Summary
While it is known that interactions between plants and soil fungi drive many essential ecosystem functions, considerable uncertainty exists over the drivers of fungal community composition in ...the rhizosphere. Here, we examined the roles of plant species identity, phylogeny and functional traits in shaping rhizosphere fungal communities and tested the robustness of these relationships to environmental change.
We conducted a glasshouse experiment consisting of 21 temperate grassland species grown under three different environmental treatments and characterised the fungal communities within the rhizosphere of these plants.
We found that plant species identity, plant phylogenetic relatedness and plant traits all affected rhizosphere fungal community composition. Trait relationships with fungal communities were primarily driven by interactions with arbuscular mycorrhizal fungi, and root traits were stronger predictors of fungal communities than leaf traits. These patterns were independent of the environmental treatments the plants were grown under.
Our results showcase the key role of plant root traits, especially root diameter, root nitrogen and specific root length, in driving rhizosphere fungal community composition, demonstrating the potential for root traits to be used within predictive frameworks of plant–fungal relationships. Furthermore, we highlight how key limitations in our understanding of fungal function may obscure previously unmeasured plant–fungal interactions.
Recently, acidic ionic liquid water mixtures based on the hydrogen sulfate anion have been shown to effectively extract lignin from lignocellulosic biomass. This study analyses Miscanthus ...giganteuslignin isolated after extraction with the protic ionic liquid 1-butylimidazolium hydrogen sulfate (HC sub(4)imHSO sub(4)) followed by precipitation with the antisolvent water. Several analytical techniques were employed, such as quantitative super(13)C-NMR, super(1)H- super(13)C HSQC NMR, super(31)P-NMR, Py-GC-MS, GPC and elemental analysis. The analysis shows that the ionic liquid pretreatment breaks lignin-hemicellulose linkages and depolymerizes the lignin through the cleavage of glycosidic, ester and beta -O-4 ether bonds. This is accompanied by solubilization of the newly generated lignin fragments. At longer pretreatment times, repolymerization of lignin fragments through condensation reactions occurs. The isolated lignins were carbohydrate-free, had low sulfur contents, low molecular weights. Early stage lignins were structurally similar to ball-milled lignin, while more treated lignins were enriched in p-hydroxyphenyl and guaiacyl units and had a high phenolic hydroxyl group content. We conclude that, depending on the treatment conditions, lignins with a variety of characteristics can be isolated using this type of ionic liquid solution.
Recent progress has been made in paleontology with respect to resolving pigmentation in fossil material. Morphological identification of fossilized melanosomes has been one approach, while a second ...methodology using chemical imaging and spectroscopy has also provided critical information particularly concerning eumelanin (black pigment) residue. In this work we develop the chemical imaging methodology to show that organosulfur-Zn complexes are indicators of pheomelanin (red pigment) in extant and fossil soft tissue and that the mapping of these residual biochemical compounds can be used to restore melanin pigment distribution in a 3 million year old extinct mammal species (Apodemus atavus). Synchotron Rapid Scanning X-ray Fluorescence imaging showed that the distributions of Zn and organic S are correlated within this fossil fur just as in pheomelanin-rich modern integument. Furthermore, Zn coordination chemistry within this fossil fur is closely comparable to that determined from pheomelanin-rich fur and hair standards. The non-destructive methods presented here provide a protocol for detecting residual pheomelanin in precious specimens.
Mobilization of Arctic permafrost carbon is expected to increase with warming-induced thawing. However, this effect is challenging to assess due to the diverse processes controlling the release of ...various organic carbon (OC) pools from heterogeneous Arctic landscapes. Here, by radiocarbon dating various terrestrial OC components in fluvially and coastally integrated estuarine sediments, we present a unique framework for deconvolving the contrasting mobilization mechanisms of surface vs. deep (permafrost) carbon pools across the climosequence of the Eurasian Arctic. Vascular plant-derived lignin phenol ¹₄C contents reveal significant inputs of young carbon from surface sources whose delivery is dominantly controlled by river runoff. In contrast plant wax lipids predominantly trace ancient (permafrost) OC that is preferentially mobilized from discontinuous permafrost regions, where hydrological conduits penetrate deeper into soils and thermokarst erosion occurs more frequently. Because river runoff has significantly increased across the Eurasian Arctic in recent decades, we estimate from an isotopic mixing model that, in tandem with an increased transfer of young surface carbon, the proportion of mobilized terrestrial OC accounted for by ancient carbon has increased by 3-6% between 1985 and 2004. These findings suggest that although partly masked by surface carbon export, climate change-induced mobilization of old permafrost carbon is well underway in the Arctic.
