Biogeochemical Cycles Of Carbon Research Articles

Hyperexpansion of genetic diversity and metabolic capacity of extremophilic bacteria and archaea in ancient Andean lake sediments

BackgroundThe Andean Altiplano hosts a repertoire of high-altitude lakes with harsh conditions for life. These lakes are undergoing a process of desiccation caused by the current climate, leaving terraces exposed to extreme atmospheric conditions and serving as analogs to Martian paleolake basins. Microbiomes in Altiplano lake terraces have been poorly studied, enclosing uncultured lineages and a great opportunity to understand environmental adaptation and the limits of life on Earth. Here we examine the microbial diversity and function in ancient sediments (10.3–11 kyr BP (before present)) from a terrace profile of Laguna Lejía, a sulfur- and metal/metalloid-rich saline lake in the Chilean Altiplano. We also evaluate the physical and chemical changes of the lake over time by studying the mineralogy and geochemistry of the terrace profile.ResultsThe mineralogy and geochemistry of the terrace profile revealed large water level fluctuations in the lake, scarcity of organic carbon, and high concentration of SO42--S, Na, Cl and Mg. Lipid biomarker analysis indicated the presence of aquatic/terrestrial plant remnants preserved in the ancient sediments, and genome-resolved metagenomics unveiled a diverse prokaryotic community with still active microorganisms based on in silico growth predictions. We reconstructed 591 bacterial and archaeal metagenome-assembled genomes (MAGs), of which 98.8% belonged to previously unreported species. The most abundant and widespread metabolisms among MAGs were the reduction and oxidation of S, N, As, and halogenated compounds, as well as aerobic CO oxidation, possibly as a key metabolic trait in the organic carbon-depleted sediments. The broad redox and CO2 fixation pathways among phylogenetically distant bacteria and archaea extended the knowledge of metabolic capacities to previously unknown taxa. For instance, we identified genomic potential for dissimilatory sulfate reduction in Bacteroidota and α- and γ-Proteobacteria, predicted an enzyme for ammonia oxidation in a novel Actinobacteriota, and predicted enzymes of the Calvin–Benson–Bassham cycle in Planctomycetota, Gemmatimonadota, and Nanoarchaeota.ConclusionsThe high number of novel bacterial and archaeal MAGs in the Laguna Lejía indicates the wide prokaryotic diversity discovered. In addition, the detection of genes in unexpected taxonomic groups has significant implications for the expansion of microorganisms involved in the biogeochemical cycles of carbon, nitrogen, and sulfur.EPcqnK6xUD66cr6MUL2q3UVideo

Bacterial community and dissolved organic matter networks in urban river: The role of human influence

Human activities have significantly altered the biogeochemical cycles of carbon, nitrogen, and sulfur in aquatic ecosystems, leading to ecological problems.This study utilized 16S rRNA gene high-throughput sequencing and excitation-emission matrix parallel factor analysis (EEM-PARAFAC) to evaluate the bacterial community composition and dissolved organic matter structure in the upstream (less impacted) and downstream (severely impacted) sections of the river, with a focus on the interactions between bacterial diversity and dissolved organic matter (DOM) characteristics.Results indicated significant spatial diversity in bacterial communities, with a higher α-diversity upstream compared to the more polluted downstream sections. Environmental parameters, particularly total phosphorus (TP) and dissolved oxygen (DO), were found to significantly influence the distribution and composition of bacterial phyla through redundancy analysis. The pattern of bacterial community assembly has shifted from predominantly deterministic to predominantly stochastic as a result of human activities. The analysis of DOM through EEM-PARAFAC identified three main fluorescent components, reflecting varied sources and interactions with bacterial communities. Upstream, microbial activities predominantly contributed to autochthonous DOM, while downstream, increased inputs of allochthonous DOM from human activities were evident. Furthermore, the study revealed that through the introduction of various organic pollutants and nutrient loads that shift microbial metabolic functions towards increased degradation and transformation of complex organic compounds downstream. Structural equation modeling (SEM) revealed that upstream human activities primarily affected bacterial communities indirectly by altering DOM properties. In contrast, downstream activities had both direct and indirect effects due to higher pollutant loads and more complex environmental conditions. These interactions underline the profound effect of anthropogenic factors on riverine ecosystems and emphasize the importance of managing human impacts to preserve microbial biodiversity and water quality.

