Impact of sea-level and climatic changes on the Amazon coastal wetlands during the late Holocene

Wetland dynamics in northern Brazil during the Holocene were studied by pollen analysis and AMS radiocarbon dating of three cores. Near the Amazon mouth region, covered mainly by primary Amazon coastal forest and herbaceous vegetation, the pollen record indicates the dominance of mangroves between 4800 and 1100 cal yr b.p. A contraction of the mangrove area and an expansion of herbaceous and fern vegetation occurred between 1100 and 750 cal yr b.p. The period between 750 and 200 cal yr b.p. is characterized by an expansion of mangrove and a decrease in herbaceous and fern vegetation. This trend continued until the present. On Atalaia Island, the sediment core indicates a period with poor pollen preservation between 830 and 630 cal yr b.p. Between 630 and 330 cal yr b.p., mangroves expanded. Later, up to 45 cal yr b.p., the mangrove area decreased and the herbaceous vegetation expanded. During the last hundred years, the relative sea-level rise most probably favored the mangrove expansion as far as the topographically highest sector on this island, while the herbaceous vegetation decreased. The pollen data from água Preta Lake indicate dry conditions, as reflected by the poor pollen preservation between 390 and 240 cal yr b.p. Between 240 and 60 cal yr b.p., restinga and Amazon coastal forest with palms dominated this region. For the last 120 years, the record indicates an expansion of the mangrove area. However, recent confinement of mangrove development to the topographically highest area, and the loss of mangrove areas on the lowest surfaces have led to a net loss of mangrove coverage during the last decades.     

Dynamics of nitrogen and phosphorus retention during wetland ecosystem succession

We compared the mechanisms of nitrogen (N) and phosphorus (P) removal in four young (<15 years old) constructed estuarine marshes with paired mature natural marshes to determine how nutrient retention changes during wetland ecosystem succession. In constructed wetlands, N retention begins as soon as emergent vegetation becomes established and soil organic matter starts to accumulate, which is usually within the first 1–3 years. Accumulation of organic carbon in the soil sets the stage for denitrification which, after 5–10 years, removes approximately the same amount of N as accumulating organic matter, 5–10 g/m²/yr each, under conditions of low N loadings. Under high N loadings, the amount of N stored in accumulating organic matter doubles while N removal from denitrification may increase by an order of magnitude or more. Both organic N accumulation and denitrification provide for long-term reliable N removal regardless of N loading rates. Phosphorus removal, on the other hand, is greatest during the first 1–3 years of succession when sediment deposition and sorption/precipitation of P are greatest. During this time, constructed marshes may retain from 3 g P/m²/yr under low P loadings to as much as 30 g P/m²/yr under high loadings. However, as sedimentation decreases and sorption sites become saturated, P retention decreases to levels supported by organic P accumulation (1–2 g P/m²/yr) and sorption/precipitation with incoming aqueous and particulate Fe, Al and Ca. Phosphorus cycling in wetlands differs from forest and other terrestrial ecosystems in that conservation of P is greatest during the early years of succession, not during the middle or late stages. Conservation of P by wetlands is largely regulated by geochemical processes (sorption, precipitation) which operate independently of succession. In contrast, the conservation of N is controlled by biological processes (organic matter accumulation, denitrification) that change as succession proceeds.     

Untersuchungen über die Wirkung des hydrostatischen Druckes auf das Wachstum von Delesseria sanguinea (L.) Lamour. aus der westlichen Ostsee

Observations on the effect of hydrostatic pressure on the growth of Delesseria sanguinea (L.) Lamour. from the western Baltic Sea.The post-treatment effects of hydrostatic pressures (100–500 atm) on the growth in lenght and breadth of young prolifications of D. sanguinea were studied at 15°C. Growth activity was compared amongst the prolifications separated from the midrib and not separated ones, and cell-viability as influenced by high pressures was also observed under the microscope. Pressure-temperature relationship was investigated, in which the pressure effects on growth were studied at different temperatures (5°–22°C), using prolifications which were previously adapted to corresponding temperatures. Long-termed experiments were also set up to study the capability of pressure adaptation in young leaflets. In this regard the growth activity was measured after long-termed exposure to relatively smaller pressures (20–60 atm).

