Deciphering competitive interactions: Phosphate and organic matter binding on goethite through experimental and theoretical insights.

The adsorption of phosphorus (P) onto active soil surfaces plays a pivotal role in immobilizing P, thereby influencing soil fertility and the filter function of soil to protect freshwater systems from eutrophication. Competitive anions, such as organic matter (OM), significantly affect the strength of this P-binding, eventually controlling P mobility and release, but surprisingly, these processes are insufficiently understood at the molecular level. In this study, we provide a molecular-level perspective on the influence of OM on P binding at the goethite-water interface using a combined experimental-theoretical approach. By examining the impact of citric acid (CIT) and histidine (HIS) on the adsorption of orthophosphate (OP), glycerol phosphate (GP), and inositol hexaphosphate (IHP) through adsorption experiments and molecular dynamics simulations, we address fundamental questions regarding P binding trends, OM interaction with the goethite surface, and the effect of OM on P adsorption. Our findings reveal the complex nature of P adsorption on goethite surfaces, where the specific OM, treatment conditions (covering the surface with OM or simultaneous co-adsorption), and initial concentrations collectively shape these interactions. P adsorption on goethite exhibits a binding strength increasing in the order of GP < OP < IHP. Crucially, this trend remains consistent across all adsorption experiments, regardless of the presence or absence of OM, CIT, or HIS, and irrespective of the specific treatment method. Notably, OP is particularly susceptible to inhibition by OM, while adsorption of GP depends on specific OM treatments. Despite being less sensitive to OM, IHP shows reduced adsorption, especially at higher initial P concentrations. Of significance is the strong inhibitory effect of CIT, particularly evident when the surface is pre-covered, resulting in a substantial 70 % reduction in OP adsorption compared to bare goethite. The sequence of goethite binding affinity to P and OM underscores a higher affinity of CIT and HIS compared to OP and GP, suggesting that OM can effectively compete with both OP and GP and replace them at the surface. In contrast, the impact of OM on IHP adsorption appears insignificant, as IHP exhibits a higher affinity than both CIT and HIS towards the goethite surface. The coverage of goethite surfaces with OM results in the blocking of active sites and the generation of an unfavorable electric potential and field, inhibiting anion adsorption and consequently reducing P binding. It is noteworthy that electrostatic interactions predominantly contribute more to the binding of P and OM to the surface compared to dispersion interactions.

The dark side of orange: Multiorganismic continuum dynamics within a lichen of the Atacama Desert.

Over the decades our understanding of lichens has shifted to the fact that they are multiorganismic, symbiotic microecosystems, with their complex interactions coming to the fore due to recent advances in microbiomics. Here, we present a mutualistic-parasitic continuum dynamics scenario between an orange lichen and a lichenicolous fungus from the Atacama Desert leading to the decay of the lichen's photobiont and leaving behind a black lichen thallus. Based on isolation, sequencing, and ecophysiological approaches including metabolic screenings of the symbionts, we depict consequences upon infection with the lichenicolous fungus. This spans from a loss of the lichen's photosynthetic activity and an increased roughness of its surface to an inhibition of the parietin synthesis as a shared pathway between the photobiont and the mycobiont, including a shift of secondary metabolism products. This degree of relations has rarely been documented before, although lichenicolous fungi have been studied for over 200 years, adding an additional level to the view of interactions within lichens.

Effects of pyrolysis and incineration on the phosphorus fertiliser potential of bio-waste- and plant-based materials.

Land application of biomass materials and their products of thermal treatment (biochars and ashes) can offset the unsustainable use of soluble P fertilisers. However, few evaluations of P fertiliser potential have systematically addressed diverse biomass types with contrasting P contents. This paper evaluates the relative P fertiliser potential of four P-rich biowastes (animal bone, poultry manure, pig slurry, and a municipal sewage sludge) and three low-P, plant-based materials (reeds [Phragmites australis L.], rice husks [Oryza sativa L.] and cocoa prunings [Theobroma cacao L.]) and their biochars and ashes. We utilised three complementary approaches: P extractability in single solvents (2% formic and citric acids, and 1 M neutral ammonium citrate); sequential chemical P fractionation, and P dissolution/desorption kinetics. In most cases, pyrolysis and incineration of the P-rich biowastes increased P extractability (% TP) in the single solvents, whilst decreasing water-soluble P. For pig slurry, for example, pyrolysis reduced water-soluble P 20-fold, with corresponding increases observed not only in the solvent-extractable P but also in the pool of potentially plant available, NaHCO3-Pi fraction (e.g., 17 to 35% TP). These complementary datasets were also evident for the low-P feedstocks and thermal products; e.g., pyrolysis increased the NaHCO3-Pi fraction in reed feedstock from 6 to 15% TP. For all biomass feedstocks, biochars and ashes, pseudo-second order P-release kinetics provided the best fit with the experimental data. The data demonstrate scope for using pyrolysis to upgrade the P fertiliser value of a wide range of biomass materials whilst reducing their environmental impact.

