Nitrogen mineralization from organic amendments during the second year following application

Estimates of nitrogen (N) available from long-term application of organic amendments are required to balance N inputs with crop N requirements. Two studies were conducted to (1) determine N mineralized from organic amendments (manures and composts) during year 2 after application, and (2) compare plant-available N (PAN) determined via in situ microplot incubations with PAN determined via laboratory incubations under aerobic and anaerobic conditions. In the first study, soil samples were collected from field plots with and without a history of screened dairy solids application at Oregon State University Vegetable Research Farm near Corvallis, OR. Amounts of N mineralized were estimated using a microplot technique. Microplots, open-ended cyclinders 5 cm i.d. x 15 cm long, were equipped with pillows that contained ion exchange resins at the base. The resins trapped nitrate ions leached from soil in the cylinders. Field microplot estimates of PAN were compared with estimations of PAN from aerobic and anaerobic laboratory incubations. Screened dairy solids immobilized PAN for approximately 700 degree days (0°C base temperature) after application, and then mineralized N after 700 degree days. In soil that had received screened dairy solids application for 2 to 3 previous years, the increase in net mineralization rate was approximately 0.01 mg N kg⁻¹ dry soil degree day⁻¹. Field microplot and aerobic laboratory estimates of PAN were well correlated. Our study showed that a small fraction of amendment total N was mineralized during years 2, 3 and 4 following amendment application. For example, dairy solids applied from 200 1-2002 contained 1,728 kg N ha⁻¹. Only approximately 56 kg N ha⁻¹, or 3.2% of total cumulative manure-N applied was mineralized in 2003. Other field studies were conducted at the North Willamette Research Extension Center near Aurora, OR and at the Washington State University Puyallup Research Center near Puyallup, WA. At these field sites a variety of organic amendment treatments were applied in 2003. In 2004, our study measured sweet corn crop response parameters including: N recovery from crop N uptake + postharvest soil NO3-N, ear yield, and leaf SPAD meter readings. In the laboratory, soil samples from the field sites were incubated under aerobic and anaerobic conditions to estimate PAN. Year 2 (2004) PAN averaged across all organic amendment treatments and both field locations was 6% of total N applied in year 1 (2003). PAN mineralized in the laboratory aerobic incubation was similar to PAN measured in field microplots and PAN determined by a fertilizer equivalence method at the field sites. This study found similar year 2 PAN for a variety of manure and compost treatments

Response of copper concentrations and stable isotope ratios to artificial drainage in a French Retisol

Copper is a redox-sensitive trace element, which can be both, an essential micronutrient and a pollutant. We therefore analyzed Cu concentrations and stable isotope ratios (δ65Cu values) in a drained Retisol to trace the response of Cu to a changing hydrological regime and enhanced clay eluviation. The study soil was artificially drained 16 years before sampling resulting in macroscopically visible pedogenetic changes and is thus a suitable site to investigate the influence of pedogenetic processes on the fate of Cu. Samples were collected from all horizons along a trench at four distances from the drain: 0.6 m, 1.1 m, 2.1 m and 4.0 m. In the E&Bt horizon, four different soil volumes (ochre, pale brown, white-grey and black) were sampled at all four distances from the drain. Furthermore, we analyzed soil solutions sampled with piezometer, porous cups, and at the drain outlet. The Cu concentrations were lowest in the surface (Ap) horizons (6.5–8.5 μg g− 1) and increased with depth to the clay-rich Bt horizons (10.5–12 μg g− 1), because of clay eluviation and associated Cu transport. The δ65Cu values significantly decreased from the surface (Ap = − 0.25 ± 0.07‰) to the deeper horizons, but showed no significant variation among the deeper horizons (− 0.41 ± 0.28‰) and no correlation with the clay content, indicating that clay eluviation did not significantly affect δ65Cu values. The isotopically heavier δ65Cu values in the Ap horizons can probably be explained by agricultural management practices like sludge application and fertilization. Close to the drain (position 0.6 m), Cu concentrations were depleted and the lighter Cu isotope was enriched (− 0.91 ± 0.15‰) in the uppermost part of the E&Bt horizon. We attribute this to the changing redox conditions, caused by the lowering of the water level close to the drain. Copper concentrations in black and ochre volumes were significantly higher than in pale-brown and white-grey volumes. The black volume had significantly higher δ65Cu values than the ochre volume indicating preferential sorption/occlusion of the heavy Cu isotope by Fe oxides. Enhanced clay eluviation in bulk soil close to the drain and in specific soil volumes did not affect δ65Cu values. Cu concentrations (2.1–14 μg L− 1) and δ65Cu (0.04–0.42‰) values in water samples showed no clear relation with redox changes along the trench perpendicular to the drain. The enrichment of the heavy Cu isotope in the solution samples (Δ65Cu(soil-solution) = − 0.61 ± 0.41) indicates that reductive Cu mobilization is not the main driver of Cu leaching, because this would preferentially mobilize isotopically light Cu. We conclude that the eluviation of the < 2 μm fraction, strongly controlled Cu concentrations, but had no discernible effect on δ65Cu values. The changing redox conditions did not seem to control Cu concentrations and the stable isotope distribution in most of the bulk soil, soil volumes and soil water. Instead, weathering, complexation of leached Cu, Cu application with fertilizers and sorption processes within the soil controlled its δ65Cu values

