Manganese as an ecological factor in salt marshes

The plant available manganese concentration (Mn²⁺) of salt-marsh sediments was compared to that of acidic and neutral soils. The mean soil-manganese concentration was higher in the top 1 cm of salt-marsh soil than in the neutral soil and comparable to that of the acidic soil (0–5 cm). A peak in the soil-manganese concentration in the upper marsh was observed one week after the spring tide but this effect was not evident in the lower marsh. Despite these differences, there was no correlation between mean manganese concentration and position on the marsh.The response to manganese of salt-marsh halophytes was studied by measuring growth and root elongation in a range of Mn²⁺ concentrations with and without sodium chloride. Although there was a differential response to manganese between salt-marsh species, manganese resistance was not related to position on the marsh. Most of the species investigated were tolerant of Mn²⁺ at concentrations higher than normally recommended for plant growth. Moreover a salt-marsh ecotype of Festuca rubra was found to have a higher manganese resistance than an inland ecotype of the same species.When sodium chloride was included in the growth medium, salt-marsh plants had a greatly increased resistance to manganese associated with a reduced uptake. This effect is reflected in the tissue-manganese concentration which was lower than in Deschampsia flexuosa although both groups of plants were exposed to a similar range of Mn²⁺ concentrations. It is concluded that sodium chloride markedly reduces the phytotoxicity of manganese in salt marshes.Nomenclature following Clapham, Tutin & Warburg (1968). Flora of the British Isles.The work was carried out while one of us (C. E. Singer) was in receipt of an SERC studentship, which is gratefully acknowledged.     

Selective effect of the herbicide DCMU on unicellular algae — a potential tool to maintain monoalgal mass culture ofNannochloropsis

The selective effect of DCMU on photosynthetic activity and growth rate was examined in several marine unicellular algae:Nannochloropsis sp. (Eustigmatohyceae),Dunaliella salina (Chlorophyceae)Isochrysis galbana (Prymnesiophyceae) andChaetoceros sp. (Bacillariophyceae). DCMU at 10^–7 M caused an immediate decrease in the photosynthetic rate ofDunaliella andIsochrysis (about 50% inhibition), whereas 10^–6 M imposed 80% inhibition in the photosynthetic rate ofChaetoceros. InNannochloropsis the rate was affected only when DCMU concentration exceeded 10^–6M. Cellular growth rate of all studied algae was affected by DCMU in a similar manner to photosynthesis. The differential effect of DCMU was further examined in mixed cultures in whichNannochloropsis was cultivated together with an additional species simulating a contamination situation of aNannochloropsis culture. When DCMU was added at concentrations higher than 10^–7 M, the growth of the competing algae significantly decreased, whileNannochloropsis maintained a relatively high growth rate. Consequently, after a growth period of 4 to 7 days a clear domination ofNannochloropsis was observed. These results demonstrate that DCMU and probably other herbicides of similar characteristics can be used effectively as a selective tool to suppress contaminating unicellular algae in open ponds in order to maintain a monoculture ofNannochloropsis.     

Transfer of broad-host-range antibiotic resistance plasmids in soil microcosms

Broad-host-range plasmids, belonging to IncP (RP4 and pUPI102) and IncC (R57.b), were studied for intrageneric and intergeneric gene transfer in three different soil microcosms. RP4 was transferred intragenerically in clay loam, sandy loam, and sandy microcosms at frequencies of 0.71×10^–2, 0.83×10^–2, and 0.41×10^–2 respectively, optimally at 37°C and at 100% vol/wt moisture content. Under similar conditions, R57.b was also transferred at frequencies of 0.38×10^–2, 0.58×10^–2, and 0.80×10^–5 respectively at 30°C. Both RP4 and R57.b were transferred at low frequency at 20°C. Kinetics of plasmid transfer revealed that 48 h was the optimum time for intrageneric conjugal gene transfer. Gene transfer frequency was tenfold higher in all nutrient-amended soil microcosms than in the absence of nutrient amendment. RP4 was transferred to an indigenous soil bacteriumBeijerinckia indica in a nonsterile soil microcosm and to other indigenous soil bacteria, viz.Xanthomonas campestris, Azotobacter chroococcum, Acinetobacter calcoaceticus, Achromobacter agili, andRhizobium meliloti in sterile soil microcosms. pUPI102 was transferred fromA. calcoaceticus BD413 toEscherichia coli K12 J53 at a frequency of 0.75×10^–6 and 1.1×10^–6 in clay loam and sandy loam microcosms respectively. However, no gene transfer was observed in any soil microcosm when strains ofA. calcoaceticus BD413 (pUPI102) andE. coli K12 J53.2 (RP4) were used for conjugal mating. Plasmid RP4 was found to be 100% stable in all the above microorganisms.     

