Detection and Quantification with 16S rRNA Probes of Planktonic Methylotrophic Bacteria in a Floodplain Lake

Abstract Two approaches employing 16S rRNA oligonucleotide probes, in situ hybridization combined with ³³P-autoradiography and ³²P-labeled slot-blot hybridizations on nitrocellulose filters, were used to enumerate methylotrophic bacteria in the water column of Ryans 1 Billabong, a small floodplain lake in northeastern Victoria, Australia. Methylotrophic bacterioplankton numbered 0.6–1.2 × 10⁹ cells liter⁻¹ in the winter of 1994, and 0.8–5.5 × 10⁹ cells liter⁻¹ in the summer of 1994–95. This was equivalent to 10–46% of total bacterioplankton cell counts, determined via epifluorescence microscopy. Methylotrophic bacteria were not detected in the water column of the nearby Kiewa River, and a set of laboratory controls indicated that the high abundance of methylotrophs in the billabong samples was not a methodological artifact. There was no change, with water depth, in total bacterioplankton or methylotroph abundance in winter, a result consistent with the water column being well mixed at this time of year (dissolved O₂ concentrations 5–7 mg liter⁻¹; dissolved methane concentrations <60 μg liter⁻¹, or <5% methane saturation, at all depths). In summer the billabong became diurnally stratified (dissolved O₂ concentrations <2 mg liter⁻¹ at water depths of >45 cm; dissolved methane concentrations <100 μg liter⁻¹ at the surface, but >500 μg liter⁻¹ near the sediments) and there was a correspondingly marked increase in the abundance of total bacterioplankton and methylotrophs with depth. In situ hybridizations and slot-blot hybridizations both indicated that type II methylotrophs (detected with a probe specific for the 9-α subgroup of Proteobacteria) were markedly less abundant than were type I and X methylotrophs (detected with a probe specific for the 10-γ subgroup of Proteobacteria). Received: 12 March 1996; Accepted: 2 October 1996     

Characterization of depth-related bacterial communities and their relationships with the environmental factors in the river sediments

To better understand the bacterial processes in river sediments, it is necessary to investigate the depth-related bacterial communities in the whole sediment profile. Sediment samples were collected to a depth of 25 cm from the Pearl River. Bacterial abundance, activity, cell-specific respiration rate, and diversity were measured, respectively, by 4′, 6-diamidino-2-phenylindole direct count, 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) staining, electron transport system by CTC reduction, and denaturing gradient gel electrophoresis analysis of 16S rRNA amplification fragments. Results showed that the bacterial metabolism activities decreased with the sediment depth. The total bacterial abundance was highest in the surface sediment with 65.1 × 10⁷ cells g⁻¹, and decreased to 11.1 × 10⁷ cells g⁻¹ below 20 cm in the sample location that suffered from heavy sewage inputs. The active bacteria accounted for 7.50–46.7% of the total bacterial number and decreased with the sediment depth. Electron transport system by the CTC reduction showed that bacterial respiration rate declined from 1.093 μmol CTC-formazan h⁻¹ g⁻¹ in the surface sediment to a half in the bottom sediment, while the cell-specific respiration increased significantly with the depth from 3.56 to 93.75 fmol CTC-formazan cell⁻¹. The bacterial diversity also changed with the depth. Beta-Proteobacteria were the dominant species in the surface sediment, whereas Delta-Proteobacteria were the main species below 10 cm. Results of canonical correspondence analysis (CCA) indicated that the distribution of bacteria was affected by the combined effect of various dissolved inorganic matter, while the respiration rate was independent of the nutrient conditions. The specific bacterial distribution contributed to not only the nutrient cycle but also enhanced pollutant decomposition in sediment of the Pearl River. The results showed that some specific bacterial species had a strong activity in the deeper layers. Therefore, the metabolic functions of the deeper bacterial species should not be neglected.     