Polymer-lipid interactions:biomimetic self-assembly behaviour and surface properties of poly(styrene-alt-maleic acid) with diacylphosphatidylcholines

Abstract Various lubricating body fluids at tissue interfaces are composed mainly of combinations of phospholipids and amphipathic apoproteins. The challenge in producing synthetic replacements for them is not replacing the phospholipid, which is readily available in synthetic form, but replacing the apoprotein component, more specifically, its unique biophysical properties rather than its chemistry. The potential of amphiphilic reactive hypercoiling behaviour of poly(styrene-alt-maleic acid) (PSMA) was studied in combination with two diacylphosphatidylcholines (PC) of different chain lengths in aqueous solution. The surface properties of the mixtures were characterized by conventional Langmuir-Wilhelmy balance (surface pressure under compression) and the du Noüy tensiometer (surface tension of the non-compressed mixtures). Surface tension values and 31P NMR demonstrated that self-assembly of polymer-phospholipid mixtures were pH and concentration-dependent. Finally, the particle size and zeta potential measurements of this self-assembly showed that it can form negatively charged nanosized structures that might find use as drug or lipids release systems on interfaces such as the tear film or lung interfacial layers. The structural reorganization was sensitive to the alkyl chain length of the PC

Response of Cu partitioning to flooding: A δ65Cu approach in a carbonatic alluvial soil

The mobility and bioavailability of Cu in soils depend on the chemical Cu forms and are strongly influenced by water-induced changes in soil redox conditions. We chose an experimental approach by flooding a carbonatic floodplain soil and incubating it in a glovebox for 35 days. We used a five-step sequential chemical extraction to characterize the changes in chemical partitioning (F1–F5; NH4NO3-extractable, NaOAc-extractable, NH4Ox-extractable, hot H2O2/NH4OAc-extractable and residual fractions, respectively) of Cu and δ65Cu values in the soil during the 35 days. After flooding, Cu concentrations decreased in F1–F3 and increased in F4–F5. Overall, 73% of the total Cu was redistributed among the five studied fractions. Before flooding (Day 0), δ65Cu values in F1–F4 followed the estimated bonding strengths of Cu in the respective fractions, indicating equilibrium distribution of Cu at the beginning of the experiment. The total variation in δ65Cu values among F1–F5 changed strongly from 0.83 ± 0.18‰ on Day 0 to a maximum of 2.18 ± 0.17‰ on Day 7. This change indicates the reduction of Cu2 + to Cu+ or Cu0 after flooding. The strongest variations in δ65Cu values occurred in F3 (0.09 ± 0.07‰ to 1.43 ± 0.13‰) and F4 (− 0.24 ± 0.07‰ to 0.55 ± 0.07‰), while flooding had no or small effects on the δ65Cu values of F1, F2 and F5. Our results suggest a direct transfer of Cu from F3 to F4 because both concentration changes and changes in δ65Cu values were balanced between the two fractions. The responses of Cu partitioning and δ65Cu values to flooding are in line with the formation of CuxS or other reduced Cu species and reduction of Cu associated to Fe (oxyhydr)oxides. Our results emphasize the strong influence of redox conditions on Cu partitioning in soils and indicate a reduction in Cu availability under anoxic redox conditions