Biomass relationship to growth and phosphate uptake ofPseudomonas fluorescens,Escherichia coli andAcinetobacter radioresistens in mixed liquor medium

The ability ofPseudomonas fluorescens, Escherichia coli andAcinetobacter radioresistenns to remove phosphate during growth was related to the initial biomass as well as to growth stages and bacterial species. Phosphate was removed by these bacteria under favourable conditions as well as under unfavourable conditions of growth. Experiments showed a relationship between a high initial cell density and phosphate uptake. More phosphate was released than removed when low initial cell densities (10²–10⁵ cells ml^–1) were used. At a high initial biomass concentration (10⁸ cells ml^–1), phosphate was removed during the lag phase and during logarthmic growth byP. fluorescens. Escherichia coli. at high initial biomass concentrations (10⁷ cells ml^–1), accumulated most of the phosphate during the first hour of the lag phase and/or during logarithmic growth and in some cases removed a small quantily of phosphate during the stationary growth phase.Acinetobacter radioresistens, at high initial cell densities (10⁶, 10⁷ cells ml^–1) removed most of phosphate during the first hour of the lag phase and some phosphate during the stationary growth phase.Pseudomonas fluorescens removed phosphate more thanA. radioresistens andE. coli with specific average ranges from 3.00–28.50 mg L^–1 compared to average ranges of 4.92–17.14 mg L^–1 forA. radioresistens and to average ranges of 0.50–8.50 mg L^–1 forE. coli.     

Die wachstumsfördernde Wirkung von Tannin auf Getreidekoleoptilen

Zusammenfassung Schwach konzentrierte Tanninlösungen (5·10^–5 bis 5·10^–8 molar) vermochten das Wachstum 10 mm langer Koleoptilabschnitte von 15 Kulturformen vonAvena sativa, Hordeum distichon, Hordeum vulgare, Zea mays, Triticum aestivum undSecale cereale um etwa 6–25% zu fördern. Die mögliche Beteiligung von Gerbstoffen am Streckungswachstum höherer Pflanzen wurde diskutiert.

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Summary The growth of 10 mm coleoptile sections of 15 cultivars ofAvena sativa, Hordeum distichon, Hordeum vulgare, Zea mays, Triticum aestivum andSecale cereale was stimulated by dilute tannin-solutions (5·10^–5 to 5·10^–8 molar) from 6 up to 25%. The possible role of tannins in elongation growth of higher plants was discussed.

     

In vitro plant regeneration from leaf callus inPiper colubrinum Link

Callus-mediated shoot regeneration from leaf explants ofPhytophthora resistant pepper (Piper colubrinum Link.) is described. The effect of basal media composition and growth regulators onin vitro response of explants was evaluated. Shoot buds were induced and elongated on half-strength MS medium containing 2.0 mg l^–1 BA and 0.5 mg l^–1 NAA , as well as 1.0 mg l^–1 BA and 0.5 mg l^–1 2,4-D. The shoots were rooted in half-strength MS medium with or without IAA or IBA, and then were transferred to soil with 100% survival.     

A simple bioassay for abscisic acid using cucumber hypocotyls

A simple bioassay based on the inhibition by abscisic acid (ABA) of cucumber (Cucumis sativus L., cv. National Pickling) hypocotyl elongation was developed. Sections of 3-day-old dark-grown cucumber hypocotyl taken from 0–5 mm immediately below the cotyledon were used for the assay. A dark incubation period of 20 h was followed by an exposure to light for 24 h. Under these conditions, the inhibition of hypocotyl elongation is proportional to the abscisic acid applied. The minimum detectable level of abscisic acid was 10^–9 M, and the range of linear response to abscisic acid was between 10^–7 and 10^–3 M. This assay is 10 times more sensitive than the cucumber cotyledon greening bioassay for abscisic acid.     