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Institut für Meereskunde an der Universität Kiel, B. R. D.

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Meinem hochverehrten Doktorvater, Herrn Prof. Dr. Fritz Gessner, zum ersten Wiederkehr seines Todestages am 20.12.1973 gewidmet.     

Summer monsoon precipitation variations in central China over the past 750 years derived from a high-resolution absolute-dated stalagmite

A 2–3-year resolution record of stalagmite oxygen isotope variations from the south flank of the Qinling Mountains, central China, has revealed the Asian summer monsoon (ASM) precipitation variations in the investigated area over the past 750 years. The summer monsoon precipitation gradually increased since 1249 AD, reaching its highest values in the period 1535–1685 AD, and then decreased with substantial decadal- to centennial-scale fluctuations. The monsoon precipitation increased again between 1920 and 1970 AD. Three intervals of high monsoon precipitation were identified: 1535–1685 AD, 1755–1835 AD, and 1920–1970 AD. Three intervals of low precipitation were inferred in 1249–1325 AD, 1390–1420 AD, and 1890–1915 AD. The δ¹⁸O composition and lithological features of the stalagmite coincidently indicate a wetter climate during the Little Ice Age (LIA), which is also confirmed by climate records from Chinese historical documents within this area. A comparison with other high-resolution speleothem records indicates regional differences in monsoon precipitation variability from the south to the north of central China in the last 750 years on decadal- to centennial-scale. Power spectrum analysis of the δ¹⁸O record shows significant 117.8-, 34.6-, 14-, 10.3-, and ~ 6-year periodicities. These periodicities are widely observed in the climate records from ASM-controlled areas of China and are consistent with the Gleissburg periodicity, Brϋckner periodicity, sunspot periodicity of solar activity, and El Nińo–Southern Oscillation (ENSO) periodicity. These correlations suggest that both solar activity and ENSO periodicity may have had important influences on ASM precipitation in China over the past 750 years.     

Electrophoretic and chromatographic separation of two fructose-1,6-bisphosphatase forms from Synechococcus leopoliensix

d-Fructose-1,6-bisphosphatase (EC 3.1.3.11) activity in crude extracts of the blue-green alga Synechococcus leopoliensis (Anacystis nidulans) has been investigated using high resolving electrophoretic and chromatographic separation techniques. Two catalytically active enzyme forms which exhibited isoelectric points of 4.7–4.8 (designated from A) and 4.5–4.6 (designated form B) were resolved by isoelectric focusing. Both enzyme forms acted specifically on fluctose-1,6-bisphosphate. No interconversion between the A and B forms of fructose bisphosphatase activity was detected after refocusing. The apparent molecular weight of the two enzyme forms was determined by non denaturing polyacrylamide gradient electrophoresis; the values were 67,000–70,000 and 60,000–65,000 for A and B, respectively. Both enzyme forms were separated by preparative scale chromatofocusing. Kinetic measurements performed with the separated and partially purified fructose bisphosphatase forms indicated that both enzyme forms differ in their AMP sensitivity. The two enzymes were completely inactivated by the addition of cysteamine and reactivated by dithiols but the reactivation kinetics were different.Abbreviations DTT dl-Dithiothreithol - MTT 3(4,5-dimethylthiazolyl-2)-2,5-diphenyl tetrazolium bromide - PMS phenazine methosulfate - TCA trichloroacetic acid - Tris tris(hydroxymethyl)-aminomethane     

Bioreactor culture of Picea mariana Mill. (black spruce) and the species complex Picea glauca-engelmannii (interior spruce) somatic embryos. Growth parameters

