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The oxygen isotope composition of diatom frustules, δ18Odiatom, is thought to reflect the isotopic composition of the ambient seawater at the time of biomineralization. However, the δ18Odiatom can be overprinted due to the susceptibility of silanol groups (both external and internal) to isotope exchange. Here, using high-resolution imaging, we investigate what factors may influence this post-mortem isotopic alteration during the initial stages of diagenesis in the sediment. A diatomaceous clay was incubated with 18O-enriched seawater with fresh diatom detritus placed at the sediment–water interface (SWI) and at depth in the sediment. NanoSIMS analysis showed that the fresh diatom detritus as well as fossil frustules became significantly enriched in 18O, and that a relationship between Al-content and 18O-exchange could be observed. To further study the potential role of Al as an inhibitor of oxygen exchange, we measured Al on the surface of fossil frustules and performed additional incubations of diatom detritus in seawater with various concentrations of dissolved Al. The presence of Al-rich material bound to the surface of fossil frustules did not reduce the extent of 18O-enrichment in the underlying silica. However, exposure of diatoms detritus to dissolved Al, which led to a significant increase in frustule Al/Si ratio and a homogenously distributed Al in the frustule valve, significantly lowered the amount of 18O-enrichment. We hypothesize that Al incorporated into the silica structure can slow down 18O exchange while Al present as surface contaminants (clays or other aluminosilicates) has no inhibitory role.

Summary Questions about in vivo substrates for proanthocyanidin (PA) biosynthesis and condensation have not been resolved and wide gaps in the understanding of transport and biogenesis in ‘tannosomes’ persist. Here we examined the evolution of PA biosynthesis in ferns not previously reported, asking what PAs are synthesised and how.Chemical and gene‐expression analyses were combined to characterise PA biosynthesis, leveraging genome annotation from the floating fern Azolla filiculoides. In vitro assay and phylogenomics of PIP‐dehydrogenases served to infer the evolution of leucoanthocyanidin reductase (LAR).Sporophyte‐synthesised (epi)catechin polymers, averaging only seven subunits, accumulated to 5.3% in A. filiculoides, and 8% in A. pinnata biomass dry weight. Consistently, a LAR active in vitro was highly expressed in A. filiculoides. LAR, and paralogous fern WLAR‐enzymes with differing substrate binding sites, represent an evolutionary innovation of the common ancestor of fern and seed plants.The specific ecological niche of Azolla ferns, a floating plant–microbe mat massively fixing CO2 and N2, shaped their metabolism in which PA biosynthesis predominates and employs novel fern LAR enzymes. Characterisation of in vivo substrates of these LAR, will help to shed light on the recently assigned and surprising dual catalysis of LAR from seed plants.

Cable bacteria are multicellular sulfide oxidizing bacteria that display a unique metabolism based on long-distance electron transport. Cells in deeper sediment layers perform the sulfide oxidizing half-reaction whereas cells in the surface layers of the sediment perform the oxygen-reducing half-reaction. These half-reactions are coupled via electron transport through a conductive fiber network that runs along the shared cell envelope. Remarkably, only the sulfide oxidizing half-reaction is coupled to biosynthesis and growth whereas the oxygen reducing half-reaction serves to rapidly remove electrons from the conductive fiber network and is not coupled to energy generation and growth. Cells residing in the oxic zone are believed to (temporarily) rely on storage compounds of which polyphosphate (poly-P) is prominently present in cable bacteria. Here we investigate the role of poly-P in the metabolism of cable bacteria within the different redox environments. To this end, we combined nanoscale secondary ion mass spectrometry with dual-stable isotope probing (13C-DIC and 18O-H2O) to visualize the relationship between growth in the cytoplasm (13C-enrichment) and poly-P activity (18O-enrichment). We found that poly-P was synthesized in almost all cells, as indicated by 18O enrichment of poly-P granules. Hence, poly-P must have an important function in the metabolism of cable bacteria. Within the oxic zone of the sediment, where little growth is observed, 18O enrichment in poly-P granules was significantly lower than in the suboxic zone. Thus, both growth and poly-P metabolism appear to be correlated to the redox environment. However, the poly-P metabolism is not coupled to growth in cable bacteria, as many filaments from the suboxic zone showed poly-P activity but did not grow. We hypothesize that within the oxic zone, poly-P is used to protect the cells against oxidative stress and/or as a resource to support motility, while within the suboxic zone, poly-P is involved in the metabolic regulation before cells enter a non-growing stage.

Lava tubes on Mars hold exciting potential for the preservation of biosignatures, which may survive on geological timescales in these isolated, stable environments. To support the development of future astrobiological mission concepts, we turn to terrestrial lava tubes, host to a variety of microbial communities and secondary minerals. Following a multidisciplinary sampling protocol, we retrieved biological, molecular, and mineralogical data from several lava tubes in Iceland. We report on blue-colored copper-rich secondary minerals and their associated bacterial communities using a multi-method approach, and an amalgam of 16S rRNA gene sequencing, Raman spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy data sets. We found numerous bacterial genera known for their high metal resistance and ability to survive in low-nutrient environments. Both are characteristics to be expected for any potential life in Martian lava tubes, and should be considered when checking for contaminants in Mars mission preparations. Associated with the microbial mats, we identified several types of copper-rich secondary minerals, indicating localized copper enrichments in the groundwater, possibly stemming from overlying ash deposits and nearby hyaloclastite formations. Molecular analysis revealed carotenoid signals preserved within the copper speleothems. If found in Martian lava tubes, blue copper-rich mineral precipitates would be deserving of astrobiological investigation, as they have potential to preserve biosignatures and harbor life. Plain Language Summary Subterranean lava tubes on Mars are exciting locations to study in the potential discovery of signs of life outside of Earth, as the surface of Mars does not have conditions conducive to the preservation of life as we know it. In order to better study these Martian environments we look first to comparable lava tubes on Earth. Within Icelandic lava tubes we found blue-colored copper minerals, host to microbial life. The microbes that thrive in these caves are able to withstand extreme conditions, and leave behind detectable molecular traces indicative of life, a type of biosignature. Using a variety of tools and techniques, we describe the nature of the blue minerals and their provenance, the role of the microbial populations within them, and the value of the molecular traces as biosignatures. We discuss the potential for such minerals and microbes in Martian lava tubes, and how we might successfully sample them in future missions to Mars.

The chemical composition of foraminiferal calcite reflects seawater variables and is therefore a popular paleoceanographic tool. The sedimentary record of foraminiferal shell chemistry is, however, mostly interpreted using empirical calibrations. Since geochemical patterns in foraminifera often deviate from inorganic analogues, there is an ongoing need for a more mechanistic understanding of foraminiferal biomineralization . One of the most elusive, but potentially important parameters characterizing foraminiferal biomineralization is the rate of calcite precipitation. Using a combination of labelling experiments and sub-micrometer imaging of the incorporated label with NanoSIMS , we show that the benthic foraminifer Ammonia beccarii precipitates its calcite at a rate of ∼24 ± 4 nmol/cm2/min. These values are close to maximum reported rates for inorganic calcite precipitation from Mg-depleted seawater, which is consistent with the strong fractionation against Mg during biomineralization. At the same time, the measured precipitation rate is in accordance with the similarity between the foraminiferal Sr/Ca values and ratios from calcite precipitated inorganically at these rates. Our results also show that the observed precipitation rate is surprisingly uniform among specimens and within chamber walls, indicating that the small-scale element banding is not reflecting variability in precipitation rate. Based on our results, we present a conceptual model where foraminiferal calcification is characterized by two major processes: first, active ion transport determines the composition of the calcifying fluid, whereas thermodynamics and process kinetics dictate fractionation and partitioning during the subsequent calcium carbonate precipitation. This model also accounts for a role of seawater transport, which may be important in the first steps of calcification to explain geochemical signatures of other foraminiferal taxa.

