The evaluation of plant-available sulphur in soils. II

Summary The availability to oats of adsorbed sulphate in soils and of sulphate impurity in calcium carbonate was studied in pot-culture experiments.When calcium carbonate was added to soils with pH values ranging from 5.7 to 7.4 the uptake of sulphur by oats was increased, due probably to enhanced mineralization of soil organic sulphur. When the calcium carbonate contained sulphate impurity the uptake of sulphur was further increased by an amount comparable with the release of sulphate which could be expected from a reaction of the calcium carbonate with the exchangeable hydrogen of the soil. Sulphate in excess of this amount appeared to be largely unavailable. Uptake of sulphur by oats from calcareous sands containing large amounts of insoluble sulphate associated with calcium carbonate also suggested that soil sulphur in this form had very low availability to plants.Substantial increases in the amounts of sulphur extracted by reagents commonly used for the determination of adsorbed sulphate in soils occurred when soils were airdried at about 20°C. Decreases in adsorbed sulphate in soils following the growth of oats in pot culture confirmed that adsorbed sulphate is readily available to plants.     

Some factors influencing production of sulphate by oxidation of elemental sulphur and thiosulphate in upper horizons of spruce forest soils

Some factors influencing the oxidative activity of upper horizons of spruce forest soils (a mixture of fermentative and humus layers) toward intermediates of the oxidative part of the sulphur cycle were investigated. Preincubation of the soil with added cysteine, sulphide, elemental sulphur or thiosulphate was found to stimulate enzyme systems oxidating any of these compounds. Sulphite and sulphate were ineffective in this respect. The oxidation of elemental sulphur was stimulated by CaCO3, technical urea and high doses of superphosphate and potassium sulphate. It was inhibited by KH2PO4, pure urea, 40 % potassium salt, ammonium nitrate with calcium carbonate and the fertilizer NPK I. It proceeded at the highest rate at approximately 60 % capillary capacity (61 % of mass water content). Oxidation of thiosulphate was stimulated by KH2PO4, pure urea, superphosphate, potassium sulphate and only slightly by the fertilizer NPK I. It was inhibited by CaCO3, 40 % potassium salt and only slightly by ammonium nitrate with calcium carbonate. Potassium chloride, glucose and technical urea were without effect. The oxidation proceeded at the highest rate at 35 % maximal capillary capacity (48 % mass water content).     

The evaluation of plant-available sulphur in soils

Summary Examination of a range of naturally occurring calcium carbonates and calcareous soils has shown that insoluble sulphate associated with calcium carbonate may comprise an important fraction of soil sulphur. One soil contained as much as 93 per cent of its sulphur in this form. It seems likely that this sulphate occurs as a co-precipitated or co-crystallized impurity in the calcium carbonate.Most surface soils had only low capacity to adsorb sulphate and contained only small amounts of sulphur in this form. Two acid surface soils and many acid subsoils, however, adsorbed sulphate quite strongly and in some acid subsoil clays adsorbed sulphate made up an important fractions of the total sulphur.Sulphate adsorption was found to be negligible above pH 6.5 and adsorbed sulphate may be determined by aqueous extraction after increasing the pH above this value by addition of solid calcium carbonate. Adsorption of sulphate during acid extraction of soils can lead to low values in the determination of acid-soluble sulphates. Sulphate so adsorbed can be determined by a second extraction with water after the addition of solid calcium carbonate to increase the pH to a value greater than 6.5.     

Sulphur oxidation by a Streptomyces sp. growing in a carbon-deficient medium and autoclaved soil

Streptomyces colonies, apparently all of the same species, were isolated from a range of soils using a polysulphide medium lacking an organic carbon source. Growth on this medium, and clearing of the otherwise white, opaque overlay, suggested that the organisms were capable of growing autotrophically. However, investigation of one of these isolates showed that it was unable to fix ¹⁴CO₂ and did not possess the enzyme ribulose bisphosphate carboxylase, showing that it was incapable of autotrophic growth. The isolate oxidized elemental sulphur, thiosulphate and tetrathionate to sulphate in vitro in carbon-deficient medium, and also oxidized elemental sulphur to sulphate when inoculated into autoclaved soil supplemented with sulphur. It also oxidized polysulphide when growing on Czapek Dox and plate count agars. The isolate can therefore grow heterotrophically in both carbon-rich media and in media lacking organic carbon — presumably by scavenging organic carbon from the laboratory atmosphere. The possible role of these organisms in sulphur oxidation in soils is commented upon.     

