Transformations of fertilizer nitrogen in soil

Summary Five crops of oats were grown over a 14-month period on a Chester silt loam soil fertilized with N¹⁵-labelled (NH₄)₂SO₄. All plant material from the first four crops was returned to the soil. Following a fifth crop, oat tops and roots were harvested, and the soil was subjected to repeated extractions by autoclaving in 0.01M CaCl₂. The distribution of N¹⁵ and of indigenous soil N among chemical fractions of the extracts, and in the acid-soluble and acid-soluble and acid-insoluble portions of the soil residues following 0.01M CaCl₂ extraction, was remarkably similar. Since appreciable equilibrations between added N¹⁵ and the more resistant forms of soil organic N is unlikely, it is postulated that fertilizer N became incorporated in newly-formed complexes, similar to those already present in the soil. This view is in harmony with the finding that percentage removals of total and N¹⁵-labelled N remained almost the same, even with recovery of approximately 55 per cent of the amounts originally present. N mineralization capacity of the soil was reduced appreciably as a result of extraction.     

Low-molecular-weight carbohydrates in some salt-stressed plants

A study was made of the effects of salinity on the concentrations of free sugars, glycinebetaine, proline and other chemical components of Aster tripolium L., Daucus carota L., Honkenya peploides (L.) Ehr. and Plantago coronopus L. (Dicotyledones); and Carex extensa Good., Eleocharis uniglumis (Link) Schutt., Juncus maritima Lam. and Schoenoplectus tabernaemontani (C. C. Gmel.) Palla (Monocotyledones) grown in the laboratory. In Plantago coronopus the level of the polyol sorbitol increased when the plants were subjected to NaCl stress, while in Honkenya peploides the cyclitol pinitol accumulated. No consistent pattern emerged with respect to the changes in free sugar contents in either the monocotyledonous or dicotyledonous plants, though the monocotyledonous plants generally had higher sugar contents.     

Detection of micro-organisms in soil after in situ hybridization with rRNA-targeted, fluorescently labelled oligonucleotides.

rRNA sequences were used as targets for synthetic oligonucleotides labelled with the fluorescent dye tetramethylrhodamine isothiocyanate (Tritc) for in situ hybridizations to detect micro-organisms directly in soils that have different contents of soil minerals and organic material. Introduced Pseudomonas aeruginosa cells were directly fixed in soils and applied to slides after separation of large soil minerals only. Remaining soil minerals (clay minerals) and organic material (up to 8%) did not significantly interfere with signal expression after hybridization. Background signals were mainly caused by autofluorescence of organic material. Non-specific binding of labelled oligonucleotides to soil particles was not observed. In situ detection of introduced cells of Pseudomonas cepacia in a sandy loam spiked with a mixture of selected soil micro-organisms was possible after hybridization with a specific probe. Analysis of natural bacterial populations in soil, however, was not possible by in situ hybridization without activation of these micro-organisms by adding nutrients. Growing cells, e.g. Streptomyces scabies hyphae growing in amended soil, were easily detected.     

Synthesis,and p.m.r. and mass spectra of some boronic esters of carbohydrates

The synthesis of boronic esters of L-fucose, D-glucose, D-fructose,, and DL-glyceraldehyde is described. The structures of these compounds and appropriate derivatives, based on p.m.r. and mass-spectral data, are discussed.     

