrent wildfire disturbance and varying burn severities in a mixed conifer forest

Wildfire is a pervasive disturbance in mixed-conifer forests, yet the relative influence of fire recurrence versus burn severity on soil biogeochemistry and microbial communities remains poorly quantified. We examined a natural gradient of fire history (0–3 prior fires) and burn severity (low–high) spanning 50 yr in a mixed-conifer ecosystem to assess how repeated fire shapes soil carbon (C) and nitrogen (N) pools, their isotopic signatures, mineral and particulate fractions, microbial community composition, carbon-use, CO₂ fluxes, and vegetation cover. Successive fires produced progressively higher bare-ground percentages and lower tree cover, which were tightly linked to declines in microbial diversity and reductions bulk %C, and %N. δ 13 C increased with fire frequency, indicating preferential loss of labile C through combustion or enhanced microbial oxidation, thereby explaining the observed net soil-C decline. Conversely, δ 15 N decreased and pH increased as tree density declined, reflecting altered N cycling and reduced acidification in post-fire soils. Fire recurrence, more than severity, corresponded with a marked shift in the bacterial community: for example, Xanthobacteraceae—key N-fixers and C-cyclers—diminished, while N-fixing Bacillaceae increased, underscoring the tightly coupled nature of soil nutrient dynamics and microbiome composition after repeated burns. Our results demonstrate that fire recurrence appears to be a stronger driver of post-fire soil ecosystem responses in this mixed-conifer forest, influencing both abiotic nutrient pools and the functional potential of the soil microbiome. These findings provide a more enhanced assessment and understanding to date of the biogeochemical consequences of repeated wildfire disturbance that can be used to inform management strategies aimed at preserving soil health in fire-prone landscapes.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Plutonium mobilization from contaminated estuarine sediments, Esk Estuary (UK)

Since 1952, liquid radioactive effluent containing 238-242 Pu, 241 Am, 237 Np, 137 Cs, and 99 Tc has been released with authorization from the Sellafield nuclear complex (UK) into the Irish Sea. This represents the largest source of plutonium (Pu) discharged in all western Europe, with 276 kg having been released. In the Eastern Irish Sea, the majority of the transuranic activity has settled into an area of sediments (Mudpatch) located off the Cumbrian coast. Radionuclides from the Mudpatch have been re-dispersed via particulate transport in fine-grained estuarine and intertidal sediments to the North-East Irish Sea, including the intertidal saltmarsh located at the mouth of the Esk Estuary. Saltmarshes are highly dynamic systems which are vulnerable to external agents (sea level change, erosion, sediment supply, and freshwater inputs), and their stability remains uncertain under current sea level rise projections and possible increases in storm activity. In this work, we examined factors affecting Pu mobility in contaminated sediments collected from the Esk Estuary by conducting leaching experiments under both anoxic and oxic conditions. Here, leaching experiments were conducted over a 9-month period and were periodically sampled to determine solution phase Pu via multicollector-inductively coupled plasma-mass spectrometry (MC-ICP-MS), and to measure redox indicators (Eh, pH and extractable Fe(II)). Microbial community composition was also characterized in the sediments, and at the beginning and end of the anoxic/oxic experiments. Results show that: 1) Pu leaching is about three times greater in solutions leached under anoxic conditions compared to oxic conditions, 2) the sediment slurry microbial communities shift as conditions change from anoxic to oxic, 3) Pu leaching is enhanced in the shallow sediments (0–10 cm depth), and 4) the magnitude of Pu leached from sediments is not correlated with total Pu, indicating that the biogeochemistry of sediment-associated Pu is spatially heterogeneous. These findings provide constraints on the stability of redox sensitive Pu in biogeochemically dynamic/transient environments on a timescale of months and suggests that anoxic conditions can enhance Pu mobility in estuarine systems.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2024