Drivers of microbial carbon biomass variability in two oceanic regions of the Gulf of Mexico

The microbial plankton community is an integral part of the pelagic ecosystem. It hosts essential functional groups that play a vital role in organic carbon production, release, uptake, and degradation within open-ocean ecosystems. Given its significance, carbon biomass estimates are urgently needed, especially in oligotrophic regions, to provide and enhance our knowledge of biogenic carbon pools. They also aid in validating biogeochemical models that characterize the functioning of these extensive marine ecosystems within the global carbon cycle. This study addresses the temporal variability of microbial community biomass in two oceanic zones: the west-central (Perdido) and southern (Coatzacoalcos) areas of the Gulf of Mexico. During three seasonally contrasting periods (nortes, rainy, and dry seasons), seawater samples were collected from the euphotic zone in both regions to estimate the carbon biomass of different pico- (<2–3 µm), nano-, and microplankton groups (>3–200 µm). Carbon biomass assessments for the microbial groups were based on their abundance and carbon conversion factors. Overall, we found a significant contribution of pico-prokaryotic components (heterotrophic bacteria, Prochloroccocus, and Synechoccocus) to the total microbial carbon stock of the euphotic zone (84–89 % global estimates). The finding suggests these microorganisms are key functional groups that drive carbon production and fate in the Gulf of Mexico ecosystem. Pico-cyanobacteria, especially Prochloroccocus, were the dominant primary producers (68–82 % total autotrophic carbon), mainly in the upper layer of the oligotrophic euphotic zone. This vertical pattern implies that the deep chlorophyll-a maximum (DCM) depth level was unrelated to a net increase in phytoplankton biomass in the three study periods. The distribution of microbial carbon biomass exhibited striking differences associated with winter mixing (the nortes season), high river discharge accompanied by cross-shelf transport (the rainy season), and the dynamics of mesoscale structures. Ecological aspects, such as the habitat preference of the organisms and the seasonal complementary development of mixotrophic and heterotrophic grazers and their prey, were also essential drivers in regulating the microbial carbon pool of both oceanic regions. The microbial carbon assessments conducted in this study contribute to identifying and quantifying key planktonic functional groups involved in the biogeochemical carbon cycle in the Gulf of Mexico open-ocean ecosystem.

Overexpression of native carbonic anhydrases increases carbon conversion efficiency in the methanotrophic biocatalyst Methylococcus capsulatus Bath.

Methanotrophic bacteria play a vital role in the biogeochemical carbon cycle due to their unique ability to use CH4 as a carbon and energy source. Evidence suggests that some methanotrophs, including Methylococcus capsulatus, can also use CO2 as a carbon source, making these bacteria promising candidates for developing biotechnologies targeting greenhouse gas capture and mitigation. However, a deeper understanding of the dual CH4 and CO2 metabolism is needed to guide methanotroph strain improvements and realize their industrial utility. In this study, we show that M. capsulatus expresses five carbonic anhydrase (CA) isoforms, one α-CA, one γ-CA, and three β-CAs, that play a role in its inorganic carbon metabolism and CO2-dependent growth. The CA isoforms are differentially expressed, and transcription of all isoform genes is induced in response to CO2 limitation. CA null mutant strains exhibited markedly impaired growth compared to an isogenic wild-type control, suggesting that the CA isoforms have independent, non-redundant roles in M. capsulatus metabolism and physiology. Overexpression of some, but not all, CA isoforms improved bacterial growth kinetics and decreased CO2 evolution from CH4-consuming cultures. Notably, we developed an engineered methanotrophic biocatalyst overexpressing the native α-CA and β-CA with a 2.5-fold improvement in the conversion of CH4 to biomass. Given that product yield is a significant cost driver of methanotroph-based bioprocesses, the engineered strain developed here could improve the economics of CH4 biocatalysis, including the production of single-cell protein from natural gas or anaerobic digestion-derived biogas.IMPORTANCEMethanotrophs transform CH4 into CO2 and multi-carbon compounds, so they play a critical role in the global carbon cycle and are of interest for biotechnology applications. Some methanotrophs, including Methylococcus capsulatus, can also use CO2 as a carbon source, but this dual one-carbon metabolism is incompletely understood. In this study, we show that M. capsulatus carbonic anhydrases are critical for this bacterium to optimally utilize CO2. We developed an engineered strain with improved CO2 utilization capacity that increased the overall carbon conversion to cell biomass. The improvements to methanotroph-based product yields observed here are expected to reduce costs associated with CH4 conversion bioprocesses.