Advances in understanding the phosphate binding to soil constituents: A Computational Chemistry perspective.

Phosphorus (P) is an indispensable element to all forms of life and its efficient use in fertilizers is one of the conditions for food security. The efficiency of P fertilizers is affected by P mobilization and P fixation, both depending on the P binding strength to soil constituents. This review provides an overview of the P binding to soil constituents, especially to P-fixing mineral surfaces and its investigation using state-of-the-art Computational Chemistry (CC). A particular focus will be on goethite (α-FeOOH), which is highly significant in the context of P fixation in soils, given its prevalence, high susceptibility to P, and wide distribution across both oxic and anoxic environments. First, a brief overview will be given on experimental efforts related to the P adsorption at mineral surfaces and the factors affecting this process. Here, we will discuss the process of P adsorption, with a focus on important factors that influence this process, such as pH, surface crystallinity and morphology, competing anions, and electrolyte solutions. We will also explore the various techniques used to study this process and investigate the resulting binding motifs. Next, a brief introduction into common CC methods, techniques, and applications is presented, highlighting the advantages and limitations of each approach. Then, a comprehensive discussion of a wide range of the most relevant computational studies related to the phosphate binding issue will be provided. This will be followed by the main part of this review which is focusing on a possible strategy to cope with the soil heterogeneity by breaking down the complexity of P behavior in soil into well-defined models that can be discussed in terms of particular key factors. Hence, different molecular model systems and molecular simulations are introduced to reveal the P binding to soil organic matter (SOM), metal ions, and mineral surfaces. Simulation results provided an in-depth understanding of the P binding problem and explained at a molecular level the effects of surface plane, binding motif, kind and valency of metal ions, SOM composition, water, pH, and redox potential on the P binding in soil. On this basis, an overall molecular picture of P binding in soil can be then obtained by combining results for the different models. Eventually, challenges and further modifications of the existing molecular modeling approaches are discussed, such as steps necessary to bridge the molecular with the mesoscale.

Implications of Free and Occluded Fine Colloids for Organic Matter Preservation in Arable Soils.

Colloidal organo-mineral associations contribute to soil organic matter (OM) preservation and mainly occur in two forms: (i) as water-dispersible colloids that are potentially mobile (free colloids) and (ii) as building units of soil microaggregates that are occluded inside them (occluded colloids). However, the way in which these two colloidal forms differ in terms of textural characteristics and chemical composition, together with the nature of their associated OM, remains unknown. To fill these knowledge gaps, free and occluded fine colloids <220 nm were isolated from arable soils with comparable organic carbon (Corg) but different clay contents. Free colloids were dispersed in water suspensions during wet-sieving, while occluded colloids were released from water-stable aggregates by sonication. The asymmetric flow field-flow fractionation analysis on the free and occluded colloids suggested that most of the 0.6-220 nm fine colloidal Corg was present in size fractions that showed high abundances of Si, Al, and Fe. The pyrolysis-field ionization mass spectrometry revealed that the free colloids were relatively rich in less decomposed plant-derived OM (i.e., lipids, suberin, and free fatty acids), whereas the occluded colloids generally contained more decomposed and microbial-derived OM (i.e., carbohydrates and amides). In addition, a higher thermal stability of OM in occluded colloids pointed to a higher resistance to further degradation and mineralization of OM in occluded colloids than that in free colloids. This study provides new insights into the characteristics of subsized fractions of fine colloidal organo-mineral associations in soils and explores the impacts of free versus occluded colloidal forms on the composition and stability of colloid-associated OM.

Rice hull biochar enhances the mobilization and methylation of mercury in a soil under changing redox conditions: Implication for Hg risks management in paddy fields.