Fate of 15N labelled urine on four soil types

A field lysimeter experiment was conducted over a 406 day period to determine the effect of different soil types on the fate of synthetic urinary nitrogen (N). Soil types included a sandy loam, silty loam, clay and peat. Synthetic urine was applied at 1000 kg N ha^-1, during a winter season, to intact soil cores in lysimeters. Leaching losses, nitrous oxide (N₂O) emissions, and plant uptake of N were monitored, with soil ¹⁵N content determined upon destructive sampling of the lysimeters. Plant uptake of urine-N ranged from 21.6 to 31.4%. Soil type influenced timing and form of inorganic-N leaching. Macropore flow occurred in the structured silt and clay soils resulting in the leaching of urea. Ammonium (NH ₄ ⁺ –N), nitrite (NO ₂ ^- –N) and nitrate (NO₃ ^-–N) all occurred in the leachates with maximum concentrations, varying with soil type and ranging from 2.3–31.4 g NH ₄ ⁺ –N mL^-1, 2.4–35.6 g NO ₂ ^- –N mL^-1, and 62–102 g NO ₃ ^- –N mL^-1, respectively. Leachates from the peat and clay soils contained high concentrations of NO ₂ ^- –N. Gaseous losses of N₂O were low (<2% of N applied) over a 112 day measurement period. An associated experiment showed the ratio of N₂–N:N₂O–N ranged from 6.2 to 33.2. Unrecovered ¹⁵N was presumed to have been lost predominantly as gaseous N₂. It is postulated that the high levels of NO ₂ ^- –N could have contributed to chemodenitrification mechanisms in the peat soil.     

Transformations in isolated polyhooks.

Polyhooks from certain non-flagellated mutants of Salmonella and Escheriohia coli are known to be helix-shaped under physiological conditions. However, two non-helical forms were found to occur in isolated polyhooks under appropriate conditions. One form is straight, and appeared when the pH was decreased to 3.2 or lower. The helical-to-straight transformation was reversible. The other form is a doughnut with a fairly constant diameter of above 0.1 μm, which was produced when polyhooks were heated at 75 °C in the absence of salts.     

Amino acids and low-molecular-weight carbohydrates of some marine red algae

Amino acids and low-MW carbohydrates of 18 red algae have been analyzed. Several non-protein amino acids have been identified, including pyrrolidine-2,5-dicarboxylic acid (3c) and N-methylmethionine sulfoxide (5), new natural products, and 13 known compounds, citrulline, β-alanine, γ-aminobutyric acid, baikiain (1), pipecolic acid (2), domoic acid (3a), kainic acid (3b), azetidine-2-carboxylic acid (4), methionine sulfoxide taurine, N-methyltaurine, N,N-dimethyltaurine and N,N,N-trimethyltaurine. Sugars present were mainly floridoside, isofloridoside and mannoglyceric acid. Details of the structural elucidation of new compounds are also given.     

Nitrogen transformation in soil during humification of straw labelled with15N

Summary The decomposition and humification of oat straw labelled with¹⁵N were followed in the soil during 80 days. The influence of NaNO₃ and (NH₄)₂ SO₄ on these processes were also investigated. It was ascertained that addition of NH₄–N acted more efficiently than NO₃–N on both the decomposition of straw and the mineralization of the organic nitrogen compounds of the soil. In the presence of NH₄–N, straw¹⁵N predominated in humic acids, while in the presence of NO₃–N it predominated in fulvic acids.The incorporation of straw¹⁵N into the humic compounds occurred in proportion to the progressing decomposition of straw. The greatest similarity in the proportions of soil-N and straw-¹⁵N in isolated fractions was ascertained after 80 days of incubation in the presence of NH₄–N.     

The fate of18O labelled phosphate in soil/plant systems

KH₂PO₄ labelled with¹⁸O and³²P was mixed with soil that was placed in pots in which grass seed was sown. Grass samples were taken after 5, 7, and 12 weeks. The dilution factor (DF) for¹⁸O in the first cut was much greater than the DF for³²P, indicating that the bulk of the¹⁸O in the absorbed phosphate was lost. The DFs for¹⁸O and³²P determined in phosphate extracted from the soil at the end of the pot experiment indicated that half the¹⁸O excess in the applied phosphate was lost.A succeeding experiment showed no loss of¹⁸O when the treated soil was shaken for 3 months with water to which a germicide was added. Thus, the loss of¹⁸O was presumably caused by biochemical processes which brought about the replacement of¹⁸O by¹⁶O. We suggest that the loss of¹⁸O from applied labelled phosphate may be used as a measure of biological activity in soil.     

