The ecology of the Calanus ponticus population in the deeper layer of its concentration in the Black Sea

The layer of daytime concentration of Calanus ponticus (VC andVI C) performing daily vertical migrations and the layer of‘winter stock’ aggregation are confined to the depthof maximal gradient of the main pycnocline under an unusuallysharp oxycline. The concentration layer thickness ranges from2 to 20–30 m and the Calanus concentration in it is >250ind. m^–3, sometimes being 3500 ind. m^–3 and evenmore. The population in the concentration layer is divided intotwo ecological groups: I, feeding and migrating specimens ofcopepodite stages V and VI, their body lipid contents being25–60 µg min.^–1; and II, non-feeding and non-migratingspecimens of copepodite stage V, their body lipid contents being100–150 µg ind.^–1. The relationship with oxygenconcentration was studied in both ecogroups. The experimentsshow that specimens of ecogroup II can exit at an oxygen concentrationof 0.06 ml 1^–1, but at such concentration falling intoanabiosis. They die at 0.04 ml O₂ 1^–1. Estimates of respirationof the group II specimens (‘winter stock’) showthat lipids they store are sufficient for 7 months' survival.Depth of Calanus concentration is determined by water densityrather than concentration of oxygen.     

Dynamics of microplankton communities at the ice-edge zone of the Lazarev Sea during a summer drogue study

Microzooplankton grazing and community structure were investigatedin the austral summer of 1995 during a Southern Ocean Drogueand Ocean Flux Study (SODOFS) at the ice-edge zone of the LazarevSea. Grazing was estimated at the surface chlorophyll maximum(5–10 m) by employing the sequential dilution technique.Chlorophyll a concentrations were dominated by chainformingmicrophytoplankton (>20 µm) of the genera Chaetocerosand Nitzschia. Microzooplankton were numerically dominated byaloricate ciliates and dinoflagellates (Protoperidinium sp.,Amphisoleta sp. and Gymnodinium sp.). Instantaneous growth ratesof nanophytoplankton (<20 µm) varied between 0.019and 0.080 day^–1, equivalent to between 0.03 and 0.12 chlorophylldoublings day^–1. Instantaneous grazing rates of microzooplanktonon nanophytoplankton varied from 0.012 to 0.052 day^–1.This corresponds to a nanophytoplankton daily loss of between1.3 and 7.0% (mean = 3.76%) of the initial standing stock, andbetween 45 and 97% (mean = 70.37%) of the daily potential production.Growth rates of microphytoplankton (>20 µm) were lower,varying between 0.011 and 0.070 day^–1, equivalent to 0.015–0.097chlorophyll doublings day^–1. At only three of the 10 stationsdid grazing by microzooplankton result in a decrease in microphytoplanktonconcentration. At these stations instantaneous grazing ratesof microzooplankton on microphytoplankton ranged between 0.009and 0.015 day^–1, equivalent to a daily loss of <1.56%(mean = 1.11%) of initial standing stock and <40% (mean =28.55%) of the potential production. Time series grazing experimentsconducted at 6 h intervals did not show any diel patterns ofgrazing by microzooplankton. Our data show that microzooplanktongrazing at the ice edge were not sufficient to prevent chlorophylla accumulation in regions dominated by rnicrophytoplankton.Here, the major biological routes for the uptake of carbon thereforeappear to be grazing by metazoans or the sedimentation of phytoplanktoncells. Under these conditions, the biological pump will be relativelyefficient in the drawdown of atmospheric CO₂.     

