Iron toxicity and other chemical soil constraints to rice in highland swamps of Burundi

Iron toxicity is suspected to be a major nutritional disorder in rice cropping systems established on flooded organic soils that contain reductible iron. A pot trial was carried out to assess Fe toxicity to rice in flooded Burundi highland swamp soils with a wide range of organic carbon contents. Soil and leaf analyses were performed and total grain weight was determined. Clear Fe toxicity was diagnosed, based on leaf Fe content at panicle differentiation. Leaf Fe contents higher than 250 g g^–1 dry matter induced lower Mg (and probably Mn) uptake, and a 50% total grain weight reduction. These features were associated with exchangeable Fe equivalent fractions higher than 86%. Besides, several non-Fe toxic soils exhibited an Mg-Mn imbalance.     

Effect of shock-loading of heavy metals on total organic carbon and phosphate removal in an anaerobic-aerobic activated sludge process

The effect of shock-loading of zinc, copper and cadmium ions on the removal of total organic carbon (TOC) and phosphate in an anaerobic-aerobic activated sludge process was investigated. TOC removal was not sensitive to shock-loading of Zn²⁺ and Cd²⁺ ions, and complete removal was achieved even at 20 mg Zn²⁺/l and 20 mg Cd²⁺/l. However, with over 1 mg Cu²⁺/1 TOC removal efficiency decreased. PO _inf4 ^sup3- removal, in contrast, was extremely sensitive to these metal ions, with the threshold being 1 mg Zn²⁺/l and 1 mg Cd²⁺/l. Higher concentrations adversely affected PO _inf4 ^sup3- removal. Copper again proved detrimental; no PO _inf4 ^sup3- removal was achieved even at 1 mg Cu/l. These results highlight the sensitivity of the removal efficiencies of TOC and PO _inf4 ^sup3- to shock loadings of these heavy metals.Y.P. Ting is with the Department of Chemical Engineering, National University of Singapore, Kent Ridge, 0511, Singapore; H. Imai and S. Kinoshita are with the Department of Chemical Process Engineering, Hokkaido University, Sapporo 060, Japan.     

Desulphurization of dibenzothiophene by bacteria

Four out of 187 strains, from enrichment cultures of dibenzothiophene (DBT), grew on DBT or thiophene 2-carboxylate as S sources. The four isolates, presumptively identified as Agrobacterium sp., Xanthomonas sp. and Corynebacterium spp., individually and together desulphurized DBT, producing 2-hydroxybiphenyl and sulphate.M. Constanti and A. Bordons are with the Departament de Bioquímica i Biotecnologia, and J. Giralt is with the Departament d'Enginyeria Química, both of the Universitat Rovira i Virgili, Pl. Imperial Tarraco 1, 43005 Tarragona, Catatonia, Spain     

Mobilization of different phosphate fractions in the rhizosphere

Availability of soil P fractions and mechanisms of acquisition by plants were studied. Plants mobilize soil P by desorption via depletion of P solution concentration around roots. In an oxisol, the process was enhanced by nitrate N nutrition of ryegrass, which increased soil pH, and by carboxylate release by white lupin. Ligand exchange and Fe/Al solubilization are assumed to be the mechanisms. Ammonium N nutrition of ryegrass decreased pH and allowed P mobilization in a luvisol but had no such effect in an oxisol, due to acid solubility of P in these soils. Organic P dissolved in soil solution contributed one third to the P uptake of field-grown barley on a luvisol. Laboratory experiments suggest that organic P is hydrolyzed by phosphatases at the root surface and replenished by micro-organisms.     