Biochar amendment to paddy soils was promising to mitigate mercury (Hg) accumulation in rice; thus, it was applied to reduce human Hg exposure via rice consumption. However, how biochar affects Hg mobilization and MeHg formation in soil under changed redox potential (Eh) conditions remained unknown. Here, we explored the change of dissolved total Hg (DTHg) and dissolved MeHg (DMeHg), and their controlling biogeochemical factors in a soil with(out) biochar amendment under changing Eh conditions using biogeochemical microcosm. Biochar amendment resulted in a widen Eh range (-300 to 400 mV) compared to the control (-250 to 350 mV), demonstrating that biochar promoted reduction-oxidization reactions in soil. Biochar amendment enhanced Hg mobilization by mediating reductive dissolution of Fe/Mn (hydr)oxides. Thus, the increased Hg availability promoted MeHg formation in the soils. Biochar amendment changed the soil organic matter (SOM) composition. Positive correlations between the relative abundance of LIPID (lipids, alkanes/alkenes), ALKYL (alkylaromatics), and suberin and MeHg concentrations indicate that these SOM groups might be related to MeHg formation. Biochar enhanced the releasing and methylation of Hg by promoting the mobilization of Fe(oxyhydr)oxides and alternation of carbon chemistry under dynamic Eh conditions. There is an unexpected environmental risk associated with biochar application to paddy soils under dynamic Eh condition, and one should be aware this risk when applying biochar aiming to minimize human Hg exposure health risks via rice consumption.

Sulfur speciation in drained and restored minerotrophic peatland types of northeastern Germany.

Restoring drained peatlands has been practiced to mitigate climate change, regulate water quality, and restore biodiversity. However, no information is available on the long-term impact of drainage and restoration of peatlands on total sulfur (St), fractions, and S species. We investigated the long-term drained and restored forested and coastal peatlands and percolation mires using the sequential S fractionation and S K-edge X-ray near-edge absorption structure (XANES) spectroscopy analysis to address this knowledge gap. The St concentrations in the drained forested peatland and percolation mire were low by 4 and 1.5 folds compared to their respective restored peatlands at the topsoil horizons. Similarly, the H2O-S and NaH2PO4-S fractions in the drained forested peatland (28 and 18 mg kg-1) were lower than in the restored forested peatland (165 and 166 mg kg-1). However, the S fractions were higher in the drained percolation mire (449 and 247 mg kg-1) than in the restored percolation mire (150 and 41 mg kg-1). The relative proportion of the residual-S fraction (70-97% of St) was equivalent to the relative proportion of organic S species (76-97% of St) derived from the XANES analysis. The XANES analysis revealed the reduced organic S (44-62%), organic S with intermediate oxidation states (16-47%), strongly reduced (0-21%) and oxidized inorganic S species (4-12%) of the St. The results indicate that long-term restoration conserved St, decreased labile S fractions and enriched the strongly reduced inorganic and organic S species.

Preference and possible consumption of provided enrichment and bedding materials and disinfectant powder by growing pigs.

BACKGROUND: Domestic pigs have an evolutionary conserved exploratory behaviour. To comply with this requirement, the European Union aims at setting standards for appropriate enrichment materials for pigs (Council Directive 2008/120/EC). As recommended characteristics include 'chewable' and 'edible', pigs might also consume these materials (Commission Recommendation (EU) 2016/336), which are often additionally advertised to enhance lying comfort and hygienic conditions in stables. To date, a wide range of bedding, enrichment and disinfectant materials is available on the market to ensure environmental enrichment, a dry, hygienic environment or lying comfort. Previous studies revealed considerable amounts of undesirable substances in some of these materials possibly being a risk for food safety considering oral uptake by the animal. To determine interest and indicators for consumption of different types of materials by pigs during exploratory behaviour, a camera-assisted observational study with 12 female pigs (German Landrace) was conducted. We tested their preference for a disinfectant powder, peat, biochar and straw as reference material in a 4 × 6 factorial arrangement. RESULTS: Pigs manipulated and consumed all offered materials. However, longest manipulation time per pig was observed for biochar (63 min/day) and peat (50 min/day) (p < 0.05). Analyses of the bulk molecular-chemical composition and n-alkanes and acid insoluble ash as markers in the materials and in faeces clearly revealed the consumption of these materials by pigs. CONCLUSIONS: Whether the consumption of considerable amounts together with certain levels of undesirable substances represents a risk for pig and consumer health could yet not be established. Future studies will address the quantitative contribution of undesirable substances by oral ingestion of bedding and enrichment materials and disinfectant powders to the daily feed ration.