Oil spills are a global challenge, contaminating the environment with organics and metals known to elicit toxic effects. Ecosystems within Nigeria's Niger Delta have suffered from prolonged severe ...spills for many decades but the level of impact on the soil microbial community structure and the potential for contaminant bioremediation remains unclear. Here, we assessed the extent/impact of an oil spill in this area 6 months after the accident on both the soil microbial community/diversity and the distribution of polycyclic aromatic hydrocarbon ring-hydroxylating dioxygenase (PAH-RHDGNα) genes, responsible for encoding enzymes involved in the degradation of PAHs, across the impacted area. Analyses confirmed the presence of oil contamination, including metals such as Cr and Ni, across the whole impacted area and at depth. The contamination impacted on the microbial community composition, resulting in a lower diversity in all contaminated soils. Gamma-, Delta-, Alpha- proteobacteria and Acidobacteriia dominated 16S rRNA gene sequences across the contaminated area, while Ktedonobacteria dominated the non-contaminated soils. The PAH-RHDαGN genes were only detected in the contaminated area, highlighting a clear relationship with the oil contamination/hydrocarbon metabolism. Correlation analysis indicated significant positive relationships between the oil contaminants (organics, Cr and Ni), PAH-RHDαGN gene, and the presence of bacteria/archaea such as Anaerolinea, Spirochaetia Bacteroidia Thermoplasmata, Methanomicrobia, and Methanobacteria indicating that the oil contamination not only impacted the microbial community/diversity present, but that the microbes across the impacted area and at depth were potentially playing an important role in degrading the oil contamination present. These findings provide new insights on the level of oil contamination remaining 6 months after an oil spill, its impacts on indigenous soil microbial communities and their potential for in situ bioremediation within a Niger Delta's ecosystem. It highlights the strength of using a cross-disciplinary approach to assess the extent of oil pollution in a single study.
Display omitted
•Potential impact of oil spill on soil microbial community in the Niger Delta•Evidence of oil contamination at depth from geochemical and microbial analyses•Distinct microbial community composition across oil contaminated area•Strong correlation between oil contamination and PAH-RHDαGN gene•PAH-RHDαGN gene could potentially be used to estimate bioremediation potential
Fossil melanin granules (melanosomes) are an important resource for inferring the evolutionary history of colour and its functions in animals. The taphonomy of melanin and melanosomes, however, is ...incompletely understood. In particular, the chemical processes responsible for melanosome preservation have not been investigated. As a result, the origins of sulfur‐bearing compounds in fossil melanosomes are difficult to resolve. This has implications for interpretations of original colour in fossils based on potential sulfur‐rich phaeomelanosomes. Here we use pyrolysis gas chromatography mass spectrometry (Py‐GCMS), fourier transform infrared spectroscopy (FTIR) and time of flight secondary ion mass spectrometry (ToF‐SIMS) to assess the mode of preservation of fossil microstructures, confirmed as melanosomes based on the presence of melanin, preserved in frogs from the Late Miocene Libros biota (NE Spain). Our results reveal a high abundance of organosulfur compounds and non‐sulfurized fatty acid methyl esters in both the fossil tissues and host sediment; chemical signatures in the fossil tissues are inconsistent with preservation of phaeomelanin. Our results reflect preservation via the diagenetic incorporation of sulfur, i.e. sulfurization (natural vulcanization), and other polymerization processes. Organosulfur compounds and/or elevated concentrations of sulfur have been reported from melanosomes preserved in various invertebrate and vertebrate fossils and depositional settings, suggesting that preservation through sulfurization is likely to be widespread. Future studies of sulfur‐rich fossil melanosomes require that the geochemistry of the host sediment is tested for evidence of sulfurization in order to constrain interpretations of potential phaeomelanosomes and thus of original integumentary colour in fossils.
Centennial‐scale records of sea‐surface temperature and opal composition spanning the Last Glacial Maximum and Termination 1 (circa 25–6 ka) are presented here from Guaymas Basin in the Gulf of ...California. Through the application of two organic geochemistry proxies, the U37K′ index and the TEX86H index, we present evidence for rapid, stepped changes in temperatures during deglaciation. These occur in both temperature proxies at 13 ka (∼3°C increase in 270 years), 10.0 ka (∼2°C decrease over ∼250 years) and at 8.2 ka (3°C increase in <200 years). An additional rapid warming step is also observed in TEX86H at 11.5 ka. In comparing the two temperature proxies and opal content, we consider the potential for upwelling intensity to be recorded and link this millennial‐scale variability to shifting Intertropical Convergence Zone position and variations in the strength of the Subtropical High. The onset of the deglacial warming from 17 to 18 ka is comparable to a “southern hemisphere” signal, although the opal record mimics the ice‐rafting events of the north Atlantic (Heinrich events). Neither the modern seasonal cycle nor El Niño/Southern Oscillation patterns provide valid analogues for the trends we observe in comparison with other regional records. Fully coupled climate model simulations confirm this result, and in combination we question whether the seasonal or interannual climate variations of the modern climate are valid analogues for the glacial and deglacial tropical Pacific.