Estimating regional carbon stocks and spatially covarying edaphic factors using soil maps at three scales

Most estimates of regional and global soil carbon stocks are based on extrapolations of mean soil C contents for broad categories of soil or vegetation types. Uncertainties exist in both the estimates of mean soil C contents and the area over which each mean should be extrapolated. Geographic information systems now permit spatially referenced estimates of soil C at finer scales of resolution than were previously practical. We compared estimates of total soil C stocks of the state of Maine using three methods: (1) multiplying the area of the state by published means of soil C for temperate forests and for Spodosols; (2) calculating areas of inclusions of soil taxa in the 1:5,000,000 FAO/UNESCO Soils Map of the World and multiplying those areas by selected mean carbon contents; and (3) calculating soil C for each soil series and map unit in the 1:250,000 State Soil Geographic Data Base (STATSGO) and summing these estimates for the entire state. The STATSGO estimate of total soil C was between 23% and 49% higher than the common coarse scale extrapolations, primarily because STATSGO included data on Histosols, which cover less than 5% of the area of the state, but which constitute over one-third of the soil C. Spodosols cover about 65% of the state, but contribute less than 39% of the soil C. Estimates of total soil C in Maine based on the FAO map agreed within 8% of the STATSGO estimate for one possible matching of FAO soil taxa with data on soil C, but another plausible matching overestimated soil C stocks. We also compared estimates from the 1:250,000 STATSGO database and from the 1:20,000 Soil Survey Geographic Data Base (SSURGO) for a 7.5 minute quadrangle within the state. SSURGO indicated 13% less total soil C than did STATSGO, largely because the attribute data on depths of soil horizons in SSURGO are more specific for this locality. Despite localized differences, the STATSGO database offers promise of scaling up county soil survey data to regional scales because it includes attribute data and estimates of areal coverage of C-rich inclusions within map units. The spatially referenced data also permit examination of covariation of soil C stocks with soil properties thought to affect stabilization of soil C. Clay content was a poor predictor of soil C in Maine, but drainage class covaried significantly with soil C across the state.     

Remote sensing of sea surface and coastal features in the area of the Golfe d'Arguin,Mauritania

The analysis of a series of NOAA AVHRR satellite data recorded between July and September 1986 shows the interaction between northerly and southerly water masses during summer as well as the northern limit of the northward advance of water masses originating from the South Equatorial Current. Two upwelling situations analysed by means of NOAA data show the intrusion of suspended matter from the ocean into the Golfe d'Arguin and illustrate the water circulation within the coastal zone. This circulation pattern is detailed by LANDSAT and SPOT data. A SPOT picture from October 1987 shows the structure of the intertidal and coastal geomorphology.     

Dramatic enhancement of enzymatic activity in organic solvents by lyoprotectants

When seven different hydrolytic enzymes (four proteases and three lipases) were lyophilized from aqueous solution containing a ligand, N-Ac-L-Phe-NH(2), their catalytic activity in anhydrous solvents was far greater (one to two orders of magnitude) than that of the enzymes lyophilized without the ligand. This ligand-induced activation was expressed regardless of whether the substrate employed in organic solvents structurally resembled the ligand. Furthermore, nonligand lyoprotectants [sorbitol, other sugars, and poly(ethylene glycol)] also dramaticaliy enhanced enzymatic activity in anhydrous solvents when present in enzyme aqueous solution prior to lyophilization. The effects of the ligand and of the lyoprotectants were nonadditive, suggesting the same mechanism of action. Excipient activated and nonactivated enzymes exhibited identical activities in water. Also, addition of the excipients directly to suspensions of nonactivated enzymes in organic solvents had no appreciable effect on catalytic activity. These observations indicate that the mechanism of the excipient-induced activation is based on the ability of the excipients to alleviate reversible denaturation of enzymes upon lyophilization. Activity enhancement induced by the excipients is displayed even after their removal by washing enzymes with anhydrous solvents. Subtilisin Carlsberg, lyophilized with sorbitol, was found to be a much more efficient practical catalyst than its "regular" counterpart. (c) 1993 John Wiley & Sons, Inc.     

