A survey of symbiotic nitrogen fixation by white clover grown on metal contaminated soils

There is conflicting evidence about toxic effects of heavy metals in soil on symbiotic nitrogen fixation. This study was set-up to assess the general occurrence of such effects. Soils with metal concentration gradients were sampled from six established field trials, where sewage sludge or metal salts have been applied, or from a transect in a sludge treated soil. Additional contaminated soils were sampled near metal smelters, in floodplains, in sludge amended arable land and in a metalliferous area. Symbiotic nitrogen fixation was measured with ¹⁵N isotope dilution in white clover (Trifolium repens L.) grown in potted soil that was not re-inoculated, and using ryegrass (Lolium perenne L.) as reference crop. The fraction nitrogen in clover derived from fixation (N_dff) varied from 0 to 88% depending on soil. Pronounced metal toxicity on N_dff was only confirmed in a sludge treated soil where nitrogen fixation was halved from the control value at soil total metal concentration of 737 mg Zn kg⁻¹, 428 mg Cu kg⁻¹ and 10 mg Cd kg⁻¹. The N_dff was significantly reduced by increasing metal concentration in soils from two other sites where N_dff was low throughout and where these effects might be attributed to confounding factors. No significant effects of metals on N_dff were identified in all other gradients even up to elevated total metal concentration (e.g. 55 mg Cd kg⁻¹). The variation of N_dff among all soils (n=48), is mainly explained by the number of rhizobia in the soil (log MPN, log (cells g⁻¹ soil)), whereas correlations with total or soil solution metal concentrations were weak (R²<0.25). The is significantly affected by the presence or absence of the host plant at the sampling site. No effects of metals were identified at even at total Zn concentrations of about 2000 mg Zn kg⁻¹, whereas metal toxicity could be identified at lower most probable number (MPN) values. This survey shows that the metal toxicity on symbiotic nitrogen fixation cannot be generalized and that survival of a healthy population of the microsymbiont is probably the critical factor.     

The Use of Biofilters to Reduce Atmospheric Methane Emissions from Landfills: Part I. Biofilter Design

Previous laboratory research has shown that biofilters have the potential to reduce CH₄ emissions from landfills by as much as 83%. However, to achieve this level of CH₄ reduction biofilters must be properly designed. The present study was conducted to develop a method for properly designing biofilters based on landfill size and location. A quadratic equation was developed to describe the dependence of CH₄ oxidation rate in a sandy loam textured soil as a function of soil temperature, soil moisture and ammonium nitrogen concentration. Using this equation and the average monthly soil temperature and moisture contents for the largest cities of each of the 48 contiguous states, the monthly CH₄ oxidation rate at each location was calculated. Then, assuming a standard landfill depth of 27.6 m, and a standard area of 121,500 m², the required biofilter size was calculated. Finally, the ratio of biofilter size to landfill size was calculated. Design calculations for biofilters located in the states of Alabama, Florida, Georgia, Louisiana, Mississippi, North Carolina, South Carolina and Texas where the CH₄ oxidation rates are relatively high throughout the year indicate that the necessary biofilter sizes are small. In addition, biofilters in these states may be expected to be effective throughout the year. In contrast, the calculations indicated biofilter systems in the states of Idaho, Minnesota and North Dakota will have much lower efficiencies during much of the year due to unfavorable soil moisture and temperature ranges. Given proper design, installation and management, a biofilter should be capable of achieving a significant reduction in atmospheric CH₄ emission as compared to emissions from the same landfill without a biofilter.     

Chemical comparison of goldenseal (Hydrastis canadensis L.) root powder from three commercial suppliers

The characterization of herbal materials is a significant challenge to analytical chemists. Goldenseal (Hydrastis canadensis L.), which has been chosen for toxicity evaluation by NIEHS, is among the top 15 herbal supplements currently on the market and contains a complex mixture of indigenous components ranging from carbohydrates and amino acids to isoquinoline alkaloids. One key component of herbal supplement production is botanical authentication, which is also recommended prior to initiation of efficacy or toxicological studies. To evaluate material available to consumers, goldenseal root powder was obtained from three commercial suppliers and a strategy was developed for characterization and comparison that included Soxhlet extraction, HPLC, GC-MS, and LC-MS analyses. HPLC was used to determine the weight percentages of the goldenseal alkaloids berberine, hydrastine, and canadine in the various extract residues. Palmatine, an isoquinoline alkaloid native to Coptis spp. and other common goldenseal adulterants, was also quantitated using HPLC. GC-MS was used to identify non-alkaloid constituents in goldenseal root powder, whereas LC-MS was used to identify alkaloid components. After review of the characterization data, it was determined that alkaloid content was the best biomarker for goldenseal. A 20-min ambient extraction method for the determination of alkaloid content was also developed and used to analyze the commercial material. All three lots of purchased material contained goldenseal alkaloids hydrastinine, berberastine, tetrahydroberberastine, canadaline, berberine, hydrastine, and canadine. Material from a single supplier also contained palmatine, coptisine, and jatrorrhizine, thus indicating that the material was not pure goldenseal. Comparative data for three commercial sources of goldenseal root powder are presented.     

