Temporal and vertical variation of chlorophyll a concentration, phytoplankton photosynthetic activity and light attenuation in Lake Kinneret: possibilities and limitations for simulation by remote sensing

The relationship between chlorophyll a (Chl a) and primary productivity(PP) in the uppermost water layer and the water column-based(0–15 m) integral values of those variables were examinedusing measurements taken in Lake Kinneret (Israel) from 1990to 2003. In 81% of all Chl a profiles examined, the distributionwas fairly uniform within the entire 0–15 m water column,and 12.3% of instances showed a prominent subsurface maximum,when the lake phytoplankton was dominated by the dinoflagellatePeridinium gatunense. Chl a can be reliably estimated by remotesensing techniques in the productive and turbid water of LakeKinneret, since Chl a concentration at surface layers can beextrapolated to the entire water column. Light vertical attenuationcoefficient average for wavelengths from 400 to 700 nm, K_d,ranged from 0.203 to 1.954 m^–1 and showed high degreeof temporal variation. The maximal rate of photosynthetic efficiency,P_B^opt [average 3.16 (±1.50)], ranged from 0.25 to 8.85mg C m^–3 h^–1 mg Chl a^–1. Using measured dataof Chl a, P_B^opt, and light as an input, a simple depth-integratedPP model allowed plausible simulation of PP. However, a lackof correlation between photosynthetic activity and temperature(or other variable with remotely sensed potential) renders theuse of models that require input of photosynthetic efficiencyto calculate integrated PP of little value in the case of productiveand turbid Lake Kinneret.     

Spatial patterns of chlorophyll, primary production, macrozooplankton biomass, and physical structure in the central North Pacific Ocean

The relation between the large-scale horizontal patterns ofbiological properties (primary production and the standing stocksof phytoplankton and macrozooplankton) and physical structurein the North Pacific central gyre is described based upon samplingon a north-south section in August 1980 (expedition FIONA).Primary production in the central North Pacific is nutrientlimited and the large-scale patterns in the measured biologicalproperties appear to be determined by physical processes whichaffect the vertical flux of new nutrients from deeper waterto the euphotic zone. The observed biological patterns can thusbe used to infer horizontal variations in physical processeswhich affect the rate of nutrient supply to the euphotic zone.A mesoscale eddy in the southern part of the section decreasedthe local level of primary production by pushing density andnutrient surfaces to deeper depths. In addition, there was alarge-scale, south-to-north decrease within the central gyrein chlorophyll, primary production and macrozooplankton biomass.This biological gradient was not related in any simple way tothe horizontal distribution of light penetration or the depthsof the nutricline or chlorophyll maximum layer. The hypothesisthat horizontal patterns of nutrient input and production weredetermined by vertical Fickian diffusion and, thus, should bepositively correlated with the vertical nutrient gradient andnegatively correlated with the vertical density gradient, wastested. This simple model however was not supported, suggestingthat either some other process drives the large-scale patternsof vertical nutrient input to the euphotic zone, or that k₂(the vertical eddy diffusivity) is uncorrelated with the meanvertical density gradient. There was some support for a previoushypothesis that enhanced mixing is associated with the densityvariance maximum, and that the relation of the depth of thevariance maximum to the depth of the top of the nutricline mayaffect the large-scale biological patterns.     

Vertical water column resource partitioning by a ciliated protozoan population under stratified conditions in the northern Adriatic

The vertical distribution of the ciliated protozoan stock, potentialprey and potential predators were repeatedly sampled over twodiurnal cycles at an eutrophic site off the Po River delta duringsummer when the water column was strongly stratified. A subsurfaceciliated protozoan maximum (SCPM) was associated with a subsurfacenanoplankton chlorophyll maximum (SCM), which was located belowthe pycnocline at the nutricline. A subsurface oxygen maximumindicated that the SCM resulted from in situ growth. The associatedSCPM appeared to result from the interaction of two primaryfactors: (i) the availability of a high prey biomass (i.e. nanoplankton)and (ii) low grazing pressure from potential predators (i.e.macrozooplankton).     