Key Points
Rapid shifts in tropical Pacific SST and opal production during deglaciation
Evolving upwelling intensity linked to ITCZ and Subtropical High positions
Data/model comparison reveals challenges for application of modern analogues
Abstract
Enhanced warming of the Northern high latitudes has intensified thermokarst processes throughout the permafrost zone. Retrogressive thaw slumps (RTS), where thaw-driven erosion caused by ...ground ice melt creates terrain disturbances extending over tens of hectares, represent particularly dynamic thermokarst features. Biogeochemical transformation of the mobilized substrate may release CO
2
to the atmosphere and impact downstream ecosystems, yet its fate remains unclear. The Peel Plateau in northwestern Canada hosts some of the largest RTS features in the Arctic. Here, thick deposits of Pleistocene-aged glacial tills are overlain by a thinner layer of relatively organic-rich Holocene-aged permafrost that aggraded upward following deeper thaw and soil development during the early Holocene warm period. In this study, we characterize exposed soil layers and the mobilized material by analysing sediment properties and organic matter composition in active layer, Holocene and Pleistocene permafrost, recently thawed debris deposits and fresh deposits of slump outflow from four separate RTS features. We found that organic matter content, radiocarbon age and biomarker concentrations in debris and outflow deposits from all four sites were most similar to permafrost soils, with a lesser influence of the organic-rich active layer. Lipid biomarkers suggested a significant contribution of petrogenic carbon especially in Pleistocene permafrost. Active layer samples contained abundant intrinsically labile macromolecular components (polysaccharides, lignin markers, phenolic and N-containing compounds). All other samples were dominated by degraded organic constituents. Active layer soils, although heterogeneous, also had the highest median grain sizes, whereas debris and runoff deposits consisted of finer mineral grains and were generally more homogeneous, similar to permafrost. We thus infer that both organic matter degradation and hydrodynamic sorting during transport affect the mobilized material. Determining the relative magnitude of these two processes will be crucial to better assess the role of intensifying RTS activity in CO
2
release and ecosystem carbon fluxes.
Organic matter in the environment is involved in many biogeochemical processes, including the mobilization of geogenic trace elements, such as arsenic, into groundwater. In this paper we present the ...use of fluorescence spectroscopy to characterize the dissolved organic matter (DOM) pool in heavily arsenic-affected groundwaters in Kandal Province, Cambodia. The fluorescence DOM (fDOM) characteristics between contrasting field areas of differing dominant lithologies were compared and linked to other hydrogeochemical parameters, including arsenic and dissolved methane as well as selected sedimentary characteristics. Absorbance-corrected fluorescence indices were used to characterize depth profiles and compare field areas. Groundwater fDOM was generally dominated by terrestrial humic and fulvic-like components, with relatively small contributions from microbially-derived, tryptophan-like components. Groundwater fDOM from sand-dominated sequences typically contained lower tryptophan-like, lower fulvic-like and lower humic-like components, was less bioavailable, and had higher humification index than clay-dominated sequences. Methane concentrations were strongly correlated with fDOM bioavailability as well as with tryptophan-like components, suggesting that groundwater methane in these arsenic-prone aquifers is likely of biogenic origin. A comparison of fDOM tracers with sedimentary OM tracers is consistent with the hypothesis that external, surface-derived contributions to the aqueous DOM pool are an important control on groundwater hydrogeochemistry.
Display omitted
•Fluorescence spectroscopy used to characterize organic matter in a Cambodian aquifer.•Organic matter characteristics vary widely across field area with contrasting lithology.•Groundwater generally dominated by humic and fulvic-like organic components.•Fluorescence indices compared with groundwater arsenic, methane and sedimentary proxies.
To determine the role of organic matter in the attenuation of acid rock drainage (ARD), microcosm-based experiments were performed using ARD stimulated with plants and manures. Initial mineralogical, ...organic geochemical and microbial analyses indicated a predominance of goethite, a substantial amount of organic carbon originating from local sources, and a bacterial community comparable with those detected in a range of ARD sites worldwide. After 100 days of incubation, changes in the mineralogical, organic and microbiological composition of the ARD demonstrated that the plant additions stimulate microbes with the potential to degrade this organic matter but do not necessarily cause substantial Fe(III) reduction. Conversely, the greatest observed stimulation of Fe(III) reduction, associated with an increase in pH to near-neutral values, was observed using manure additions. These results demonstrate that the use of the optimal natural carbon source is important and can promote the metabolism of microorganisms potentially fuelling a range of geomicrobial processes, including iron and sulfate reduction.
PDF