Studies on the Movement of Water Through Apple Trees

Resistances to the flow of water through young potted appletrees were estimated by measuring the transpiration rate oftrees with and without root systems. Root system resistanceswere obtained by difference. Whole-plant resistances were ofthe order 10 x 10¹³ Pa s m^–3 and there was some evidencethat root resistances (R_r) varied with transpiration rate; theratio R_r:R_x (where R_x is resistance to water flow in the stemsystem) altered from 2:1 at relatively high transpiration ratesto 1:1 at lower rates. The trunk of a 9-year-old orchard tree (trunk diameter {smalltilde}7 cm, height {small tilde}2.5 m) was cut under water andestimates of the flow resistances in this tree were obtained.These were much lower than the resistances to flow in the pottedtrees. Capacitance (defined as the change in stored water content perunit change in plant water potential) values were calculatedfor the small trees and the large tree from measurements ofweight and water potential changes after the trees were removedfrom water. They were very similar on a weight basis (approx.2.0 x 10^–8 kg kg^–1 Pa^–1). Leaf capacitancevalues ({small tilde}1 x 10^–8 kg Pa^–1 m^–2)were also obtained. Stomatal conductances decreased with water potential and increasedwith short-wave radiation, but the relationships were not definitive.Estimates of boundary layer conductance in a greenhouse (verylow wind speeds) were of the same order ({small tilde}5 mm s^–1)as values obtained previously.     

Chemical composition and oxygen consumption rates of the ctenophore Bolinopsis infundibulum from the Gulf of Maine

Quantitative determinations of chemical composition and oxygenconsumption rates were made for a deep-living population ofthe lobate ctenophore Bolinopsis infundibulum. Animals werecollected in the Gulf of Maine with the submersible ‘Johnson-Sea-Link’during September 1989 at depths ranging from 120 to 240 m. Carbonand nitrogen contents were similar to values reported for epipelagicctenophores. Lipid and protein levels were lower than valuestypical of epipelagic ctenophores, but higher than those ofmesopelagic species. Carbohydrate was nearly an order of magnitudehigher than previously recorded for B.infundibulum. Oxygen consumptionrates ranged from 0.004 to 0.235 µl O₂ mg^–1 dryweight h^– at temperatures ranging from 5 to 7°C. Carbon-specificmetabolic rates ranged from 0.21 to 12.73 µl O₂ mg^–1C h^–1. Energy expenditures estimated from respirationdata (     

Diel Buoyancy Changes by the Cyanobacterium Aphanizomenon ovalisporum from a Shallow Reservoir

In the summer of 1999, a bloom (11 100 filaments ml^–1)of the gas vacuolate cyanobacteriumAphanizomenon ovalisporumdeveloped in a shallow (1.7 m deep) reservoir containing nutrient-enrichedwater from Lake Kinneret (Israel). During 4 days, A. ovalisporumshowed a marked diel periodicity in buoyancy: the proportionof floating filaments fluctuated between 76–84% from middayto evening and 94–98% at the end of the night, in bothsurface and bottom samples. Buoyant filaments were present throughoutthe water column, presumably due to wind-driven vertical mixing.Aphanizomenonfilaments collected from the reservoir were maintained undermean photon irradiances of 15 (LL), 150 (ML) and 1100 (HL) µmolm^–2 s^–1 in a computer-controlled set-up, which simulatedthe diel light changes at different depths in the reservoir.In the LL cultures, filament buoyancy showed no diel fluctuationpatterns during the 4 days of incubation, but ML and HL culturesshowed regular diel changes, with a higher proportion of filamentsfloating at the end of the night than during midday–evening.There was no evidence for either turgor-driven collapse of gasvesicles or dilution of gas vesicles by cell growth by any ofthe treatments. Gas vesicles of A. ovalisporum had a relativelylow mean critical pressure (p_c of 0.57 MPa), but the daytimerise in turgor pressure was too small to cause gas vesicle collapse.The observed diel buoyancy changes may be explained by accumulationof carbohydrate ballast during the day and decrease during thenight.     

Unequal distribution of potassium and anions within the Phaseolus pulvinus during circadian leaf movement

