Michael E. Essington

Metallohistins: A New Class of Plant Metal-Binding Proteins

Two small multimeric histidine-rich proteins, AgNt84 and Ag164, encoded by two nodule-specific cDNAs isolated from nodule cDNA libraries of the actinorhizal host plant Alnus glutinosa, represent a new class of plant metal binding proteins. This paper reports the characterization of the purified in vitro-expressed proteins by size exclusion chromatography, circular dichroism, equilibrium dialysis, metal affinity chromatography coupled with mass spectrometry, and nuclear magnetic resonance spectroscopy. These analyses reveal that each polypeptide is capable of binding multiple atoms of Zn2+, Ni2+, Co2+, Cu2+, Cd2+ and Hg2+. A reversible shift in histidine Cε1 and Cδ2 protons in NMR analysis occurred during titration of this protein with ZnCl2 strongly suggesting that histidine residues are responsible for metal binding. AgNt84 and Ag164 are not related to metal binding metallothioneins and phytochelatins and represent a new class of plant metal binding proteins that we propose to call metallohistins. Possible biological roles in symbioses for AgNt84 and Ag164, and their potential for use in bioremediation are discussed.

Phosphorus Availability And Speciation In Long-term No-till And Disk-till Soil

Conservation tillage results in the concentration of plant-available P near the soil surface. We studied the effects of conservation tillage on P speciation by examining the distribution of P in inorganic and organic chemical pools. Depth-incremented soil samples were collected from long-term (9- an

Adsorption of aniline and toluidines on montmorillonite

Bentonite clay liners are commonly employed to mitigate the movement of contaminants from waste disposal sites. In order to assess the ability of clay liner material to restrict the mobility of amine compounds under a variety of chemical conditions and to further elucidate amine adsorption characteristics, the adsorption of aniline and o-, m-, and p-toluidine on Ca2+- and K+-saturated Wyoming bentonite (SWy-1) was investigated. Adsorption experiments were performed under conditions of varied pH and ionic environment. Amine adsorption on montmorillonite is pH dependent. Maximum amine adsorption occurs when solution pH is approximately equal to the pKa of the anilinium ion deprotonation reaction (pH 4.45–5.08). An amine adsorption envelope results from the combined influence of increasing anilinium ion and anilinium-aniline complex formation (as pH decreases to the pKa) and amine competition with H+ for surface sites, decreasing anilinium-aniline complex concentration, and decreasing aniline available for water bridging with exchangeable Ca2+ and K+ (as solution pH decreases below the pKa). For any given amine, maximum adsorption increases with decreasing ionic strength. Maximum amine adsorption is greater in the Ca2+ systems than in the K+ systems at equivalent cation charge and reflects the formation of an amine water bridge with the exchangeable Ca2+. Amine adsorption is also greater in chloride systems compared with sulfate systems at comparable cation concentrations, possibly due to the formation of aqueous anilinium-sulfate complexes. The amine compounds are retained mainly by bentonite through a cation exchange process, the capacity of the clay to adsorb the amine compounds being a significant percentage of the exchange capacity at the pKa. However, amine retention decreases with increasing pH and is minimal at solution pH values greater than 7

An application of a modified microwave total dissolution technique for soils

Abstract Application of a microwave dissolution technique to soil materials aided by acid digestion procedures has many advantages, but the incomplete dissolution of sandy soils has been noted. The objectives of this study were to modify a microwave oven digestion technique to facilitate the determination of the total elemental content of soils and geologic materials containing greater than 45% sand and apply these data to determine natural separations in parent materials. A microwave dissolution technique using aqua regia (HNO3 and HCl) and hydrofluoric acid (HF) was modified such that the HF is added to the solid 16 hours prior to aqua‐regia addition and subsequent microwave heating. Elemental recoveries were validated using a NBS coal fly ash standard. This procedure was applied to soil core samples representing a wide range of geological and pedological weathering sequences and soil textural classes. Separations in the parent material were determined by observing natural breaks in the elemental concen...

Effect of pH on surface characteristics of switchgrass-derived biochars produced by fast pyrolysis.