Process technologies, such as composting, anaerobic digestion, or lactic acid fermentation, greatly influence the resulting organic amendments (OAs) characteristics even when the same raw material is used. However, it is still unclear how these process technologies indirectly modify the effect of OAs on soil microbial activity and soil aggregation. To determine the effect of OA produced using pre-treatment technologies on the soil microbial activity and soil aggregation, we ran a soil column experiment in which we applied compost, digestate and lactic acid fermentation product made of the same model bio-waste. The results indicated that OAs produced under anaerobic conditions (fermented product and digestate) increased microbial activity, biomass, and soil micro- and macro-aggregation compared to compost and control treatments. Soil microbial activity strongly correlated to C, Ca, Mg, extracellular polymeric substances (EPS), fungal biomass, and macroaggregate formation (rs>0.7, p0.7, p

Melt transport mechanisms have an important impact on the chemical composition of the percolated host rock and the migrating melts. Melt migration is usually assumed to occur at grain boundaries. However, microstructural studies revealed the occurrence of polyphase inclusions along dislocations, subgrain boundaries and microcracks in single mineral grains. The inclusions are interpreted as crystallized melt pockets suggesting that melts can migrate within deformed crystals. Intracrystalline melt migration and diffusive re-equilibration can lead to significant mineral trace element enrichments when associated with dissolution–precipitation reactions. In this contribution, we study a body of replacive troctolites associated with the Erro-Tobbio ophiolitic mantle peridotites (Ligurian Alps, Italy). The replacive formation of the olivine-rich troctolite involved extensive impregnation of a dunitic matrix, i.e. partial dissolution of olivine and concomitant crystallization of interstitial phases. The olivine matrix is characterized by two distinct olivine textures: (i) coarse deformed olivine, representing relicts of the pre-existing mantle dunite matrix (olivine1), and (ii) fine-grained undeformed olivine, a product of the melt–rock interaction process (olivine2). Previous studies documented a decoupling between olivine texture and trace element composition, namely enriched trace element compositions in olivine1 rather than in olivine2, as would be expected from the dissolution–precipitation process. Notably, the trace element enrichments in deformed olivines are correlated with the occurrence of elongated 10 µm size polyphase inclusions (clinopyroxene, Ti-pargasite, chromite) preferentially oriented along olivine crystallographic axes. These inclusions show irregular contacts and have no crystallographic preferred orientation with the host olivine, and the phases composing the inclusions show similar chemical compositions to the vermicular phases formed at the grain boundaries during late-stage reactive crystallization of the troctolite. This suggests that the investigated inclusions did not form as exsolutions of the host olivine but rather by input of metasomatic fluids percolating through the deformed olivine grains during closure of the magmatic system. We infer that strongly fractionated volatile-rich melts were incorporated in oriented microfractures within olivine1 and led to the crystallization of the polyphase inclusions. The presence of intracrystalline melt greatly enhanced diffusive re-equilibration between the evolved melt and the percolated olivine1, in turn acquiring the enriched character expected in neoformed olivine crystals. Intracrystalline melt percolation can have strong geochemical implications and can lead to efficient re-equilibration of percolated minerals and rocks.

Cable bacteria are multicellular, Gram-negative filamentous bacteria that display a unique division of metabolic labor between cells. Cells in deeper sediment layers are oxidizing sulfide, while cells in the surface layers of the sediment are reducing oxygen. The electrical coupling of these two redox half reactions is ensured via long-distance electron transport through a network of conductive fibers that run in the shared cell envelope of the centimeter-long filament. Here we investigate how this unique electrogenic metabolism is linked to filament growth and cell division. Combining dual-label stable isotope probing (13C and 15N), nanoscale secondary ion mass spectrometry, fluorescence microscopy and genome analysis, we find that the cell cycle of cable bacteria cells is highly comparable to that of other, single-celled Gram-negative bacteria. However, the timing of cell growth and division appears to be tightly and uniquely controlled by long-distance electron transport, as cell division within an individual filament shows a remarkable synchronicity that extends over a millimeter length scale. To explain this, we propose the “oxygen pacemaker” model in which a filament only grows when performing long-distance transport, and the latter is only possible when a filament has access to oxygen so it can discharge electrons from its internal electrical network.

Sponges produce distinct fatty acids (FAs) that (potentially) can be used as chemotaxonomic and ecological biomarkers to study endosymbiont-host interactions and the functional ecology of sponges. Here, we present FA profiles of five common habitat-building deep-sea sponges (class Demospongiae, order Tetractinellida), which are classified as high microbial abundance (HMA) species. Geodia hentscheli, G. parva, G. atlantica, G. barretti, and Stelletta rhaphidiophora were collected from boreal and Arctic sponge grounds in the North-Atlantic Ocean. Bacterial FAs dominated in all five species and particularly isomeric mixtures of mid-chain branched FAs (MBFAs, 8- and 9-Me-C16:0 and 10- and 11-Me-C18:0) were found in high abundance (together ≥ 20% of total FAs) aside more common bacterial markers. In addition, the sponges produced long-chain linear, mid- and a(i)-branched unsaturated FAs (LCFAs) with a chain length of 24‒28 C atoms and had predominantly the typical Δ5,9 unsaturation, although the Δ9,19 and (yet undescribed) Δ11,21 unsaturations were also identified. G. parva and S. rhaphidiophora each produced distinct LCFAs, while G. atlantica, G. barretti, and G. hentscheli produced similar LCFAs, but in different ratios. The different bacterial precursors varied in carbon isotopic composition (δ13C), with MBFAs being more enriched compared to other bacterial (linear and a(i)-branched) FAs. We propose biosynthetic pathways for different LCFAs from their bacterial precursors, that are consistent with small isotopic differences found in LCFAs. Indeed, FA profiles of deep-sea sponges can serve as chemotaxonomic markers and support the concept that sponges acquire building blocks from their endosymbiotic bacteria.