Detection Methanogens in Newly Settled Sediments from Xuanwu Lake in Nanjing, China

Sediments from Xuanwu Lake have been dredged in the past 3 years to improve the water quality, but methanogenesis should still exist in the newly settled sediment. Methane production, methanogens, and physiochemical parameters were detected in the surface sediments (0–5 cm) and/or vertical sediments (0–21 cm, segmented at interval of 3 cm). Methane flux at water–air interface varied among five detected sites. Principal component analysis showed that CH₄ flux, content of water and the concentration of total nitrogen (TN), CH₄ and organic matters (OM) weighed most heavily on the component I in surface sediments while different patterns were observed for vertical sediments. The copy number of the 16S rRNA gene for bacteria was lower in the surface sediment (0–6 cm) than that in deeper sediments (12–21 cm), while 16S rRNA genes of Archaea were almost evenly distributed in the vertical sediments. Representatives belonging to the orders Methanobacteriales, Methanomicrobiales, and Methanosarcinales were detected in all samples of the vertical sediments, except that no members of the Methanococcales were detected in the samples at 0–6 cm. The level of Methanobacteriales reached a highest density at 18.1 × 10⁴ copies g⁻¹ dry weight (dw) at 6–9 cm; for Methanosarcinales (76.89 × 10⁶ copies g⁻¹ dw) and Methanococcales (82.70 × 10³ copies g⁻¹ dw) at 12–15 cm, whereas for Methanomicrobiales (43.37 × 10⁶ copies g⁻¹ dw) at 9–12 cm. Methanosarcinaceae and Methanosaetaceae reached to their highest densities at 6–9 and 9–12 cm, respectively. These data provided useful information for better understanding the methanogenesis in the newly settled sediments of a recently dredged lake.     

Palaeolimnology of Lake Hess (Patagonia,Argentina): multi-proxy analyses of short sediment cores

In contrast with the extensive palaeolimnological studies carried out in North America and Europe, relatively few studies have described the anthropogenic and/or climate impacts in Patagonian lakes. We addressed these issues by analysing geochemistry, lithology, pigments and chironomid remains from sediment cores collected from Lake Hess (41°22′20″S, 71°44′0″W) located in the Nahuel Huapi National Park in northern Patagonia. The aim of this study is to provide a palaeoenvironmental and climate reconstruction of the past ca. three centuries for this cold oligotrophic, quasi-pristine lake which receives meltwaters from the Tronador ice cap. Chronology was based on ¹³⁷Cs and ²¹⁰Pb measurements of the upper sediments, and the inferred sedimentation rate of 23.2 mg cm⁻² y⁻¹ (0.15 cm y⁻¹) was consistent with both sets of measurements. The sediment from Lake Hess was rich in tephra deposits particularly evident in the lower part of the cores. Tephras are valuable to use for core correlation and can be traced through peaks in the magnetic susceptibility (MS) profiles. Results from the multiproxy analyses in the longest core (83 cm) identify three main phases of change. From the bottom up to 42 cm (ca. ad 1800), the sediment is composed of light-grey organically rich clays. Both pigments and chironomids suggest variable trends in productivity and precipitation regime. At the end of the Little Ice Age chronozone (ad 1770–1850), pigment concentrations were very low. From 42 cm to ca. 25 cm (ad 1800–1940), the sedimentary record is composed of alternating black and dark organic-matter rich mud with variable amounts of macrophyte remains. Pigment concentrations and chironomid head capsule counts were also very low. These facies are composed of very fine plastic sediments with some faintly laminated intervals and an organic matter composition gradually decreasing towards the top of the zone. A sharp change occurs at 25 cm (ca. ad 1940) showing a strong increase in organic matter content, algal nutrients and plant pigments together with a change in the chironomid assemblages. This might document a change in the trophic condition of the lake associated with changes in erosion/deposition rates. Although there are records of human impact in the area studied, involving the use of fires, most of the observed chemical and biological changes in Lake Hess sediment sequence were interpreted in terms of climate changes, especially to changes in moisture balance brought about by variations in the strength of the westerlies. Guest editors: K. Buczkó, J. Korponai, J. Padisák & S. W. Starratt Palaeolimnological Proxies as Tools of Environmental Reconstruction in Fresh Water     