Ion and saccharide concentrations in the upper and lower partsof the laminar pulvinus of the primary leaf of Phaseolus vulgariswere measured in relation to the circadian movement. Concentrations of K⁺, Na⁺, Ca²⁺, Mg²⁺, Cl^–, organic acid,NO₃^–, H₂PO₄^–, fructose and fructose-yielding saccharidesin the pulvinus were 75–120, 0.3–0.7, 5–8,6–12, 40–60, 60–73, 19–35, 2–9and 1–5 mM, respectively, and the osmotic pressure ofthe pulvinus was considered to be due to these ions. The cell volume in the expanding part was larger than that inthe contracting part. The change of the cell volume alteredthe molar concentration in the cell sap and therefore the amountof solutes actually transported from the upper to the lowerpart and vice versa was estimated from the concentration expressedin moles per gram of dry weight. Results showed that K⁺, Cl^–, organic acid (or H⁺) andNO₃^– moved from the upper to lower parts or vice versain the pulvinus in relation to its deformation, keeping theelectroneutrality among those ions, whereas C_a2⁺ and Mg²⁺ didnot move. The difference in the K⁺ concentration between theupper and lower parts when the leaf was up or down amountedto 30% of the whole osmotic pressure. This lead to the conclusionthat the endogenous clock-controlled unequal distribution ofK⁺, Cl^–, organic acid (or H⁺) and NO₃^– in the pulvinuscould be the force for the circadian leaf movement. (Received August 7, 1979; )     

Photosynthetic characteristics of Dinophysis norvegica Claparede & Lachmann, a red-tide dinoflagellate

The relationships between photosynthesis and photosyntheticphoton flux densities (PPFD, P-l) were studied during a red-tideof Dinophysis norvegica (July-August 1990) in Bedford Basin.Dinophysis norvegica, together with other dinoflagellates suchas Gonyaulax digitate, Ceratium tripos, contributed {small tilde}50%of the phytoplankton biomass that attained a maximum of 16.7µg Chla 1^– and 11.93 10⁶ total cells I^–1.The atomic ratios of carbon to nitrogen for D.norvegica rangedfrom 8.7 to 10.0. The photosynthetic characteristics of fractionatedphytoplankton (>30 µm) dominated by D.norvegica weresimilar to natural bloom assemblages: o (the initial slope ofthe P-l curves) ranged between 0.013 and 0.047 µg C [µgChla]^–1 h–1 [µmol m^– s^–1]^–1the maximum photosynthetic rate, p^B_m, between 0.66 and 1.85µg C [µghla]^–1 h^–1; l_k (the photoadaptationindex) from 14 to 69 µ,mol m^–2 s^–1. Carbonuptake rates of the isolated cells of D.norvegica (at 780 µmolm^–2 s^–1) ranged from 16 to 25 pg C cell^–1h^– and were lower than those for C.tripos, G.digitaleand some other dinoflagellates. The variation in carbon uptakerates of isolated cells of D.norvegica corresponded with P^B_mof the red-tide phytoplankton assemblages in the P-l experiments.Our study showed that D.norvegica, a toxigenic dinoflagellate,was the main contributor to the primary production in the bloom.     

Diel variations in gut pigment content, diel vertical migration and estimates of grazing impact for copepods in the southern Benguela upwelling region in October 1987

The gut fluorescence technique was used to estimate ingestionand filtration rates of the adult female copepods Paracalanusparvus, Cenlropages brachiatus and Calanus austrails, and copepoditestages 3, 4 and 5 of C.australis in the southern Benguela upwellingregion. During the study period chlorophyll concentrations withinthe upper 20 m of the water column were high, 5 µg I^–1in mid-shelf waters and 15–30 µg I^–1 in innershelf waters. Copepod gut pigment content was low and constantduring the day then increased sharply during the first 2 h aftersunset. Gut pigment content was 2–6 times higher duringthe night compared with daytime values. Small non-migratingcopepods (Paracalanus parvus) showed the smallest diel differencein gut pigment content and large migrating copepods (Centropagesbrachiatus and Calanus australis) the largest difference. Eggproduction rates were 20 and 50% of maximum at the mid-shelfand inner shelf stations respectively, suggesting food-limitation.Comparison of ingestion rates calculated from egg productiondata with ingestion rates calculated from gut pigment data suggestedthat the copepods were feeding omnivorously at the inner shelfstations but herbivorously at the mid-shelf stations. Assumingthat all of the phytoplankton was available as food, the nearshorecopepod assemblage grazed {small tilde}1% of the standing cropeach day, and the mid-shelf assemblage grazed 5% day^–1.Because of errors and uncertainties associated with the gutfluorescence technique, the feeding impact could be underestimatedby 2–4-fold. We discuss several approaches which couldlead to more precise estimates of feeding rates. ³Present address: Marine Sciences, SUNY, Stony Brook, NY, 11794-5000,USA     