While the use of fire has long been recognised as a crucial innovation in the cultural evolution of humankind, much research has focused on the (debated) chronology of its earliest use and control, and less on the ways in which fire was used in the deep past. At its latest by the Upper Palaeolithic, hunter-gatherers routinely used fire to heat a wide range of materials, adjusting parameters like temperature, exposure time and fuel type to the specific requirements of the treated materials, for instance in food preparation or tool production. Comparing analyses of the chemical and physical properties of modern materials, heated under a range of controlled conditions in a laboratory, to archaeological ones might allow the reconstruction of the “heating history” of excavated materials and hence to infer the function of particular fires in the past - provided changes affecting the properties of the heated archaeological material during burial time are taken into consideration. To investigate the feasibility of such an approach, heated materials sampled from ~40,000 to 25,000 year old fireplaces (hearths) and their sedimentary matrices from the Upper Palaeolithic Abri Pataud rock shelter in South-Western France are used here to study (1) the fuel type(s) used by the site’s occupants, (2) the temperatures reached in fireplaces and (3) the potential changes in human activities related to fireplaces over time, with the influence of post-depositional processes taken into explicit consideration throughout. For this purpose, we used a range of methods to analyse macroscopically visible as well as “invisible” (microscopic and molecular) heat-altered materials. The results suggest that charred organic materials (COM) encountered in the samples predominantly result from the fuel used in fireplaces, including the earliest reported use of dung as fuel. Earlier suggestions about the use of bone as fuel at the Abri Pataud are not supported by this study. The heating temperature of COM increased gradually from 350 °C in the Aurignacian to 450 °C in Gravettian levels. Py-GC–MS studies identified a range of organic compounds, biomolecules derived from plant as well as animal sources, still preserved in the sediments after exposure to heat and burial in the rock shelter more than 20,000 years ago. Mammalian mtDNA was identified in sediment samples retrieved from the fireplaces, including ancient mtDNA fragments that originated from one or more modern human-like mitochondrial genome(s). This makes the Abri Pataud the first archaeological site for which ancient modern human mtDNA has been retrieved from sediment samples. The absence of specific organic compounds (furans) in the Aurignacian levels and their presence in the Gravettian ones, the changes in temperatures reached through the Aurignacian-Gravettian sequence as well as changes in the character of the fireplaces (presence/absence of lining river pebbles) suggest that the functions of hearths changed through time. These results highlight the potential of multi-proxy analyses of macro- and microscopic traces of ancient fireplaces, and especially of a shift in focus towards molecular traces of such activities. Systematic sampling of fireplaces and their sedimentary matrix should become a standard part of the excavation protocol of such features, to improve our understanding of the activities of humans in the deep past., The genetic work was funded by the Max Planck Society and the European Research Council (grant no. 694707 to Svante Pääbo). We thank B. Nickel, J. Richter, B. Schellbach and A. Weihmann for work in the ancient DNA laboratory of the Max Planck Institute for Evolutionary Anthropology at Leipzig.

Analytical capabilities of Nanoscopic Secondary Ion Mass Spectrometry (nano-SIMS) and Synchrotron Radiation based X-ray Fluorescence (SR nano-XRF) techniques were compared for nanochemical imaging of polymorphonuclear human neutrophils (PMNs). PMNs were high pressure frozen (HPF), cryosubstituted, embedded in Spurr’s resin and cut in thin sections (500 nm and 2 mm for both techniques resp.) Nano-SIMS enabled nanoscale mapping of isotopes of C, N, O, P and S, while SR based nano-XRF enabled trace level imaging of metals like Ca, Mn, Fe, Ni, Cu and Zn at a resolution of approx. 50 nm. The obtained elemental distributions were compared with those of whole, cryofrozen PMNs measured at the newly developed ID16A nano-imaging beamline at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. Similarities were observed for elements more tightly bound to the cell structure such as phosphorus and sulphur, while differences for mobile ions such as chlorine and potassium were more pronounced. Due to the observed elemental redistribution of mobile ions such as potassium and chlorine, elemental analysis of high pressure frozen (HPF), cryo-substituted and imbedded cells should be interpreted critically. Although decreasing analytical sensitivity occurs due to the presence of ice, analysis of cryofrozen cells - close to their native state - remains the golden standard. In general, we found nanoscale secondary ion mass spectrometry (nano-SIMS) and synchrotron radiation based nanoscopic X-ray fluorescence (SR nano-XRF) to be two supplementary alternatives for nanochemical imaging of single cells at the nanoscale.

The Integrated Ocean Drilling Program Arctic Coring Expedition on Lomonosov Ridge, Arctic Ocean (IODP Expedition 302 in 2004) delivered the first Arctic Ocean sea surface temperature (SST) and land air temperature (LAT) records spanning the Paleocene-Eocene Thermal Maximum (PETM; ~56 Ma) to Eocene Thermal Maximum 2 (ETM2; ~54 Ma). The distribution of glycerol dialkyl glycerol tetraether (GDGT) lipids indicated elevated SST (ca. 23 to 27 °C) and LATs (ca. 17 to 25 °C). However, recent analytical developments have led to: (i) improved temperature calibrations and (ii) the discovery of new temperature-sensitive glycerol monoalkyl glycerol tetraethers (GMGTs). Here, we have analyzed GDGT and GMGT distributions in the same sediment samples using new analytical procedures, interpret the results following the currently available proxy constraints and assess the fidelity of new temperature estimates in our study site. The influence of several confounding factors on TEX86 SST estimates, such as variations in export depth and input from exogenous sources, are typically negligible. However, contributions of isoGDGTs from land, which we characterize in detail, complicate TEX86 paleothermometry in the late Paleocene and part of the interval between the PETM and ETM2. The isoGDGT distribution further supports temperature as the likely variable controlling TEX86 values and we conclude that background early Eocene SSTs generally exceeding 20 °C, with peak warmth during the PETM (~26 °C) and ETM2 (~27 °C). We also report high abundances of branched glycerol monoalkyl glycerol tetraethers throughout (branched GMGTs), most likely dominantly marine in origin, and show that their distribution is sensitive to environmental parameters. Further analytical, provenance and environmental work is required to test if and to what extent temperature may be an important factor. Published temperature constraints from branched GDGTs and terrestrial vegetation also support remarkable warmth in the study section and elsewhere in the Arctic basin, with vegetation proxies indicating coldest month mean temperatures of 6–13 °C. If TEX86-derived SSTs truly represent mean annual SSTs, the seasonal range of Arctic SST was in the order of 20 °C, higher than any open marine locality in the modern ocean. If SST estimates are skewed towards the summer season, seasonal ranges were comparable to those simulated in future ice-free Arctic Ocean scenarios. This uncertainty remains a fundamental issue, and one that limits our assessment of the performance of fully-coupled climate models under greenhouse conditions.

Background and Aims The cuticle of a limited number of plant species contains cutan, a chemically highly resistant biopolymer. As yet, the biosynthesis of cutan is not fully understood. Attempting to further unravel the origin of cutan, we analysed the chemical composition of enzymatically isolated cuticular membranes of Agave americana leaves. Methods Cuticular waxes were extracted with organic solvents. Subsequently, the dewaxed cuticular membrane was depolymerized by acid-catalysed transesterification yielding cutin monomers and cutan, a non-hydrolysable, cuticular membrane residue. The cutan matrix was analysed by thermal extraction, flash pyrolysis and thermally assisted hydrolysis and methylation to elucidate the monomeric composition and deduce a putative biosynthetic origin. Key Results According to gas chromatography–mass spectrometry analyses, the cuticular waxes of A. americana contained primarily very-long-chain alkanoic acids and primary alkanols dominated by C32, whereas the cutin biopolyester of A. americana mainly consisted of 9,10-epoxy ω-hydroxy and 9,10,ω-trihydroxy C18 alkanoic acids. The main aliphatic cutan monomers were alkanoic acids, primary alkanols, ω-hydroxy alkanoic acids and alkane-α,ω-diols ranging predominantly from C28 to C34 and maximizing at C32. Minor contributions of benzene-1,3,5-triol and derivatives suggested that these aromatic moieties form the polymeric core of cutan, to which the aliphatic moieties are linked via ester and possibly ether bonds. Conclusions High similarity of aliphatic moieties in the cutan and the cuticular wax component indicated a common biosynthetic origin. In order to exclude species-specific peculiarities of A. americana and to place our results in a broader context, cuticular waxes, cutin and cutan of Clivia miniata, Ficus elastica and Prunus laurocerasus leaves were also investigated. A detailed comparison showed compositional and structural differences, indicated that cutan was only found in leaves of perennial evergreen A. americana and C. miniata, and made clear that the phenomenon of cutan is possibly less present in plant species than suggested in the literature.