Organic sulphur sources for the growth of the dermatophyte microsporum gypseum

The suitability of 30 organic compounds (of them 19 sulphur-containing amino acids) at a concentration of 1mm as sulphur sources for the growth of the dermatophyteMicrosporum gypseum was investigated. The dry mass of the mycelium after an 11-d growth served as a measure of utilizability. Of sulphur amino acids cystine, cysteine, reduced and oxidized glutathione, cysteic and cysteinesulphinic acids, S-sulphocysteine, lanthionine, taurine and serine sulphate were the best sources. Methionine and methionine-sulphone were utilized slightly less effectively. Other compounds were medium to poor sources and only S-carboxymethylcysteine was not utilized at all. All organic compounds that are not of amino acid type were poor sulphur sources or were utilized at all. Sodium dodecyl sulphate inhibited germination and growth completely.     

Sulphate reduction and calcite precipitation in relation to internal eutrophication of groundwater fed alkaline fens

Although in Europe atmospheric deposition of sulphur has decreased considerably over the last decades, groundwater pollution by sulphate may still continue due to pyrite oxidation in the soil as a result of excessive fertilisation. Inflowing groundwater rich in sulphate can change biogeochemical cycling in nutrient-poor wetland ecosystems. Incoming sulphate loads may induce internal eutrophication as well as the accumulation of dissolved sulphide, which is phytotoxic. We, however, argue that upwelling sulphate rich groundwater may also promote the conservation of rare and threatened alkaline fens, since excessive fertilisation and pyrite oxidation also produces acidity, which invokes calcite dissolution, and increased alkalinity and hardness (Ca²⁺ + Mg²⁺) of the inflowing groundwater. Our observations in a very species-rich wetland nature reserve show that sulphate is reduced and effectively precipitates as iron sulphides when this calcareous and sulphate rich groundwater flows upward through the organic soil of the investigated nature reserve. Furthermore, we show that sulphate reduction coincides with an increase in alkalinity production, which in our case results in active calcite precipitation in the soil. In spite of the occurring sulphate reduction we found no evidence for internal eutrophication. Extremely low phosphorous concentration in the pore water could be attributed to a high C:P ratio of soil organic matter and co-precipitation with calcite. Our study shows that seepage dependent alkaline fen ecosystems can be remarkably resilient to fertilisation and pyrite oxidation induced groundwater quality changes.     

The role of soil microbes in plant sulphur nutrition

Chemical and spectroscopic studies have shown that in agricultural soils most of the soil sulphur (>95%) is present as sulphate esters or as carbon-bonded sulphur (sulphonates or amino acid sulphur), rather than inorganic sulphate. Plant sulphur nutrition depends primarily on the uptake of inorganic sulphate. However, recent research has demonstrated that the sulphate ester and sulphonate-pools of soil sulphur are also plant-bioavailable, probably due to interconversion of carbon-bonded sulphur and sulphate ester-sulphur to inorganic sulphate by soil microbes. In addition to this mineralization of bound forms of sulphur, soil microbes are also responsible for the rapid immobilization of sulphate, first to sulphate esters and subsequently to carbon-bound sulphur. The rate of sulphur cycling depends on the microbial community present, and on its metabolic activity, though it is not yet known if specific microbial species or genera control this process. The genes involved in the mobilization of sulphonate- and sulphate ester-sulphur by one common rhizosphere bacterium, Pseudomonas putida, have been investigated. Mutants of this species that are unable to transform sulphate esters show reduced survival in the soil, indicating that sulphate esters are important for bacterial S-nutrition in this environment. P. putida S-313 mutants that cannot metabolize sulphonate-sulphur do not promote the growth of tomato plants as the wild-type strain does, suggesting that the ability to mobilize bound sulphur for plant nutrition is an important role of this species.     