A Brief Review of Effects of Aluminum on Marine Diatoms.

Aluminum (Al) is the most abundant metal element in the Earth's crust, yet it is present in trace levels in seawater. Growing evidence suggests potential effects of Al on the biogeochemical cycles of carbon (C) and silicon (Si) in the marine environment. By accumulation, sinking, and deposition, diatoms play a center role in coupling these three elements' biocycles in the oceans. However, it is still a challenge to elucidate the behaviors of diatoms influenced by Al. Our review aims to present the current knowledge of Al biogeochemistry in marine environment and its impact on marine phytoplankton, with a focus on how Al influences diatoms. Previous researches indicate that Al can promote the growth of diatoms, and diatoms have the ability to incorporate Al into their frustules. Given this, we paid particular attention on the interaction between Al and diatom frustules, and the influences of Al on the physiology and ecology of diatoms. Furthermore, it is suggested that Al alters the accumulation of other nutrients such as nitrogen, phosphorus and iron in diatoms; the subsequent responses of diatoms are also discussed. The objective of this review is to address the potential roles of Al in diatoms and offer insights into the possible biogeochemistry implications.

Impacts of wastewater treatment plant effluents on dissolved inorganic carbon in highly urbanized karst rivers, Southwest China

Wastewater treatment plants (WWTPs) are an important manifestation of the impact of urbanization on aquatic ecosystems, and the influences of effluents discharge from WWTPs on receiving river carbon biogeochemical cycle processes has been a research hotspot. However, our knowledge about potential impacts of WWTP effluents on dissolved inorganic carbon (DIC) cycle in karst rivers is rather limited. This study investigates the water chemistry and carbon isotope composition (δ13CDIC) in the urbanized reach of a river that drains the world’s largest continuous karst region in Southwest China, in an attempt to determine the effects of WWTP effluents on karst river DIC cycle and source discrimination. The results reveal: (1) Partial pressure of dissolved carbon dioxide (pCO2) levels in the river increased noticeably during the dry and normal seasons after receiving WWTP effluents; (2) There existed an ionic ratio overlap between end-members of silicate rock weathering and WWTP effluents which requires caution in identifying end-members of rock weathering in urbanized karst rivers; (3) DIC in the highly urbanized karst rivers was affected by complex geochemical processes and these processes varied in different seasons; (4) The contribution of WWTP effluents to the riverine DIC pool was 21±13 %, 58±21 % and 66±33 % in the wet, dry, and normal seasons, respectively. These findings highlight the interference of WWTP effluents with DIC carbon cycling in the receiving karst rivers. Since DIC from WWTPs do not relate with consuming atmospheric or soil CO2, it is important to exclude their contribution from the watershed’s rock weathering carbon sink budget. Based on these findings, we insist that the role and effect of WWTP effluents should be carefully considered when examining DIC carbon source and cycling in rivers that drain urbanized watersheds with abundant wastewater treatment plants.