Highlights • Alkaline protein extraction was tested on the aquatic weed Azolla. • A strong effect of pH on extraction yield was observed in Azolla and related ferns. • Condensed tannins were likely responsible for limiting extraction yields at mild pH. • Two methods are introduced to improve protein yield, but reduce CT binding. • Alkaline extraction also yielded a co-product rich in polysaccharides., The aquatic weed Azolla is a potential protein crop due to its prolific growth and high protein content, supported entirely by nitrogen-fixing symbionts. Alkaline protein extraction at pH 8 followed by acid precipitation allowed recovery of 16–26% of the biomass nitrogen, while at pH 10.5 nitrogen recovery improved to 35–54%. This pH effect was typical of ferns of the family Salviniaceae, and may be explained by high concentrations of condensed tannins (CTs) in the biomass that precipitate protein at mild pH. Two approaches were tested to increase protein yield and reduce protein binding by CTs. Pre-extraction with aqueous acetone (70 v/v%) removed 76–85% of the CTs and subsequent alkaline extraction at pH 12.5 and 95 °C recovered 38% of the biomass nitrogen. Extraction with 1.5% of PEG as a CT-binding agent, also permitted to recover 38% of the nitrogen, under milder conditions of pH 8 and 45 °C.

Soil organic matter (SOM) represents a major reservoir of stored carbon (C). However, uncertainties regarding the composition and origin of stabilized SOM hinder the implementation of sustainable management strategies. Here, we synthesize data on the contribution of plant- and microbial-derived compounds to stabilized SOM, i.e., aggregates and mineral-associated organic matter (MAOM), and review the role of environmental factors influencing this contribution. Extrapolating amino sugar concentrations in soil based on molecular stoichiometry, we find that microbial necromass accounts for ~50% (agroecosystems) or less (forest ecosystems) of the C stabilized within aggregates and MAOM across studies. This implies that plant biomolecules, including lipids, lignin, and sugars, might account for a substantial portion (≥50%) of the organic matter protected by minerals and aggregates. Indeed, plant-specific sugars and lipids can each account for as much as 10% of organic C within mineral soil fractions, and most reported quantities of plant-specific lipids and lignin in mineral soil fractions are likely underestimates due to irreversible sorption to minerals. A relatively balanced contribution of plant and microbial biomolecules to stabilized SOM in aggregates and MAOM is inconsistent with recent suggestions that stable SOM is comprised mostly of microbial compounds. Land use and soil type appear to profoundly affect the contribution of plant and microbial compounds to stabilized SOM. Consistent with studies of bulk soils, favorable conditions for microbial proliferation in grasslands or fertile Chernozems or Luvisols appear to increase the contribution of microbial compounds, while less favorable conditions for microbial proliferation in forest soils or Podzols/Alisols appear to favor the abundance of plant compounds in stabilized SOM. Combined with a tight link between substrate quality and the abundance of microbial compounds in stabilized SOM, and a potentially inverse relationship between substrate quality and the abundance of plant compounds, these results provide evidence that plant biomolecules might be preferentially stabilized by organo-mineral interactions in some ecosystems. Various areas warrant further research. For example, difficulties in distinguishing direct and indirect effects of temperature and precipitation on the composition of stabilized SOM may be overcome by long-term observational studies that include climate manipulations. Knowledge gaps in the contribution of plant and microbial compounds to stabilized SOM in soil layers below 30 cm depth may simply be closed by extending the sampling depth. Moreover, a refined focus on soil fauna, with potentially strong effects on microbial and plant compounds in stabilized SOM, will provide new insights into SOM dynamics. Future studies should quantify both microbial and plant biomolecules in mineral soil fractions to allow direct comparisons and overcome limitations in existing data. For example, because biomarker-based estimates of microbial-derived C can only indirectly estimate the maximum amount of plant-derived C, exhaustive studies of plant biomarker concentrations could be conducted, including estimates of plant-specific lipids, sugars, and lignin (and biomarkers released following mineral dissolution). Generally, more integrative studies, e.g., combining molecular and isotopic tracers of organic matter inputs with targeted sampling of mineral fractions, are required to improve knowledge of the formation and persistence of stabilized SOM.

Temperature and the oxygen isotopic composition (δ18O) of meteoric water are both important palaeoclimatic variables, but separating their influences on proxies such as the δ18O of lake carbonates is often problematic. The large temperature variations that are known to have occurred in the northern mid-latitudes during the Late Glacial make this interval an excellent test for a novel approach that combines oxygen-isotope analyses of chironomid larval head capsules with co-occurring endogenic carbonate. We apply this approach to a Late Glacial lake sediment sequence from Hawes Water (NW England). Oxygen-isotope values in chironomid head capsules show marked variations during the Late Glacial that are similar to the oxygen isotope record from endogenic carbonate. However, summer temperature reconstructions based on the paired isotope values and fractionation between chironomids and calcite yield values between −20 and −4 °C, which are unrealistic and far lower than reconstructions based on chironomid assemblages at the same site. The composition of a limited number of samples of fossil chironomid larval head capsules determined using Pyrolysis gas-chromatography mass spectrometry indicates the presence of aliphatic geopolymers, suggesting that diagenetic alteration of the head capsules has systematically biased the isotope-derived temperature estimates. However, a similar trend in the isotope records of the two sources suggests that a palaeoclimate signal is still preserved.

By storing carbon in the soil, forests contribute to climate change mitigation. Edaphic (soil-related) factors, such as soil pH, as well as tree species affect forest carbon cycles, but are difficult to disentangle. We studied how conversion of deciduous stands to mono-culture spruce plantations affected the soil organic matter (SOM) composition along a lithological gradient in the Mullerthal (Luxembourg) and Gaume (south-east Belgium) regions. Parent materials in these regions range from decalcified sands to calcareous marls. A twin plot setup of adjacent deciduous and coniferous stands on the same parent material was used to evaluate the effect of edaphic factors versus litter input differences on SOM composition and soil organic carbon (SOC) stocks. Lignin and cutin/suberin molecular proxies were identified with thermally assisted hydrolysis and methylation (THM), to distinguish litter sources (coniferous vs deciduous and leaf litter vs roots) in the studied stands. In this study, SOC stocks were influenced more by parent material than by forest type. Lignin yield, composition and degradation state were influenced both by litter input chemistry and edaphic context. There appear to be important interaction effects between the two, as the relative importance of parent material and litter quality was site specific. We therefore advice that carbon stock models include data on both vegetation history as well as edaphic context. ispartof: ORGANIC GEOCHEMISTRY vol:134 pages:66-76 status: published

Present-day ocean deoxygenation has major implications for marine ecosystems and biogeochemical cycling in the oceans. Chromium isotopes are used as a proxy to infer changes in past oceanic redox state. Chromium isotopes in carbonates, including the prime proxy carrier foraminifera, were initially thought to record the seawater composition during crystallisation. However, the uptake of Cr into foraminiferal tests and carbonates is still poorly understood and recent studies question this assumption. We assess whether Cr in foraminiferal calcite is taken up during biomineralisation, has a post depositional origin or is a combination of the two. Laser Ablation-MC-ICP-MS analyses and NanoSIMS imaging of individual tests were used to characterise the distribution of Cr in both planktic and benthic foraminifera. Foraminifera in sediment core-top samples have up to two orders of magnitude more Cr than sediment trap, plankton net, and culture samples. In cultured specimens, Cr is incorporated in foraminiferal tests at low concentrations (0.04 – 0.13 ppm) with a distribution coefficient of ~250 ± 43 (2SE) which is an upper estimate due to substantial loss of dissolved Cr during the experiment. Part of the Cr signal in sedimentary foraminifera may be primary, but this primary signal is likely often overprinted by the uptake of Cr from bottom and pore waters. In sediment samples, there is no significant isotopic offset between individual species and bulk foraminiferal calcite from the same size fraction. The >500 µm fraction has a heavier isotopic composition than the smaller 250 – 500 µm fraction with an offset of -0.3 to -0.5‰ due to an increase in surface area to volume. We propose that Cr in foraminifera is predominantly post-depositional and records bottom/pore water signals. This is contrary to current interpretations of the foraminiferal Cr isotope proxy as a surface seawater redox proxy.