Sulphur oxidation by soil fungi including some species of mycorrhizae and wood-rotting basidiomycetes

Abstract The mycorrhizal fungi Amanita muscaria, Paxillus involutus, Hymenoscyphus ericae, Pisolithus tinctorius, Rhizopogon roseolus , and Suillus bovinus oxidized elemental sulphur to thiosulphate and sulphate in vitro. In some, but not all cases, tetrathionate was also formed. Limited oxidation of elemental sulphur by R. roseolus also occurred when growing in association with Pinus contorta in unsterilized peat. Although yeasts capable of oxidizing sulphur could not be isolated from a wide range of soils, a yeast-like fungus ( Monilia sp.) isolated from deciduous woodland soil oxidized elemental sulphur to sulphate, forming thiosulphate, but not tetrathionate. This fungus also oxidized tetrathionate to sulphate but showed only limited ability to oxidize thiosulphate to tetrathionate. Both Aspergillus niger and Trichoderma harzianum oxidized elemental sulphur in mixed culture with Mucor flavus . Larger amounts of sulphate were initially formed in mixed, compared to single culture; but by week 5 of the incubation period sulphate formation was greatest in single culture. The wood-rotting fungi, Hypholoma fasciculare and Phanerochaete velutina showed a limited ability to oxidize elemental sulphur in vitro but were incapable of oxidizing the element when growing as mycelial cords in non-sterilized soils. The relevance of these results to the possibility that fungi play a role in sulphur oxidation in soils is commented upon.     

Effects of organic matter on sulphur oxidation in soil and influence of sulphur oxidation on soil nitrification

Summary The effects of wheat straw and pressed sugar beet pulp on sulphur oxidation were determined in a loam soil amended with 1% (w/w) elemental sulphur. Wheat straw stimulated the oxidation of elemental sulphur over the first 2 to 3 weeks of the incubation period, resulting in an increase in LiCl-extractable sulphate. After 4 to 7 weeks incubation however, the only significant increase in soil sulphate followed the 1% straw addition, while at week 7 sulphate concentrations in the 0.25% and 5.0% straw amended soils were lower than the control. Pressed sugar beet pulp (1% w/w) initially stimulated the oxidation of elemental sulphur in the soil, but by weeks 3 to 7 of the incubation period rates of oxidation in pulp-amended soils were lower than the control. Towards the end of the incubation period however, sulphate concentrations in the amended soils exceeded the control values, significantly so by week 11. The concentration of thiosulphate and tetrathionate also increased in soils receiving sugar beet pulp. Nitrification was inhibited in soils in which sulphur oxidation was actively occurring. Although possible alternatives are mentioned, such inhibition appears to result from a decrease in soil pH brought about by the oxidation of elemental sulphur to sulphuric acid.     

Sulphate and methionine as sulphur sources for cysteine and cephalosporin C synthesis in Cephalosporium acremonium

Three prototrophic strains of Cephalosporium acremonium with different potentials for cephalosporin C production show pronounced differences in pools of intracellular sulphur amino acids. The superior strain exhibits the largest pool, particularly of cysteine (four times that of the non-producing strain). In fermentations with this strain methionine was found to be a much better sulphur source than sulphate for both cysteine and antibiotic synthesis. In the presence of methionine the utilization of sulphate is strongly depressed.     

The effect of sodium chloride and sulphate on sulphur oxidation in soil

Summary The effect of sodium chloride on sulphur oxidation in Terra Rossa and Rendzina soils was studied by incubation and perfusion techniques. Sulphur oxidation was observed at concentrations up to 8 per cent NaCl, but was completely arrested at 10 per cent sodium chloride. Sodium chloride caused a delay in the onset of sulphur oxidation, its rate being only slightly affected. A relationship between sulphate appearance and decrease in pH was observed only in sulphur-amended Terra Rossa soil. Under optimal conditions, 53 and 54 per cent of added sulphur (5000 ppm) was recovered as SO₄-S from the Terra Rossa and Rendzina soils, respectively. This maximal level of sulphate production was only slightly affected by the addition of sulphate up to 3000 ppm S.It was concluded that inhibition in further sulphur oxidation was not caused by sulphate accumulation.     

Catalytic and regulatory properties of sulphur metabolizing enzymes in cyanobacterium Synechococcus elongatus PCC 7942

Synechococcus elongatus PCC 7942 was able to grow with several S sources. The sulphur metabolizing enzymes viz. ATP sulphurylase, cysteine synthase, thiosulphate reductase and L- and D-cysteine desulphydrases were regulated by sulphur sources, particularly by sulphur amino acids and organic sulphate esters. Sulphur starvation reduced ATP sulphurylase and cysteine synthase whereas reduced glutathione appreciated Cys degradation activity. With partially purified enzymes apparent Km values for sulphate, ATP, D- and L-Cys, thiosulphate, sulphide and O-acetyl serine were in a range of 12-50 microM. p-Nitrophenyl sulphate inhibited ATP sulphurylase competitively. Met was a feedback inhibitor of several key enzymes.     