Spatial and Temporal Aspects of Growth in the Primary Root of Cotton Seedlings: Effects of NaCl and CaCl2

Seedlings of cotton (Gossypium hirsutum L. cv. Acala SJ-2) weregrown in modified Hoagland nutrient solution with various combinationsof NaCl and CaCl₂. Marking experiments and numerical analysiswere conducted to characterize the spatial and temporal patternsof cotton root growth at varied Na/Ca ratios. At 1 mol m^–3Ca, 150 mol m^–3 NaCl reduced overall root elongation rateto 60% of the control, while increasing Ca to 10 mol m^–3at the same NaCl concentration restored the elongation rateto 80% of the control. Analysis of the spatial distributionof elongation revealed that the presence of 150 mol m^–3NaCl in the medium shortened the growth zone by about 2 mm fromthe approximate 10 mm in the control and also reduced the relativeelemental elongation rate (i.e. the longitudinal strain rate,defined as the derivatives of displacement velocity of a cellularparticle with respect to position on root axis). Supply of 10mol m^–3 Ca at the high salt condition restored partiallythe relative elemental elongation rate, but not the length ofthe growth zone. Compared to the control, the growth trajectoriesshowed that at 1 mol m^–3 CaCl2 it took more time for acellular particle to move through the growth zone at 150 molm^–3 NaCl, while at 10 mol m^–3 CaCl it took lesstime and there was no difference between the NaCl treatments Key words: Gossypium hirsutum, salinity stress, root growth kinematics     

Effects of diffusion and upwelling on the formation of red tides

In this paper, records on the timing and location of specificred tides monitored once or twice a week in Mikawa Bay, Japan,are related to horizontal and vertical mixing rates determinedfrom a numerical model. Horizontal (K_h) and vertical (K_z) diffusioncoefficients, and upwelling velocities, were estimated usinga box model analysis. In the wind-mixed period and in the upperlayer during the stratified period, K_h was estimated to be ofthe order of 10² m² s^–1. During the stratified period,K_z was estimated to be of the order of 10^–5 m² s^–1.The upwelling velocity was calculated to be in the range 0.35–5.1m day^–1 with an average of 1.5 m day^–1. Comparisonbetween the literature values of the specific growth rate (µ)of the red tide-forming diatoms and calculated K_h values duringthe red tides show that diatoms which have a low µ cannotform red tides in a strongly diffusive environment, while specieshaving a high µ can form red tides even in a strong diffusiveenvironment. On the other hand, no clear relationship was foundbetween µ of the flagellate group and K_h, although theflagellate group formed red tides even in severe diffusive conditions.From the comparison between the literature values of sinkingrate and swimming speed and the physical parameters associatedwith vertical processes, it was concluded that flagellates willform red tides, even in severe diffusive conditions, by usingtheir swimming ability, while diatoms form red tides by theirhigh growth rates with the aid of vertical diffusion and theupwelling movement of water.     

Photosynthetic Properties of Guard Cell Protoplasts from Vicia faba L.

Guard cell protoplasts were isolated enzymatically from theepidermis of Vicia faba L. and their photosynthetic activitieswere investigated. Time courses of light-induced changes inthe chlorophyll a fluorescence intensity of these protoplastsshowed essentially the same induction kinetics as found formesophyll protoplasts of Vicia. The transient change in thefluorescence intensity was affected by DCMU, an inhibitor ofphotosystem II; by phenylmercuric acetate, an inhibitor of ferredoxinand ferredoxin NADP reductase; and by methyl viologen, an acceptorof photosystem I. Low temperature (77 K) emission spectra ofthe protoplasts had peaks at 684 and 735 nm and a shoulder near695 nm. A high O₂ uptake (175 µmol mg^–1 Chl hr^–1)was observed in guard cell protoplasts kept in darkness, whichwas inhibited by 2 mM KCN or NaN₃ by about 60%. On illumination,this O₂ uptake was partially or completely suppressed, but itssuppression was removed by DCMU, which indicates that oxygenwas evolved (150 µmol mg^–1 Chl hr^–1) photosynthetically.We concluded that both photosystems I and II function in guardcell chloroplasts and that these protoplasts have high respiratoryactivity. (Received January 30, 1982; Accepted May 15, 1982)     

