In situ specific loss and growth rates of purple sulfur bacteria in Lake Cisó

Abstract Growth rates and population dynamics of phototrophic bacteria in Lak Cisó were analysed by measuring bacterial abundances and determining specific rates of growth and loss. Net growth rates were calculated from actual changes in biomass assuming exponential growth. Values ranged between −0.072 and 0.037 per day (d⁻¹) for Chromatium , and between −0.043 and 0.022 d⁻¹ for Amoebobacter . Exponential loss rates through sedimentation, decomposition and washout were determined independently. Values ranged between 0 and 0.025 d⁻¹ in the case of Chromatium and between 0 and 0.015 d⁻¹ in the case of Amoebobacter . Finally, gross growth rates were calculated by adding net growth to losses. Maximal values were 0.063 d⁻¹ for Chromatium and 0.037 d⁻¹ for Amoebobacter . In the case of Chromatium , population growth rates were found to be correlated with the amount of light available per unit of growing biomass. It was concluded that growth of phototrophic bacteria in Lake Cisó was limited by light availability. Altogether, purple sulfur bacteria seemed to maintain a very large biomass with very slow growth, thanks to very slow losses during stratification. During holomixis the situation was more dynamic. Washout of cells and disappearance of algal cells allowed more light to reach the bacteria. Therefore, high growth rates were found towards the end of the winter. A similar pattern repeated itself from year to year. These are the first estimates of in situ growth rates for populations of phototrophic bacteria.     

Milk consumption and estimates of growth energetics in pouch young of the northern brown bandicoot, Isoodon macrourus (Peramelidae, Marsupialia), in captivity

Milk consumption was measured in pouch young of the northern brown bandicoot, Isoodon macrourus , using the ²²Na turnover technique. Milk consumption rates increased from about 2.3 ml young⁻¹ d⁻¹ at 23 days post-partum to about 17.2ml young⁻¹ d⁻¹ at 52 days, just prior to weaning. Young increased in mass from 8.5 g to around 112 g over the same period. Masś gained for each ml of milk consumed ranged from 0.28 to 0.65 gml⁻¹. The efficiency with which young converted milk energy and protein into body energy and protein ranged from 16.1 to 39.6% and 38.4 to 82.3%, respectively.     

Effects of experimental small-scale grassland fragmentation on spatial distribution, density, and persistence of ant nests

Abstract.  1. Grassland fragmentation is expected to influence the abundance of different invertebrate species to a different extent. Fragmentation-related effects are of particular importance in species that interact with many other species.
2. The density and spatial distribution of nests of 15 ant species in experimentally fragmented calcareous grasslands at three sites in the Northern Swiss Jura mountains were examined. Fragments of different size (0.25 m², 2.25 m², and 20.25 m²) were isolated by a 5-m wide strip of frequently mown vegetation. Control plots of corresponding size were situated in adjacent undisturbed grassland.
3. Three years after initiation of the experiment, ant nest density did not differ between fragments and control plots. Six years after initiation of the experiment, however, ant nest density and forager abundance were higher in large fragments than in large control plots. Ant nests tended to occur more frequently along the edge of fragments than in the core area. Persistence time of nests of the most abundant species, Lasius paralienus , tended to be shorter in fragments than in control plots. Furthermore, persistence time was longer in nests situated close to the fragment edge than in nests in the core area.
4. Effects on nest density, edge effects on the spatial distribution of nests, and the relationships between nest density and environmental factors were more pronounced when only nests of L. paralienus were considered. The implications of these findings for plant and other invertebrate species are discussed.     