Some factors affecting the mineralization of organic sulphur in soils

Summary Factors affecting the release of sulphate from a number of eastern Australian soils were studied.All of the soils released sulphate when dried. The amounts released were influenced by the manner in which the soil was dried. Air-drying in the laboratory at 20°C released least sulphate.Sulphate was mineralized in all soils by incubation at 30°C but the amounts mineralized could not be related to soil type or any single soil property. The ratio of nitrogen mineralized: sulphur mineralized varied widely between soils and was generally appreciably greater than the ratio of total nitrogen: organic sulphur in the soils.A rapid flush of mineralization of both sulphur and nitrogen took place when some of the soils were rewetted and incubated after they had been dried in the laboratory and stored for 4 to 5 months. Following this, the rate of mineralization was similar to that in the original undried soil. During this flush, the enhancement of sulphur mineralization was relatively greater than that of nitrogen so that the ratio of nitrogen mineralized: sulphur mineralized was considerably smaller than that during later phases of the incubation or that of the original moist soil. Soils collected after they had remained dry in the field for a similar period of time did not show this type of mineralization although they had initially done so when collected moist and air-dried in the laboratory.The effects of temperature, soil moisture, toluene and formaldehyde, and the addition of calcium carbonate to soils on the mineralization of sulphur were similar to their effects on the mineralization of nitrogen.     

Dynamics of oxidation of inorganic sulphur compounds in upper soil horizons of spruce forests

Dynamics of oxidation of inorganic sulphur compounds to sulphate by the soil of spruce forests was investigated. Sulphide, sulphite and thiosulphate are oxidized to sulphate at a maximal rate at the beginning of the reaction, oxidation of elemental sulphur exhibits a lag phase. Linear relationships between the amounts of the produced sulphate and concentrations of substrates in the soil could be detected. On the basis of this finding a method for comparison of the oxidative activity of various soils was proposed.     

The bacteria of the sulphur cycle

This paper concentrates on the bacteria involved in the reductions and oxidations of inorganic sulphur compounds under anaerobic conditions. The genera of the dissimilatory sulphate-reducing bacteria known today are discussed with respect to their different capacities to decompose and oxidize various products of fermentative degradations of organic matter. The utilization of molecular hydrogen and formate by sulphate reducers shifts fermentations towards the energetically more favourable formation of acetate. Since acetate amounts to about two-thirds of the degradation products of organic matter, the complete anaerobic oxidation of acetate by several genera of the sulphate-reducing bacteria is an important function for terminal oxidation in sulphate-sufficient environments. The results of pure culture studies agree well with ecological investigations of several authors who showed the significance of sulphate reduction for the complete oxidation of organic matter in anaerobic marine habitats. In the dissimilatory sulphur-reducing bacteria of the genus Desulfuromonas the oxidation of acetate is linked to the reduction of elemental sulphur. Major characteristics of the anaerobic, sulphide-oxidizing phototrophic green and purple sulphur bacteria as well as of some facultative anoxygenic cyanobacteria, are given. By the formation of elemental sulphur and sulphate, these bacteria establish sulphur cycles with the sulphide-forming bacteria. In view of the morphological diversity of the sulphate-reducing bacteria and question of possible evolutionary relations to phototrophic sulphur bacteria is raised.     

Nutritional factors affecting nisin production by Lactococcus lactis subsp. actis NIZO 22186 in a synthetic medium

L. DE VUYST. 1995 A minimal synthetic medium (SM8) for nisin-producing Lactococcus lactis subsp. lactis strains has been designed; it consists of eight growth-stimulating amino acids (glutamic acid, methionine, valine, leucine, threonine, arginine, isoleucine and histidine), five vitamins (biotin, calcium pantothenate, nicotinic acid, pyridoxine and riboflavin) and the mineral salts dihydrogen phosphate, disodium hydrogen phosphate, sodium chloride, magnesium sulphate and trisodium citrate. Nisin biosynthesis is strongly dependent on the presence of a sulphur source, either an inorganic salt (magnesium sulphate or sodium thiosulphate) or the amino acids methionine, cysteine or cystathionine. The amino acids serine, threonine and cysteine highly stimulate nisin production without affecting the final cell yield, indicating their precursor role during nisin biosynthesis.     