Somatic embryo cultures of Picea mariana and the species complex P. glauca-engelmannii were each grown in 7.5-l-capacity mechanically-stirred bioreactors containing 61 medium (LP, von Arnold and Eriksson) with 30 mm sucrose. Growth of both species occurred with no observable signs of shear stress due to mechanical agitation. Growth kinetics were analysed using an array of parameters (settled culture volume, packed culture volume, osmolarity, conductivity, pH). These were compared with fresh weight, dry weight, and somatic embryo number in order to determine what parameters were highly correlated with growth and embryo number. Increasing the sucrose concentration from 30 mm to 60 mm resulted in an increase in biomass and total number of somatic embryos. For P. mariana a maximum dry weight of 6.3 gl^–1 and 3076 embryos ml^–1 occurred in LP medium with 60 mm sucrose after 10–12 days of culture. For P. glauca-engelmannii a maximum dry weight of 4.3 gl^–1 and 2278 embryos ml^–1 occurred in LP medium with 60 mm sucrose after 6–8 days culture. For all sucrose concentrations, fresh weight, dry weight and embryo number were closely correlated with packed culture volume and conductivity for P. mariana, and settled culture volume, packed culture volume and conductivity for P. glauca-engelmannii.Correspondence to: D. I. Dunstan     

On the dynamics of exploited populations ofTisbe holothuriae (Copepoda,Harpacticoidae)

A total of 90, weekly exploited populations of the harpacticoid copepodTisbe holothuriae Humes were exposed to 148, 222, 333, 500, 750 or 1125µg Cd⁺⁺ l^–1, combined with exploitation rates of 10, 30, 50, 70 or 90% under conditions of surplus food supply at 22° C and 30 S. All populations exposed to concentrations down to 500µg Cd⁺⁺ l^–1 and 3 populations (out of 15) exposed to 333µg l^–1 became extinct within the experimental period of 30 weeks. Survival time significantly depended on concentration. A recovery phase from an initially high mortality preceded eventual population extinction after adding 500µg Cd⁺⁺ l^–1. In the initial phase, higher nauplii mortality prevailed. During these experiments on acute intoxication, no relationship could be established between survival and exploitation rate. However, experiments on the effects of stepwise increases in Cd concentration (results not yet published) produced evidence of such a relationship. In spite of increased mortality, no significant numbers of dead copepods were detected in weekly samples because of their rapid decomposition and cannibalism, which depends on the amount of food available. Sampling regimes of 5 times per week yielded significant numbers of dead individuals.     

Production of planktonic Rotatoria in Ormajärvi,an eutrophicated lake in southern Finland

The production of planktonic rotifers was studied in eutrophic Lake Ormajärvi. Of the total annual production of rotifers (2.9 g org. C m^–2 or 231 mg dry weight m^–3) 49% was achieved during one month (July) and 88% during 3 months of summer. The most important producers were Keratella cochlearis (1.2 g C m^–2), Asplanchna priodonta (0.8 g C m^–2) and Conochilus unicornis (0.6 g C m^–2). The P/B ratio for the total rotifer community during the growing season (7 months) was 25.0; monthly P/ B values varied between 0.3 and 5.2. The daily P/ B values were highest among species of Collotheca. The relationships of rotifers to some biotic and abiotic factors (invertebrate predators — Mesocyclops, Cladocera, planktonic Protozoa and temperature) are briefly discussed.     