Stepwise redox changes alter the speciation and mobilization of phosphorus in hydromorphic soils.

Sustainable engineering and management of hydromorphic arable soils need deep knowledge about the redox-mediated interactions between nutrients and soil colloids. Consequently, we examined the redox-mediated interactions of P with metal oxides and organic carbon (OC) in toe-, mid-, and upper-slope arable soils under dynamic redox changes using geochemical (biogeochemical microcosm), spectroscopic (XANES), and molecular (quantum chemical calculations (QCC)) approaches. We controlled the redox potential (EH) in two directions i.e., 1) slowly oxidizing direction (SOD; EH increased from -286 to +564 mV); and 2) slowly reducing direction (SRD; EH decreased from +564 to -148 mV). In the SOD of all soils, P, Fe2+ and OC mobilized at EH ≤ 200 mV, due to the pH decrease from 7.2 to 4.1 and dissolution of Fe-oxyhydroxides/carbonates, as indicated by the decrease of Fe-P and Ca-P determined by P-K-edge-XANES. At EH > 200 mV, P immobilized due to the strong P binding with Fe3+ as suggested by QCC. In the SRD of mid-slope-soil, P immobilized with decreasing EH, due to pH increase and P retention by aromatic carbon and/or precipitation by carbonates, as supported by increase of organic-P and Ca-P. These findings help for management of P in arable soils.

Microbial Diversity in Subarctic Biocrusts from West Iceland following an Elevation Gradient.

Biological soil crusts (biocrusts) are essential communities of organisms in the Icelandic soil ecosystem, as they prevent erosion and cryoturbation and provide nutrients to vascular plants. However, biocrust microbial composition in Iceland remains understudied. To address this gap in knowledge, we applied high-throughput sequencing to study microbial community composition in biocrusts collected along an elevation gradient (11-157 m a.s.l.) stretching away perpendicular to the marine coast. Four groups of organisms were targeted: bacteria and cyanobacteria (16S rRNA gene), fungi (transcribed spacer region), and other eukaryotes (18S rRNA gene). The amplicon sequencing of the 16S rRNA gene revealed the dominance of Proteobacteria, Bacteroidetes, and Actinobacteria. Within the cyanobacteria, filamentous forms from the orders Synechococcales and Oscillatoriales prevailed. Furthermore, fungi in the biocrusts were dominated by Ascomycota, while the majority of reads obtained from sequencing of the 18S rRNA gene belonged to Archaeplastida. In addition, microbial photoautotrophs isolated from the biocrusts were assigned to the cyanobacterial genera Phormidesmis, Microcoleus, Wilmottia, and Oscillatoria and to two microalgal phyla Chlorophyta and Charophyta. In general, the taxonomic diversity of microorganisms in the biocrusts increased following the elevation gradient and community composition differed among the sites, suggesting that microclimatic and soil parameters might shape biocrust microbiota.

Degradation of glyphosate in water by the application of surface corona discharges.

Glyphosate (GLP) is one of the most widely applied herbicides, and is found ubiquitously in the environment. The removal of glyphosate from waste water and soil is challenging and can be achieved with chemical or biological methods, which, nevertheless, suffer from different disadvantages. The application of a physical plasma for the removal of GLP in water was examined by the application of surface corona discharges in a wire-to-cylinder setup filled with argon. The plasma was ignited at the liquid surface without any additives. By applying a photometric method, GLP was detected after derivatisation with fluorenyl methoxycarbonyl chloride, whereas phosphate was determined with ammonium molybdate. A GLP degradation rate of 90.8% could be achieved within a treatment time of 30 minutes with an estimated energy efficiency of 0.32 g/kWh.

AMPA-15N - Synthesis and application as standard compound in traceable degradation studies of glyphosate.