Optimization of alkyl beta-D-galactopyranoside synthesis from lactose using commercially available beta-galactosidases

Commercially available lactase (beta-D-galactoside galactohydrolase, EC 3.2.1.23) enzymes produced from Kluyveromyces fragilis and Kluyveromyces lactis were accessed as catalysts for use in the production of beta-galactopyranosides of various alcohols using lactose as galactosyl donor. The yield of galactoside was enhanced by using the highest practical concentrations of both lactose and alcohol acceptor. The concentrations and thus yield, were limited by the solubility of the substrates. The increase in galactoside yield with increasing lactose concentration appeared to be specific to the lactose substrate and not due to water activity alterations, because addition of maltose to a fixed concentration of lactose had no effect. During the course of the reaction, the yield of galactoside peaked after around 70% to 80% of the lactose was consumed, due to hydrolysis of the product by the enzyme. A wide variety of compounds with primary or secondary hydroxyl groups could act as acceptors, the essential requirement being at least some water solubility. Addition of organic cosolvents had little effect on galactoside yield except when it increased the water solubility of sparingly soluble alcohols. Some galactosides were synthesized on a gram scale to determine practical product recoveries and improve purification methods for large-scale synthesis. Initial purification by hydrophobic chromatography (for galactosides of hydrophobic alcohols) or strong anion-exchange chromatography (for galactosides of hydrophilic alcohols) separated galactosides, galactobiosides, and higher oligomers from reducing sugars. A facile separation of the galactoside and galactobioside could then be effected by flash chromatography on silica gel. (c) 1993 John Wiley & Sons, Inc.     

Activity of mushroom polyphenol oxidase in organic medium

A kinetic study of the activity of mushroom polyphenol oxidase in an organic system was carried out to obtain detailed enzyme kinetic data in relation to optimization of reaction conditions and substrate specificity. A simple method for consistent measurement of reaction rates in the heterogeneous enzyme/organic solvent system (consisting of immobilized polyphenol oxidase and a hydrated solution of the substrate in chloroform) was designed. The aqueous content of the system was optimized using p-cresol as the substrate. With this system, a crude extract of Agaricus bisporus was used to hydroxylate and oxidize a range of selected p-substituted phenolic substrates, yielding o-quinone products. Michaelis-Menten kinetics were used to obtain apparent K(M) and V(max) values with respect to each of these substrates. Results from this analysis indicated a correlation between the enzymic kinetic parameters obtained and the steric requirements of the substrates, which could be rationalized in terms of the restricted flexibility of the enzyme when it is in chloroform and also in terms of substrate and solvent hydrophobicity. In the course of the investigation UV molar absorption coefficients of several o-quinones were measured by a novel method: (1)H nuclear magnetic resonance (NMR) spectroscopy was employed to determine component concentrations in reaction mixtures resulting from the transformation of phenols by polyphenol oxidase in chloroform. Thus the UV molar absorption coefficients could be obtained directly, avoiding the necessity to isolate the water-sensitive, unstable o-quinones. (c) 1993 John Wiley & Sons, Inc.     

Initial soil organic carbon stocks govern changes in soil carbon: Reality or artifact?

Changes in soil organic carbon (SOC) storage have the potential to affect global climate; hence identifying environments with a high capacity to gain or lose SOC is of broad interest. Many cross-site studies have found that SOC-poor soils tend to gain or retain carbon more readily than SOC-rich soils. While this pattern may partly reflect reality, here we argue that it can also be created by a pair of statistical artifacts. First, soils that appear SOC-poor purely due to random variation will tend to yield more moderate SOC estimates upon resampling and hence will appear to accrue or retain more SOC than SOC-rich soils. This phenomenon is an example of regression to the mean. Second, normalized metrics of SOC change—such as relative rates and response ratios—will by definition show larger changes in SOC at lower initial SOC levels, even when the absolute change in SOC does not depend on initial SOC. These two artifacts create an exaggerated impression that initial SOC stocks are a major control on SOC dynamics. To address this problem, we recommend applying statistical corrections to eliminate the effect of regression to the mean, and avoiding normalized metrics when testing relationships between SOC change and initial SOC. Careful consideration of these issues in future cross-site studies will support clearer scientific inference that can better inform environmental management.