Vivianite oxidation is not photocatalyzed

Vivianite is a hydrous Fe2+ phosphate mineral found in anoxic environments that plays an integral role in P cycling and environmental biogeochemistry. Imbued in the vivianite literature dating as far back as 1918 is the notion that vivianite is light-sensitive and susceptible to rapid photooxidation induced entirely by solar light. However, despite an exhaustive search, to our knowledge this conventionally accepted assumption has never been directly tested, nor has the band gap ever been measured. Resolving this question of photochemical control of vivianite redox chemistry is important for performing and interpreting experiments involving vivianite reactivity with contaminants, and potentially iron and phosphate cycling in the photic zone of aquatic systems. The present study was specifically designed to add¬ress this question. Pure synthetic vivianite samples were irradiated in aqueous suspensions with a Xe lamp at conditions mimicking the solar spectrum and compared to dark controls. Particles stirred in anoxic suspensions for up to 66 days showed no detectable oxidation irrespective of light exposure, according to colorimetric Fe2+/Fe3+ assays, micro X-ray diffraction, and Raman spectroscopy. In contrast, the same experiment performed using air-equilibrated suspensions showed systematic oxidation of up to ~80% mol% Fe(II) at 66 days, but again with no detectable light exposure effect. To test for UV reactivity, further experiments on vivianite powders under air versus N2 atmosphere were performed using a Hg lamp with a longpass filter. In contrast to oxidation in air where no effect of light was detected, after 24 hrs irradiation anoxically, 0.78% Fe was oxidized compared to dark controls, and after 13 days only an additional 0.3% Fe was oxidized. The band gap of pure vivianite was measured by the Tauc method to be 3.5 eV. Contrary to previous reports, solar light has minimal impact on the oxidation of pure vivianite, insignificant in particular when compared to its relatively fast oxidation by oxygen exposure. As such, light does not need to be excluded when running typical vivianite laboratory experiments. Long-term storage of natural vivianite in museums or private collections should continue protective measures given that a possible photocatalytic role of impurities cannot yet be ruled out. Nonetheless, at all depths in natural aquatic systems it appears that the primary abiotic control on the reactivity and half-life of vivianite particles should be the dissolved oxygen concentration, not light exposure.

Vivianite, photochemistry, oxidation↗
DOE OSTI2021

Warming promotes the use of organic matter as an electron acceptor in a peatland

Peatlands store approximately one-half of terrestrial soil organic carbon (C) and the future of this C in the face of ongoing global change remains a key question in global biogeochemistry. Particularly pressing is the need to understand if this C will remain in peatland soils or be returned to the atmosphere as the potent greenhouse gas methane (CH 4 ) in response to warming. Past work has demonstrated that the microbial reduction of organic matter (OM) as an alternative terminal electron acceptor (TEA) under anaerobic conditions can suppress CH 4 production and is a key mechanistic control of peatland CH 4 dynamics. Here we show that warming directly enhances rates of potential OM reduction in peatland soils, enhancing acetate availability and allowing for a faster onset of CH 4 production. Finally, using soils collected from the ecosystem-scale Spruce and Peatland Responses Under Changing Environments (SPRUCE) experiment, we also show that while there were no indirect effects of 2 years of soil warming on potential OM reduction through changes in soil quality, warming-mediated lowering of the water table increased the volume of oxidized OM which will suppress CH 4 production following rewetting events.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Antimony redox processes in the environment: A critical review of associated oxidants and reductants

The environmental behavior of antimony (Sb) has recently received greater attention due to the increasing global use of Sb in a range of industrial applications. Although present at trace levels in most natural systems, elevated Sb concentrations in aquatic and terrestrial environments may result from anthropogenic activities. The mobility and toxicity of Sb largely depend on its speciation, which is dependent to a large extent on its oxidation state. To a certain extent, our understanding of the environmental behavior of Sb has been informed by studies of the environmental behavior of arsenic (As), as Sb and As have somewhat similar chemical properties. However, recently it has become evident that the speciation of Sb and As, especially in the context of redox reactions, may be fundamentally different. Therefore, it is crucial to study the biogeochemical processes impacting Sb redox transformations to understand the behavior of Sb in natural and engineered environments. Currently, there is a growing body of literature involving the speciation, mobility, toxicity, and remediation of Sb, and several reviews on these general topics are available; however, a comprehensive review focused on Sb environmental redox chemistry is lacking. Herein, we provide a review of research conducted within the past two decades examining the redox chemistry of Sb in aquatic and terrestrial environments and identifies knowledge gaps that need to be addressed to develop a better understanding of Sb biogeochemistry for improved management of Sb in natural and engineered systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Integrating field observations and process-based modeling to predict watershed water quality under environmental perturbations