Stable isotope labeling of pollutants is a valuable tool to investigate their environmental transport and degradation. For the globally most frequently used herbicide glyphosate, such studies have, so far, been hampered by the absence of an analytical standard for its labeled metabolite AMPA-15N, which is formed during the degradation of all commercially available glyphosate isotopologues. Without such a standard, detection and quantitation of AMPA-15N, e.g. with LC-MS/MS, is not possible. Therefore, a synthetic pathway to AMPA-15N from benzamide-15N via the hemiaminal was developed. AMPA-15N was obtained in sufficient yield and purity to be used as a standard compound for LC-MS/MS analysis. Suitable MS-detection settings as well as a calibration using the internal standard (IS) approach were established for Fmoc-derivatized AMPA-15N. The use of different AMPA isotopologues as IS was complicated by the parallel formation of [M+H]+ and [M]+• AMPA-Fmoc precursor ions in ESI-positive mode, causing signal interferences between analyte and IS. We recommend the use of either AMPA-13C-15N, AMPA-13C-15N-D2 or a glyphosate isotopologue as IS, as they do not affect the linearity of the calibration curve. As a proof of concept, the developed analysis procedure for AMPA-15N was used to refine the results from a field lysimeter experiment investigating leaching and degradation of glyphosate-2-13C-15N. The newly enabled quantitation of AMPA-15N in soil extracts showed that similar amounts (0.05 - 0.22 mg·kg-1) of the parent herbicide glyphosate and its primary metabolite AMPA persisted in the topsoil over the study period of one year, while vertical transport through the soil column did not occur for either of the compounds. The herein developed analysis concepts will facilitate future design and execution of experiments on the environmental fate of the herbicide glyphosate.

Dissolved organic matter concentration, molecular composition, and functional groups in contrasting management practices of peatlands.

About 91,300 ha of peatlands has been rewetted in western Europe since the mid-1990s. Still, it is unknown how long-term rewetting alters the dissolved organic matter (DOM) concentration, molecular composition, and functional groups. We examined these DOM characteristics in three peatland types subjected to 47- to 231-yr drainage and 18- to 24-yr rewetting to address this knowledge gap. Cold water-extractable DOM was characterized by pyrolysis field ionization mass spectrometry (Py-FIMS) and X-ray absorption near-edge structure (XANES) spectroscopy. The dissolved organic carbon (DOC) concentration in the rewetted forest peatland was 2.7 times higher than in the drained forest peatland. However, rewetting decreased the DOC concentrations by 1.5 and 4 times in the coastal peatland and percolation mire, respectively, compared with their respective drained peatlands at the topsoil horizons. The Py-FIMS analysis revealed that all nine DOM compound classes' relative abundances differed between the rewetted and drained forest peatland with the lower relative abundances of the labile DOM compound classes in the rewetted forest peatlands. However, most DOM compound classes' relative abundances were similar between the rewetted and drained coastal peatlands and percolation mires. The XANES also revealed nine carbon and seven nitrogen functional groups with no apparent differences between the two contrasting management practices. The influence of drainage and rewetting on DOC concentration and molecular composition depends on peatland type, drainage period, rewetting intensity, and peat degradation status that should be considered in future research for understanding DOM transformation and transportation from degraded and restored peatland ecosystems.

Redox-induced mobilization of phosphorus in groundwater affected arable soil profiles.

Mobilization of phosphorus (P) in arable soils might be affected by groundwater fluctuations and the associated changes in redox potential (EH). However, the impact of systematic changes of EH on P mobilization in redoximorphic arable soils along a catena has not been studied so far. Therefore, we investigated P mobilization under different redox conditions in top- and sub-soil horizons of three groundwater affected arable soils along a slight slope (toe-, mid-, and upper-slope position) in Northern Germany using an automated biogeochemical microcosm system. The impact of pH, Al, Fe, Mn, and dissolved organic carbon (DOC) on P mobilization was also studied. The initial EH (+351 to +431 mV) and pH (6.5-7.0) decreased in all soil samples (EH = -280 mV; pH = 4.4) when creating a slurry. Thereafter, the pH increased to 7.1 and 6.4 with increasing EH in the mid-and toe-slope soil, respectively. Concentrations of dissolved P ranged between 20.8 mg L-1 under low EH in the toe slope topsoil and 0.69 mg L-1 under high EH in the toe- and mid-slop subsoil. Concentrations (mg L-1) of dissolved Fe (0.31-13.3) and DOC (92-2651) increased under low EH and decreased under high EH. The increase of P mobilization under low EH and pH in the soils might be due to the release of P via the reductive and acidic dissolution of Fe-(oxhydr)oxides and/or due to soil organic matter mineralization. The high mobilization of P under reducing conditions may increase its bioavailability; however, it may increase its loss in the soils, particularly in the toe slope profile.