Phytoplankton and pelagic primary productivity in Øvre Heimdalsvatn

A phytoplankton investigation was carried out in the subalpine, low-productive Norwegian lake Øvre Heimdalsvatn in 1969–70 and 1972. This paper describes the temporal and spatial distribution of the standing stock of phytoplankton, and phytoplankton primary productivity. The annual average primary productivity in 1972 was 4.0–4.9 mg C m⁻³ d⁻¹; the annual average standing stock varied from 120 mg m⁻³ (freshweight) in 1969–70, to 250 mg m⁻³ in 1972. Phytoplankton species composition and size distribution is discussed. Throughout the year the phytoplankton is dominated by small (ultraplankton) species; μ-algae (< 5 μm) showed cell concentrations up to 15 mill. cells 1⁻¹. The dominating group was chrysophytes; cryptophytes, dinoflagellates or green algae were at times abundant. A phytoplankton monthly budget and a diagram showing annual average carbon flow through the standing stock of phytoplankton are presented; the phytoplankton dynamics in Øvre Heimdalsvatn is compared to that of other low-productive lakes.     

Role of benthic insect feces in a Rocky Mountain stream: fecal production and support of consumer growth

The feces of stream insects may be a major component of fine particulate organic matter (FPOM) available to collector organisms. In Mink Creek, Idaho, winter defecation rates for 9 species ranged from 86 mg dry feces (g dry body wt)⁻¹ d⁻¹ (Ephemerella spinifera) to 154 mg g⁻¹ d⁻¹ (Paraleptophlebia heteronea) . Detailed studies of 3 species in summer revealed that rates were much greater than in winter and exhibited high between-individual variation (e.g., 695 ± 184.8 mg (g body wt)⁻¹ d⁻¹ for Baetis tricaudatus ). By combining measured and literature values, it is estimated that the benthic insect community egests approximately 3.4 kg feces m⁻² yr⁻¹. This value lies within the range of FPOM estimated to be derived from degradation of leaf litter input (0.7–9.9 kg m⁻² yr⁻¹, depending upon assimilation efficiency of the organisms).
Short-term winter growth experiments showed that, with two exceptions, collectors fed on fecal detritus will grow as well as on other food resources; relative growth rates depend upon the species. Because fecal detritus is abundant throughout the year, and is treated by many species as a source of food, it could be a major mechanism by which seasonal fluctuation in availability of allochthonous litter input is minimized and homeostasis of structure and function maintained.     

Larval settlement of the green sea urchin, Strongylocentrotus droebachiensis, in the southern Gulf of Maine

Abstract. Settlement timing and differential settlement for the larval stage of the green sea urchin, Strongylocentrotus droebachiensis , in the southern Gulf of Maine was studied during the summer of 1996. Settlement densities on astroturf panels were highest in June and early July (13 to 37 m ⁻² d⁻¹), and peaked in mid-June (199 m⁻² d⁻¹). Settlement was low to nonexistent from mid-July through August (0 to 2 m⁻² d⁻¹). During the peak in settlement, no selection for substrate type was observed. In the remainder of the settlement period, differential settlement occurred, with a preference for substrate covered with live coralline algae. Test diameter of newly settled urchins varied among the substrates, with urchins settling on live coralline algae having the largest test diameter (0.43 ± 0.01 mm). There were no differences in test diameter among the different weeks in which sampling was done. Sustained onshore winds occurred only during peak settlement, suggesting that wind drift currents may concentrate larvae and influence patterns of larval settlement.     

Soluble fractions of Solanum tuberosum enchnce call and pigment production of semi-continous cultures of the microlga Phaeodactylum tricornutum

J. FÁBREGAS, E. MORALES, N. POLANCO, M. PATINO AND A. OTERO. 1996. Soluble fractions of Solanum tuberosum extracted with different methods were tested on semicontinuous mixotrophic cultures of the marine microalga Phaeodactylum tricornutum maintained with renewal rate at 15%. The highest stabilization cell density, 78.2 x 10⁶ cells ml⁻¹, was obtained with an autoclaved non-fermented soluble fraction obtained with distilled water. Highest productivities and carotenoids, 0.9 mg 1⁻¹ d⁻¹, and chlorophyll, 2.9 mg 1⁻¹, d⁻¹, were obtained with a non-autoclaved nonfermented fraction extracted in sea water. The bacterial population associated to the microalgal cultures changed depending on the nutrient availability of each of the potato-soluble fractions.     