Soil Strain of Bacillus subtilis Harboring a Large Plasmid That Mediates High-Frequency Conjugal Mobilization

The ability of a soil strain of Bacillus subtilis harboring a large plasmid, p19, to mobilize a small staphylococcal plasmid, pUB110, was studied. The latter plasmid was transferred to the recipient cells of Bacillus subtilis168 at a high frequency (about 10^–2 per recipient cell) both on the filter surface and in liquid medium. Mobilization was initiated 40 min after the beginning of the contact between donor and recipient cells.     

Influence of L-tryptophan and auxins applied to the rhizosphere on the vegetative growth of Zea mays L.

Glasshouse experiments were conducted to evaluate the influence of L-TRP in comparison with indole-3-acetamide (IAM), tryptophol (TOL) and indole-3-acetic acid (IAA) on the growth of Zea mays L. var. Early Sunglow. L-TRP (25 to 2.5×10^–5 mg kg^–1 soil), IAM (22 to 2.2×10^–5 mg kg^–1 soil), TOL (20 to 2.0×10^–5 mg kg^–1 soil), and IAA (22 to 2.2×10^–5 mg kg^–1 soil) were applied as a soil drench to established uniform seedlings. All treatments were applied in a completely randomized design with 10 replicates. IAM had no significant effect on the plant growth parameters. Shoot height, uppermost leaf collar base distance, internodal distance, and shoot dry and fresh weights were significantly improved upon the addition of TOL (2.0×10^–2 mg kg^–1 soil), however, the highest concentration (20 mg kg^–1 soil) caused a 14.6% reduction in leaf width. L-TRP (2.5×10^–3 mg kg^-1 soil) also had a significant influence on shoot height, uppermost leaf collar base distance, internodal distance and fresh weight of shoot compared with the control. The highest concentration of L-TRP (25=mg kg^–1 soil) had a negative effect on leaf width and dry weight of the shoot. The most pronounced response on the corn growth parameters was observed with the application of IAA at lower concentrations (2.2×10^–5 to 2.2×10^–2 mg kg^–1 soil) specifically improving root growth. The highest concentration (22 mg kg^–1 soil) of IAA had a significant negative effect on plant height, leaf width, stem diameter, shoot fresh and dry weight. These findings indicate that L-TRP applied at the appropriate concentrations can have positive effects on corn growth comparable to pure auxins (TOL and IAA).     

Occurrence and bioassay responses of G

A growth regulator (G) occurs at high concentrations in adult leaves of E. grandis Maiden. Low concentrations of G are present in juvenile leaves of this species and also in adult leaves of some other Myrtaceae. Low concentrations of G (5×10^–6 and 10^–5 M) promote rooting in mung-bean cuttings and elongation in Avena coleoptile sections; high concentrations (5×10^–4 M) inhibit. These and other bioassay results indicate that G may have auxin-like activity.     

Larviculture of the fairy shrimp,Streptocephalus proboscideus (Crustacea: Anostraca): effect of food concentration and physical and chemical properties of the culture medium

Food concentration (0.5 × 10³ – 5 × 10⁵ Scenedesmus cells m1^–1) significant influenced the somatic growth, maturation and survivorship ofS. proboscideus larvae. A density of 5 × 10⁴ cells m1^–1 was optimal for early larval stages. Of four temperature tested (20–35 °C), 30 °C resulted in the best growth and survival. Maturation time was inversely related to temperature, and was size- rather that age-dependent. Larvae were tolerant of a wide conductivity range, but optimal growth and survival were observed at 260 µS cm^–1. Nitrate-Nitrogen (NO₂-N) caused a larval mortality of 50% after 24 h at 0.58 mg1^–1.     

Effect of peat-bran inoculum ofTrichoderma species on biological control ofRhizoctonia solani in lettuce

A range of known biocontrol or plant growth-stimulating species ofTrichoderma orGliocladium were grown on peat-bran substrate to yield between 5×10⁷–3×10¹⁰ colony forming units (cfu's)g^–1 substrate after 14 days growth. Inocula were incorporated into peat:sand potting compost infested withRhizoctonia solani to give 7–8 × 10⁴ cfu's of antagonist g^–1 compost and assessed for biological control activity using lettuce seedlings. Six of the eight antagonists decreased daming-off and three of these consistently increased yield in comparison withR. solani treatment alone.Subsequently, peat-bran inoculum ofT. harzianum isolate TH1 was incorporated at 0.5% w/v intoR. solani infested potting compost. Both autoclaved and nonautoclaved inoculum ofT. harzianum TH1 decreased disease and increased yield. Incorporation of ethyl acetate-extracted autoclaved inoculum ofT. harzianum TH1 resulted in similar levels of biocontrol and improved plant growth as did incorporation of nonautoclaved and autoclavedT. harzianum TH1 inoculum. The need to standardize inocula and controls is emphasized.     