N deposition, N transformation and N leaching in acid forest soils

Nitrogen deposition, mineralisation, uptake and leaching were measured on a monthly basis in the field during 2 years in six forested stands on acidic soils under mountainous climate. Studies were conducted in three Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] plantations (D20: 20 year; D40: 40 yr; D60: 60 yr) on abandoned croplands in the Beaujolais Mounts; and two spruce (Picea abies Karst.) plantations (S45: 45 yr; S90: 90 yr) and an old beech (Fagus sylvatica L.) stand (B150: 150 yr) on ancient forest soils in a small catchment in the Vosges Mountains. N deposition in throughfall varied between 7–8 kg ha^–1 year^–1 (D20, B150, S45) and 15–21 kg ha^–1 yr^–1 (S90, D40, D60). N in annual litterfall varied between 20–29 kg ha^–1 (D40, D60, S90), and 36–43 kg ha^–1 (D20, S45, B150). N leaching below root depth varied among stands within a much larger range, between 1–9 kg ha^–1 yr^–1 (B150, S45, D60) and 28–66 kg ha^–1 yr^–1 (D40, S90, D20), with no simple relationship with N deposition, or N deposition minus N storage in stand biomass. N mineralisation was between 57–121 kg ha^–1 yr^–1 (S45, D40, S90) and between 176–209 kg ha^–1 yr^–1 in (B150, D60 and D20). The amounts of nitrogen annually mineralised and nitrified were positively related. Neither general soil parameters, such as pH, soil type, base saturation and C:N ratio, nor deposition in throughfall or litterfall were simply related to the intensity of mineralisation and/or nitrification. When root uptake was not allowed, nitrate leaching increased by 11 kg ha^–1 yr^–1 at S45, 36 kg ha^–1 yr^–1 at S90 and between 69 and 91 kg ha^–1 yr^–1 at D20, D40, B150 and D60, in relation to the nitrification rates of each plot. From this data set and recent data from the literature, we suggest that: high nitrification and nitrate leaching in Douglas-fir soils was likely related to the former agricultural land use. High nitrification rate but very low nitrate leaching in the old beech soil was related to intense recycling of mineralised N by beech roots. Medium nitrification and nitrate leaching in the old spruce stand was related to the average level of N deposition and to the deposition and declining health of the stand. Very low nitrification and N leaching in the young spruce stand were considered representative of fast growing spruce plantations receiving low N deposition on acidic soils of ancient coniferous forests. Consequently, we suggest that past land use and fine root cycling (which is dependent on to tree species and health) should be taken into account to explain the variability in the relation between N deposition and leaching in forests.     

Pollen morphology ofSonchus and related genera,and a general discussion

The pollen morphology of the taxa belonging to the generaAetheorhiza Cass.,Launaea Cass.,Reichardia Roth andSonchus L. in the Iberian Peninsula has been studied with light and electron microscopy. The pollen is 3(-4)-zonocolporate and echinolophate (without polar lacunae, but in general with prelacunae), with equatorial ridges and 15–20 lacunae: 3–4 poral, 6–8 abporal and 6–8 paraporal. Small to medium size, P × E = 19–36 × 23–42 µm; sometimes two different sizes have been found. Exine 3–9 µm thick and ornamentation microreticulate and echinate. The results clearly show the relationships between genera. Moreno-Socías, E., Mejías, J. A., Díez, M. J., 1994: Morfología polínica deLactuceae (Asteraceae) en la Península Ibérica, I.Lactuca y géneros relacionados. — Acta Bot. Malacitana.19: 103–113.     

Reproduction, population dynamics, growth and production ofScrobicularia plana da costa (pelecypoda) in the Bidasoa estuary, Spain

The breeding cycle, recruitment, population dynamics, growth and production ofScrobicularia plana were studied at one station in the Bidasoa estuary (SE of the Biscay Bay, Spain) during a period of 3 or 4 years. To complete this study, the reproduction for a period of 1 year was analysed at two other sites of the estuary. At none of the stations important differences in spawning activity were observed between the different years. The animals reproduced for the first time when they reached the age of two years. The histological data and the recruitment analysis showed only one spawning period between June and mid-September, with a peak in July-August. This breeding pattern differs from those shown by other southern European populations. The recruitment of spat (0.25–0.50 mm) occurred from June–July to October–December in different years. The population showed different annual patterns of density and population structure, depending on recruitment success. Growth was most rapid in spring and summer. The bivalves reached a mean length of 21.8 mm at the age of approximately 16 months; in the following year they grew to 30 mm. The growth during the life span fitted the theoretical growth equation of Von Bertalanffy. Annual production was in the range of 59.0–83.4 g AFDW m^–2 year^–1. The P/B ratios of the population varied between 0.84 and 1.48 (1.06 ± 1.36; ¯x ± 95% C.I.).     