Plankton distribution across a slope current-induced front in the southern Bay of Biscay

Relatively warm (12.50–12.75°C) and high-salinity[<35.640 practical salinity units (PSU)] water flowing eastwardwas detected at the shelf-break during a cruise carried Outin the southern Bay of Biscay in Spring 1987. The slope currentinduced the formation of a convergent front separating well-mixedoceanic waters from haline-stratified coastal waters. Very highconcentrations of dissolved oxygen (295 µmol kg^–1)and chlorophyll a(>4.5 mg m^–3) were found at the outeredge of the frontal boundary. Small autotrophic flagellatesdominated the phytoplankton community. Primary production peakedat the boundary region. Estimated phytoplankton growth ratesindicated that active growth was taking place, with lower turnovertimes integrated over the water column at the frontal station(2.5–5 days) than at coastal (1.5–2.8 days) or oceanic(1.5–3.5 days) stations. The lowest doubling times (1–2days) were calculated for surface frontal populations. Accumulationof zooplankton was also observed associated with the convergentphysical structure, although this relationship was less markedthan for phytoplankton. Copepods, mainly Paracalanus parvus,Acartia clausi and Oithona helgolandica, formed the bulk ofthe mesozooplankton biomass. Compatibility between the sizeof phytoplankton cells and copepod size spectra indicate highfood availability for these animals, particularly in the vicinityof the front. The distribution of fish eggs and fish larvaewas also coupled with the slope current-induced front. Sardinelarvae were more abundant at the coastal side of the front,whereas larval stages of blue whiting reached the highest densitiesat off-shelf stations. Larvae of lamellibranch molluscs andbryozoa were restricted to nearshore waters, as the frontalboundary prevented larval dispersion to the open ocean. Theresults presented in this paper suggest that the Iberian slopecurrent and its associated shelf-break frontal structure werecrucial in controlling phytoplankton primary production, activityof grazers, distribution of larvae of fishes and benthic invertebrates,and ultimately in determining the structure of the pelagic foodweb in the southern Bay of Biscay during the seasonal periodof vertical mixing.     

Effect of Oxygen on Photosynthetic 14CO2 Fixation in Chroomonas sp. (Cryptophyta) II. Effects of Inhibitors, Uncouplers and an Artificial Electron Mediator on the Inhibition of 14CO2 Fixation by Anaerobiosis

In "air-grown" Chroomonas sp. cells, low concentrations of DCMU(less than 0.1 µM) could prevent the inhibition of ¹⁴CO₂fixation by anaerobiosis under light-saturating conditions (morethan 40 W.m^–2), with phenazine methosulfate showing asimilar effect. Antimycin A, carbonyl cyanide m-chlorophenylhydrazone(CCCP), and N,N'-dicyclohexylcarbodiimide strongly inhibitedanaerobic photosynthesis at concentrations which did not significantlyinhibit the rate under 2% O₂ at high light intensity (200 W.m^–2),although 0.2 µM CCCP stimulated the rate under 2% O₂ tosome extent. On the other hand, KCN inhibited the rate muchmore strongly under 2% O₂ than N₂, although it inhibited therate very strongly at concentrations above 5 µM both underN₂ and 2% O₂. These results suggest that the inhibition of photosynthetic¹⁴CO₂ fixation by anaerobiosis in this alga result from ATPdeficiency caused by over-reduction of electron carriers ofthe cyclic electron flow and that oxygen can prevent the over-reduction.Cyclic electron flow seems to be necessary to provide additionalATP for CO₂ reduction under anaerobic conditions, although itseems to be less necessary under aerobic conditions. (Received July 21, 1983; Accepted January 23, 1984)     

Size-fractionated phytoplankton carboxylase activities in the Indian sector of the Southern Ocean

