Association between soil organic carbon and calcium in acidic grassland soils from Point Reyes National Seashore, CA

Organo-mineral and organo-metal associations play an important role in the retention and accumulation of soil organic carbon (SOC). Recent studies have demonstrated a positive correlation between calcium (Ca) and SOC content in a range of soil types. However, most of these studies have focused on soils that contain calcium carbonate (pH > 6). To assess the importance of Ca-SOC associations in lower pH soils, we investigated their physical and chemical interaction in the grassland soils of Point Reyes National Seashore (CA, USA) at a range of spatial scales. Multivariate analyses of our bulk soil characterisation dataset showed a strong correlation between exchangeable Ca (Ca$_{Exch}$; 5–8.3 c.mol$_{c}$ kg$^{−1}$) and SOC (0.6–4%) content. Additionally, linear combination fitting (LCF) of bulk Ca K-edge X-ray absorption near-edge structure (XANES) spectra revealed that Ca was predominantly associated with organic carbon across all samples. Scanning transmission X-ray microscopy near-edge X-ray absorption fine structure spectroscopy (STXM C/Ca NEXAFS) showed that Ca had a strong spatial correlation with C at the microscale. The STXM C NEXAFS K-edge spectra indicated that SOC had a higher abundance of aromatic/olefinic and phenolic C functional groups when associated with Ca, relative to C associated with Fe. In regions of high Ca-C association, the STXM C NEXAFS spectra were similar to the spectrum from lignin, with moderate changes in peak intensities and positions that are consistent with oxidative C transformation. Through this association, Ca thus seems to be preferentially associated with plant-like organic matter that has undergone some oxidative transformation, at depth in acidic grassland soils of California. Our study highlights the importance of Ca-SOC complexation in acidic grassland soils and provides a conceptual model of its contribution to SOC preservation, a research area that has previously been unexplored

Organizational level responses to the COVID-19 outbreak : challenges, strategies and framework for academic institutions

The outbreak of the novel coronavirus, severe acute respiratory syndrome (SARS)–CoV-2, has gained unprecedented global attention. SARS-CoV-2, which causes the newly described coronavirus disease 2019 (COVID-19), has affected millions of people and led to over 1.9 million deaths worldwide by the beginning of January 2021. Several governments have opted for lockdown as one of the measures to combat the rapidly increasing number of COVID-19 cases. Academic institutions (i.e., universities, colleges, research centers and national laboratories), which are home to thousands of students, researchers, technicians, and administrative staff, have strictly followed government regulations. Due to the lockdown, the majority of academics have been facing various challenges, especially in transitioning from classroom to remote teaching and conducting research activities from a home office. This article from an early-career researchers’ perspective addresses the common challenges that academic institutions have encountered and possible strategies they have adopted to mitigate those challenges at the individual organizational level. Furthermore, we propose a framework to facilitate the handling of such crisis in any near future at the organizational level. We hope academics, policymakers and (non) government organizations across the globe will find this perspective a call to better improve the overall infrastructure of academic institutions

Catalytic effects of photogenerated Fe(II) on the ligand-controlled dissolution of Iron(hydr)oxides by EDTA and DFOB