Recovery of cover-crop-N in the soil-plant system in the Guinea savannah zone of Ghana

In order to understand the efficiency of residue-N use and to estimate the minimum input required to obtain a reasonable level of crop response, it is important to quantify the fate of the applied organic-N. The recovery of N from ¹⁵N-labelled Crotalaria juncea was followed in the soil and the succeeding maize crop. Apparent N recovery (ANR) by maize from unlabelled Crotalaria juncea, Crotalaria retusa, Calopogonium mucunoides, Mucuna pruriens and mineral fertilizer at three locations were also evaluated. The maize crop recovered 4.7% and 7.3% of the ¹⁵N-labelled C. juncea-N at 42 days after sowing (DAS) and at final harvest, respectively. The corresponding ¹⁵N recovery from the soil was 92.4% and 58.5%. The highest mean ANR of 57.4% was with mineral fertilizer, whereas the mean ANR of 14.3% from C. retusa was the lowest. A large pool substitution and added-N interaction effect was observed when comparing N recovery from the labelled and unlabelled C. juncea. The amount of residue-N accounted for by the isotope dilution method at 42 DAS was 97.1% and at final harvest 65.8%. The large residue-N recovery in the soil organic-N pool explains the residual effect usually observed with organic residue application.     

Effects of soil pH and soil water content on prosulfuron dissipation

The sulfonylurea herbicide prosulfuron, 1-(4-methoxy-6-methyltriazin-2-yl)-3-[2-(3,3,3-trifluoropropyl)phenylsulfonyl]urea, is used for the selective control of broadleaf weeds in corn, sorghum, and cereal grains. To investigate its fate in soils, this study examined the effects of soil pH and water content on the rates of dissipation processes and the products formed under aerobic conditions. Radiometry and chromatography analyses were used to quantify the degradation products and bound residues formed in incubations of 10 different soils. The pH-dependent hydrolysis of the sulfonylurea bridge to form phenyl sulfonamide was the primary transformation process. Significant microbial degradation of prosulfuron occurred in 2 of the 10 soils, yielding (14)CO(2) and desmethyl prosulfuron among the major products. The time required for 50% dissipation of the herbicide (DT(50)) was determined for each soil and water content treatment. At equivalent water contents, prosulfuron DT(50) values were positively correlated with soil pH (P < 0.0001), varying from 6.5 days at pH 5.4 to 122.9 days at pH 7.9. Soil pH and water content strongly influence the fate of sulfonylurea herbicides in agricultural fields. Differences in the effect of soil water content on dissipation kinetics in a comparison of two soils were attributed to differences in soil pH, texture, and the ability of indigenous microorganisms to transform the herbicide.     

Heat-induced aggregation of whey proteins: comparison of cheese WPC with acid WPC and relevance of mineral composition

Heat-induced aggregation of whey proteins in solutions made from two commercial whey protein concentrates (WPCs), one derived from mineral acid whey (acid WPC) and the other from cheese whey (cheese WPC), was studied using polyacrylamide gel electrophoresis (PAGE), size exclusion chromatography (SEC), and transmission electron microscopy (TEM). Heat treatment (75 degrees C) of acid WPC solutions (12.0%, w/w, pH 6.9) resulted in formation of relatively small "soluble" aggregates that were predominantly disulfide-linked. By contrast, heat treatment of the cheese WPC solutions (under the same conditions) caused formation of relatively large aggregates, containing high proportions of aggregates linked by noncovalent associations. The rate of aggregation of both beta-lactoglobulin and alpha-lactalbumin at 75 degrees C, measured as the loss of native proteins by PAGE, was higher in the cheese WPC solution than in the acid WPC solution. Cross dialysis of the two WPC solutions resulted in alteration of the mineral composition of each WPC solution and reversing their heat-induced aggregation behavior. The results demonstrated that the mineral composition is very important in controlling the aggregation behavior of WPC products.     

Specific fluctuations in the composition of lipoxygenase- and glycosidase-generated flavors in some cultivated teas of Assam

Variations of fatty acid compositions, glycosides precursors, and lipoxygenase and glycosidase enzymatic activities were used simultaneously to differentiate for nine genetically different cultivated teas, four seasonal changes, and the affect of leaf maturity. The muscatel flavor of second-flush teas was associated with increased activities of glycosidase and several terpenes, phenolics, and aliphatic compounds bound to glycosides, whereas high levels of fatty acids and lipoxygenase activity biosynthesized more green volatiles in monsoon teas. Sequential hydrolysis of lipids and lipoxygenase-mediated reactions, during withering and rolling, showed a 3-fold increase of hexenol, hexenal, and related volatiles, but they decreased to the levels of fresh leaf during drying. However, a 4-fold increase of the floral bend of volatiles found in black tea developed due to the hydrolysis of the glycoside precursors throughout processing stages. About 45 key volatiles were monitored for flavor superiority among different clones. Various parameters affecting yield of volatiles were optimized and recommended.     