Predicting dominant phytoplankton quantities in a reservoir by using neural networks

A 14.6 m long profile from the northern part of the Hulun lake, the furthest north of the large lakes of China, has provided a sedimentary and diatom record since the late Glacial. The chronological sequence was established based on 10 radiocarbon dates. Sedimentological study and diatom analysis are synthesized for the reconstruction of the history of lake-level changes. The results show that the Hulun basin was not occupied by a lake during the Last Glaciation. A rapid transition to a deep lake occurred since 12850 yr B.P., and this high level phase lasted to 11200 yr B.P., although there existed several subordinate lake level fluctuations. An abrupt lake level drop and dry climatic conditions occurred during 11200–10600 yr B.P. The lake became deeper again from 10600 yr B.P. to 10300 yr B.P. Hulun lake at the early Holocene was characterized by the low lake-level, and the lake level rose again in 7200–5800 yr B.P., though the lake-levels changed quite variably. A dry condition occurred and lake level declined again during 5800–3000 yr B.P. The presence of the palaeosol on the top of this profile indicates the persistence of low lake levels after 3000 yr B.P. The comparison with the other lake-level records from northern China has suggested that the Hulun Lake shows a different lake level history from the lakes in monsoon areas.     

Foraminiferal response to Holocene environmental changes of a tidal estuary in Victoria, southeastern Australia

The Holocene strata in the Anderson Inlet area in Victoria can be stratigraphically divided into four units, Unit I, Unit II, Unit III, and Unit IV. Unit I and Unit IV lack fossils and were deposited in non-marine, probably fluvial environments. Unit II and Unit III contain abundant foraminifera with molluscs, ostracods and bryozoans. Foraminiferal analysis suggests that Unit III was formed in a partially sheltered marine environment, while the high plankton content and relatively high diversity of benthic species in Unit II indicate that this unit was deposited in an open bay at water depths possibly less than 5 m. The foraminiferal data are integrated with radiocarbon dates to arrive at the following Holocene palaeoenvironmental history in this area: (1) low alluvial plain stage (10,000–7000 yr B.P.); (2) open bay environment stage (7000–5500 yr B.P.); (3) partially sheltered marine environment stage (5500–4500 yr B.P.); (4) alluvial plain and coastal lagoon environment stage (since about 4500 yr B.P.). The foraminiferal fauna show a clear response to these palaeoenvironmental changes. Globigerina bulloides can be used as an indicator for cold water marine environments. The high concentration of this species in these middle Holocene sediments shows a strong cold water influence on the coastal environments which reduced the effect of regional warm currents during this period. The Holocene palaeoenvironmental changes in the area were controlled by the Holocene sea-level fluctuations associated with the deglaciation history during this period. Similar integrated studies of shallow to marginal marine strata in southern Africa, America and New Zealand will lead to a better understanding of Holocene relative sea-level change and the interplay between Holocene cold and warm water regimes in the Southern Hemisphere.     

Life-history strategies and production of Tinodes waeneri (L.) (Trichoptera) in Lake Esrom,Denmark

The life cycle and production of Tinodes waeneri (L.) was examined at five shallow littoral localities in Lake Esrom, Denmark, during 1979/80. Five larval instars were demonstrated. The differences in temporal composition of instars indicated three different life cycles. A bivoltine strategy was shown for the most exposed locality which also had the highest average abundance equal to 11 500 ind. m^–2. A univoltine population was found in the more sheltered NW part of the lake with an average density of 1 500 ind. m^–2. At the three remaining stations the life cycles were partly bivoltine with wintering populations of mixed cohorts and densities between 10 500 and 3 000 ind. m^–3. Two distinct flight periods with maxima in June and August were demonstrated for bi- and partly bivoltine populations. Differences in rates of growth and elimination added to the variability in life cycle. Growth rates peaked in August (5.0–7.4% d^–1) at an average temperature of 20°C. Estimates of production ranged from 1.9 to 17.5 g AFDW m^–2 a^–1 with an average of 8.0 g AFDW m^–2. The P/B ratios, which were within the expected range for uni- and bivoltine populations of trichopterans, were 5.73 for the bivoltine population and 3.31 for the univoltine population.Estimates of consumption revealed that the populations could be sustained by autochthonous epilithic production in the habitats. Variability in the quality and seasonal availability of food were judged to influence the type of life cycle.Lake Esrom Littoral Research Publ. No. 8. Publication No. 385 from the Freshwater Biological Laboratory, University of Copenhagen, 51, Helsingørsgade, DK-3400 Hillerød, Denmark.Lake Esrom Littoral Research Publ. No. 8. Publication No. 385 from the Freshwater Biological Laboratory, University of Copenhagen, 51, Helsingørsgade, DK-3400 Hillerød, Denmark.     