Screening for microbial markers in Miocene sediment exposed during open-cast brown coal mining

Viable microorganisms were found in Miocene lacustrine clays of the cypris formation excavated from 200-m below the surface as spoil during open-cast brown coal mining (Sokolov Brown Coal Basin, North-Western Bohemia, Czech Republic). Both saprotrophic microfungi of the genera Penicillium, Verticillium, Cladosporium and Aspergillus as well as heterotrophic bacteria were isolated from an intact sediment cores. Heterotrophic bacteria were classified by the MIS Sherlock System as representatives of genera Nocardiopsis, Arthrobacter, Micrococcus, Kocuria, Rothia, Clavibacter, Bacillus, Paenibacillus, Brevibacillus, Microbacterium, Acinetobacter and Pseudomonas. A bacterium found among the strains had an atypical fatty acids profile enriched by branched fatty acids and polyunsaturated fatty acid (18:36) and gave no MIS Sherlock match. Phospholipid fatty acids analysis indicates a relatively high (535 pmol g⁻¹) but inhomogeneously distributed viable microbial biomass. Fatty acids analyses of non-fractioned lipids (representing viable, storage and dead biomass; 8390  pmol  g⁻¹) detected rich and homogenous profiles with fungal, bacterial and actinomycetal markers but no protozoan and algal fatty acids markers.     

Characterization of Viable Bacteria from Siberian Permafrost by 16S rDNA Sequencing

Abstract Viable bacteria were found in permafrost core samples from the Kolyma-Indigirka lowland of northeast Siberia. The samples were obtained at different depths; the deepest was about 3 million years old. The average temperature of the permafrost is −10°C. Twenty-nine bacterial isolates were characterized by 16S rDNA sequencing and phylogenetic analysis, cell morphology, Gram staining, endospore formation, and growth at 30°C. The majority of the bacterial isolates were rod shaped and grew well at 30°C; but two of them did not grow at or above 28°C, and had optimum growth temperatures around 20°C. Thirty percent of the isolates could form endospores. Phylogenetic analysis revealed that the isolates fell into four categories: high-GC Gram-positive bacteria, β-proteobacteria, γ-proteobacteria, and low-GC Gram-positive bacteria. Most high-GC Gram-positive bacteria and β-proteobacteria, and all γ-proteobacteria, came from samples with an estimated age of 1.8–3.0 million years (Olyor suite). Most low-GC Gram-positive bacteria came from samples with an estimated age of 5,000–8,000 years (Alas suite). Received: 11 April 1996 Accepted: 8 May 1996     

Artificial Cyanobacterial Mats: Growth, Structure, and Vertical Zonation Patterns

Abstract The formation of cyanobacterial mats (originally induced by incubation of sediment cores in which metazoans and most other eukaryotes had been removed) was followed over approximately 2.6 years. The thickness of the mats increased at a rate of 2–3 mm per year because of accumulation of empty cyanobacterial sheaths and as a result of carbonate deposition; the fraction of living biomass remained relatively constant over at least 2 years, but there was a slow accumulation of nonliving organic C (≈ 1 mmol yr⁻¹). Biota composition (dominated by five types of filamentous cyanobacteria, unicellular cyanobacteria, diatoms, anoxygenic phototrophs, and heterotrophic bacteria) and vertical zonation patterns in the upper 2–3 mm of the mats were also almost constant over time. Using transmission electron microscopy and stereological analysis it was possible to quantify the vertical distribution of major groups of organisms. Received: 20 December 1999; Accepted: 10 June 2000; Online Publication: 28 August 2000     

Microbial communities of the stratified soda Lake Doroninskoe (Transbaikal region)