Phosphate Influx and Dust Deposition Create Zonal and Meridional Biogeochemical Gradients in Trichodesmium Abundance

AbstractTrichodesmium plays a key role in the biogeochemical cycling of carbon, nitrogen and phosphorus in the Tropical Atlantic Ocean. A complex interplay of physicochemical factors control the growth of Trichodesmium. However, owing to the large spatial and temporal variability, the relative influence of these factors in controlling Trichodesmium distribution and abundance remains unclear. In this study, we examined the basin‐scale distribution pattern of Trichodesmium in the upper 200 m water column of the Atlantic Ocean (25°N–30°S and 70°W–20°E) using a large data set (n = 33,235) and tried to constrain the distribution based on various physicochemical parameters. We suggest that the combined effect of warm temperatures and phosphate (PO43−) availability determines the zonal spatial extent and the abundance of Trichodesmium in the Tropical North Atlantic Ocean. However, the availability of dissolved iron, along with high sea surface temperatures and meteorological parameters such as the wind direction and precipitation, likely govern the meridional distribution of Trichodesmium across the Atlantic Ocean. Excess PO43− at the surface rules out the possibility of PO43− limitation in regulating the meridional distribution of the Trichodesmium. Depth‐integrated nitrogen fixation rates, based on a multiple linear regression, vary from 0.07 to 306 μmol N m−2 d−1. The presence of Trichodesmium colonies down to a depth of 200 m and the depth‐integrated nitrogen fixation rates reflect the pivotal role of Trichodesmium in the nitrogen budget of this region.

Aluminum substitution stabilizes organic matter in ferrihydrite transforming into hematite: A molecular analysis

The association of soil organic matter (SOM) with iron (Fe) oxyhydroxides, particularly ferrihydrite, plays a pivotal role in the biogeochemical cycling of carbon (C) in both terrestrial and aquatic environment. The aging of ferrihydrite to more crystalline phases can impact the stability of associated organic C, a process potentially influenced by aluminum (Al) substitution due to its abundance. However, the molecular mechanisms governing the temporal and spatial distribution of SOM during the aging process of Al-substituted Fe oxyhydroxides remain unclear. This study aims to bridge this knowledge gap through a comprehensive approach, utilizing batch experiments, solid characterization techniques, and atomic force microscopy (AFM) based peak-force quantitative nanomechanical mapping (PF-QNM). Batch experiments revealed that humic acid (HA) was released into the aqueous phase during aging, with Al inhibiting this release. Various solid characterization methods collectively suggested that Al hindered the crystalline transformation of ferrihydrite and significantly preserved HA on the surface of newly formed hematite, rather than it being occluded within the interior of the new minerals. Results from 3-Dimensional fluorescence spectroscopy (3D-EEM) and Fourier-transform infrared spectroscopy (FTIR) indicated that the structure of HA remained constant, with the carboxyl-rich and hydroxyl-rich portions of HA fixed at the mineral interface during the aging period. Furthermore, we developed AFM-based PF-QNM to both quantify and visualize the interactions between Fe oxyhydroxides and HA, demonstrating variations in HA affinity among different Fe oxyhydroxides and highlighting the influence of the Al substitution rate.

Molecular-level insight into the origin-dependent adsorption fractionation of dissolved organic matter on ferrihydrite in aquatic environment: Implications for carbon sink in eutrophic lakes

Molecular fractionation of dissolved organic matter (DOM) induced by adsorption on minerals plays a significant role in carbon biogeochemical cycling in water environment. However, the molecular-level adsorption of algae-derived DOM (ADOM) on minerals in eutrophic lakes remains poorly understood. Herein, we investigated the ferrihydrite-induced adsorptive fractionation of ADOM and humic DOM for comparison by using spectral analysis, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and solid characterization methods. We observed higher adsorption rate but lower adsorption capacity for ADOM than humic DOM. Spectroscopy and FT-ICR-MS indicated compounds with large molecular weight (>350 Da), high unsaturated and oxygen-rich were preferentially adsorbed for both ADOM and humic DOM. Specifically, the adsorption affinity order was aromatics > lignin-like > aliphatic compounds. Furthermore, tannin-like and condensed aromatics were predominantly adsorbed in humic DOM and protein-like formulas in ADOM. The solid characterization of ferrihydrite before and after adsorption further confirmed the dominant adsorption of aromatic and carboxylic-containing species in humic DOM and aliphatic materials in ADOM. Additionally, the contribution variation of oxygen atom to double bond in the molecular formula before and after adsorption identified absorbed oxygen-containing substances were predominantly aromatic carboxylic acids for humic DOM, but few aliphatic hydrocarbons substituted with ethers and alcohols for ADOM. These findings provided new insights into mineral-induced carbon sequestration, that is, increased release of ADOM in eutrophic lakes might influence the amount of organic carbon settled by ferrihydrite, and alter its quality from aromatic to aliphatic compounds transfer from water column to sediment through ferrihydrite adsorption.