Taxonomic and Functional Diversity of Heterotrophic Protists (Cercozoa and Endomyxa) from Biological Soil Crusts.

Biological soil crusts (biocrusts) accommodate diverse communities of phototrophic and heterotrophic microorganisms. Heterotrophic protists have critical roles in the microbial food webs of soils, with Cercozoa and Endomyxa often being dominant groups. Still, the diversity, community composition, and functions of Cercozoa and Endomyxa in biocrusts have been little explored. In this study, using a high-throughput sequencing method with taxon-specific barcoded primers, we studied cercozoan and endomyxan communities in biocrusts from two unique habitats (subarctic grassland and temperate dunes). The communities differed strongly, with the grassland and dunes being dominated by Sarcomonadea (69%) and Thecofilosea (43%), respectively. Endomyxa and Phytomyxea were the minor components in dunes. Sandonidae, Allapsidae, and Rhogostomidae were the most abundant taxa in both habitats. In terms of functionality, up to 69% of the grassland community was constituted by bacterivorous Cercozoa. In contrast, cercozoan and endomyxan communities in dunes consisted of 31% bacterivores, 25% omnivores, and 20% eukaryvores. Facultative and obligate eukaryvores mostly belonged to the families Rhogostomidae, Fiscullidae, Euglyphidae, Leptophryidae, and Cercomonadidae, most of which are known to feed mainly on algae. Biocrust edaphic parameters such as pH, total organic carbon, nitrogen, and phosphorus did not have any significant influence on shaping cercozoan communities within each habitat, which confirms previous results from dunes.

Molecular level picture of the interplay between pH and phosphate binding at the goethite-water interface.

The soil pH plays a substantial role in controlling phosphorus (P) adsorption and mobilization. These processes are strongly affected by the phosphate interaction strength with P-fixing soil minerals such as goethite. The target of the current contribution is to draw a molecular level picture of the interplay between pH and phosphate binding at the goethite-water interface via a joint experimental-theoretical approach. Periodic density functional theory (DFT) calculations were carried out to provide a molecular level understanding of the pH dependence of P adsorption. To validate the modeling approach, adsorption experiments of phosphate at goethite were performed in the pH range of 4-12. There was agreement between experiments and simulations in the description of the adsorption behavior by two pH-dependent successive stages. The adsorption increases along the pH change from 4 to 8. A further increase of pH leads to a decrease of adsorption. By comparing with literature data it is concluded that the first stage will be observed only if there is no significant change of the surface charge at low pH. Moreover, the molecular modeling results point to the abundance of the monodentate (M) binding motif at both extremely low and high pH ranges. Otherwise, the bidentate (B) one is predominant along the intermediate pH range. These observations could resolve the existing debate about the assignment of phosphate-goethite binding motifs. Furthermore, the results point to a decrease of pH upon phosphate sorption due to an induced acidification of soil solution. The present joint experimental-theoretical approach provides a better understanding and description of the existing phosphate sorption experiments and highlights new findings at the atomistic/molecular scale.

Lichens Bite the Dust - A Bioweathering Scenario in the Atacama Desert.

Bioweathering mediated by microorganisms plays a significant role in biogeochemical cycles on global scales over geological timescales. Single processes induced by specific taxa have been described but could rarely be demonstrated for complex communities that dominate whole landscapes. The recently discovered grit crust of the coastal Atacama Desert, which is a transitional community between a cryptogamic ground cover and a rock-bound lithic assemblage, offers the unique chance to elucidate various bioweathering processes that occur simultaneously. Here, we present a bioweathering scenario of this biocenosis including processes such as penetration of the lithomatrix, microbial responses to wet-dry cycles, alkalinolysis, enzyme activity, and mineral re-localization. Frequently occurring fog, for example, led to a volume increase of microorganisms and the lithomatrix. This, together with pH shifts and dust accumulation, consequently results in biophysical breakdown and the formation of a terrestrial protopedon, an initial stage of pedogenesis fueled by the grit crust.

Biodiversity of Algae and Cyanobacteria in Biological Soil Crusts Collected Along a Climatic Gradient in Chile Using an Integrative Approach.