The importance of avian-contributed nitrogen (N) and phosphorus (P) to Lake Grand-Lieu,France

The largest natural lake in France, Grand-Lieu, has suffered eutrophication. The objective of the study was to estimate the annual input of nutrients (N, P) resulting from avian excrement, deposited by birds feeding out of the lake and returning to its waters for breeding or roosting, as compared to the input by the rivers that enter in the lake. Two years are compared: 1981–82 and 1990–91. About 1600–2000 breeding herons and cormorants, 20 000–33 000 wintering ducks, gulls and cormorants and 1–2.4 million starlings deposited about 5800 kg total N in 1981–82 and 7640 kg in 1990–91. Respectively, 2000 and 2530 kg total P were deposited over the same time periods. These represent 0.7% and 0.4% of the total N input of the lake and 2.4 and 6.6% of the total P input in 1981–82 and 1990–91. Starlings account for 74% of the N and mallards most of the rest. P input by starlings (36% in 1981–82, 41% in 1990–91), and by mallards and herons (35% and 27% in 1981–82 and 22% and 24% in 1990–91 respectively) plays an appreciable role among birds. During the plant growing period (April–September), the contribution by birds can increase to 37% of total P input of the lake. Piscivorous bird colonies concentrate Phosphorus 42 times more within the colony than outside the colony. Overall, the role birds play in total N and P input is relatively small due to very high inputs from human sewage and agriculture run off. The monthly mean concentration of the water of the two rivers reaches currently 10 mg l^–1 of N (to 23 mg during peak floods) and 394 mg m^–3 of P (to 468 mg during peak floods). Earlier, for example in the 1960's, water in Brittany only contained 0.1 to 1.1 mg 1^–1 of N and 1 to 5 mg m^–3 of P during the maximum flow period. At this time, birds could probably have represented annually up to 37% of the N input and up to 95% of the P input to the lake.     

Production by Hexagenia limbata in a warm-water reservoir and its association with chlorophyll content of the water column

We investigated the productivity of nymphs of the mayfly Hexagenia limbata in Lake Waco, a central Texas reservoir, and assessed its association with chlorophyll content of the water. We hypothesized that food availability measured as chlorophyll content of the water may directly associate with growth of Hexagenia and predict population productivity. To test this, we compared production by mayfly populations at two stations in the same reservoir; a northern station receiving water input with high chlorophyll content, and a southern station receiving water with low chlorophyll content. Both stations had similar substrate type and abundant mayflies. Benthic samples were collected from October 1984 through September 1985, and dissolved oxygen and temperature of the water were monitored.Annual production (size-frequency method) was 1270 mg m^–2 (P/B = 7.5) at the northern station and 1990 mg m^–2 (P/B = 6.1) at the southern station. The mean standing crop was 323 mg m ^{– 2} at the southern station and 169mg m^–2 at the southern station. Densities of mayflies at the two stations were not significantly different.Mean chlorophyll concentration (total mg pigment) during the sampling period was 23.5 mg m^–3 at the northern station and 16.7 mg m ^{– 3} at the southern station. Therefore, the station with lower mean chlorophyll content had higher secondary productivity by Hexagenia. Conversely, the station with higher mean chlorophyll content had lower mayfly productivity. The productivity of the mayfly populations did not positively associate with the chlorophyll content of the water, and chlorophyll content did not predict the success of the population of Hexagenia. Variation in mayfly growth success was associated with differences in temperature and dissolved oxygen. The northern station with higher chlorophyll content and lower productivity had low dissolved oxygen and temperatures higher than optimum for growth.     