Molecular-level carbon traits of fine roots: unveiling adaptation and decomposition under flooded conditions

Abstract. Fine roots are vital for plant development and carbon biogeochemical cycling in terrestrial ecosystems. Flooding is known to regulate the physiology and morphology in plant roots; however, its impact on molecular-level characteristics of carbon compounds (carbon traits) in fine roots remains largely unexplored, which limits our understanding of root adaptation and decomposition under changing environments. Here, we used a sequential extraction method, starting from nonpolar to polar solvents, in order to obtain dichloromethane- and methanol-extractable (FDcMe) fractions, base-hydrolyzable (FKOHhy) fractions, and CuO-oxidizable (FCuOox) fractions from fine roots of Dysoxylum binectariferum, which is naturally grown in soil and water. Subsequently, we characterized them using targeted gas chromatography–mass spectrometry and nontargeted Fourier transform ion cyclotron resonance mass spectrometry. Also, decomposition experiments were conducted on soil- and water-grown roots under aerobic and anoxic conditions. Results showed a consistent increase in the unsaturation degree and aromaticity of the analytes from FDcMe to FCuOox fractions. Both analyses were sufficiently sensitive to show that, compared to soil-grown roots, the water-grown roots developed more polyphenolics with a high unsaturation degree and aromaticity and had more nonstructural compositions. Furthermore, although flooding provided an anoxic condition that slowed down root decomposition, the adaptive strategy of developing more nonstructural labile components in water-grown roots accelerated root decomposition, thereby counteracting the effects of anoxia. This advances our understanding of biogeochemical processes in response to global environmental change.

Precessional forcing of biogeochemical and nutrient cycling in the tropical western Pacific during the late Pleistocene

Unravelling the biogenic material export production and its relationship to surface ocean nutrient conditions, along with their external forcing, will provide insights into the ocean carbon biogeochemical cycle. In this study, we present data on coccolith particulate inorganic carbon (PIC) export production, coccolith carbon isotopic vital effects, and planktonic foraminifer cadmium to calcium ratio in the tropical western Pacific over the past 250 kiloyears (kyr). These proxies indicate the strength of the coccolith-based carbonate counter pump or coccolithophore productivity, and phosphate concentration in the surface ocean. Our results show that low phosphate concentration correlates with enhanced coccolith-based carbonate counter pump in the precessional band (a cyclicity of 19–23 kyr). Additionally, low phosphate concentration, which indicates high degree of phosphorus utilization, is coupled with enhanced nitrogen fixation, as shown by a nitrogen isotope record in the tropical western Pacific. Greater precipitation in Papua New Guinea (PNG) can occur during local insolation maxima, suggesting a dominant control of precession. This will in turn drive the biogeochemical and nutrient cycling in the tropical western Pacific. We propose that higher amounts of the PNG riverine input caused by greater precipitation can provide additional nutrients and trace element iron (Fe) for phytoplankton. An increased bioavailable Fe in the surface ocean can promote the growth of nitrogen-fixing diazotrophs, which results in a high degree of phosphorus utilization and relieves a potential nitrogen limitation. This may ultimately lead to increased biological productivity, e.g., the coccolith PIC.