Low bioavailability of iron due to poor solubility of iron(hydr)oxides limits the growth of microorganisms and plants in soils and aquatic environments. Previous studies described accelerated dissolution of iron(hydr)oxides under continuous illumination, but did not distinguish between photoreductive dissolution and non-reductive processes in which photogenerated Fe(II) catalyzes ligand-controlled dissolution. Here we show that short illuminations (5–15 min) accelerate the dissolution of iron(hydr)oxides by ligands during subsequent dark periods under anoxic conditions. Suspensions of lepidocrocite (Lp) and goethite (Gt) (1.13 mM) with 50 μM EDTA or DFOB were illuminated with UV-A light of comparable intensity to sunlight (pH 7.0, bicarbonate-CO2 buffered solutions). During illumination, the rate of Fe(II) production was highest with Gt-EDTA; followed by Lp-EDTA > Lp-DFOB > Lp > Gt-DFOB > Gt. Under anoxic conditions, photochemically produced Fe(II) increased dissolution rates during subsequent dark periods by factors of 10–40 and dissolved Fe(III) reached 50 μM with DFOB and EDTA. Under oxic conditions, dissolution rates increased by factors of 3–5 only during illumination. With DFOB dissolved Fe(III) reached 35 μM after 10 h of illumination, while with EDTA it peaked at 15 μM and then decreased to below 2 μM. The observations are explained and discussed based on a kinetic model. The results suggest that in anoxic bottom water of ponds and lakes, or in microenvironments of algal blooms, short illuminations can dramatically increase the bioavailability of iron by Fe(II)-catalyzed ligand-controlled dissolution. In oxic environments, photostable ligands such as DFOB can maintain Fe(III) in solution during extended illumination.ISSN:0045-6535ISSN:1879-129

Linking Isotope Exchange with Fe(II)-Catalyzed Dissolution of Iron(hydr)oxides in the Presence of the Bacterial Siderophore Desferrioxamine-B

Dissolution of Fe(III) phases is a key process in making iron available to biota and in the mobilization of associated trace elements. Recently, we have demonstrated that submicromolar concentrations of Fe(II) significantly accelerate rates of ligand-controlled dissolution of Fe(III) (hydr)oxides at circumneutral pH. Here, we extend this work by studying isotope exchange and dissolution with lepidocrocite (Lp) and goethite (Gt) in the presence of 20 or 50 mu M desferrioxamine-B (DFOB). Experiments with Lp at pH 7.0 were conducted in carbonate-buffered suspensions to mimic environmental conditions. We applied a simple empirical model to determine dissolution rates and a more complex kinetic model that accounts for the observed isotope exchange and catalytic effect of Fe(II). The fate of added tracer Fe-57(II) was strongly dependent on the order of addition of Fe-57(II) and ligand. When DFOB was added first, tracer Fe-57 remained in solution. When Fe-57(II) was added first, isotope exchange between surface and solution could be observed at pH 6.0 but not at pH 7.0 and 8.5 where Fe-57(II) was almost completely adsorbed. During dissolution of Lp with DFOB, ratios of released Fe-56 and Fe-57 were largely independent of DFOB concentrations. In the absence of DFOB, addition of phenanthroline 30 min after tracer Fe-57 desorbed predominantly Fe-56(II), indicating that electron transfer from adsorbed Fe-57 to Fe-56 of the Lp surface occurs on a time scale of minutes to hours. In contrast, comparable experiments with Gt desorbed predominantly Fe-57(II), suggesting a longer time scale for electron transfer on the Gt surface. Our results show that addition of 1-5 mu M Fe(IT) leads to dynamic charge transfer between dissolved and adsorbed species and to isotope exchange at the surface, with the dissolution of Lp by ligands accelerated by up to 60-fold

Linking Isotope Exchange with Fe(II)-Catalyzed Dissolution of Iron(hydr)oxides in the Presence of the Bacterial Siderophore Desferrioxamine-B