Isotopic variation of dissolved and colloidal iron and copper in a carbonatic floodplain soil after experimental flooding

Many floodplain soils worldwide are contaminated by present and past industrial and mining activities. During flooding redox potential decreases, triggering the release of dissolved and colloidal metals. We used an anaerobic microcosm incubation to simulate flooding of a carbonate-rich floodplain soil for 40 days. Soil solution samples were extracted to determine the release of dissolved (< 0.02 μm) and colloidal fractions (0.02–10 μm). We analyzed stable isotope ratios of colloidal and dissolved Fe and Cu representing two groups of metals with different release behavior; release of Fe was steadily increasing, while that of Cu peaked sharply after flooding and decreased afterwards. The temporal trend of δ56Fe values of total Fe in solution indicated dissimilatory iron reduction. The apparent isotopic fractionation between dissolved and colloidal Fe (Δ56Fedissolved-colloidal = δ56Fedissolved − δ56Fecolloidal) varied from 0.31 ± 0.04‰ to − 1.86 ± 0.26‰. Low δ56Fecolloidal (− 1.16 ± 0.04‰) values on day 4 of the experiment suggested colloid formation by precipitation of dissolved Fe, while the strong temporal variation in Δ56Fedissolved-colloidal indicated subsequent changes in colloid mineralogy, sorption to soil components and/or electron transfer-atom exchange. The variations in δ65Cu values (Δ65Cudissolved-colloidal from 0.81 ± 0.03‰ to 1.58 ± 0.09‰) are probably linked to the changing oxidation state of colloidal Cu. While at the beginning of the experiment colloidal Cu and solid soil Cu exchange, these systems decouple after the onset of sulfate reduction in the second half of the experiment. The experimental results fit well to findings from redoximorphic soils described in the literature and highlight the importance of colloids for metal release and the isotopic pattern in carbonatic soils

The role of counterions in the membrane-disruptive properties of pH-sensitive lysine-based surfactants

Surfactants are among the most versatile and widely used excipients in pharmaceuticals. This versatility, together with their pH-responsive membrane-disruptive activity and low toxicity, could also enable their potential application in drug delivery systems. Five anionic lysine-based surfactants which differ in the nature of their counterion were studied. Their capacity to disrupt the cell membrane was examined under a range of pH values, concentrations and incubation times, using a standard hemolysis assay as a model for endosomal membranes. The surfactants showed pH-sensitive hemolytic activity and improved kinetics at the endosomal pH range. Low concentrations resulted in negligible hemolysis at physiological pH and high membrane lytic activity at pH 5.4, which is in the range characteristic of late endosomes. With increasing concentration, the surfactants showed an enhanced capacity to lyse cell membranes, and also caused significant membrane disruption at physiological pH. This observation indicates that, at high concentrations, surfactant behavior is independent of pH. The mechanism of surfactant-mediated membrane destabilization was addressed, and scanning electron microscopy studies were also performed to evaluate the effects of the compounds on erythrocyte morphology as a function of pH. The in vitro cytotoxicity of the surfactants was assessed by MTT and NRU assays with the 3T3 cell line. The influence of different types of counterion on hemolytic activity and the potential applications of these surfactants in drug delivery are discussed. The possibility of using pH-sensitive surfactants for endosome disruption could hold great promise for intracellular drug delivery systems in future therapeutic applications