The physicochemical properties, species composition, and vertical distribution of microorganisms in the water column, shoreline microbial mat, and small shoreline mud volcanoes of the stratified soda Lake Doroninskoe were investigated in September 2007. The lake is located in the Transbaikal region, in the permafrost zone (51°25′N; 112°28′E). The maximal depth of the contemporary lake is about 6 m, the pH value of the water is 9.72, and the water mineralization in the near-bottom horizon is 32.3 g l⁻¹. In summer, the surface oxygen-containing horizon of the water column becomes demineralized to 26.5 g l⁻¹; at a depth of 3.5–4.0 m, an abrupt transition occurs to the aerobic zone containing hydrosulfide (up to 12.56 g l⁻¹). Hydrosulfide was also detected in trace quantities in the upper water horizons. The density stratification of the water column usually ensures stable anaerobic conditions until the freezing period (November and December). The primary production of oxygenic phototrophs reached 176–230 μg l⁻¹. High rates of dark CO₂ assimilation (61–240 μg l⁻¹) were detected in the chemocline. Within this zone, an alkaliphilic species of sulfur-oxidizing bacteria of the genus Thioalkalivibrio was detected (10⁴ cells ml⁻¹). Lithoheterotrophic bacteria Halomonas spp., as well as bacteriochlorophyll a-containing aerobic anoxygenic phototrophic bacteria (AAP) Roseinatronobacter sp. capable of thiosulfate oxidation, were isolated from samples collected from the aerobic zone (0–3 m). The water transparency in September was extremely low; therefore, no visible clusters of anoxygenic phototrophic bacteria (APBs) were detected at the boundary of the hydrosulfide layer. However, purple sulfur bacteria which, according to the results of the 16S rRNA gene analysis, belong to the species Thioalkalicoccus limnaeus, Ectothiorhodospira variabilis, “Ect. magna,” and Ect. shaposhnikovii, were isolated from samples of deep silt sediments. Ect. variabilis and Ect. shaposhnikovii were the major APB species in the shoreline algo-bacterial mat. The halotolerant bacterium Ect. shaposhnikovii, purple nonsulfur bacteria of the genus Rhodobacter, and AAP of Roseococcus sp. were isolated from the samples collected from mud volcanoes. All these species are alkaliphiles, moderate halophiles, or halotolerant microorganisms.     

Seasonal variation in sulfate reduction and methanogenesis in peaty sediments of eutrophic Lake Loosdrecht,The Netherlands

During one year, concentration profiles of sulfate and methane were measured in sediment cores of eutrophic Lake Loosdrecht. Sulfate concentrations decreased exponentially with depth towards a constant threshold value of 7.6 ± 6.1 μM. Concentration profiles were used to calculate fluxes of sulfate and methane and to estimate the anaerobic mineralization rate. Anaerobic mineralization was highest in autumn which was probably due to an increased sedimentation of easily degradable organic carbon. At high rates (>600 μ mol organic carbon .m⁻².h⁻¹), sulfate reduction appeared to be limited by sulfate and methanogenesis accounted for over 80% of the anaerobic mineralization. At low anaerobic mineralization rates, measured in winter and spring, sulfate reduction was predominant. There was little methanogenesis below 5 cm depth in the sediment which indicated a rapid decrease of degradable organic matter with depth. There was a remarkable difference, especially in winter, between methane fluxes which were measured in batch experiments and those calculated from the concentration profiles in the sediment. These differences may be due to methane diffusing upward from deep layers.     