Patch-clamp study of isolated taste receptor cells of the frog

Summary Taste discs were dissected from the tongue ofR. ridibunda and their cells dissociated by a collagenase/low Ca/mechanical agitation protocol. The resulting cell suspension contained globular epithelial cells and, in smaller number, taste receptor cells. These were identified by staining properties and by their preserved apical process, the tip of which often remained attached to an epithelial (associated) cell. When the patch pipette contained 110mm KCl and the cells were superfused with NaCl Ringer's during whole-cell recording, the mean zero-current potential of 22 taste receptor cells was –65.2 mV and the slope resistance 150 to 750 M. Pulse-depolarization from a holding voltage of –80 mV activated a transient TTX-blockable inward Na current. Activation became noticeable at –25 mV and was half-maximal at –8 mV. Steady-state inactivation was half-maximal at –67 mV and complete at –50 mV. Peak Na current averaged –0.5 nA/cell. The Ca-ionophore A23187 shifted the activation and inactivation curve to more negative voltages. Similar shifts occurred when the pipette Ca was raised. External Ni (5mm) shifted the activation curve towards positive voltages by 10 mV. Pulse depolarization also activated outward K currents. Activation was slower than that of Na current and inactivation slower still. External TEA (7.5mm) and 4-aminopyridine (1mm) did not block, but 5mm Ba blocked the K currents. K-tail currents were seen on termination of depolarizing voltage pulses. A23187 shifted theI _K(V)-curve to more negative voltages. Action potentials were recorded when passing pulses of depolarizing outward current. Of the frog gustatory stimulants, 10mm Ca caused a reversible 5-to 10-mV depolarization in the current-clamp mode. Quinine (0.1mm, bitter) produced a reversible depolarization accompanied by a full block of Na current and, with slower time-course, a partial block of K currents. Cyclic AMP (5mm in the external solution or 0.5 m in the pipette) caused reversible depolarization (to –40 to –20 mV) due to partial blockage of K currents, but only if ATP was added to the pipette solution. Similar responses were elicited by stimulating the adenylate cyclase with forskolin. Blockage of cAMP-phosphodiesterase enhanced the response to cAMP. These results suggest that cAMP may be one of the cytosolic messengers in taste receptor cells. Replacement of ATP by AMP-PNP in the pipette abolished the depolarizing response to cAMP. Inclusion of ATP--S in the pipette caused slow depolarization to –40 to –20 mV, due to partial blockage of K currents. Subsequently, cAMP was without effect. The remaining K currents were blockable by Ba. These results suggest that cAMP initiates phosphorylation of one set of K channels to a nonconducting conformation.     

Effects of agricultural production on phosphorus losses from paddy soils: a case study in the Taihu Lake Region of China