Isolation and study of two strains ofLeptospirillum-like bacteria from a natural mixed population cultured on a cobaltiferous pyrite substrate

Two strains ofLeptospirillum-like bacteria, L6 and L8, have been isolated from a mixed inoculum, also containingThiobacillus ferrooxidans andT. thiooxidans, cultured for one year with a colbaltiferous pyrite as energy substrate in a 100 I continuous bioleaching laboratory unit. Several physiological properties of the strains are described. The vibrio-shaped microorganisms grew at pH values lower than 1.3. Their growth rate was maximum between 2.5 and 8.0 g l¹ ferrous iron. The optimal growth temperature was 37.5° C. Ferric iron had a stimulative effect on bacterial development up to 8 g l^–1, and growth was as rapid at 14 g l^–1 ferric iron as at 8 g l^–1. The negative influence of cobalt on the final cell concentration was observed at 0.5 g l^–1, but the growth rate was not affected up to 2 g l^–1. The G + C content of strains L8 is 55.6 mol%.     

Transformation of15N-labelled urea in rice-wheat cropping system

Summary In a udic chromusterts the transformation of an initial application of¹⁵N-urea @ 80 kg N ha^–1 to rice (Oryza sativa L.) in rice-wheat (R-W) and to wheat (Triticum aestivum L.) in wheat-rice (W-R) rotations was followed in 6 successive crops in each rotation. All rice crops were grown in irrigated wetland and wheat in irrigated upland conditions.The first wheat crop in W-R rotation utilized 22 kg fertilizer N ha^–1 as compared to 19 kg by the corresponding rice crop in R-W rotation. But the latter absorbed more soil N than the former. About 69% of the total N uptake in rice was derived from mineralization of soil organic N as compared to 61% in wheat.The succeeding wheat crop in R-W rotation utilized 6.7% of the residual fertilizer N in the soil but the corresponding rice crop in W-R rotation only 2.2%. The higher utilization appeared to be related to a greater incorporation of labelled fertilizer N in mineral and hexosamine fractions of the soil N. After the second crop in each rotation, the average residual fertilizer N utilization in the next 4 crops ranged between 3 and 4%.The total recovery of¹⁵N-urea in all crops amounted to 21.7 and 24.3 kg N ha^–1 in R-W and W-R rotation, respectively. At the end of the experiment, about 9 to 10 kg ha^–1 of the applied labelled N was found in soil upto 60 cm depth. Most of the labelled soil N (69–76%) was located in the upper 0–20 cm soil layer indicating little movement to lower depths despite intensive cropping for 4 years.     

Parallel plastic tank experiments with cultures of marine diatoms

The reproductibility of tank experiments concerning unicellular marine algal development was analyzed by means of parallel experiments with cultures ofThalassiosira rotula andSkeletonema costatum, using large flexible plastic tanks under semi-natural conditions. The tanks (3–4 m³, 4–5 m deep) were exposed in the German Bight at a station in the outer harbour of helgoland. The water was obtained from the open North Sea in towable tanks; it was filtered (plate filter), enriched with nitrate (20–30 gat dm^–3), phosphate (1.3–2.3 gat dm^–3) and silicate (15–23 gat dm^–3)-nearly natural springtime concentrations in this area-and inoculated with 10³–10⁵ cells dm^–3. The water was mixed with non-metal stirring equipment. Within 5 days, concentrations of 10⁶–10⁷ cells dm^–3 in an exponential growth phase were obtained. In experiments withT. rotula a parallel development was achieved in spite of some contamination by surrounding water. This is the case for nearly all parameters analyzed (nutrient salts, phytoplankton, bacteria, C, N and particulate carbohydrates). The heterotrophic bacteria, which were determined by means of the plate method, reached concentrations of up to 10⁶ (T. rotula) and 10⁵ (S. costatum) CFU cm^–3, respectively. They showed a consistent retrograde development at diatom concentrations above a certain level. The crop did not increase again until the diatoms had reached the stationary phase. During exponential growth ofT. rotula (G=8.9–11.7 h) a partially synchronous cell division was observed. There were also rhythms with respect to cell size (pervalvar axes) and chain length (number of cells). For the experiments withS. costatum (G=10–11.4 h) diurnal variations of cell size and chain length occurred. The present results indicate acceptable reproducibility of algal development and related phenomena in enclosed water bodies.     