Transformations and plant uptake of urine-sulphate in urine-affected areas of pasture soil

The fate of sheep urine sulphate in the soil and its plant uptake was monitored using ³⁵S-labelled sulphate-S in undisturbed pasture microplots in two glasshouse experiments. The extent of macropore flow of simulated urine immediately following a sheep urination was also investigated at 5 pasture sites in the field. Immediately following urination to pasture microplots in the glasshouse, the amounts of urinederived ³⁵S recovered in the 0–2.5, 2.5–7.5, 7.5–15 and 15–30 cm soil layers were 38, 28, 18 and 9%, respectively. In the field study on 5 contrasting soils, a similar pattern was found with 55–70, 20–35 and 13–20% of simulated urine being recovered in the 0–5, 5–10 and 10–15 cm soil layers, respectively. There was insignificant loss below 15 cm. If urine had moved via simple displacement in these soils the wetting front would have reached only 2.0–2.5 cm in depth suggesting that significant downward movement of urine via macropore flow occurs after urination. In a 15-day period following urine application to a pasture soil there was a rapid rate of incorporation of ³⁵S into organic forms, while between 15 and 64 days the rate of incorporation declined. After 7 days, 27% of added ³⁵S had been incorporated into organic forms with 19% being C-bonded S and 8% Hl-reducible S. This rapid incorporation was attributed to the large and active microbial biomass present in the rhizosphere. Since urine application depressed pasture growth, due to ‘urine burn’, less than 10% of applied ³⁵S was absorbed by pasture plants over a 64-day period. A second experiment using microplots of contrasting soil types, confirmed that the majority of the ³⁵S incorporated into the organic form was present as C-bonded S. Results showed that of the ³⁵S remaining in the 0–2.5 cm layer 35 days after application, 20–40% was present as sulphate, 10–20% as Hl-reducible S and 50–60% as C-bonded S. Plant uptake of S accounted for only 7–12% of applied ³⁵S over the 35-day period.     

Permeability of the peritrophic membranes of some Diptera to labelled dextrans

The permeability of the continuous, tube-like peritrophic membrane of some Diptera was investigated. Dyes, haemoglobin, cytochrome c, horseradish peroxidase, and especially dextran fractions labelled with the fluorescent dye fluorescein isothiocyanate were used as markers. The peritrophic membrane of larvae of Aedes aegypti was permeable only to dextran with a molecular weight of less than 2,400 Daltons; Evans Blue (960.8 Daltons) permeated only slowly through this peritrophic membrane. Labelled dextran with a mol. wt of 32,000 Daltons did not penetrate the peritrophic membrane of larvae of Anopheles stephensi. Dextrans larger than 32,000 Daltons did not permeate through the peritrophic membrane of Culex pipiens, Odagmia ornata, Anisopus (Phryne) cinctus, Sarcophaga barbata and Calliphora erythrocephala. Labelled dextran with mol. wt of 4,000–6,000 Daltons penetrated only slowly, and dextran of 6,200 Daltons did not penetrate the peritrophic membranes of adults of Sarcophaga barbata. The peritrophic membranes of the blowfly, Calliphora erythrocephala, were permeated slowly by dextran of 6,200 Daltons but not by dextran of 17,200 Daltons. Dextrans are readily soluble in water where the long chains form coils of round or oval shape. Charged protein molecules are more compact with smaller radii when compared to a dextran fraction of the same molecular weight. Therefore the results of investigations on permeability have to be compared in terms of the effective radii and not of the molecular weight.     

Combinatorial synthesis of carbohydrates.

Combinatorial chemistry principles have been applied to the generation of oligosaccharide libraries, both in solution and on the solid phase, with a view to producing inhibitors of carbohydrate-protein binding. The rich stereochemistry and high degree of functionalization of sugars has also resulted in their increasing use in the synthesis of glycomimetics and as scaffolds for the presentation of pharmacophore groupings to receptors that are noncarbohydrate-recognizing proteins.