Redox Changes of Iron Caused by Erosion,Resuspension and Sedimentation in Littoral Sediment of a Freshwater Lake

Depth profiles of oxygen concentration and the redox status of acid-extractable iron were measured in littoral sediment cores of Lake Constance after mechanical removal of surface sediment, mixing, and re-deposition. In undisturbed sediment cores, oxygen penetrated down to 2.9±0.4 mm or 4.6±0.4 mm depth, respectively, after 12 h of incubation in the dark or light; causing a net diffusive flux of 108±20 nmol cm⁻² h⁻¹ oxygen into or 152±35 nmol cm⁻² h⁻¹ out of the sediment. The uppermost 20 mm layer of the undisturbed sediment cores contained 10.2± 0.7 μmol cm⁻³ ferrous and 3.8±1.1 μmol cm⁻³ ferric iron. After erosion, the oxic–anoxic interface in the newly exposed sediment was shifted to about 2 mm depth within 30 min, causing an oxygen flow into the sediment. During the following 12 h, oxygen penetrated deeper into the sediment, and in the light oxygen was produced photosynthetically. Ferrous iron was largely oxidized within two days after erosion. The oxidation rates were higher in oxic than in anoxic sediment layers, and decreased with time. This oxidation process took the longer and was confined closer to the surface the more reduced the exposed sediment had been before. Resuspension of eroded sediment in aerated lake water did not cause a significant oxidation or reduction of iron. After re-deposition, the oxic–anoxic interface in the re-sedimented material shifted to about 2 mm depth within 30 min, causing an oxygen flow into the sediment. During the following 12 h, the oxygen penetration depth and the oxygen flow rate into the re-deposited sediment did not change any further, and no oxygen was produced in the light. Ferric iron was reduced during the first day after re-deposition, and partly re-oxidized during the second day. The extent of reduction was stronger and the extent of oxidation weaker the more reduced the resuspended sediment was before. Oxic conditions in the sediment surface were established faster and ferrous iron was oxidized to a larger extent after erosion of sediment than after resuspension and sedimentation.     

The rates of sediment-water exchange of oxygen and sediment bioturbation in Lough Neagh,Northern Ireland

Oxygen is transported 30 mm into the sediment at an 8 m depth site in eutrophic Lough Neagh by the irrigational activities of the benthic fauna. Faunal activity also mixes the upper 20 mm of sediment. Sediment oxygen uptake rate, redox potential-depth profile and the chlorophylla concentration were measured in the upper sediment layers from February to November 1979. Chlorophylla input to the sediment, following the Spring phytoplankton maximum, remained in the 0–1 cm sediment layer but did cause the redox potential profile to change from one with potentials around 400 mV in the upper 50 mm to one with a strong gradient over the 0–30 mm region. The start of benthic faunal activity in May caused the chlorophylla to be mixed into the 1–2 cm layer and also caused oxygen to be transported into the sediment at a rate sufficient to change the redox potential back to its initial state. The biodiffusion coefficient for solids in the upper 20 mm was estimated to be 6 × 10⁻⁸ cm² s⁻¹. Oxygen transport in the pore, waters of the upper sediment layers was considered to be best described as advection, caused by the irrigational activities of the benthic fauna.     

Vertical distribution in and isolation of bacteria from Lake Vanda: an Antarctic lake

Vertical distribution of bacteria in Lake Vanda, an Antarctic meromictic lake, was examined by the acridine orange epifluorescence direct count method. Total bacteria were 10⁴–10⁵ cells · ml^–1 in the water at 55 m depth and above, and increased drastically to 10⁷ cells · ml^–1 in the bottom water. Filamentous or long rodshaped bacteria occurred at a high frequency in the upper layers, but in the bottom layers most bacteria were coccoidal or short rods. Mean bacterial cell volume in water of between 10 m and 60 m deep was fairly large compared with common bacterial populations in seawater and lake water. Aerobic heterotrophic bacteria were recovered from the water of a depth of 30 m and above, and were assumed to belong to Caulobacter. Viable heterotrophic bacteria were not recovered from the high salinity deep water by media prepared with the same deep water. Phototrophic purple non-sulphur bacteria were isolated by enrichment cultures from water at 55 m depth.     