During the ANTARES 3 cruise in the Indian sector of the SouthernOcean in October–November 1995, the surface waters ofKerguelen Islands plume, and the surface and deeper waters (30–60m) along a transect on 62°E from 48°36'S to the iceedge (58°50'S), were sampled. The phytoplankton communitywas size-fractionated (2 µm) and cell numbers, chlorophyllbiomass and carbon assimilation, through Rubisco and ß-carboxylaseactivities, were characterized. The highest contribution of<2 µm cells to total biomass and total Rubisco activitywas reported in the waters of the Permanent Open Ocean Zone(POOZ) located between 52°S and 55°S along 62°E.In this zone, the picophytoplankton contributed from 26 to 50%of the total chlorophyll (a + b + c) with an average of 0.09± 0.02 µg Chl l^–1 for <2 µm cells.Picophytoplankton also contributed 36 to 64% of the total Rubiscoactivity, with an average of 0.80 ± 0.30 mg C mg Chla^–1 h^–1 for <2 µm cells. The picophytoplanktoncells had a higher ß-carboxylase activity than largercells >2 µm. The mixotrophic capacity of these smallcells is proposed. From sampling stations of the Kerguelen plume,a relationship was observed between the Rubisco activity perpicophytoplankton cell and apparent cell size, which variedwith the sampled water masses. Moreover, a depth-dependent photoperiodicityof Rubisco activity per cell for <2 µm phytoplanktonwas observed during the day/night cycle in the POOZ. In thenear ice zone, a physiological change in picophytoplankton cellsfavouring phosphoenolpyruvate carboxykinase (PEPCK) activitywas reported. A species succession, or an adaptation to unfavourableenvironmental conditions such as low temperature and/or availableirradiance levels, may have provoked this change. The high contributionof picophytoplankton to the total biomass, and its high CO₂fixation capacity via autotrophy and mixotrophy, emphasize thestrong regeneration of organic materials in the euphotic layerin the Southern Ocean.     

Comparisons of the Respiratory Effluxes of Nodules and Roots in Six Temperate Legumes

The specific respiration rates of nodulated root systems, ofnodules and of roots were determined during active nitrogenfixation in soya bean, navy bean, pea, lucerne, red clover andwhite clover, by measurements on whole plants before and afterthe removal of nodule populations. Similar measurements weremade on comparable populations of the six legumes, lacking nodulesbut receiving abundant nitrate-nitrogen, to determine the specificrespiration of their roots. All plants were grown in a controlled-environmentclimate which fostered rapid growth. The specific respiration rates of nodulated root systems ofthe three grain and three forage legumes during a 7–14-dayperiod of vegetative growth varied between 10 and 17 mg CO₂g^–1 (dry weight) h^–1. This mean value consistedof two components: a specific root respiration rate of 6–9mg CO₂ g^–1 h^–1 and a specific nodule respirationrate of 22–46 mg CO₂ g^–1 h^–1. Nodule respirationaccounted for 42–70 per cent of nodulated root respiration;nodule weight accounted for 12–40 per cent of nodulatedroot weight. The specific respiration rates of roots lackingnodules and utilizing nitrate nitrogen were generally 20–30per cent greater than the equivalent rates of roots from nodulatedplants. The measured respiratory effluxes are discussed in thecontext of nitrogen nitrogen fixation, nitrate assimilation. Glycine max, Phaseolus vulgaris, Pisum sativum, Medicago sativa, Trifolium pratense, Trifolium repens, soya bean, navy bean, pea, lucerne, red clover, white clover, nodule respiration, root respiration, fixation, nitrate assimilation     

Influence of Wind Speed on the Sensitivity of Ryegrass to SO2

The sensitivity of S23 Lolium perenne L. to 11 parts 10^–8SO₂ was investigated at two different wind speeds. At the higherwind speed of 25 m min^–8, SO₂ caused significant reductionsin leaf area, root/shoot ratio, and all dry weight fractionsmeasured. At the lower wind speed of 10 m min^–1 growthreductions were not found. The differences in sensitivity ofplants to SO₂ at different wind speeds is discussed in relationto boundary layer resistances of leaves. It is concluded thatthe sensitivity of a plant to a particular pollutant shouldno longer be measured in terms of only the concentration andlength of exposure.     