Earthworms co-determine whether soil, as the largest terrestrial carbon reservoir, acts as source or sink for photosynthetically fixed CO2. However, conclusive evidence for their role in stabilising or destabilising soil carbon has not been fully established. Here, we demonstrate that earthworms function like biochemical reactors by converting labile plant compounds into microbial necromass in stabilised carbon pools without altering bulk measures, such as the total carbon content. We show that much of this microbial carbon is not associated with mineral surfaces and emphasise the functional importance of particulate organic matter for long-term carbon sequestration. Our findings suggest that while earthworms do not necessarily affect soil organic carbon stocks, they do increase the resilience of soil carbon to natural and anthropogenic disturbances. Our results have implications for climate change mitigation and challenge the assumption that mineral-associated organic matter is the only relevant pool for soil carbon sequestration., Gerrit Angst et al. report the function of earthworms as biochemical reactors in soil by converting labile plant-derived carbon into stabilized microbial-derived carbon. They show that earthworms increase the resilience of carbon in soil to natural and anthropogenic disturbances.

Early Eocene global climate was warmer than much of the Cenozoic and was punctuated by a series of transient warming events or ‘hyperthermals’ associated with carbon isotope excursions when temperature increased by 4–8 °C. The Paleocene-Eocene Thermal Maximum (PETM, ~55 Ma) and Eocene Thermal Maximum 2 (ETM2, 53.5 Ma) hyperthermals were of short duration (

This is a correction to:Annals of Botany, Volume 126, Issue 1, 29 June 2020, Pages 141–162, https://doi-org.proxy.library.uu.nl/10.1093/aob/mcaa056

Earthworms are integral parts of many ecosystems and may play a decisive role in determining whether soils function as carbon (C) sink or source. However, information on how earthworms affect the composition and stability of soil organic matter (SOM) is scarce. Particularly their effect on organic matter deriving from leaves and roots with distinct composition and, thus, susceptibility to decomposition and stabilization remains unclear. Here, we combine cutin- and suberin-derived lipids as specific markers for leaf- and root-derived SOM with their 13C composition and physical fractionations of soil. We show that earthworms overprint the protective role of organo-mineral associations and aggregates to favor the accumulation of root- relative to leaf-derived SOM. This gradual accumulation contributes to the often-observed dominance of root-derived organic matter in soil and emphasizes the need to consider molecular level effects of earthworms on SOM dynamics.

The microbial communities inferred in silica sinter rocks, based on multiscale morphological features (fabrics and textures) and the presence of lipid biomarkers and their carbon isotopic composition, are evaluated in the Krýsuvík geothermal area of Iceland. Close to vent environments (T &gt, 75 °C and pH 1.7‒3), stream floors are capped with homogeneous vitreous crusts and breccia levels, with no distinct recognizable silicified microbes. About 4 m far from the vents (T 75‒60 °C and pH 3‒6) and beyond (T &lt, 60 °C and pH 6‒7.6), microbial sinters, including wavy and palisade laminated and bubble fabrics, differ between abandoned meanders and desiccated ponds. Fabric and texture variances are related to changes in the ratio of filament/coccoid silicified microbes and associated porosity. Coatings of epicellular silica, less than 2 µm thick, favor identification of individual microbial filaments, whereas coalescence of opal spheres into agglomerates precludes recognition of original microbial textures and silicified microbes. Episodic fluctuations in the physico-chemical conditions of surface waters controlled the acidic hydrolysis of biomarkers. Wavy laminated fabrics from pond margins comprise fatty acids, mono- and dialkyl glycerol, mono- and diethers, monoalkyl glycerol esters and small traces of 10-methyl branched C16 and C18 fatty acids and archaeol, indicative of intergrowths of cyanobacteria, Aquificales, and sulfate reducing bacteria and methanogenic archaea. In contrast, wavy laminated fabrics from abandoned meanders and palisade laminated fabrics from ponds differ in their branched fatty acids and the presence vs. absence of bacteriohopanetetrol, reflecting different cyanobacterial contributions. δ13C values of biomarkers range from −22.7 to −32.9‰, but their values in the wavy (pond) and bubble fabrics have much wider ranges than those of the wavy (meander), palisade, and vitreous fabrics, reflecting dissolved inorganic carbon (DIC) sources and a decrease in 13C downstream outflow channels, with heavier values closer to vents and depleted values in ponds.

The main common idea of two conference papers delivered at OMEE-2017 was to demonstrate an importance of the speciation level knowledge in modern adsorption materials science. In order to prove this, two groups of adsorptive materials were used: three samples of Mg–Al–CO3 layered double hydroxides produced by di erent synthesis methods and ten samples of Fe–Ce oxide-based composites with various ratios of Fe-to-Ce. In both cases of studies, it was not possible to find direct correlation between adsorptive performances of the materials and their structural properties obtained by conventional characterisation techniques. However, anion adsorptive removals of each group of inorganic composites correlated with their structural properties studied on the level of speciation. It was shown that strong anion removal potential of Mg–Al–CO3 layered double hydroxides was associated with richness in speciation of chemical elements (Mg, Al) and interlayer anions (CO2 3 −) as well as with generous hydration. Adsorptive performances of inorganic anion exchangers based on Fe–Ce hydrous oxides were explained by simulation extended X-ray absorption fine structures simulation. The best anion removers were found to be those Fe/Ce oxide-based composites whose Fe outer shells were formed from backscattering oscillations from both O and Fe atoms.

Ferns are the closest sister group to all seed plants, yet little is known about their genomes other than that they are generally colossal. Here, we report on the genomes of Azolla filiculoides and Salvinia cucullata (Salviniales) and present evidence for episodic whole-genome duplication in ferns—one at the base of ‘core leptosporangiates’ and one specific to Azolla. One fern-specific gene that we identified, recently shown to confer high insect resistance, seems to have been derived from bacteria through horizontal gene transfer. Azolla coexists in a unique symbiosis with N2-fixing cyanobacteria, and we demonstrate a clear pattern of cospeciation between the two partners. Furthermore, the Azolla genome lacks genes that are common to arbuscular mycorrhizal and root nodule symbioses, and we identify several putative transporter genes specific to Azolla–cyanobacterial symbiosis. These genomic resources will help in exploring the biotechnological potential of Azolla and address fundamental questions in the evolution of plant life.