Surface properties of switchgrass-derived biochars produced at fast pyrolysis temperatures of 450, 600 and 800 °C were characterized at different solution pHs in order to determine the structural and chemical changes of artificially-weathered biochars when incorporated into soil. As biochars were acidified from pH 7 to 3, crystalline minerals dissolved slowly releasing nutrients; however, residual minerals were still detected in biochars produced at higher pyrolysis temperatures after pH treatment. Moreover, the amount of exchangeable bases and other inorganic compounds released from the biochars increased when pH decreased. As minerals dissolved from the biochars, total surface area and pore volume were found to increase. Surface functional groups and water vapor adsorption capacity at 0.8 P/Po also increased, whereas the potential CEC of biochars decreased due to the replacement of exchangeable sites by hydrogen ion. Therefore, during the aging process, it is predicted that soil-incorporated biochars will slowly release nutrients with changes in surface functionality and porosity, which are expected to enhance water holding capacity of soil and provide a beneficial habitat for microbial colonization.

Fluometuron behavior in long-term tillage plots

Fluometuron (N, N-dimethyl-N′ -[3-(trifluoromethyl) phenyl] urea) is a preemergence herbicide used widely for weed control in cotton (Gossypium hirsutum L.). Field research results suggest that many herbicides, including fluometuron, may be subject to preferential transport and leaching through the soil profile. The objectives of this study were to evaluate the distribution and leaching of fluometuron in a Lexington silt loam (Typic Paleudalf) through 3 years of study by analyzing depth incremented soil samples and tension-free pan lysimeter leachates collected at a soil depth of 90 cm under no-till (NT) and conventional tillage (CT, disc 2× - roller harrowed) management. Fluometuron depth distribution following application and subsequent rainfall was related to soil organic carbon content, with tillage effects restricted to the surface 2-cm. The amount of herbicide remaining in the soil profile after application decreased with increasing rainfall amounts. On average, 11% of applied herbicide in NT and 6% in CT remained in the surface 15 cm after 1 year. Fluometuron was detected in all lysimeter leachates during the 3-year period. Peak herbicide leachate concentrations ranged from 68 mg L−1 to 1700 mg L−1, depending on herbicide application in relation to rainfall timing. Annual leaching losses ranged from 5 to 53% of applied fluometuron during the study. Of the amounts lost to leaching, 68 to 100% (averaging 87% of the total lost to leaching) were lost during the first two or three significant rainfall events after treatment. Rainfall timing in relation to herbicide application was the dominant effect in herbicide mobilization through the soil profile. Antecedent soil moisture content (predicted from rainfall amounts prior to fluometuron application) also influenced the appearance of leachate and herbicide in the lysimeters, with lower soil moisture conditions at application producing lower preferential flow. Depth-incremented soil sampling after initial rainfall events was a poor mechanism for detecting fluometuron mobility through the soil profile. The rapidity at which fluometuron was detected in the lysimeter leachates, the exceedingly high fluometuron concentrations, and the variability in leachate collection by the lysimeters, illustrated the significance of preferential flow. The influence of tillage practice on the volume of drainage collected by the lysimeters and on fluometuron leaching was of little significance when compared with the influence of natural infiltration heterogeneity.

NITROGEN FERTILIZATION OF CONSERVATION-TILLED WHEAT. I. SOURCES AND APPLICATION RATES

ABSTRACT Selection of the nitrogen (N) source and rate for application is critical to ensure profitable wheat (Triticum aestivum L.) yields. The research objective was to evaluate several N sources and spring application rates for conservation tillage wheat production. Research was initiated in the fall of 1997 and continued through 2000 on Collins silt loam (Aquic Udifluvents). A different cultivar was seeded each of the three years. The experimental design was a split-plot with 0, 34, 67, 101, 134, and 168 kg N ha−1 rates the main plots and N sources (ammonium nitrate, urea, urea-ammonium nitrate, ammonium sulfate and UAN+Ca(NO3)2 co-mixture) the sub-plots. The yield response to N rate varied with year and N source. For the three years, yields were increased by applying either 67 or 101 kg N ha−1. Broadcasting AN produced higher yields than urea-containing N sources (urea or UAN) for two of the three years. Broadcasting urea or UAN restricted yields approximately 12% apparently due to N volatilization losses. Broadcasting AS was as effective as AN one of the two years while broadcasting the UAN+ Ca(NO3)2 co-mixture resulted in higher yields at a lower N rate than AN for one of two years. Yield differences due to N source were small when rainfall occurred within two days of soil application. Take-all root rot affected yield one of three years with AN and AS being more efficient N sources. Sulphur fertilization was not needed for wheat production on this soil.