Watersheds play a critical role in supplying water resources needed for human use and ecosystem health. Understanding and predicting how, when, and where changes in the quantity and quality of water resources occur under different environmental stresses including extreme events is crucial for sustainable management of water resources under a changing environment. However, few studies have attempted to quantify or identify the factors and process interactions controlling the impact of extreme events across water-shed systems. Only few large-scale studies include coordinated monitoring and modeling efforts, which limits our ability to assess the large-scale impact of extreme events on water supply and quality. Methods are lacking to propagate uncertainty in process understanding through an integrated hydro-biogeochemical model framework and evaluate its importance, thus failing to take full advantage of the information potentially available through transformative advances in characterization technologies from high-resolution mass spectrometry to airborne and satellite-based remote sensing. There are consequent risks to our nations water security and to human and ecosystem health that may become exacerbated with the increasing frequency of extreme events that is projected for the coming decades. This paper reviews the current status of watershed science for both water quantity and quality and identifies critical gaps in our current knowledge and modeling capability in addressing the emergent needs in predicting watershed hydrologic and biogeochemical responses (i.e., water quantity and quality) under natural and anthropogenic perturbations. We highlight the need to (1) understand how environmental perturbations including extreme events like floods and droughts propagate through watershed systems and assess their short- and long-term impacts on watershed biogeochemistry, water quality and their recovery pathways; (2) develop and improve a watershed water quality model that reflects the state of scientific understanding gained from observations; and (3) construct a data-model fusion system for watershed characterization, process identification, and mechanistic model parameterization. A large base of modeling, monitoring and data capabilities have been built by various federal government agencies given the relevance of water to their critical missions. An emerging need is to build an integrated national capability for watershed water availability and quality that can address water-related missions across multiple federal agencies.

13 HYDRO ENERGY↗
DOE OSTI2022

Plankton energy flows using a global size-structured and trait-based model

Plankton community models are critical tools for understanding the processes that shape marine plankton communities, how plankton communities impact biogeochemical cycles, and the feedbacks between community structure and function. Here, using the flexible Marine Biogeochemistry Library (MARBL), we present the Size-based Plankton ECological TRAits (MARBL-SPECTRA) model, which is designed to represent a diverse plankton community while remaining computationally tractable. MARBL-SPECTRA is composed of nine phytoplankton and six zooplankton size classes represented using allometric scaling relationships for physiological traits and interactions within multiple functional types. MARBL-SPECTRA is embedded within the global ocean component of the Community Earth System Model (CESM) and simulates large-scale, emergent patterns in phytoplankton growth limitation, plankton phenology, plankton generation time, and trophic transfer efficiency. The model qualitatively reproduces observed global patterns of surface nutrients, chlorophyll biomass, net primary production, and the biogeographies of a range of plankton size classes. In addition, the model simulates how predator:prey dynamics and trophic efficiency vary across gradients in total ecosystem productivity. Shorter food chains that export proportionally more carbon from the surface to the ocean interior occur in productive, eutrophic regions, whereas in oligotrophic regions, the food chains are relatively long and export less organic matter from the surface. The union of functional type modeling with size-resolved, trait-based modeling approaches allows MARBL-SPECTRA to capture both large-scale elemental cycles and the structure of planktonic food webs affecting trophic transfer efficiency.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Sink or source? Insights into the behavior of copper and zinc in the sediment porewater of a constructed wetland by peepers

The H-02 free water surface constructed wetland has been applied to remove heavy metals, mainly copper (Cu) and zinc (Zn), from wastewater on the Savannah River Site (Aiken, SC, USA). More and more studies focus on the metal behavior between the sediment and the overlying water, which directly reflects the stability of metals after sedimentation in constructed wetlands. This study focused on the biogeochemical pathways in metal bioavailability and remobilization in the sediment after metals were removed from the overlying water. The dialysis sampling devices (peepers) were used to collect porewater samples from eight depths in the sediment for the measurement of Cu, Zn, dissolved organic carbon (DOC), and major anions (sulfate and chloride). Surface water samples were also collected for the measurement of Cu, Zn, DOC, and anions. Different temporal trends were observed for dissolved Cu between the surface and bottom waters, but not for dissolved Zn. There were no obvious changes in porewater metal concentrations with increasing depths in the sediment. Sediment served as a sink for Cu as only 3% of porewater samples showed higher labile Cu concentrations than the surface water during the entire year. Furthermore, sediment served as a source for Zn in summer and winter as 32% of porewater samples showed higher labile Zn concentrations than the surface water, and these samples were collected at all sediment depths. We think the seasonal changes in the behaviors of Cu and Zn were primarily controlled by the sulfur dynamics and the metal removal processes in the constructed wetland, as well as the different complexing chemistry between Cu and Zn. Also, our study supports that peeper is a powerful tool for studying the biogeochemistry of metals in the sediment.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Year-around survey and manipulation experiments reveal differential sensitivities of soil prokaryotic and fungal communities to saltwater intrusion in Florida Everglades wetlands