Microalgae for use in tropical aquaculture II: Effect of salinity on growth,gross chemical composition and fatty acid composition of three species of marine microalgae

The influence of salinity on the growth, gross chemical composition and fatty acid composition of three species of marine microalgae,Isochrysis sp.,Nannochloropsis oculata andNitzschia (frustulum), was investigated. There was no significant change in growth rate ofIsochrysis sp. andN. (frustulum) over the experimental range of salinity (10–35 ppt), whileN. oculata had a significantly slower growth rate only at 35 ppt. The ash content of all three species increased with increasing salinity. Two species,Isochrysis sp. andN. oculata, showed significant linear increases in total lipid content with increasing salinity over the range 10 to 35 ppt.N. (frustulum) showed significant linear decrease in total lipids, with the highest percentage at low salinity within the range 10–15 ppt. Variation in salinity had only a slight effect on the total protein, the soluble carbohydrate and chlorophylla content of all species. All species responded to change in salinity by modifying their cellular fatty acid compositions. Significant positive correlations were observed between increase in salinity and increase in the percentage ofcis-9-hexadecenoic acid [16:1 (n-7)] over the entire experimental range inN. (frustulum) and between 25–35 ppt inN. oculata. There were curved relationships between salinity and percentage of hexadecanoic acid [16:0] inN. oculata andN. (frustulum), with maxima within the range 25–30 ppt for both species. A curved relationship was found between salinity and percentage of eicosapentaenoic acid [20–5(n-3)], forN. (frustulum), with lowest percentages of the fatty acid within the range 25–30 ppt. There was no consistent pattern in the percentages of other major fatty acids as functions of salinity. The Northern Territory isolateN. (frustulum) was unusual in having a substantial increase in total fatty acids with decreasing salinity (85 mg g^–1 dry wt at 10 ppt compared with 33 mg g^–1 at 35 ppt). The optimum salinities for the production of maximum amount of lipids and the essential fatty acids 20:5(n-3) and/or 22:6(n-3) were as follows:25 ppt forIsochrysis sp. [22:6(n-3)]; 20–30 ppt forN. oculata [20:5(n-3)]; 10–15 ppt forN. (frustulum) [20:5(n-3) and 22:6(n-3)].Author for correspondence     

Extracellular amylase activities ofRhizomucor pusillus andHumicola lanuginosa at initial stages of growth

Among thermophilic fungi,Rhizomucor Pusillus andHumicola lanuginosa have been reported to be among the most prolific producers of amylase, an apparently heat stable enzyme vital to the incorporation of carbon from macromolecular sources such as starch. Yet the highest levels of extracellular amylase in starch-yeast cultures of these fungi were measured after most of the growth had occurred; pre-growth levels appeared to be very small. Since these low levels are the significant ones for growth, a procedure was devised to measure them: 1.162×10^–2 units (mg maltose/ml/min) were measured after two days of growth ofR. pusillus and 6.230×10^–3 units measured after four days of the slower-growingH. lanuginosa. Re-assays of these after dialysis to remove most of the reducing sugars gave 1.689 × 10^–2 units and 1.234 × 10^–2 units, respectively, with all correlation coefficients 0.96 or better.     