Environmental change is increasing the concentration of dissolved organic matter (DOM) in catchments of the Northern Hemisphere. This study aims to assess the causes of high DOM concentrations in streams and reservoirs of the Harz National Park (Germany), by means of molecular characterization using thermally assisted hydrolysis and methylation (THM-GC–MS). In order to formulate proxies of the prevailing origin of the numerous THM products of polyphenols, carbohydrates, proteins, aliphatic macromolecules, resins and other DOM precursors, we created a reference sample set of potential sources (spruce, birch, blueberry, heather, peat moss, soils) from the area. Besides solid-state reference samples (bulk organic matter; BOM) we obtained and analyzed their leachates (water-extractable OM; WEOM). Finally, an existing THM-GC–MS dataset of the DOM from the Oder river, which crosses the boundary between peat and forest biomes in the Harz, was extended and explored chemometrically using Principal Component Analysis (PCA) to test the proxies for stream DOM assessment. The results show large differences between BOM and WEOM, which suggests that the solid-to-leachate transition is highly selective or significantly alters the major biomolecular constituents. THM compounds that tend to be more abundant in WEOM than in BOM are G-type phenolic compounds (1,2-dimethoxybenzenes, from lignin and tannin), nitrogen-containing moieties and benzene carboxylic acids, whereas WEOM is depleted in products of polysaccharides, syringyl lignin and aliphatic macromolecules (cutin and suberin). The lignin fingerprint of the WEOM also differs significantly from that of BOM, being depleted in the vast majority of the typical products of macromolecular lignin (G7, G8, G14, G15) and enriched in the acid moiety (G6, predominantly from vanillic acid), especially for spruce wood. THM chromatograms of DOM from the forest section of the Oder show an extraordinary abundance of G6, most probably from spruce-derived lignin. This may indicate a major role of DOM released from decaying spruce logs and forest soils. The results highlight both the potential and the pitfalls associated with source identification of DOM using THM-GC–MS.

We present 275 new metal-silicate partition coefficients for P, S, V, Cr, Mn, Co, Ni, Ge, Mo, and W obtained at moderate P (1.5 GPa) and high T (1683–1883 K). We investigate the effect of silicate melt composition using four end member silicate melt compositions. We identify possible silicate melt dependencies of the metal-silicate partitioning of lower valence elements Ni, Ge and V, elements that are usually assumed to remain unaffected by changes in silicate melt composition. Results for the other elements are consistent with the dependence of their metal-silicate partition coefficients on the individual major oxide components of the silicate melt composition suggested by recently reported parameterizations and theoretical considerations. Using multiple linear regression, we parameterize compiled metal-silicate partitioning results including our new data and report revised expressions that predict their metal-silicate partitioning behavior as a function of P-T-X-fO2. We apply these results to constrain the conditions that prevailed during core formation in the angrite parent body (APB). Our results suggest the siderophile element depletions in angrite meteorites are consistent with a CV bulk composition and constrain APB core formation to have occurred at mildly reducing conditions of 1.4 ± 0.5 log units below the iron-wüstite buffer (ΔIW), corresponding to a APB core mass of 18 ± 11%. The core mass range is constrained to 21 ± 8 mass% if light elements (S and/or C) are assumed to reside in the APB core. Incorporation of light elements in the APB core does not yield significantly different redox states for APB core-mantle differentiation. The inferred redox state is in excellent agreement with independent fO2 estimates recorded by pyroxene and olivine in angrites.

Gypsum (CaSO4·2H2O) provides an opportunity to obtain information from both the oxygen isotopic composition of the water and sulfate of its formation waters, where these components are commonly sourced from different reservoirs (e.g., meteoric vs. magmatic). Here, we present δ18O values for gypsum and parent spring waters fed by the Kawah Ijen crater lake in East Java, Indonesia, and from these natural samples derive gypsum-fluid oxygen isotope fractionation factors for water and sulfate group ions of 1.0027 ± 0.0003‰ and 0.999 ± 0.001‰, respectively. Applying these fractionation factors to a growth-zoned gypsum stalactite that records formation waters from 1980 to 2008 during a period of passive degassing, and gypsum cement extracted from the 1817 eruption tephra fall deposit, shows that these fluids were in water-sulfate oxygen isotopic equilibrium. However, the 1817 fluid was >5‰ lighter. This indicates that the 1817 pre-eruption lake was markedly different, and had either persisted for a much shorter duration or was more directly connected to the underlying magmatic-hydrothermal system. This exploratory study highlights the potential of gypsum to provide a historical record of both the δ18Owater and δ18Osulfate of its parental waters, and provides insights into the processes acting on volcanic crater lakes or any other environment that precipitates gypsum.

BACKGROUND: Since available arable land is limited and nitrogen fertilizers pollute the environment, cropping systems ought to be developed that do not rely on them. Here we investigate the rapidly growing, N2-fixing Azolla/Nostoc symbiosis for its potential productivity and chemical composition to determine its potential as protein feed. RESULTS: In a small production system, cultures of Azolla pinnata and Azolla filiculoides were continuously harvested for over 100days, yielding an average productivity of 90.0-97.2kg dry weight (DW) ha-1d-1. Under ambient CO2 levels, N2 fixation by the fern's cyanobacterial symbionts accounted for all nitrogen in the biomass. Proteins made up 176-208gkg-1 DW (4.9 × total nitrogen), depending on species and CO2 treatment, and contained more essential amino acids than protein from soybean. Elevated atmospheric CO2 concentrations (800ppm) significantly boosted biomass production by 36-47%, without decreasing protein content. Choice of species and CO2 concentrations further affected the biomass content of lipids (79-100gkg-1 DW) and (poly)phenols (21-69gkg-1 DW). CONCLUSIONS: By continuous harvesting, high protein yields can be obtained from Azolla cultures, without the need for nitrogen fertilization. High levels of (poly)phenols likely contribute to limitations in the inclusion rate of Azolla in animal diets and need further investigation.

Few astronomically calibrated high-resolution (5 kyr) climate records exist that span the Oligocene-Miocene time interval. Notably, available proxy records show responses varying in amplitude at frequencies related to astronomical forcing, and the main pacemakers of global change on astronomical time-scales remain debated. Here we present newly generated X-ray fluorescence core scanning and benthic foraminiferal stable oxygen and carbon isotope records from Ocean Drilling Program Site 1264 (Walvis Ridge, southeastern Atlantic Ocean). Complemented by data from nearby Site 1265, the Site 1264 benthic stable isotope records span a continuous ~13-Myr interval of the Oligo-Miocene (30.1–17.1 Ma) at high resolution (~3.0 kyr). Spectral analyses in the stratigraphic depth domain indicate that the largest amplitude variability of all proxy records is associated with periods of ~3.4 m and ~0.9 m, which correspond to 405- and ~110-kyr eccentricity using a magnetobiostratigraphic age model. The phase relation between the ~110-kyr cycles and eccentricity is evident with maxima in CaCO3 content, 18O and 13C corresponding to eccentricity minima. The strong expression of these cycles in combination with the weakness of the precession- and obliquity-related signals allow construction of an astronomical age model that is solely based on tuning to the nominal (La2011_ecc3L) eccentricity solution. Very long-period eccentricity maxima (~2.4-Myr) are marked by recurrent episodes of high-amplitude ~110-kyr 18O cycles at Walvis Ridge, indicating greater sensitivity of the climate/cryosphere system to short eccentricity modulation of climatic precession. In contrast, the responses of the global (high-latitude) climate system, cryosphere and carbon cycle, to the 405-kyr cycle, as expressed in benthic 18O and especially 13C signals, are more pronounced during ~2.4-Myr minima. The relationship between the recurrent episodes of high-amplitude ~110-kyr 18O cycles and the ~1.2-Myr amplitude modulation of obliquity is not consistent through the Oligo-Miocene time interval. Identification of these recurrent episodes at Walvis Ridge, and their pacing by the ~2.4-Myr eccentricity cycle, revises the current understanding of the main climate events of the Oligo-Miocene.