Field metabolic rates of black-browed albatrosses Thalassarche melanophrys during the incubation stage

Field metabolic rates (FMR) and activity patterns of black-browed albatrosses Thalassarche melanophrys were measured while at sea and on nest during the incubation stage at Kerguelen Island, southwestern Indian Ocean. Activity-specific metabolic rates of five albatrosses at sea (FMR_at-sea) were measured using doubly labeled water (DLW), and by equipping birds with wet-dry activity data loggers that determined when birds were in flight or on the water. The metabolic rates of four birds incubating their eggs (FMR_on-nest) were also measured using DLW. The mean±SD FMR_at-sea of albatrosses was 611±96 kJ kg⁻¹ d⁻¹ compared to FMR_on-nest of 196±52 kJ kg⁻¹ d⁻¹. While at sea, albatrosses spent 52.9±8.2% (N=3) of their time in flight and they landed on the water 41.2±13.9 times per day. The FMR of black-browed albatrosses appear to be intermediate to that of three other albatross species. Based on at-sea activity, the power requirement of flight was estimated to be 8.7 W kg⁻¹ (or 4.0×predicted BMR), which is high compared to other albatross species, but may be explained by the high activity levels of the birds when at sea. The FMR_at-sea of albatrosses, when scaled with body mass, are lower than other seabirds of similar body size, which probably reflects the economical nature of their soaring flight.     

Kinetics of FeS-mediated denitrification in sediments from the Camargue (Rhone delta, southern France)

Abstract Denitrification rates were measured in sediments after the addition of different concentrations of FeS. A decrease of the denitrification rate was observed when high concentrations of ferrous iron (> 10 mM) were present. In the experiments with no significant concentrations of free Fe²⁺, the relationship between NO₃⁻ reduction and FeS concentration followed Michaelis and Menten kinetics. The maximum rate was 0.273 mmol l⁻¹ d⁻¹, 6 times as much as the basal rate 0.046 mmol l⁻¹ d⁻¹, which was attributed to organic matter; the K_s was 1.45 mM FeS. The stoichiometry of the overall reaction involving NO₃⁻ reduction and the concomitant S²⁻ oxidation was also investigated. Measured ΔS/ΔN ratios ranged between 0.55 and 0.64, with ΣH₂S + SO₄²⁻ changing less than 10%. These values agree with the theoretically expected value of 0.56.     

Comparative primary productivity of algal epiphytes on three species of macrophyte in the littoral zone of Lake Ohrid, Yugoslavia

Primary productivity of algal epiphytes on the surfaces of Phragmites, Potamogeton , and Nuphar was measured seasonally from June 1978, through June 1979, in the littoral zone of Lake Ohrid, using ¹⁴C methodology. Surface areas of individual macrophytes were determined throughout the study period through the use of a non-miscible surfactant and a calibration curve of surfactant weight versus known, calculated surface areas.
Mean total surface area available for epiphytic colonization during the study period was 1.032 m² macrophyte surface per m² of littoral zone for Phragmites , 0.810 m² for Potamogeton , and 0.167 m² for Nuphar . Seasonal rates of mean primary productivity of algal epiphytes on Phragmites from the surface to the light-compensation depth ranged from 84–1406 mg C m⁻² littoral zone d⁻¹; ranges for epiphytes on Potamogeton and Nuphar were 77–586 and 69–268 mg C m⁻² littoral zone d⁻¹, respectively. Maximum rates were observed typically during June; minimum rates were observed typically during August to December. Mean daily productivity rates over the 12 month period were for epiphytes on Potamogeton 167.0, on Nuphar 100.4 and on Phragmites 671.2 mg C m⁻² littoral zone d⁻¹. Calculated annual production for epiphytes on Nuphar was 36.65, on Potamogeton 60.95 and on Phragmites 245.0 g C m⁻² littoral zone yr⁻¹. Epiphytic production data were typically considerably higher than production data obtained for littoral and pelagial planktonic algae and compare favorably with published data for epiphytic and periphytic production in Lawrence Lake, Marion Lake, and Borax Lake.     