Surface application of liquid swine manure : chemical variability

Abstract The determination of manure loading rates for crop production is complicated by the temporal variability in manure nutrient concentrations and the difficulty in obtaining representative samples on which to base application rates. The variation in nutrient concentrations in liquid swine manure obtained from an agitated anaerobic lagoon was examined during application to experimental plots. Grab samples were collected from a lagoon approximately two to four weeks prior to application and analyzed for nitrogen (N), phosphorus (P), and potassium (K). Based on the preliminary P analyses, swine manure application rates were computed. Manure from the lagoon was surface‐applied to corn plots to provide P rates of 15, 30, and 60 kg P/ha. During application, each tankload of manure was sampled to determine P rates for each plot. The solids content of each manure load was highly variable as were the total concentrations of manure N and P. Potassium content of the manure was also related to the solids conten...

Field-Grown Transgenic Switchgrass (Panicum virgatum L.) with Altered Lignin Does Not Affect Soil Chemistry, Microbiology, and Carbon Storage Potential

Cell wall recalcitrance poses a major challenge on cellulosic biofuel production from feedstocks such as switchgrass (Panicum virgatum L.). As lignin is a known contributor of recalcitrance, transgenic switchgrass plants with altered lignin have been produced by downregulation of caffeic acid O‐methyltransferase (COMT). Field trials of COMT‐downregulated plants previously demonstrated improved ethanol conversion with no adverse agronomic effects. However, the rhizosphere impacts of altering lignin in plants are unknown. We hypothesized that changing plant lignin composition may affect residue degradation in soils, ultimately altering soil processes. The objective of this study was to evaluate effects of two independent lines of COMT‐downregulated switchgrass plants on soils in terms of chemistry, microbiology, and carbon cycling when grown in the field. Over the first two years of establishment, we observed no significant differences between transgenic and control plants in terms of soil pH or the total concentrations of 19 elements. An analysis of soil bacterial communities via high‐throughput 16S rRNA gene amplicon sequencing revealed no effects of transgenic plants on bacterial diversity, richness, or community composition. We also did not observe a change in the capacity for soil carbon storage: There was no significant effect on soil respiration or soil organic matter. After five years of establishment, δ13C of plant roots, leaves, and soils was measured and an isotopic mixing model used to estimate that 11.2 to 14.5% of soil carbon originated from switchgrass. Switchgrass‐contributed carbon was not significantly different between transgenic and control plants. Overall, our results indicate that over the short term (two and five years), lignin modification in switchgrass through manipulation of COMT expression does not have an adverse effect on soils in terms of total elemental composition, bacterial community structure and diversity, and capacity for carbon storage.

Influence of Temperature and pH on Antimonate Adsorption by Gibbsite, Goethite, and Kaolinite

Abstract Antimony is one of the least abundant elements in natural environments. However, elevated environmental concentrations of Sb may arise from anthropogenic sources. The element has no known biological function, has high acute toxicity, and is known to induce chronic health effects. In the environment, Sb is commonly found in the anionic Sb(V) (antimonate) form where the mechanism of retention in soil and sediment is adsorption, via outer-sphere or inner-sphere complexation by variable-charge mineral surfaces. The type of adsorption mechanism dictates Sb environmental mobility and bioaccessibility. The objectives of this study were to characterize the adsorption of Sb(V) by the common soil minerals: gibbsite, kaolinite, and goethite as a function pH, Sb(V) concentration, and temperature. The results are interpreted to provide information on the general mechanism of Sb(V) retention, adsorption intensity, and capacity. Antimonate adsorption by all 3 minerals decreases with increasing pH. The adsorption isotherms are described by the Freundlich and the one- or 2-site Langmuir models. The adsorption of Sb(V) by aluminol (≡AlOH) groups on gibbsite and kaolinite is divided into high intensity–low capacity and low intensity–high capacity components. In pH 5.5 systems, both endothermic (inner-sphere) and exothermic (outer-sphere) adsorption is observed. In pH 8 systems, only exothermic adsorption is observed. Antimony adsorption by goethite ≡ FeOH groups is high intensity and endothermic in both pH 5.5 and 8 conditions. The interpretations of the adsorption isotherm data are consistent with surface spectroscopy and surface complexation modeling results.