Applying Hydrochar Affects Soil Carbon Dynamics by Altering the Characteristics of Soil Aggregates and Microbes

Hydrochar as a carbon-based fertiliser is hypothesised to permanently improve soils by modifying soil carbon quality through the regulation of soil organic carbon dynamics, aggregation properties and microbial diversity. However, the interactions between soil organic carbon (SOC) molecular structure, soil aggregates and soil microbial communities as a result of hydrochar application have not been fully elucidated. In this study, the use of hydrochar derived from duck farm biomass waste for a maize cultivation experiment verified that hydrochar had a promoting effect on maize growth, effectively increasing the nutrient supply to the soil. The application of hydrochar increased the soil organic carbon content by 78 to 253 per cent, which was dominated by CHON-type lignin, carbohydrates and condensed aromatic structural compounds. Meanwhile, hydrochar had a significant effect on both soil aromatic structures and oxygenated functional groups, forming more soil macroaggregates. In addition, hydrochar had a positive effect on soil bacterial abundance. This study suggests that the key mechanism by which hydrochar regulates soil carbon dynamics is mainly through the stabilising effect of hydrochar on macroaggregates while increasing the abundance of carbon-related microscopic bacteria. These results will help to elucidate the potential effects of aqueous carbon on the biogeochemical cycling of carbon in soils.

Experimental Study on Ecological and Biogeochemical Role of Calcimycocavites in Understanding Carbon Fluxes in the Age of Global Warming and Climate Change

The present work reports the results of calcimycocavitological studies on the seashells from beaches of north Goa, India yielding distinct microfungal forms known as calcimycocavites which are important in global climate change studies. SEM studies of the calcareous shell fragments revealed the micro tunneling behavior of the fungi. Digital analysis of SEM images using Mountain Premium 7.2 software revealed the fine topography of calcimycocavites hyphae along with unidentified presumptive biomineral encrustations. The biodegradation of mycocavitogenic insoluble Calcium Oxalate by oxalotrophic members of bacterial communities may occur using bacterial Oxalate decarboxylase and formate dehydrogenase finally releasing Carbon Di Oxide and water and Calcium oxide to the local nutrient pool. Calcimycocavites may be thus involved in the biogeochemical cycling of Carbon and Calcium in the Ocean-Beach environment. The ecological, biological, and biogeochemical implications of the findings are presented concerning the possible role of calcimycocavites in Calcium and Carbon cycling by breakdown of the calcareous shells and release of inorganic and organic components in the ecosystem. The role of calcimycocavites is stressed in global climate studies.

Unequal impacts of unidirectional freeze-thaw on different soil layers and aggregate sizes: Evidenced by microbial communities and CO2 emissions

Currently available investigations often fail to adequately recognize that soil does not freeze or thaw instantly nor uniformly, but unidirectionally and progressively. Unidirectional freeze-thaw can re-organize soil physio-, chemical- and biological-properties across layers as well among aggregates, thus posing far-reaching yet undervalued impacts on soil carbon biogeochemical cycling, especially in eroding settings. In this study, a Mollisol was refilled into soil columns, and respectively experienced complete freeze-thaw (i.e., no layer distinguished), and progressive freeze-thaw (i.e., from outer layer T1, to inner core T3). After thawing, all soils were fractionated into six size classes, and each size class was then incubated at 10℃ over 7 days to measure daily CO2 emission rate. Our results show that: (1) The soil microbial biomass carbon (SMBC) was generally reduced by 25 % after freeze-thaw, but only the finest aggregates ≤ 32 μm maintained comparable CO2 emission rates. (2) The inner core T3 thawed last and survived with significantly more SMBC and CO2, but lower respiratory quotient (qCO2), than the outer layer T1 thawed first. (3) The fine aggregates survived with more SMBC and total CO2 emissions, but significantly lower qCO2 and smaller ratios of fungal to bacterial biomass carbon, than the coarse aggregates. The disproportionally less respiratory carbon losses (i.e., lower qCO2) in T3 was probably because the lagged freezing and thus weakened water-ice phase changes in the inner core helped to better preserve the soil microbes. The fungal-dominant coarse aggregates were very responsive to freezing and evidently more respiratory active, whereas the fine aggregates were more resilient as the enhanced freezing point depression and the thus prolonged unfrozen state, fostering a better microbial survival with bacteria-dominant communities and robust basal respiration. Although limited to controlled simulation, this study may help to disentangle the role of unidirectional freeze-thaw in perturbing slope-scale soil carbon biogeochemical cycling.