Temperature dependence of sediment-water exchange in Lake Grevelingen,SW Netherlands

Extended abstract Lake Grevelingen is a brackish water lake in the SW Netherlands. The lake has an area of 108 km², a mean depth of 5.3 m (maximum 48 m), a mean chlorinity of 13 to 16%0 Cl⁻, and a hydraulic residence time of about 8 years. Mass budget studies have shown a consistent seasonal pattern in the phosphorus sediment-water exchange in Lake Grevelingen (Kelderman 1980). From May to August a P mobilization from the sediment takes place, estimated atca. 12.5 mg P · m⁻² · day⁻¹. The sediment accumulatesca. 5.5 mg P · m⁻² · day⁻¹ during the rest of the year. Temperature may be an important factor in establishing this pattern. Sediment-water exchange was studied by means of laboratory experiments under specified conditions. Sediment cores (30 cm depth, 11 cm diameter) were taken at four stations in the lake, with sediment types varying from medium- to muddy sand (Fig. 1). The cores with overlying water (ca. 21) were placed in the dark at 5 °C in thermostatically controlled water baths. After a week's incubation time the temperature was slowly raised, such that after three weeks eight cores (four sediment types, duplicates) were at 5 °C, eight were at 10 °C, eight at 15 °C and eight at 20 °C. The same procedure was applied to the four control cores, containing lake water.     

Regulation of Cell Volume by β2-adrenergic Stimulation in Rat Fetal Distal Lung Epithelial Cells

Cell-volume changes induced by terbutaline (a specific β₂-agonist) were studied morphometrically in rat fetal distal lung epithelium (FDLE) cells. Cell-volume changes qualitatively differed with the concentration of terbutaline. Terbutaline of 10⁻¹⁰–10⁻⁸ m induced transient cell swelling. Terbutaline of 10⁻⁷ m induced transient cell swelling followed by slow cell shrinkage. Terbutaline of 10⁻⁶–10⁻⁵ m induced rapid cell shrinkage followed by slow cell shrinkage. Terbutaline of 10⁻³ m induced transient cell shrinkage; then cell volume oscillated during stimulation. Benzamil of 10⁻⁶ m suppressed the cell swelling induced by 10⁻¹⁰–10⁻⁸ m terbutaline and quinine of 10⁻³ m inhibited the cell shrinkage induced by 10⁻⁶–10⁻⁵ m terbutaline. These results suggest that cell swelling would be induced by NaCl influx and the cell shrinkage is by KCl efflux. Dibutyryl cyclic AMP (DBcAMP) also induced similar cell-volume changes over a wide range of concentrations (10⁻⁹–10⁻³ m): a low concentration induced transient cell swelling; a high concentration, rapid and slow cell shrinkage. Forskolin (10⁻⁴ m), like terbutaline (10⁻⁵ m), induced rapid cell shrinkage followed by slow cell shrinkage, and this decrease in the cell volume was enhanced by the presence of benzamil. On the other hand, cell shrinkage was induced by ionomycin (even low concentration; 3 × 10⁻¹⁰ m ionomycin), and after that cell volume remained at a plateau level. Removal of extracellular Ca²⁺ abolished the cell swelling caused by terbutaline of 10⁻¹⁰–10⁻⁸ m. With removal of extracellular Ca²⁺, the initial, rapid cell shrinkage induced by 10⁻⁵ m terbutaline became transient, but we still detected slow cell shrinkage similar to that in the presence of extracellular Ca²⁺. Overall, at low concentrations (10⁻¹⁰–10⁻⁸ m), terbutaline induced benzamil-sensitive cell swelling in FDLE cells, which was cAMP- and Ca²⁺-dependent; high concentrations (≥⁻⁶) induced quinine-sensitive rapid cell shrinkage, which was Ca²⁺-dependent; high concentrations (≥⁻⁷) induced slow cell shrinkage, which was cAMP-dependent. These findings suggest that terbutaline regulates cell volume in FDLE cells by cytosolic cAMP and Ca²⁺ through activation of Na⁺ and K⁺ channels. Received: 13 March 1995/Revised: 17 January 1996     