Dissolution of Fe(III) phases is a key process in making iron available to biota and in the mobilization of associated trace elements. Recently, we have demonstrated that submicromolar concentrations of Fe(II) significantly accelerate rates of ligand-controlled dissolution of Fe(III) (hydr)oxides at circumneutral pH. Here, we extend this work by studying isotope exchange and dissolution with lepidocrocite (Lp) and goethite (Gt) in the presence of 20 or 50 μM desferrioxamine-B (DFOB). Experiments with Lp at pH 7.0 were conducted in carbonate-buffered suspensions to mimic environmental conditions. We applied a simple empirical model to determine dissolution rates and a more complex kinetic model that accounts for the observed isotope exchange and catalytic effect of Fe(II). The fate of added tracer 57Fe(II) was strongly dependent on the order of addition of 57Fe(II) and ligand. When DFOB was added first, tracer 57Fe remained in solution. When 57Fe(II) was added first, isotope exchange between surface and solution could be observed at pH 6.0 but not at pH 7.0 and 8.5 where 57Fe(II) was almost completely adsorbed. During dissolution of Lp with DFOB, ratios of released 56Fe and 57Fe were largely independent of DFOB concentrations. In the absence of DFOB, addition of phenanthroline 30 min after tracer 57Fe desorbed predominantly 56Fe(II), indicating that electron transfer from adsorbed 57Fe to 56Fe of the Lp surface occurs on a time scale of minutes to hours. In contrast, comparable experiments with Gt desorbed predominantly 57Fe(II), suggesting a longer time scale for electron transfer on the Gt surface. Our results show that addition of 1–5 μM Fe(II) leads to dynamic charge transfer between dissolved and adsorbed species and to isotope exchange at the surface, with the dissolution of Lp by ligands accelerated by up to 60-fold

Fe(II)-Catalyzed Ligand-Controlled Dissolution of Iron(hydr)oxides

Dissolution of iron(III)phases is a key process in soils, surface waters, and the ocean. Previous studies found that traces of Fe(II) can greatly increase ligand controlled dissolution rates at acidic pH, but the extent that this also occurs at circumneutral pH and what mechanisms are involved are not known. We addressed these questions with infrared spectroscopy and 57Fe isotope exchange experiments with lepidocrocite (Lp) and 50 μM ethylenediaminetetraacetate (EDTA) at pH 6 and 7. Addition of 0.2–10 μM Fe(II) led to an acceleration of the dissolution rates by factors of 7–31. Similar effects were observed after irradiation with 365 nm UV light. The catalytic effect persisted under anoxic conditions, but decreased as soon as air or phenanthroline was introduced. Isotope exchange experiments showed that added 57Fe remained in solution, or quickly reappeared in solution when EDTA was added after 57Fe(II), suggesting that catalyzed dissolution occurred at or near the site of 57Fe incorporation at the mineral surface. Infrared spectra indicated no change in the bulk, but changes in the spectra of adsorbed EDTA after addition of Fe(II) were observed. A kinetic model shows that the catalytic effect can be explained by electron transfer to surface Fe(III) sites and rapid detachment of Fe(III)EDTA due to the weaker bonds to reduced sites. We conclude that the catalytic effect of Fe(II) on dissolution of Fe(III)(hydr)oxides is likely important under circumneutral anoxic conditions and in sunlit environments

Linking Isotope Exchange with Fe(II)-Catalyzed Dissolution of Iron(hydr)oxides in the Presence of the Bacterial Siderophore Desferrioxamine-B

Dissolution of Fe(III) phases is a key process in making iron available to biota and in the mobilization of associated trace elements. Recently, we have demonstrated that submicromolar concentrations of Fe(II) significantly accelerate rates of ligand-controlled dissolution of Fe(III) (hydr)oxides at circumneutral pH. Here, we extend this work by studying isotope exchange and dissolution with lepidocrocite (Lp) and goethite (Gt) in the presence of 20 or 50 μM desferrioxamine-B (DFOB). Experiments with Lp at pH 7.0 were conducted in carbonate-buffered suspensions to mimic environmental conditions. We applied a simple empirical model to determine dissolution rates and a more complex kinetic model that accounts for the observed isotope exchange and catalytic effect of Fe(II). The fate of added tracer 57Fe(II) was strongly dependent on the order of addition of 57Fe(II) and ligand. When DFOB was added first, tracer 57Fe remained in solution. When 57Fe(II) was added first, isotope exchange between surface and solution could be observed at pH 6.0 but not at pH 7.0 and 8.5 where 57Fe(II) was almost completely adsorbed. During dissolution of Lp with DFOB, ratios of released 56Fe and 57Fe were largely independent of DFOB concentrations. In the absence of DFOB, addition of phenanthroline 30 min after tracer 57Fe desorbed predominantly 56Fe(II), indicating that electron transfer from adsorbed 57Fe to 56Fe of the Lp surface occurs on a time scale of minutes to hours. In contrast, comparable experiments with Gt desorbed predominantly 57Fe(II), suggesting a longer time scale for electron transfer on the Gt surface. Our results show that addition of 1–5 μM Fe(II) leads to dynamic charge transfer between dissolved and adsorbed species and to isotope exchange at the surface, with the dissolution of Lp by ligands accelerated by up to 60-fold