Increasing seasonal variation in the extent of rivers and lakes from 1984 to 2022

Abstract. Knowledge of the spatial and temporal distribution of surface water is important for water resource management, flood risk assessment, monitoring ecosystem health, constraining estimates of biogeochemical cycles and understanding our climate. While global-scale spatiotemporal change detection of surface water has significantly improved in recent years due to planetary-scale remote sensing and computing, it has remained challenging to distinguish the changing characteristics of rivers and lakes. Here we analyze the spatial extent of permanent and seasonal rivers and lakes globally over the past 38 years based on new data of river system extents and surface water trends. Results show that while the total permanent surface area of both rivers and lakes has remained relatively constant, the areas with intermittent seasonal coverage have increased by 12 % and 27 % for rivers and lakes, respectively. The increase is statistically significant in over 84 % of global water catchments based on Spearman's rank correlations (rho) above 0.05 and p values less than 0.05. The seasonal river extent is nearly 32 % larger than the previously observed annual mean river extent, suggesting large seasonal variations that impact not only ecosystem health but also estimations of terrestrial biogeochemical cycles of carbon. The outcomes of our analysis are shared as the Surface Area of Rivers and Lakes (SARL) database, serving as a valuable resource for monitoring and research of hydrological cycles, ecosystem accounting, and water management.

Characterizing the Atmospheric Mn Cycle and Its Impact on Terrestrial Biogeochemistry

AbstractThe role of manganese (Mn) in ecosystem carbon (C) biogeochemical cycling is gaining increasing attention. While soil Mn is mainly derived from bedrock, atmospheric deposition could be a major source of Mn to surface soils, with implications for soil C cycling. However, quantification of the atmospheric Mn cycle, which comprises emissions from natural (desert dust, sea salts, volcanoes, primary biogenic particles, and wildfires) and anthropogenic sources (e.g., industrialization and land‐use change due to agriculture), transport, and deposition, remains uncertain. Here, we use compiled emission data sets for each identified source to model and quantify the atmospheric Mn cycle by combining an atmospheric model and in situ atmospheric concentration measurements. We estimated global emissions of atmospheric Mn in aerosols (&lt;10 μm in aerodynamic diameter) to be 1,400 Gg Mn year−1. Approximately 31% of the emissions come from anthropogenic sources. Deposition of the anthropogenic Mn shortened Mn “pseudo” turnover times in 1‐m‐thick surface soils (ranging from 1,000 to over 10,000,000 years) by 1–2 orders of magnitude in industrialized regions. Such anthropogenic Mn inputs boosted the Mn‐to‐N ratio of the atmospheric deposition in non‐desert dominated regions (between 5 × 10−5 and 0.02) across industrialized areas, but that was still lower than soil Mn‐to‐N ratio by 1–3 orders of magnitude. Correlation analysis revealed a negative relationship between Mn deposition and topsoil C density across temperate and (sub)tropical forests, consisting with atmospheric Mn deposition enhancing carbon respiration as seen in in situ biogeochemical studies.

Treeline displacement may affect lake dissolved organic matter processing at high latitudes and altitudes

Climate change induced shifts in treeline position, both towards higher altitudes and latitudes induce changes in soil organic matter. Eventually, soil organic matter is transported to alpine and subarctic lakes with yet unknown consequences for dissolved organic matter (DOM) diversity and processing. Here, we experimentally investigate the consequences of treeline shifts by amending subarctic and temperate alpine lake water with soil-derived DOM from above and below the treeline. We use ultra-high resolution mass spectrometry (FT-ICR MS) to track molecular DOM diversity (i.e., chemodiversity), estimate DOM decay and measure bacterial growth efficiency. In both lakes, soil-derived DOM from below the treeline increases lake DOM chemodiversity mainly through the enrichment with polyphenolic and highly unsaturated compounds. These compositional changes are associated with reductions in bulk and compound-level DOM reactivity and reduced bacterial growth efficiency. Our results suggest that treeline advancement has the potential to enrich a large number of lake ecosystems with less biodegradable DOM, affecting bacterial community function and potentially altering the biogeochemical cycling of carbon in lakes at high latitudes and altitudes.