Effects of Spilled Oil on Bacterial Communities of Mediterranean Coastal Anoxic Sediments Chronically Subjected to Oil Hydrocarbon Contamination

The effects of spilled oil on sedimentary bacterial communities were examined in situ at 20 m water depth in a Mediterranean coastal area. Sediment collected at an experimental site chronically subjected to hydrocarbon inputs was reworked into PVC cores with or without a massive addition of crude Arabian light oil (∼20 g kg⁻¹ dry weight). Cores were reinserted into the sediment and incubated in situ at the sampling site (20 m water depth) for 135 and 503 days. The massive oil contamination induced significant shifts in the structure of the indigenous bacterial communities as shown by ribosomal intergenic spacer analysis (RISA). The vertical heterogeneity of the bacterial communities within the sediment was more pronounced in the oiled sediments particularly after 503 days of incubation. Response to oil of the deeper depth communities (8–10 cm) was slower than that of superficial depth communities (0–1 and 2–4 cm). Analysis of the oil composition by gas chromatography revealed a typical microbial alteration of n-alkanes during the experiment. Predominant RISA bands in oiled sediments were affiliated to hydrocarbonoclastic bacteria sequences. In particular, a 395-bp RISA band, which was the dominant band in all the oiled sediments for both incubation times, was closely related to hydrocarbonoclastic sulfate-reducing bacteria (SRB). These bacteria may have contributed to the main fingerprint changes and to the observed biodegradation of n-alkanes. This study provides useful information on bacterial dynamics in anoxic contaminated infralittoral sediments and highlights the need to assess more precisely the contribution of SRB to bioremediation in oil anoxic contaminated areas.     

Spatial and temporal variations of the water–sediment thermal structure in shallow ice-covered Lake Vendyurskoe (Northwestern Russia)

The thermal structures in the vicinity of the ice–water and water–sediment boundaries of a shallow lake, L. Vendyurskoe (Northwestern Russia) during four winter seasons are described. The heat flux at the water-ice boundary was 0.1–0.2 W m⁻² during winter. The maximal heat flux at the water–sediment boundary was 4.5 W m⁻² at the beginning and 0.5 W m⁻² at the end of winter. The daily average value of the solar radiation penetrating into the water was 0.5 W m⁻² during main part of winter and 2–50 W m⁻² during April. During winter, temperature showed an oscillation in the vicinity of the sediment-water interface. Most periods corresponding to the main oscillation frequencies in the near-bottom water layer (0–0.4 m) and upper layer sediment (0–0.35 m), identified by FFT analysis, fall within the scale of synoptic variations (3–10 days), and in a number of cases were equal to 1 day. The theoretical periods of the first baroclinic seiche mode of Lake Vendyurskoe are 4.5–8.5 days that compares well with identified temperature oscillation periods. The comparison between the rate of heat content change in a water column and the difference of vertical heat fluxes from sediment to water and from water to ice show that the horizontal heat transport takes place in the lake during winter as a result of heat advection along the bottom.     

Hyperpolarization-activated Ca2+-permeable Channels in the Plasma Membrane of Tomato Cells

The hyperpolarization of the electrical plasma membrane potential difference has been identified as an early response of plant cells to various signals including fungal elicitors. The hyperpolarization-activated influx of Ca²⁺ into tomato cells was examined by the application of conventional patch clamp techniques. In both whole cell and single-channel recordings, clamped membrane voltages more negative than −120 mV resulted in time- and voltage-dependent current activation. Single-channel currents saturated with increasing activities of Ca²⁺ and Ba²⁺ from 3 to 26 mm and the single channel conductance increased from 4 pS to 11 pS in the presence of 20 mm Ca²⁺ or Ba²⁺, respectively. These channels were 20–25 and 10–13 times more permeable to Ca²⁺ than to K⁺ and to Cl⁻, respectively. Channel currents were strongly inhibited by 10 μm lanthanum and 50% inhibited by 100 μm nifedipine. This evidence suggests that hyperpolarization-activated Ca²⁺-permeable channels provide a mechanism for the influx of Ca²⁺ into tomato cells. Received: 13 February 1996/Revised: 12 August 1996     