The influence of living plants on mineralization and immobilization of nitrogen

Summary Changes in the pattern of distribution of the nitrogen of the soil and seedling grass plants have been investigated when the grass plants were grown in pots of sandy soil, from a pasture, at pH 5.7. Net mineralization of soil nitrogen was not observed during an experimental period of one month in the absence of added nitrogenous fertilizer (Table 2). Addition of labeled nitrogen (as ammonium sulphate) to the soil at the beginning of the experimental period resulted in a negative net mineralization during this period (Table 4b). When none of the fertilizer nitrogen remained in its original form in the soil it was found that approximately 12 per cent of the labeled nitrogen had been immobilized in soil organic compounds. Clipping of the grass at this date was followed by a decrease in the amount of labeled soil organic nitrogen, indicating that mineralization was not depressed by living plants. The application of unlabeled ammonium sulphate subsequent to the utilization of the labeled nitrogen did not decrease the amount of immobilized labeled nitrogen in the soil organic matter, as would be expected if the organic nitrogen compounds of the soil had been decomposed to ammonia. This was thought to be due to the fact that decomposition of organic nitrogen compounds in permanent grassland results in the production of peptides, amino acids etc. which are utilized by microorganisms without deamination taking place. In pots with ageing grass plants, labeled organic nitrogen compounds were found to be translocated from the grass shoots to the soil (Table 7). Net mineralization of soil organic nitrogen was positive in the contents of pots containing killed root systems (Table 3b). About 8 per cent of the labeled nitrogen added to the contents of such pots, in the form of ammonium sulphate, was found to be present in soil organic nitrogen compounds approximately 4 weeks after application, while a total of about twice this amount of soil organic nitrogen was mineralized during that period. From the results obtained in this investigation, it is concluded that the constant presence of living plants is responsible for the accumulation of nitrogen in organic compounds in permanent grassland. No evidence was obtained that the decomposition of such compounds in the soil is inhibited by living plants.     

Sulphate Uptake in Two Mutants of Chlorella vulgaris with High and Low Sulphur Amino Acid Content

Two mutants of Chlorella vulgaris characterized by higher and lower content of sulphur amino acids compared with the wild strain were assayed for the efficiency of the sulphate uptake mechanism. In both mutants uptake exhibited positive cooperation kinetics and was strongly stimulated by sulphate starvation. Stimulation was depressed by cysteine and to a higher extent by methionine. Mutations affected the uptake efficiency concordantly with the level of sulphur amino acids. Addition to the starved strains of sulphate or chromate reduced the induced transport to the lower values of the non-starved strains. Addition of cycloheximide during the induction period prevented a further enhancement of transport without depressing the attained rate in the low sulphur mutant; it was followed by a rapid fall to the non-induced rate in the high sulphur mutant.     

High-analysis granular sulphur assemblages as sources of sulphur for lucerne

Summary A growth chamber study was conducted to compare five granulated sulphur assemblages and a commercially available prilled sulphur with gypsum and flowers of sulphur as sources of sulphur for lucerne grown on two sulphur deficient soils, one from the Armstrong area of B.C. and one from California. Following one surface application of the various sulphur supplying materials at rates of 37.5 mg, 75 mg and 150 mg of sulphur per 3750 g of soil, four consecutive harvests were removed from the Enderby silt loam during a 145 day period and three cuttings were taken over a 119 day cropping interval on the Willits soil from California.Although gypsum and finely divided sulphur were the most effective sources, three of the five assemblages also had a favourable influence upon yield of lucerne, sulphur concentration and sulphur uptake. The three acceptable assemblages were sulphur-bentonite, sulphur-goulac-ammonium sulphate and sulphur-gypsum-goulac and they produced beneficial effects upon lucerne growth that were often comparable to those obtained with finely divided sulphur.On the basis of this investigation, it appears that certain granular high-analysis sulphur assemblages made from finely divided sulphur and binding agents, such as gypsum, ammonium sulphate, goulac and bentonite have satisfactory agronomic properties. Because these assemblages have suitable agronomic and physical properties they should be ideal for bulk blending with other granular fertilizer materials or for use in direct application to the soil. Wider scale testing of the sulphur-bentonite, sulphur-goulac-ammonium sulphate and sulphur-gypsum-goulac assemblages would seem to be justified.This paper was presented before the 12th Annual Meeting of the Canadian Society of Soil Science, June 28, 1967, Macdonald College, Quebec.