Grazing by oligochaetes and snails on epiphytes

SUMMARY. 1. The isotope ³³P was used to assess the effect of grazitig by oligochaetes (mainly Stylaria lacttstris L.) and the snail, Lymnaea peregra (Muller), on epiphytes within an Equisetum fluviatile L. stand.
2. Two 1 m² polystyrene enclosures were set up within the emergent macrophyte zone of the lake. At the start of the experiment ³³P-solution was mixed with the water in both tanks. Algal and animal samples for ³³P- analysis were collected during the peak occurrence of epiphytes in June.
3. Phosphorus release rates from the animals through defaecation and excretion were measured in the laboratory. The grazing rate of oligochaetes was 2.2–4.1 mg P m⁻² (of bottom) d⁻¹ of which about two - thirds was released and recycled. The oligochaete density ranged from 13,400 to 20,900 m⁻². The snails (25 ind. m⁻²) grazed 1.2-1.5 mg P m⁻²d⁻¹of whieh about a quarter was released through defaecation and excretion.
4. Daily consumption by the oligochaetes and snails corresponded to 22–45% of the average phosphorus uptake by the epiphytes.     

The growth and mortality of larval herring, Clupea harengus L., in the River Blackwater Estuary, 1978–1980

Herring larvae were sampled in the Outer Thames Estuary and the River Blackwater Estuary in the springs of 1978, 1979 and 1980. Data were collected on larval stage, yolk sac and post yolk sac, larval length and total larval numbers. Newly hatched larvae were 6.8±0.5 mm long and the growth rate of yolk sac larvae was estimated at 0.18 mm d⁻¹ ( L = 6.8±0.186 t ). The growth rate of post yolk sac larvae increased to 0.43mm d⁻¹ ( L = 11±48.0±43 t ). Mortality estimates, derived from total numbers in the summed estuary segments, varied between the years and the cohorts within the year. In 1979 the mortality rates were 0.061 d⁻¹ and 0.074 d⁻¹ for the two cohorts. The mean size of the larval population was estimated at 2.48×10⁹ (1.63–3.77 × 10⁹) which agreed well with population size estimates from egg laying and from catch in numbers at age together with estimated fishing mortality rates.     

Diet selection and energy and water budgets of the common spiny mouse Acomys cahivinus

The common spiny mouse, Acomys cahirinus (body mass=47 g), is widely distributed in Israeli deserts where it inhabits natural crevices on rocky slopes. This omnivorous rodent consumes a varied diet, and in particular snails. We determined diet selection and energy and water balances of spiny mice when they were offered snails and seeds. The spiny mice maintained steady state body mass. Dry matter consumption of snails was 0.014 g* g⁻¹.-d⁻¹ and of seeds was 0.049g*.g⁻¹d⁻¹ for a total of 0.063 g*g⁻¹*d⁻¹. Total water intake was 0.101ml-g⁻¹.d⁻¹ and metabolizable energy intakewas 0.990 kJ. gxs^-1.d⁻¹ for a ratio (ml: kJ) of 0.102. This ratio was similar to that reported in a previously published study on free-living spiny mice. We concluded that snails and seeds allowed spiny mice to fulfil their energy and water requirements with minimal dry matter and fresh matter intakes. Furthermore, spiny mice selected a diet that provided them with a water (ml) to energy (kJ) ratio of approximately 0.1, although it appeared that they are able to survive on a much drier diet.     

C4 photosynthesis in Cyperus longus L., a species occurring in temperate climates

Abstract. Cyperus longus L. , which has a widespread but disjunct distribution throughout Europe and extends northwards into Britain, was found to be a C₄ species based upon its Kranz leaf anatomy, low CO₂ compensation point and the labelling of malate as an early product of ¹⁴CO₂ fixation. The photosynthetic characteristics of C. longus are similar to many other C₄ species with a high maximum rate of photosynthesis (> 1.5 mg CO₂ m ⁻² s ⁻¹) and a relatively high temperature optimum (30–35°C), but unlike many C₄ species the rate of photosynthesis does not decline rapidly below the optimum temperature and a substantial rate (0.6 mgCO₂ m⁻²s⁻¹)occursat 15°C. Leaf extension is very slow at 15°C and shows a curvilinear response to temperatures between 15 and 25°C. Leaves extend at a rate of almost 4 cm d⁻¹ at 25°C.     