Process technologies, such as composting, anaerobic digestion, or lactic acid fermentation, greatly influence the resulting organic amendments (OAs) characteristics even when the same raw material is used. However, it is still unclear how these process technologies indirectly modify the effect of OAs on soil microbial activity and soil aggregation. To determine the effect of OA produced using pre-treatment technologies on the soil microbial activity and soil aggregation, we ran a soil column experiment in which we applied compost, digestate and lactic acid fermentation product made of the same model bio-waste. The results indicated that OAs produced under anaerobic conditions (fermented product and digestate) increased microbial activity, biomass, and soil micro- and macro-aggregation compared to compost and control treatments. Soil microbial activity strongly correlated to C, Ca, Mg, extracellular polymeric substances (EPS), fungal biomass, and macroaggregate formation (rs>0.7, p0.7, p

Soil organic matter (SOM) represents a major reservoir of stored carbon (C). However, uncertainties regarding the composition and origin of stabilized SOM hinder the implementation of sustainable management strategies. Here, we synthesize data on the contribution of plant- and microbial-derived compounds to stabilized SOM, i.e., aggregates and mineral-associated organic matter (MAOM), and review the role of environmental factors influencing this contribution. Extrapolating amino sugar concentrations in soil based on molecular stoichiometry, we find that microbial necromass accounts for ~50% (agroecosystems) or less (forest ecosystems) of the C stabilized within aggregates and MAOM across studies. This implies that plant biomolecules, including lipids, lignin, and sugars, might account for a substantial portion (≥50%) of the organic matter protected by minerals and aggregates. Indeed, plant-specific sugars and lipids can each account for as much as 10% of organic C within mineral soil fractions, and most reported quantities of plant-specific lipids and lignin in mineral soil fractions are likely underestimates due to irreversible sorption to minerals. A relatively balanced contribution of plant and microbial biomolecules to stabilized SOM in aggregates and MAOM is inconsistent with recent suggestions that stable SOM is comprised mostly of microbial compounds. Land use and soil type appear to profoundly affect the contribution of plant and microbial compounds to stabilized SOM. Consistent with studies of bulk soils, favorable conditions for microbial proliferation in grasslands or fertile Chernozems or Luvisols appear to increase the contribution of microbial compounds, while less favorable conditions for microbial proliferation in forest soils or Podzols/Alisols appear to favor the abundance of plant compounds in stabilized SOM. Combined with a tight link between substrate quality and the abundance of microbial compounds in stabilized SOM, and a potentially inverse relationship between substrate quality and the abundance of plant compounds, these results provide evidence that plant biomolecules might be preferentially stabilized by organo-mineral interactions in some ecosystems. Various areas warrant further research. For example, difficulties in distinguishing direct and indirect effects of temperature and precipitation on the composition of stabilized SOM may be overcome by long-term observational studies that include climate manipulations. Knowledge gaps in the contribution of plant and microbial compounds to stabilized SOM in soil layers below 30 cm depth may simply be closed by extending the sampling depth. Moreover, a refined focus on soil fauna, with potentially strong effects on microbial and plant compounds in stabilized SOM, will provide new insights into SOM dynamics. Future studies should quantify both microbial and plant biomolecules in mineral soil fractions to allow direct comparisons and overcome limitations in existing data. For example, because biomarker-based estimates of microbial-derived C can only indirectly estimate the maximum amount of plant-derived C, exhaustive studies of plant biomarker concentrations could be conducted, including estimates of plant-specific lipids, sugars, and lignin (and biomarkers released following mineral dissolution). Generally, more integrative studies, e.g., combining molecular and isotopic tracers of organic matter inputs with targeted sampling of mineral fractions, are required to improve knowledge of the formation and persistence of stabilized SOM.

Unicellular nitrogen fixing cyanobacteria (UCYN) are abundant members of phytoplankton communities in a wide range of marine environments, including those with rapidly changing nitrogen (N) concentrations. We hypothesized that differences in N availability (N2 vs. combined N) would cause UCYN to shift strategies of intracellular N and C allocation. We used transmission electron microscopy and nanoscale secondary ion mass spectrometry imaging to track assimilation and intracellular allocation of 13C-labeled CO2 and 15N-labeled N2 or NO3 at different periods across a diel cycle in Cyanothece sp. ATCC 51142. We present new ideas on interpreting these imaging data, including the influences of pre-incubation cellular C and N contents and turnover rates of inclusion bodies. Within cultures growing diazotrophically, distinct subpopulations were detected that fixed N2 at night or in the morning. Additional significant within-population heterogeneity was likely caused by differences in the relative amounts of N assimilated into cyanophycin from sources external and internal to the cells. Whether growing on N2 or NO3, cells prioritized cyanophycin synthesis when N assimilation rates were highest. N assimilation in cells growing on NO3 switched from cyanophycin synthesis to protein synthesis, suggesting that once a cyanophycin quota is met, it is bypassed in favor of protein synthesis. Growth on NO3 also revealed that at night, there is a very low level of CO2 assimilation into polysaccharides simultaneous with their catabolism for protein synthesis. This study revealed multiple, detailed mechanisms underlying C and N management in Cyanothece that facilitate its success in dynamic aquatic environments.

Environmental change is increasing the concentration of dissolved organic matter (DOM) in catchments of the Northern Hemisphere. This study aims to assess the causes of high DOM concentrations in streams and reservoirs of the Harz National Park (Germany), by means of molecular characterization using thermally assisted hydrolysis and methylation (THM-GC–MS). In order to formulate proxies of the prevailing origin of the numerous THM products of polyphenols, carbohydrates, proteins, aliphatic macromolecules, resins and other DOM precursors, we created a reference sample set of potential sources (spruce, birch, blueberry, heather, peat moss, soils) from the area. Besides solid-state reference samples (bulk organic matter; BOM) we obtained and analyzed their leachates (water-extractable OM; WEOM). Finally, an existing THM-GC–MS dataset of the DOM from the Oder river, which crosses the boundary between peat and forest biomes in the Harz, was extended and explored chemometrically using Principal Component Analysis (PCA) to test the proxies for stream DOM assessment. The results show large differences between BOM and WEOM, which suggests that the solid-to-leachate transition is highly selective or significantly alters the major biomolecular constituents. THM compounds that tend to be more abundant in WEOM than in BOM are G-type phenolic compounds (1,2-dimethoxybenzenes, from lignin and tannin), nitrogen-containing moieties and benzene carboxylic acids, whereas WEOM is depleted in products of polysaccharides, syringyl lignin and aliphatic macromolecules (cutin and suberin). The lignin fingerprint of the WEOM also differs significantly from that of BOM, being depleted in the vast majority of the typical products of macromolecular lignin (G7, G8, G14, G15) and enriched in the acid moiety (G6, predominantly from vanillic acid), especially for spruce wood. THM chromatograms of DOM from the forest section of the Oder show an extraordinary abundance of G6, most probably from spruce-derived lignin. This may indicate a major role of DOM released from decaying spruce logs and forest soils. The results highlight both the potential and the pitfalls associated with source identification of DOM using THM-GC–MS.