Nitrate Effects on Pre-emergence Growth and Emergence Percentage of Wheat (Triticum aestivum L.) from Different Sowing Depths

The effects of a range of applied nitrate (NO₃^–) concentrations(0–20 mol m3) on germination and emergence percentageof Triticum aestivum L. cv. Otane were examined at 30, 60, 90and 120 mm sowing depths. Germination percentage was not affectedby either sowing depth or applied NO₃^– concentration whereasemergence percentage decreased with increased sowing depth regardlessof applied NO₃^– concentration. Nitrate did not affectemergence percentage at 30 mm sowing depth, but at 60 to 120mm depth, emergence percentage decreased sharply with an increasedapplied NO₃^– concentration of 0 to 1·0 mol m^–3then decreased only slightly with further increases in appliedNO₃^– of about 5·0 mol m^–3. Root and shoot growth, NO₃^– accumulation and nitrate reductaseactivity (NRA) of plants supplied with 0, 1·0 and 1·0mol m^–3 NO₃^– at a sowing depth of 60 mm were measuredprior to emergence. The coleoptile of all seedlings opened withinthe substrate. Prior to emergence from the substrate, shootextension growth was unaffected by additional NO₃^– butshoot fr. wt. and dry wt. were both greater at 1·0 and1·0 mol m^–3 NO₃^– than with zero NO₃^–.Root dry wt. was unaffected by NO₃^–. Nitrate concentrationand NRA in root and shoot were always low without NO₃^–.At 1·0 and 10 mol m3 NO₃^–, NO₃^– accumulatedin the root and shoot to concentrations substantially greaterthan that applied and caused the induction of NRA. Regardlessof the applied NO₃^– concentration, seedlings which failedto emerge still had substantial seed reserves one month afterplanting. Coleoptile length was substantially less for seedlingswhich did not emerge than for seedlings which emerged, but wasnot affected by NO₃^–. It is proposed that (a) decreasedemergence percentage with increased sowing depth was due tothe emergence of leaf I from the coleoptile within the substrateand (b) decreased emergence percentage with additional NO₃^–was due to the increased expansion of leaf 1 within the substrateresulting in greater folding and damage of the leaf. Key words: Triticum aestivwn L., nitrate, sowing depth, seedling growth, seedling emergence     

Species-specific phytoplankton sedimentation in relation to primary production along an inshore--offshore gradient in the Baltic Sea

The temporal and spatial variability in the quality and quantityof settling phytoplankton material in relation to concurrentprimary production was studied using sediment traps at threecoastal stations from a semi-enclosed bay (Pojo Bay) throughthe outer archipelago to the open Gulf of Finland. The fluxof settling phytoplankton was high (9.3 g C m^–2period^–1)in Pojo Bay, especially in spring, and lower in the archipelago(8.1 g C m^–2 period^–1) and open-sea area (5.2 gC m"2 period"1), although the primary production followed theopposite pattern. A large influx of allochthonous material intoPojo Bay in spring brought allochthonous phytoplankton cellsinto the traps, but limited primary production. Diatoms werethe most abundant settled phytoplankton at all stations, butthe species composition varied between Pojo Bay (Aulacoseiraspp., Rhizosolenia minima) and the outer stations (Skeletonemacostatum, Chaetoceros spp.)At the outer stations, migratingdinoflagellates (Peridiniella catenate) comprised part of thesettling material in spring. The high settling flux of the cyanophyteAphanizomenon flos-aquae is discussed. The species compositionof the phytoplankton assemblage influenced the proportion ofthe total organic carbon sedimentation that consisted of phytoplanktoncarbon.     