Biocrusts are associations of various prokaryotic and eukaryotic microorganisms in the top millimeters of soil, which can be found in every climate zone on Earth. They stabilize soils and introduce carbon and nitrogen into this compartment. The worldwide occurrence of biocrusts was proven by numerous studies in Europe, Africa, Asia and North America, leaving South America understudied. Using an integrative approach, which combines morphological and molecular characters (small subunit rRNA and ITS region), we examined the diversity of key biocrust photosynthetic organisms at four sites along the latitudinal climate gradient in Chile. The most northern study site was located in the Atacama Desert (arid climate), followed by open shrubland (semiarid climate), a dry forest region (Mediterranean climate) and a mixed broad leaved-coniferous forest (temperate climate) in the south. The lowest species richness was recorded in the desert (18 species), whereas the highest species richness was observed in the Mediterranean zone with (40 species). Desert biocrusts were composed exclusively of single-celled Chlorophyta algae, followed by cyanobacteria. Chlorophyta, Streptophyta and cyanobacteria dominated semiarid biocrusts, whereas Mediterranean and temperate Chilean biocrusts were composed mostly of Chlorophyta, Streptophyta and Ochrophyta. Our investigation of Chilean biocrust suggests high biodiversity of South American biocrust phototrophs.

Speciation and sorption of phosphorus in agricultural soil profiles of redoximorphic character.

Controlled drainage is considered as a soil management tool to improve water supply to crops and reduce nutrient losses from fields; however, its closure may affect phosphorus (P) mobilization in soil. To assess the P mobilization potential, three soil profiles with redoximorphic features were selected along a slight hill in Northern Germany. Soil samples from three depths of each profile were characterized for basic properties, total element content, oxalate- and dithionite-extractable pedogenic Al, Fe and Mn (hydr)oxides, P pools (sequential extraction), P species [P K-edge X-ray absorption near-edge structure (XANES) spectroscopy] and P sorption behavior. In topsoil (~ 10 cm depth), labile P (H2O-P + resin-P + NaHCO3-P) accounted for 26-32% of total P (Pt). Phosphorus K-edge XANES revealed that up to 49% of Pt was bound to Al and/or Fe (hydr)oxides, but sequential fractionation indicated that > 30% of this P was occluded within sesquioxide aggregates. A low binding capacity for P was demonstrated by P sorption capacity and low Kf coefficients (20-33 [Formula: see text]) of the Freundlich equation. In the subsoil layers (~ 30 and ~ 65 cm depth), higher proportions of Al- and Fe-bound P along with other characteristics suggested that all profiles might be prone to P mobilization/leaching risk under reducing conditions even if the degree of P saturation (DPS) of a profile under oxic conditions was < 25%. The results suggest that a closure of the controlled drainage may pose a risk of increased P mobilization, but this needs to be compared with the risk of uncontrolled drainage and P losses to avoid P leaching into the aquatic ecosystem.

Leaching and degradation of 13C2-15N-glyphosate in field lysimeters.

Glyphosate (GLYP), the globally most important herbicide, may have effects in various compartments of the environment such as soil and water. Although laboratory studies showed fast microbial degradation and a low leaching potential, it is often detected in various environmental compartments, but pathways are unknown. Therefore, the objective was to study GLYP leaching and transformations in a lysimeter field experiment over a study period of one hydrological year using non-radioactive 13C2-15N-GLYP labelling and maize cultivation. 15N and 13C were selectively measured using isotopic ratio mass spectrometry (IR-MS) in leachates, soil, and plant material. Additionally, HPLC coupled to tandem mass spectrometry (HPLC-MS/MS) was used for quantitation of GLYP and its main degradation product aminomethylphosphonic acid (AMPA) in different environmental compartments (leachates and soil). Results show low recoveries for GLYP (< 3%) and AMPA (< level of detection) in soil after the study period, whereas recoveries of 15N (11-19%) and 13C (23-54%) were higher. Time independent enrichment of 15N and 13C and the absence of GLYP and AMPA in leachates indicated further degradation. 15N was enriched in all compartments of maize plants (roots, shoots, and cobs). 13C was only enriched in roots. Results confirmed rapid degradation to further degradation products, e.g., 15NH4+, which plausibly was taken up as nutrient by plants. Due to the discrepancy of low GLYP and AMPA concentrations in soil, but higher values for 15N and 13C after the study period, it cannot be excluded that non-extractable residues of GLYP remained and accumulated in soil.