BACKGROUND AND AIMS: The cuticle of a limited number of plant species contains cutan, a chemically highly resistant biopolymer. As yet, the biosynthesis of cutan is not fully understood. Attempting to further unravel the origin of cutan, we analysed the chemical composition of enzymatically isolated cuticular membranes of Agave americana leaves. METHODS: Cuticular waxes were extracted with organic solvents. Subsequently, the dewaxed cuticular membrane was depolymerized by acid-catalysed transesterification yielding cutin monomers and cutan, a non-hydrolysable, cuticular membrane residue. The cutan matrix was analysed by thermal extraction, flash pyrolysis and thermally assisted hydrolysis and methylation to elucidate the monomeric composition and deduce a putative biosynthetic origin. KEY RESULTS: According to gas chromatography–mass spectrometry analyses, the cuticular waxes of A. americana contained primarily very-long-chain alkanoic acids and primary alkanols dominated by C(32), whereas the cutin biopolyester of A. americana mainly consisted of 9,10-epoxy ω-hydroxy and 9,10,ω-trihydroxy C(18) alkanoic acids. The main aliphatic cutan monomers were alkanoic acids, primary alkanols, ω-hydroxy alkanoic acids and alkane-α,ω-diols ranging predominantly from C(28) to C(34) and maximizing at C(32). Minor contributions of benzene-1,3,5-triol and derivatives suggested that these aromatic moieties form the polymeric core of cutan, to which the aliphatic moieties are linked via ester and possibly ether bonds. CONCLUSIONS: High similarity of aliphatic moieties in the cutan and the cuticular wax component indicated a common biosynthetic origin. In order to exclude species-specific peculiarities of A. americana and to place our results in a broader context, cuticular waxes, cutin and cutan of Clivia miniata, Ficus elastica and Prunus laurocerasus leaves were also investigated. A detailed comparison showed compositional and structural differences, indicated that cutan was only found in leaves of perennial evergreen A. americana and C. miniata, and made clear that the phenomenon of cutan is possibly less present in plant species than suggested in the literature.

Earthworms are integral parts of many ecosystems and may play a decisive role in determining whether soils function as carbon (C) sink or source. However, information on how earthworms affect the composition and stability of soil organic matter (SOM) is scarce. Particularly their effect on organic matter deriving from leaves and roots with distinct composition and, thus, susceptibility to decomposition and stabilization remains unclear. Here, we combine cutin- and suberin-derived lipids as specific markers for leaf- and root-derived SOM with their 13C composition and physical fractionations of soil. We show that earthworms overprint the protective role of organo-mineral associations and aggregates to favor the accumulation of root- relative to leaf-derived SOM. This gradual accumulation contributes to the often-observed dominance of root-derived organic matter in soil and emphasizes the need to consider molecular level effects of earthworms on SOM dynamics.

Gypsum (CaSO4·2H2O) provides an opportunity to obtain information from both the oxygen isotopic composition of the water and sulfate of its formation waters, where these components are commonly sourced from different reservoirs (e.g., meteoric vs. magmatic). Here, we present δ18O values for gypsum and parent spring waters fed by the Kawah Ijen crater lake in East Java, Indonesia, and from these natural samples derive gypsum-fluid oxygen isotope fractionation factors for water and sulfate group ions of 1.0027 ± 0.0003‰ and 0.999 ± 0.001‰, respectively. Applying these fractionation factors to a growth-zoned gypsum stalactite that records formation waters from 1980 to 2008 during a period of passive degassing, and gypsum cement extracted from the 1817 eruption tephra fall deposit, shows that these fluids were in water-sulfate oxygen isotopic equilibrium. However, the 1817 fluid was >5‰ lighter. This indicates that the 1817 pre-eruption lake was markedly different, and had either persisted for a much shorter duration or was more directly connected to the underlying magmatic-hydrothermal system. This exploratory study highlights the potential of gypsum to provide a historical record of both the δ18Owater and δ18Osulfate of its parental waters, and provides insights into the processes acting on volcanic crater lakes or any other environment that precipitates gypsum.

Significance Cable bacteria form centimeter-long, multicellular filaments whose energy metabolism involves cooperation among cells that separately perform oxidation of the electron donor and reduction of the electron acceptor. This cooperative division of labor is facilitated via long-range electrical currents that run from cell to cell along a network of conductive fibers. Here we show that biomass synthesis shows a surprising asymmetry along the filament: only the cells oxidizing the electron donor conserve energy for growth, while the other cells reduce electron acceptors without biosynthesis. Our study hence provides insights into the physiology of an unconventional chemolithotroph, which forms a multicellular electrically connected system with unique functional differentiation, integration, and coordination., Multicellularity is a key evolutionary innovation, leading to coordinated activity and resource sharing among cells, which generally occurs via the physical exchange of chemical compounds. However, filamentous cable bacteria display a unique metabolism in which redox transformations in distant cells are coupled via long-distance electron transport rather than an exchange of chemicals. This challenges our understanding of organismal functioning, as the link among electron transfer, metabolism, energy conservation, and filament growth in cable bacteria remains enigmatic. Here, we show that cells within individual filaments of cable bacteria display a remarkable dichotomy in biosynthesis that coincides with redox zonation. Nanoscale secondary ion mass spectrometry combined with 13C (bicarbonate and propionate) and 15N-ammonia isotope labeling reveals that cells performing sulfide oxidation in deeper anoxic horizons have a high assimilation rate, whereas cells performing oxygen reduction in the oxic zone show very little or no label uptake. Accordingly, oxygen reduction appears to merely function as a mechanism to quickly dispense of electrons with little to no energy conservation, while biosynthesis and growth are restricted to sulfide-respiring cells. Still, cells can immediately switch roles when redox conditions change, and show no differentiation, which suggests that the “community service” performed by the cells in the oxic zone is only temporary. Overall, our data reveal a division of labor and electrical cooperation among cells that has not been seen previously in multicellular organisms.

Evidence for a vital role of soil mineral matrix interactions in lipid preservation is steadily increasing. However, it remains unclear whether solvent-extractable (‘free’) or hydrolyzable (‘bound’) lipids, including molecular proxies, e.g., for cutin and suberin, are similarly affected by different stabilization mechanisms in soil (i.e., aggregation or organo-mineral association). To provide insights into the effect of these stabilization mechanisms on lipid composition and preservation, we investigated free and bound lipids in particulate and mineral soil fractions, deriving from sand- and silt-/clay-sized aggregates from a forest subsoil. While free lipids accumulated in sand-sized aggregates, the more complex bound lipids accumulated in silt- and clay-sized aggregates, particularly in the respective mineral fractions < 6.3 µm (fine silt and clay). The presence of both, cutin and suberin markers indicated input of leaf- and root-derived organic matter to the subsoil. Yet, our cutin marker (9,10,ω-trihydroxyoctadecanoic acid) was not extracted from the mineral aggregate compartments < 6.3 µm, perhaps due to its chemical structure (i.e., cross-linking via several hydroxy groups, and thus higher ‘stability’, in macromolecular structures). Combined, these results suggest that the chemical composition of lipids (and likely also that of other soil organic matter compounds) governs interaction with their environment, such as accumulation in aggregates or association with mineral soil compartments, and thus indirectly influences their persistence in soil.

BACKGROUND Since available arable land is limited and nitrogen fertilizers pollute the environment, cropping systems ought to be developed that do not rely on them. Here we investigate the rapidly growing, N2‐fixing Azolla/Nostoc symbiosis for its potential productivity and chemical composition to determine its potential as protein feed. RESULTS In a small production system, cultures of Azolla pinnata and Azolla filiculoides were continuously harvested for over 100 days, yielding an average productivity of 90.0–97.2 kg dry weight (DW) ha−1 d−1. Under ambient CO2 levels, N2 fixation by the fern's cyanobacterial symbionts accounted for all nitrogen in the biomass. Proteins made up 176–208 g kg−1 DW (4.9 × total nitrogen), depending on species and CO2 treatment, and contained more essential amino acids than protein from soybean. Elevated atmospheric CO2 concentrations (800 ppm) significantly boosted biomass production by 36–47%, without decreasing protein content. Choice of species and CO2 concentrations further affected the biomass content of lipids (79–100 g kg−1 DW) and (poly)phenols (21–69 g kg−1 DW). CONCLUSIONS By continuous harvesting, high protein yields can be obtained from Azolla cultures, without the need for nitrogen fertilization. High levels of (poly)phenols likely contribute to limitations in the inclusion rate of Azolla in animal diets and need further investigation. © 2018 The Authors. Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.