Nitrogen inputs into the euphotic zone by vertically migrating Rhizosolenia mats

Rhizosolenia mats conduct extensive vertical migrations in theoligotrophic central North Pacific (cNP) gyre that permit thesediatoms to acquire nitrate at depth and return to the surfacefor photosynthesis. The ultimate fate of this N within the ecosystemis unknown, but may include remineralization by grazing, lossto depth by sinking biomass, or N excretion by Rhizosoleniamats. Direct release of N by mats into the mixed layer wouldrepresent an upward biological pump that circumvents the diffusionbarriers and nutrient sinks at the base of the oceanic euphoticzone. We examined Rhizosolenia mat N release along a transect(28–31° N) in the summer of 2002 (Hawaii to California)and 2003 (Hawaii to west of Midway Island) using sensitive fluorometricand chemiluminescence methods. Nitrate, NO₂^– and NH₄⁺release was determined. Nitrate and NH₄⁺ release by the matsoccurred in both 2002 (22.84 ± 6.04 and 3.69 ±1.74 nmol N µg^–1 Chl a h^–1, respectively)and 2003 (23.74 ± 3.54 and 3.60 ± 0.74 nmol Nµg^–1 Chl a h^–1, respectively). Nitrite releaseonly occurred in the 2003 summer period but occurred in bothyears when Fe chelators were added. Fv/Fm values decreased westwardin 2003 suggesting a gradient of increasing physiological stresstowards the west. The various physiological measures are consistentwith concurrent Fe stress; however, other possibilities exist.Nitrate excretion was the dominant form of N release in bothyears and provided a substantial addition to the ambient nitratepool in the mixed layer. Rhizosolenia mat nitrate release suppliesat least 4–7% of the nitrate pool on daily basis, andpossibly as much as 27%. Rhizosolenia mats are part of a largephytoplankton community that appears to migrate, and rates couldbe significantly higher. Literature reports suggest little orno nitrification in the upper euphotic zone, and thus biologicaltransport and release of nitrate may be a major source to thisregion. This N release is uncoupled from upward CO₂ transportand, like N₂ fixation, provides a component of the N pool availablefor net carbon removal.     

Measurement of Yield Threshold and Cell Wal Extensibility of Intact Wheat Roots under Different Ionic, Osmotic and Temperature Treatments

Yield stress threshold (Y) and volumetric extensibility () arethe rheological properties that appear to control root growth.In this study they were measured in wheat roots by means ofparallel measurement of the growth rate (r) of intact wheatroots and of the turgor pressures (P) of individual cells withinthe expansion zone. Growth and turgor pressure were manipulatedby immersion in graded osmoticum (mannitol) solutions. Turgorwas measured with a pressure probe and growth rate by visualobservation. The influence of various growth conditions on Yand was investigated; (a) At 27 °C.In 0.5 mol m^–3 CaCl₂ r, P, Y and were20.7±4.6 µm min^–1, 0.77±0.05 MPa,0.07±0.03 MPa and 26±1.9 µm min^–1MPa^–1 (expressed as increase in length), respectively.Following 24 h growth in 10 mol m^–3 KC1 these parametersbecame 12.3±3.5 µm min^–1, 0.72±0.04MPa, 0.13±0.01 MPa and 21±0.7 µm min^–1MPa^–1. After 24 h osmotic adjustment in 150 mol m^–3mannitol/0.5 mol m^–3 CaCl₂ r= 19.6±4.2 µmmin^–1, P = 0.68±0.05 MPa and Y and were 0.07±0.04MPa and 30±0.2 µm min^–1 MPa^–01, respectively.After 24 h growth in 350 mol m^–3 mannitol/0.5 mol m^–3CaCl₂ r= 13.3±4.1 µm min^–1, P= 0.58±0.07MPa, Y=0.12±0.01 MPa and ø 32±0.2 tim min^–1MPa^–1. During osmotic adjustment in 200 mol m^–3mannitol/0.5 mol m^–3 CaCl₂, with or without KCl, the recoveryof growth rate corresponded to turgor pressure recovery (t1/2approximately 3 h). (b) At 15 °C. Lowered temperature dramatically influencedthe growth parameters which became r= 8.3±2.8 um min^–1,P=0.78 MPa, r=<0.2 MPa and =15±0.1 µm min^–1MPa^–1. Therefore, Y and are influenced by 10 mol m^–3 K⁺ ionsand low temperature. In each case the effective pressure forgrowth (P-Y) was large indicating that small fluctuations ofsoil water potential will not stop root elongation. Key words: Yield threshold, cell wall extensibility, wheat root growth, temperature, turgor pressur