Global sea-level rise is transforming coastal ecosystems, especially freshwater wetlands, in part due to increased episodic or chronic saltwater exposure, leading to shifts in biogeochemistry, plant- and microbial communities, as well as ecological services. Yet, it is still difficult to predict how soil microbial communities respond to the saltwater exposure because of poorly understood microbial sensitivity within complex wetland soil microbial communities, as well as the high spatial and temporal heterogeneity of wetland soils and saltwater exposure. To address this, we first conducted a two-year survey of microbial community structure and bottom water chemistry in submerged surface soils from 14 wetland sites across the Florida Everglades. We identified ecosystem-specific microbial biomarker taxa primarily associated with variation in salinity. Bacterial, archaeal and fungal community composition differed between freshwater, mangrove, and marine seagrass meadow sites, irrespective of soil type or season. Especially, methanogens, putative denitrifying methanotrophs and sulfate reducers shifted in relative abundance and/or composition between wetland types. Methanogens and putative denitrifying methanotrophs declined in relative abundance from freshwater to marine wetlands, whereas sulfate reducers showed the opposite trend. A four-year experimental simulation of salt-water intrusion in a pristine freshwater site and a previously saltwater-impacted site corroborated the highest sensitivity and relative increase of sulfate reducers, as well as taxon-specific sensitivity of methanogens, in response to continuously pulsing of saltwater treatment. Collectively, these results suggest that besides increased salinity, saltwater-mediated increased sulfate availability leads to displacement of methanogens by sulfate reducers even at low or temporal salt exposure. In conclusion, these changes of microbial composition could affect organic matter degradation pathways in coastal freshwater wetlands exposed to sea-level rise, with potential consequences, such as loss of stored soil organic carbon.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Global biogeography of fungal and bacterial biomass carbon in topsoil

Bacteria and fungi, representing two major soil microorganism groups, play an important role in global nutrient biogeochemistry. Biogeographic patterns of bacterial and fungal biomass are of fundamental importance for mechanistically understanding nutrient cycling. We synthesized 1323 data points of phospholipid fatty acid-derived fungal biomass C (FBC), bacterial biomass C (BBC), and fungi:bacteria (F:B) ratio in topsoil, spanning 11 major biomes. The FBC, BBC, and F:B ratio display clear biogeographic patterns along latitude and environmental gradients including mean annual temperature, mean annual precipitation, net primary productivity, root C density, soil temperature, soil moisture, and edaphic factors. At the biome level, tundra has the highest FBC and BBC densities at 3684 (95% confidence interval: 1678–8084) mg kg -1 and 428 (237–774) mg kg -1 , respectively; desert has the lowest FBC and BBC densities at 16.92 (14.4–19.89) mg kg -1 and 6.83 (6.1–7.65) mg kg -1 , respectively. The F:B ratio varies dramatically, ranging from 1.8 (1.6–2.1) in savanna to 8.6 (6.7–11.0) in tundra. An empirical model was developed for the F:B ratio and it is combined with a global dataset of soil microbial biomass C to produce global maps for FBC and BBC in 0–30 cm topsoil. Across the globe, the highest FBC is found in boreal forest and tundra while the highest BBC is in boreal forest and tropical/subtropical forest, the lowest FBC and BBC are in shrub and desert. Global stocks of living microbial biomass C were estimated to be 12.6 (6.6–16.4) Pg C for FBC and 4.3 (0.5–10.3) Pg C for BBC in topsoil. These findings advance our understanding of the global distribution of fungal and bacterial biomass, which facilitates the incorporation of fungi and bacteria into Earth system models. The global maps of bacterial and fungal biomass serve as a benchmark for validating microbial models in simulating the global C cycle under a changing climate.

59 BASIC BIOLOGICAL SCIENCES↗