Survival and recovery of perennial forage grasses under prolonged Mediterranean drought: II. Water status, solute accumulation, abscisic acid concentration and accumulation of dehydrin transcripts in bases of immature leaves

Effects of ozone on spring wheat ( Triticum aestivum L. cv. Satu) were studied in an open-top chamber experiment during two growing seasons (1992–1993) at Jokioinen in south-west Finland. The wheat was exposed to filtered air (CF), non-filtered air (NF), non-filtered air+35 nl l⁻¹ ozone for 8 h d⁻¹ (NF⁺) and ambient air (AA). Each treatment was replicated five times. Two wk after anthesis, after 4 wk of ozone treatment (NF⁺, 45 nl l⁻¹ 1000–1800 hours, seasonal mean) the net CO₂ uptake of wheat flag leaves was decreased by c . 40% relative to CF and NF treatments, both initial and total activity of Rubisco and the quantity of protein-bound SH groups were decreased significantly. Added ozone also significantly accelerated flag leaf senescence recorded as a decrease in chloroplast size. The effect was significant 2 wk after anthesis, and senescence was complete after 4 wk. In the CF and NF treatments senescence was complete 5 wk after anthesis. The significant effect of ozone on the chloroplasts and net CO₂ uptake 2 wk after anthesis did not affect the grain filling rate. However, since the grain filling period was shorter for ozone fumigated plants, kernels were smaller. The decrease in 1000-grain weight explained most of the yield reduction in the plants under NF⁺ treatment. The results indicate that wheat plants are well buffered against substantial decrease in source activity, and that shortened flag leaf duration is the major factor causing ozone-induced yield loss.     

Effect of plant succession, ploughing, and fertilization on the microbiological oxidation of atmospheric methane in a heathland soil

Abstract: The effect of plant succession on methane uptake was measured on intact soil cores collected from seven heathland sites. Six of the sites had undergone either secondary succession with grass or oak, ammonium fertilization or ploughing, while the seventh site was located in the native heathland. There was a positive relationship between methane uptake rate and time elapsed since the plant invasion had taken place in the native heathland. The native heathland site showed an insignificant atmospheric methane uptake of 0.01 mg CH₄ m⁻² d⁻¹, whereas the established oak brushwood (70 years old) and the grass invaded heathland (13 years old) showed rates of 1.36 mg CH₄ m⁻² d⁻¹ and 0.73 mg CH₄ m⁻² d⁻¹, respectively. In the fertilized heathland plot (112 kg N ha⁻¹ six years prior to this study) grass had become the dominating species and showed a methane oxidation rate of 0.28 mg CH₄ m⁻² d⁻¹. Ploughing of the heathland resulted in methane oxidation rates seven times the rates measured in the native heathland. The results suggested that an increased future atmospheric nitrogen deposition in heathlands and other nutrient poor ecosystems may have a stimulating effect on the soil sink for atmospheric methane.     

Rates of sulfate reduction and thiosulfate consumption in a marine microbial mat

Abstract The sulfur cycle in a microbial mat was studied by determining viable counts of sulfate-reducing bacteria, chemolithoautotrophic sulfur bacteria and anoxygenic phototrophic bacteria. All three functional groups of sulfur bacteria revealed a maximum population density in the uppermost 5 mm of the mat: 1.1 × 10⁸ cells of sulfate reducers cm⁻³ sediment, 2.0 × 10⁹ cells of chemolithoautotrophs cm⁻³ sediment, and 4.0 × 10⁷ cells of anoxygenic phototrophs cm⁻³ sediment. Bacterial dynamics were studied by sulfate reduction rate measurements, both under anoxic conditions (dark incubation) and oxic conditions (incubation in the light), and determination of the vertical distribution of the potential rate of thiosulfate consumption under oxic conditions. Sulfate reduction rates in the top 5 mm of the sediment were 566 nmol cm⁻³ d⁻¹ in the absence of oxygen, and 123 nmol cm⁻³ d⁻¹ in the presence of oxygen. In the latter case, the maximum rate was found in the 5–10-mm depth horizon (361 nmol cm⁻³ d⁻¹). Biological consumption of amended thiosulfate was rapid and decreased with depth, while in the presence of molybdate, thiosulfate consumption decreased to 10–30% of the original rate.     