Association between soil organic carbon and calcium in acidic grassland soils from Point Reyes National Seashore, CA.

UNLABELLED: Organo-mineral and organo-metal associations play an important role in the retention and accumulation of soil organic carbon (SOC). Recent studies have demonstrated a positive correlation between calcium (Ca) and SOC content in a range of soil types. However, most of these studies have focused on soils that contain calcium carbonate (pH > 6). To assess the importance of Ca-SOC associations in lower pH soils, we investigated their physical and chemical interaction in the grassland soils of Point Reyes National Seashore (CA, USA) at a range of spatial scales. Multivariate analyses of our bulk soil characterisation dataset showed a strong correlation between exchangeable Ca (CaExch; 5-8.3 c.molc kg-1) and SOC (0.6-4%) content. Additionally, linear combination fitting (LCF) of bulk Ca K-edge X-ray absorption near-edge structure (XANES) spectra revealed that Ca was predominantly associated with organic carbon across all samples. Scanning transmission X-ray microscopy near-edge X-ray absorption fine structure spectroscopy (STXM C/Ca NEXAFS) showed that Ca had a strong spatial correlation with C at the microscale. The STXM C NEXAFS K-edge spectra indicated that SOC had a higher abundance of aromatic/olefinic and phenolic C functional groups when associated with Ca, relative to C associated with Fe. In regions of high Ca-C association, the STXM C NEXAFS spectra were similar to the spectrum from lignin, with moderate changes in peak intensities and positions that are consistent with oxidative C transformation. Through this association, Ca thus seems to be preferentially associated with plant-like organic matter that has undergone some oxidative transformation, at depth in acidic grassland soils of California. Our study highlights the importance of Ca-SOC complexation in acidic grassland soils and provides a conceptual model of its contribution to SOC preservation, a research area that has previously been unexplored. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10533-023-01059-2

Fe(II)-Catalyzed Ligand-Controlled Dissolution of Iron(hydr)oxides

Dissolution of iron(III)phases is a key process in soils, surface waters, and the ocean. Previous studies found that traces of Fe(II) can greatly increase ligand controlled dissolution rates at acidic pH, but the extent that this also occurs at circumneutral pH and what mechanisms are involved are not known. We addressed these questions with infrared spectroscopy and 57Fe isotope exchange experiments with lepidocrocite (Lp) and 50 μM ethylenediaminetetraacetate (EDTA) at pH 6 and 7. Addition of 0.2–10 μM Fe(II) led to an acceleration of the dissolution rates by factors of 7–31. Similar effects were observed after irradiation with 365 nm UV light. The catalytic effect persisted under anoxic conditions, but decreased as soon as air or phenanthroline was introduced. Isotope exchange experiments showed that added 57Fe remained in solution, or quickly reappeared in solution when EDTA was added after 57Fe(II), suggesting that catalyzed dissolution occurred at or near the site of 57Fe incorporation at the mineral surface. Infrared spectra indicated no change in the bulk, but changes in the spectra of adsorbed EDTA after addition of Fe(II) were observed. A kinetic model shows that the catalytic effect can be explained by electron transfer to surface Fe(III) sites and rapid detachment of Fe(III)EDTA due to the weaker bonds to reduced sites. We conclude that the catalytic effect of Fe(II) on dissolution of Fe(III)(hydr)oxides is likely important under circumneutral anoxic conditions and in sunlit environments