Editorial preface to special issue: Neogene-Quaternary changes of the Indo-Pacific Warm Pool encompassing oceanic, hydrologic and carbon cycles, and their implications for future change

The Indo-Pacific Warm Pool (IPWP) is the primary supplier of heat and moisture to the global atmosphere, and exerts a significant impact on tropical and worldwide climate variability. This special issue expands our understanding of the paleoceanographic and paleoclimatic evolution of the IPWP since Neogene times with implications for understanding future change. It contains fifteen research articles addressing two primary themes: (1) Ocean-atmosphere coupled processes via the ocean water-column, sea surface, atmospheric evaporation/precipitation; and (2) Sediment source-to-sink and biogeochemical carbon-cycles, and their interactions with oceanographic, hydrological, tectonic and other factors. These contributions improve our understanding of thermocline temperature, salinity, oxygenation, hydrography, carbon cycle, biological productivity, and sedimentary response in the IPWP across Neogene and Quaternary time scales, as well as aiding in the forecast of future climate responses in the context of current global warming. The special issue will capture the attention of geologists, climatologists, and anybody else interested in global climate change.

Organic matter preservation through complexation with iron minerals in two basins of a dimictic boreal lake with contrasting deep water redox regimes

The biogeochemical cycles of iron and organic carbon (OC) are closely interconnected in terrestrial and aquatic systems. In ocean waters, the concentration of reactive Fe is tightly controlled by soluble organic ligands. In soils, Fe stabilizes OC by forming aggregates that shield OC from degradation. In lake sediments however, the role of Fe in the preservation of OC has not been explored as extensively yet. We investigated Fe-OC interactions in sediment collected from Lake Tantaré, in which two basins are characterized by contrasting redox conditions. These contrasting redox conditions provide an opportunity to assess their importance in the formation of stable Fe-OC complexes. On average, 30.1 ± 6.4 % of total OC was liberated upon reductively dissolving reactive iron. The Fe-associated and the non-Fe-associated OC pools were characterized at the elemental (OC, TN), isotopic (δ13C, δ15N) and functional group (FTIR) levels. Large differences in OC:Fe and TN:Fe ratios between the two basins were found which were not linked to OM chemical composition but rather to differences in reactive iron concentrations stemming from the higher abundance of iron sulfides in the anoxic basin. Nevertheless, since the affinity of OM for iron sulfides is lower than that for iron hydroxides, using OC:Fe and TN:Fe ratios as a diagnostic tool for the type of OM-Fe interactions should be done with care in anoxic environment. Same caution should be considered for oxic sediments due to the variation of the proportion of iron hydroxides associated with OM from sample to sample.

Effects of biodegradable microplastics on arsenic migration and transformation in paddy soils: a comparative analysis with conventional microplastics

The combined pollution of microplastics (MPs) and arsenic (As) in paddy soils has attracted more attention worldwide. However, there are few comparative studies on the effects of biodegradable and conventional MPs on As migration and transformation. Therefore, conventional (polystyrene, polyethylene, polyvinyl chloride) and biodegradable (polybutadiene styrene, polylactic acid, polybutylene adipate terephthalate) MPs were selected to explore and demonstrate their influences and mechanism on As migration from paddy soils to overlying water and As speciation transformation through microcosmic experiment with measuring the changes of As chemical distribution, physicochemical indexes and microbial community in paddy soils. The results showed that biodegradable MPs enhanced As migration and transformation more effective than conventional MPs during 60 d. Biodegradable MPs indirectly increased the content of As(Ⅲ) and bioavailable As by changing the microbial community structure and affecting the biogeochemical cycles of carbon, nitrogen, sulfur and iron in soils, and promoted the As migration and transformation. PBS showed the strongest promoting effect, transforming to more As(Ⅲ) (11.43%) and bioavailable As (4.28%) than control. This helps to a better understanding of the effects of MPs on As biogeochemical cycle and to clarify the ecological and food safety risks of their combined pollution in soils.