Methane consumption in (hyper) saline habitats of Crimea (Ukraine)

Abstract: This paper documents methane utilization in (hyper)saline environments. Methane consumption in the Crimea basins, exhibiting salinities of 8% to 33%, was as much as 1200 pmol cm⁻³ d⁻¹. This process was mainly associated with the upper layer of sediment (microbial mat), although substantial activity was also located in adjacent water. Studies of the influence of NaCl levels on the methane consumption revealed a positive correlation between optimal salt concentration and the natural salinity of the samples selected.     

The influence of fish on leaf breakdown in a Virginia pond

1. To find if fish affect leaf breakdown, sugar maple leaves ( Acer sacchrum March) were placed in a soft-water, farm pond at a depth of 1 m for up to 3 months in four treatment groups: (1) enclosure with sunfish (Lepomis macrochirus Rafinesque) (SUNFISH treatment); (2) enclosure with catfish ( Ictalurus punctatus Rafinesque) (CATFISH treatment); (3) enclosure without fish (NO FISH treatment); and (4) no enclosure (OPEN treatment). The study was conducted in spring and autumn.
2. The leaf breakdown rates, k ±95% CL, for SUNFISH (0.0082± 0.00059 and 0.0111±0.00162 d⁻¹) and CATFISH (0.0072±0.00096 and 0.0103±0.00077 d⁻¹) were greater in spring and summer, respectively, than in the OPEN treatments (0.0065 ±0.00048 and 0.0105± 0.00141 d⁻¹) and NO FISH (0.0067±0.00039 and 0.0088±0.00099 d⁻¹). However, only k for SUNFISH was significantly different from NO FISH and OPEN treatments.
3. Fish in the pond did not appear to affect breakdown rates of OPEN leaf packs in the first replicate but k approached that of the fish treatments in the second replicate.
4. Fish may have promoted leaf breakdown directly by fragmentation of leaves while foraging for food and, indirectly, by agitation of leaves, leading to increased microbial activity.     

Comparative effects of downslope water and nutrient movement on plant nutrition, photosynthesis, and growth in Alaskan tundra

Changes in water and nutrient movement are common disturbances resulting from human activities in arctic regions. To assess the influence of water and nutrient movement on different plant growth forms, we added water and NPK fertilizer along 10 to 20 m linear transects across small natural drainages on an Alaskan tundra slope. Water was added by continuous-flow emitters from a drip irrigation system at a rate of 450 L m⁻¹ d⁻¹ during the 1986 growing season and 110 L m⁻¹ d⁻¹ in the 1987 growing season. NPK in the form of Osmocote, a slow release fertilizer, was applied at 0.5 kg per linear meter in early and mid-season of the 1985 growing season. Tissue N and P contents, light-saturated photosynthetic rates, and aboveground biomass production were measured at peak season for key species 2 m above and 2 and 6 m below the water and nutrient applications in 1986 and 1987.
Mean leaf N and P of the species tested increased slightly 2 m below the water addition sites and dramatically below the fertilizer addition sites. Increases in tissue N and P were also found 6 m below the fertilizer addition points. Leaf photosynthesis tended to increase 2 m below the water and nutrient additions for the species tested. Six meters below the treatment application points, photosynthesis was minimally affected in 1986 but increased in 1987. Increases in leaf area on the irrigation treatments were found only for the evergreen species, Ledum palustre and Vaccinium vitis-idaea , 2 m below the site of addition. In contrast, fertilizer addition caused large increases in leaf area production for all species tested at 2 m below the treatment, and for some species at 6 m below treatment. The overall effects of the two treatments were similar, but were greater for the fertilizer addition.