Increasing phosphorus supply in subsurface soil in northern Australia: Rationale for deep placement and the effects with various crops

Three field experiments involving wheat, lucerne or cotton were established at different sites in the semiarid cropping regions of northern Australia, to test whether the deep placement of P fertiliser improved P availability, compared to the conventional practice of placing the fertiliser beside or adjacent to the seed. At Mulga View, near St George in southern Queensland on a red Kandosol soil with a Colwell soil test value of 19 mg P kg soil⁻¹ in the top 10 cm, there was no response to 10 kg P ha⁻¹ applied in the 5–7 cm layer. However, increasing the depth of placement of 10 kg P ha⁻¹ from 5–7 to 10–15 cm resulted in increased shoot growth and grain yield of spring wheat (Triticum aestivum) by 43 and 30%, respectively. A further grain yield increase of 43% to 3.2 t ha⁻¹ resulted when the deep P rate was increased from 10 to 40 kg P ha⁻¹. At Roma, in southern Queensland, on a grey/brown Vertosol with a Colwell soil test value of 15 mg P kg soil⁻¹, there was no difference in the winter growth of lucerne (Medicago sativa) when P fertiliser had been applied at 5–7 cm depth at rates of 10 and 40 kg P ha⁻¹. Shoot dry matter yields were around 2 t ha⁻¹. However dry matter yields increased significantly to 2.6 and 3.7 t ha⁻¹ when 10 and 40 kg P ha⁻¹, respectively were applied at the 10–15 cm depth. The third experiment was carried out on a grey Vertosol at Kununurra in Western Australia. Significant increases in the yield of seed cotton (Gossypium hirsutum) occurred when 50 kg P ha⁻¹ was applied at depth (10–15 and 25–30 cm), compared with the conventional placement at 7–10 cm, with maximum yield response to deep placement occurring with DAP, and the minimal response with MAP. The cotton was grown on raised beds and the crop was irrigated according to district practice. The response to deep P at all sites was attributed to the rapid drying of the soil surface layers, reducing the availability of soil or fertiliser P in these layers. The deep fertiliser P remained available during the growing season and alleviated the P deficiency that appears to be a feature of these soils when the surface layers become dry.     

Influence of the Hydrological Cycle on the Bacterioplankton of an Impacted Clear Water Amazonian Lake

Abstract Free-living and attached bacterial population sizes were determined fortnightly from December 1991 to December 1992 in natural and disturbed areas of an Amazonian clear water lake (Batata Lake, Pará, Brazil) impacted by bauxite tailings. The bacterioplankton showed distinct patterns during different phases of the hydrological cycle. Total bacterial population size and rates of thymidine incorporation (measured during high and low water phases) were high during low water, with values ranging from 3.3 × 10⁵ to 1.1 × 10⁶ cells ml⁻¹, and from 0.28 to 4.01 μg C l⁻¹ h⁻¹, respectively. The population size of free-living bacteria was larger at the natural station, while no differences were observed between attached bacterial populations at both stations. However, production and turnover rate of attached bacteria were high at the disturbed area. During low water, bacterial growth appeared to be driven mainly by the input of dissolved organic carbon (DOC) from phytoplankton origin. During high water, bacterial abundance was reduced, probably as the result of dilution and the input of less labile DOC from floodplains. The presence of bauxite tailings seems to influence bacterial dynamics in an indirect way, probably due to shading of phytoplankton cells and, hence, reducing the DOC supply for bacterial growth. This study, the first on the microbial ecology of an Amazonian clear water lake, demonstrated that water level variations exert a strong influence on the bacterioplankton dynamics. Received: 9 January 1996; Accepted 6 November 1996