A field plot experiment was conducted on two types of paddy soils in the Taihu Lake Region of China from June 2000 through 2002 to assess phosphorus (P) losses by runoff and drainage flow and the effectiveness of rice–wheat double cropping on reducing P losses from paddy soils. Commercial NPK compound fertilizer and single superphosphate fertilizer were applied to furnish 0, 30, 150, and 300 kg P ha^–1 for rice season trials, and 0, 20, 80, and 160 kg P ha^–1 for wheat season trials. The experiments consisted of four replicates (plots of 5 × 6 m in a randomized block design) of each treatment in Argic stagnic anthrosols (Anzhen site) and six replicates in Cumulic stagnic anthrosols (Changshu site). P30 and P20 treatments (30 and 20 kg P ha^–1 in rice and wheat seasons, respectively) were considered as conventional P application rates in this area. Higher P treatments, such as P150 and P300 for rice and P80 and P160 for wheat, were intended to simulate the status of soil P in ~10–20 years with an application of P30 or P20 kg P ha^–1 each season. Results revealed that the average concentration of total P (TP) in runoff samples was 0.870 mg P l^–1 from P30 plots during the rice season, and 0.763 mg P l^–1 from P20 plots during the wheat season in both years at the Anzhen site, while it was 0.703 and 1.292 mg P l^–1, respectively, at the Changshu site. Average TP load (mass loss) at the Anzhen site with conventional P application rates was 220.9 and 439.5 g P ha^–1 during rice season in 2000/2001 and 2001/2002, respectively, but was 382.3 and 709.4g P ha^–1 during wheat season, respectively. Mass loss at the Changshu site was 140.4 and 165.7 g P ha^–1 during the rice season and 539.1 and 1184.6 g P ha^–1 during the wheat season, respectively. P losses from paddy soils were significantly greater during the wheat season, especially at the Changshu site, indicating that planting rice reduced P. Phosphate fertilizer levels significantly affected P concentrations and P loads in runoff both seasons. Both mean concentrations and average seasonal P loads from the P150/P80 plots were lower than that from the P300/P160 plots, but significantly higher than that from the P30/P20 and P0 plots. This implied that runoff P loads would be greatly increased in 10–20 years as a result of the accumulation of soil P if 50 kg P ha^–1 (rice season plus wheat season) is applied each year.     

Allelic expression in intergeneric fox hybrids (Alopex lagopus × Vulpes vulpes). II. Erythrocyte glucose-6-phosphate dehydrogenase in arctic and silver foxes: Purification and properties

The functional properties of purified glucose-6-phosphate dehydrogenase (G6PD) from the erythrocytes of Arctic foxes (Alopex lagopus) and silver foxes (Vulpes vulpes) were investigated. It was found that pH optima for G6PD range from 8.15 to 8.25 in Arctic foxes and from 10.2 to 10.4 in silver foxes. For G6P, the estimated K _m values were 74×10^–6 m (at pH 8.2) and 166×10^–6 m (at pH 10.2) in Arctic foxes and 58×10^–6 m (at pH 10.2) and 40×10^–6 m (at pH 8.2) in silver foxes. The K _m values for NADP were estimated as 62×10^–6 m (at pH 8.2) and 86×10^–6 m (at pH 10.2) in the Arctic foxes and 15×10^–6 m (at pH 10.2) and 12×10^–6 m (at pH 8.2) in the silver foxes. It was found that Mg²⁺ ions exert a significant activating effect on G6PD in the Arctic fox and do not affect appreciably its activity in the silver fox. The experimental data indicate that slight differences in the electrophoretic mobility of G6PD are associated with considerable functional differences in this enzyme between the two fox species.     

Fed-batch production of <Emphasis Type="SmallCaps">d</Emphasis>-ribose from sugar mixtures by transketolase-deficient <Emphasis Type="Italic">Bacillus subtilis</Emphasis> SPK1

d-Ribose, a five-carbon sugar, is used as a key intermediate for the production of various biomaterials, such as riboflavin and inosine monophosphate. A high d-ribose-producing Bacillus subtilis SPK1 strain was constructed by the chemical mutation of the transketolase-deficient strain, B. subtilis JY1. Batch fermentation of B. subtilis SPK1 with 20 g l^–1 xylose and 20 g l^–1 glucose resulted in 4.78 g l^–1 dry cell mass, 23.0 g l^–1d-ribose concentration, and 0.72 g l^–1 h^–1 productivity, corresponding to a 1.5- to 1.7-fold increase when compared with values for the parental strain. A late-exponential phase was chosen as the best point for switching to a fed-batch process. Optimized fed-batch fermentation of B. subtilis SPK1, feeding a mixture of 200 g l^–1 xylose and 50 g l^–1 glucose after the late-exponential phase reduced the residual xylose and glucose concentrations to less than 7.0 g l^–1 and gave the best results of 46.6 g l^–1d-ribose concentration and 0.88 g l^–1 h^–1 productivity which were 2.0- and 1.2-fold higher than the corresponding values in a simple batch fermentation.