Effect of salinity on mycorrhizal onion and tomato in soil with and without additional phosphate

Summary Vesicular-arbuscular mycorrhizal fungi (VAM) are known to increase plant growth in saline soils. Previous studies, however, have not distinguished whether this growth response is due to enhanced P uptake or a direct mechanism of increased plant salt tolerance by VAM. In a glasshouse experiment onions (Allium cepa L.) were grown in sterilized, low-P sandy loam soil amended with 0, 0.8, 1.6 mmol P kg^–1 soil with and without mycorrhizal inoculum. Pots were irrigated with saline waters having conductivities of 1.0, 2.8, 4.3, and 5.9 dS m^–1. Onion colonized withGlomus deserticola (Trappe, Bloss, and Menge) increased growth from 394% to 100% over non-inoculated control plants when soil P was low ( 0.2 mmol kg^–1 NaHCO₃-extractable P) at soil saturation extract salinities from 1.1 dS m^–1 to 8.8 dS m^–1. When 0.8 and 1.6 mM P was added no dry weight differences due to VAM were observed, however, K and P concentrations were higher in VAM plants in saline treatments.Glomus fasciculatum (Gerdeman and Trappe) andGlomus mosseae (Nicol. and Gerd.) isolates increased growth of VAM tomato 44% to 193% in non-sterilized, saline soil (10 dS m^–1 saturation extract) despite having little effect on growth in less saline conditions when soil P was low. Higher tomato water potentials, along with improved K nutrition by VAM in onion, indicate mechanisms other than increased P nutrition may be important for VAM plants growing under saline stress. These effects appear to be secondary to the effects of VAM on P uptake.     

Effects on winter wheat seedling growth by toxin-producing rhizobacteria

Summary Root-colonizing pseudomonads capable of inhibiting seedling winter wheat (Triticum aestivum L.) root growth in an agar seedling bioassay also significantly inhibited wheat root growth in vermiculite; however, the inhibitory trait is quite labile in laboratory culturing. The extent of inhibition in both the agar and vermiculite medium depended on inoculum level. These pseudomonads were found to produce a toxin capable of inhibiting growth ofEscherichia coli C-la andBacillus subtilis. Field isolates that strongly inhibit growth of indicator bacteria also inhibited root growth. Toxin production by the bacteria appeared necessary for inhibition of root growth and indicator bacteria as toxin-negative (TOX^–) mutants no longer inhibited either. Antibiosis towardsE. coli as well as wheat seedling root inhibition in agar was reversed by L-methionine, providing further evidence that a toxin, produced by these organisms, is involved in growth retardation.Contribution in cooperation with the College of Agric. Res. Center, Washington State Univ., Pullman, WA 99164. Scientific Paper No. 6837.     

Intra-population clonal variability in allelochemical potency of the toxigenic dinoflagellate Alexandrium tamarense

Clonal variability in exponential growth rate and production of secondary metabolites was determined from clonal isolates of Alexandrium tamarense originating from a single geographical population from the east coast of Scotland. To assess variability in the selected phenotypic characteristics over a wide spectrum, 10 clones were chosen for experimentation from 67 clonal isolates pre-screened for their lytic capacity in a standardized bioassay with the cryptophyte Rhodomonas salina. Specific growth rates (μ) of the 10 clonal isolates ranged from 0.28 to 0.46 d⁻¹ and were significantly different among clones. Cell content (fmol cell⁻¹) and composition (mol%) of paralytic shellfish toxins (PSTs), analyzed by liquid chromatography with fluorescence detection (LC–FD), varied widely among these isolates, with total PST quotas ranging from 20 to 89 fmol cell⁻¹. Except for strain 3, the toxins C1/C2, neosaxitoxin (NEO), saxitoxin (STX), and gonyautoxins-1 and -4 (GTX1/GTX4), were consistently the most relatively abundant, with lesser amounts of GTX2/GTX3 evident among all isolates. Only clone 3 contained >20 mol% of toxin B1, with C1/C2, GTX2/GTX3 and NEO in almost equimolar ratios.Eight of the 10 clones caused cell lysis of both R. salina and the heterotrophic dinoflagellate Oxyrrhis marina, as quantified from the dose–response curves from short-term (24 h) co-incubation bioassays. For two clones, no significant mortality even at high Alexandrium cell concentrations (ca. 10⁴ mL⁻¹) was observed. Allelochemical activity expressed as EC₅₀ values, defined as the Alexandrium cell concentration causing lysis of 50% of target cells, varied by about an order of magnitude and was significantly different among clones. No correlation was observed between growth rate und allelochemical potency (as EC₅₀) indicating that at least under non-limiting growth conditions no obvious growth reducing costs are associated with the production of allelochemically active secondary metabolites.