SE—Structures and Environment: Optimal Control Strategies for Carbon Dioxide Enrichment in Greenhouse Tomato Crops—Part 1: Using Pure Carbon Dioxide

Two optimal control strategies for carbon dioxide (CO₂) enrichment in greenhouse tomato crops have been developed. One uses pure CO₂ from a storage tank and the other uses CO₂ contained in the exhaust gases of boilers burning natural gas. The optimal strategies maximize the financial margin between crop value and the combined costs of the CO₂ used for enrichment and the natural gas used for heating. In this paper, the strategy for optimal control using pure CO₂ is presented and compared with strategies used by growers. The optimal strategy for enrichment with exhaust gas derived CO₂ is presented in an accompanying paper. Simulations show that at a cost of £0·09 kg⁻¹ for pure CO₂ and £0·10 m⁻³ for natural gas, the optimal enrichment strategy would increase the annual margin of crop value over CO₂ and heating costs by £4·6 m⁻² (27%) compared to a basic control strategy of enrichment to a concentration of 1000 v.p.m. (parts per million by volume) when ventilators are <5% open, otherwise enrichment to 350 v.p.m. The optimal CO₂ concentration was expressed as an algebraic function of solar radiation, wind speed and ventilator opening angle, and so enabled a quasi-optimal value to be obtained using variables measured by greenhouse environmental controllers. The quasi-optimal equation, with coefficients averaged from simulations over 4 years, gave an increased margin over the basic control strategy of £4·4 m⁻² (26%).     

Sources of resistance to aflatoxin production in maize

Drought-tolerant maize genotypes (Huffman, Z08-004, Tuxpan, PH 9, NRC 5348, Chunco, Saint Croix, and Arizona) were compared in the field and laboratory to toxin-resistant GT-MAS:gk and Yellow Creole. SDS-PAGE, scanning electron microscopy of kernel cuticle, amount of kernel wax, Aspergillus flavus kernel colonization, Aspergillus ear rot, insect damage, aflatoxin production, and their relationships were examined. SDS-PAGE showed the presence of a 14 kDa trypsin inhibitor in the kernels of all genotypes except Chunco, which contains a protein of a larger molecular weight. The 14 kDa trypsin inhibitor protein content in these genotypes was higher than in GT-MAS:gk and Yellow Creole. Scanning electron microscopy revealed that Arizona, Huffman, and Chunco genotypes had abundant wax deposits on kernel surfaces and the amount of pericarp wax was equal to or above that from GT-MAS:gk and Yellow Creole. Differences in Aspergillus ear rot ratings, fungal colonization, and insect damage by corn earworm were observed in all drought-tolerant maize genotypes as well as in the controls. Kernel screening assays showed that aflatoxin B(1) levels in inoculated drought-tolerant genotypes differed significantly from those in GT-MAS:gk and Yellow Creole (LSD = 576). Aflatoxin B(1) levels in the inoculated genotypes differed significantly from those of GT-MAS:gk or Yellow Creole (LSD = 1389) when grown under drought stress conditions. Pearson correlation coefficients were significant between ear rot ratings and insect damage (r = 0.75; P = 0.01) and between Aspergillus ear rot and aflatoxin levels (r = 0.54; P = 0.05). On the basis of the parameters studied, there are indications that these genotypes were potential sources of A. flavus resistance.     

Aroma-active components of nonfat dry milk.

Application of aroma extract dilution analysis (AEDA) on the volatile components of low-, medium-, and high-heat-treated nonfat dry milks (NDM) revealed aroma-active compounds in the log(3) flavor dilution (log(3) FD) factor range of 1 to 6. The following compounds contributed the highest log(3) FD factors to overall NDM flavor: 2,5-dimethyl-4-hydroxy-3(2H)-furanone [(Furaneol), burnt sugar-like]; butanoic acid (rancid); 3-(methylthio)propanal [(methional), boiled potato-like]; o-aminoacetophenone (grape-like); delta-decalactone (sweet); (E)-4,5-epoxy-(E)-2-decenal (metallic); pentanoic acid (sweaty); 4,5-dimethyl-3-hydroxy-2(5H)-furanone [(sotolon), curry]; 3-methoxy-4-hydroxybenzaldehyde [(vanillin), vanilla]; 2-acetyl-1-pyrroline and 2-acetyl-2-thiazoline (popcorn-like); hexanoic acid (vinegar-like); phenylacetic acid (rose-like); octanoic acid (waxy); nonanal (fatty); and 1-octen-3-one (mushroom-like). The odor intensities of Furaneol, butanoic acid, methional, o-aminoacetophenone, sotolon, vanillin, (E)-4,5-epoxy-(E)-2-decenal, and phenylacetic acid were higher in high-heat-treated samples than others. However, the odor intensities of lactones, 2-acetyl-1-pyrroline, and 2-acetyl-2-thiazoline were not affected by heat treatment. Sensory evaluation results also revealed that heat-generated flavors have a major impact on the flavor profile of NDM.