Phytoplankton photosynthesis parameters in central Canadian lakes

Values for two biological parameters — (i) P^B_m, the lightsaturated rate of photosynthesis per unit of chlorophyll and(ii) , the slope of the light limited part of the photosynthesisversus light curve per unit of chlorophyll — must be knownin order to be able to estimate rates of phytoplankton primaryproduction from chlorophyll data. These parameters were measuredfor periods of up to 9 years in central Canadian lakes locatedin temperate, subarctic and arctic climatic zones. Regardlessof their geographic locations, lakes where integral photosynthesiswas nutrient limited had lower values of these parameters thandid lakes where integral photosynthesis was light limited. Temperatureset an upper limit to the variability of P^B_m but was not a goodpredictor of its actual value. Year-to-year variability of photosynthesisparameters in the most intensively studied group of lakes waslarge: annual means varied by a factor of three over a 9-yearperiod. Until the sources and extent of this variability areknown, accurate production estimates can be obtained from chlorophylldata only if P^B_m and are measured in each water body and inevery year. Implications for estimating primary production fromremotely-sensed chlorophyll data are discussed.     

Mechanisms of Electron Flow through the QB Site in Photosystem II. 3. Effects of the Presence of Membrane Structure on the Redox Reactions at the QB Site

Reduction kinetics of chloro- or methyl-substituted benzoquinones(BQs) in spinach PSII membrane fragments or n-heptyl-rß-D-thioglucoside-extractedPSII core complexes (HTG-PSII) was studied and compared to thatin cyanobacterial PSII core complexes [Satoh et al. (1995) PlantCell Physiol. 36: 597]. It was found that the BQs accept electronsat two sites (the Q_B and PQ sites) in the both spinach preparationsas in the cyanobacterial preparation. Maximum turnover rates(V_max) and binding affinities (K_m) of the two sites were estimated.Comparison of the values in PSII membrane fragments with thosein HTG-PSII showed that removal of the membrane structure orlight-harvesting chlorophyll a/b protein complexes from thePSII core complexes had little effect on the characteristicsof the Q_B site, indicating that the HTG-PSII have the intactQ_B site and are good materials to study the site. The K_m andV_max values were comparable to those in the cyanobacterial preparation. Low affinity (high K_m values) and high V_max values of methyl-substitutedBQs to the Q_B site and almost the same rate of intrinsic electronflow through the Q_B site in the both spinach preparations furthersupport the hypothesis that the plastoquinone (PQ) moleculeat the Q_B site is not replaced by another PQ molecule but, afterreduction, only its head group goes out of the Q_B pocket, andcomes back after transferring the electrons and protons to afree PQ molecule [Satoh et al. (1993) Z. Naturforsch. 48c: 174]. (Received May 2, 1996; Accepted July 26, 1996)     

Subsurface chlorophyll maxima in the north-western Bay of Bengal

The depth profiles of phytoplanlkton pigments in the north-westernBay of Bengal are generally characterized by a subsurface chlorophyllmaximum The occurrence of subsurface chlorophyll maxima is discussedin relation to other information on water column propertiesin the study area. The gradual deepening of the subsurface maximumfrom inshore to offshore waters coincides with the deepeningof the thermocline Significant correlation between the depthof the subsurface chlorophyll maximum and depth of thermoclinesuggests that the formation of the subsurface maximum is influencedby the presence of seasonal thermocline. Further the subsurfacechlorophyll maximum is noticed within the depth ranges of ammoniummaximum and intracline, suggesting the regenerated nutrientsmay also extend a more important influence on the subsurfacemaxima. The presence of chlorophyll b and a high ratio of chlorophylla/phaeopigments in the subsurface layers substantiates the formationof the subsurface maximum due to growth of the photosyntheticallyactive phytoplanlkton community     

Red tide assemblage formation in an estuarine upwelling ecosystem: Ria de Vigo

Red tides are conspicuous in the upwelling system of Galicia(NW Iberian Peninsula). At present, there are conflicting hypothesesabout the generation site of these phytoplankton assemblages.It is interesting to know whether the rias can be sites of redtide formation or if they act only as accumulation sites ofpopulations advected from shelf waters. A study in the Ra deVigo, carried out during late September 1990, showed the developmentof a red tide assemblage, composed of Alexandrium affinis, Ceraiiumfusus and Gymnodinium catenaium, during a 2 week upwelling-downwellingcycle. Growth occurred at the bottom of the thermocline-topof the nutricline. Above this assemblage, a diatom assemblage(large diatoms) was blooming. Prior to the formation of thered tide, a subsurface chlorophyll maximum made up of smalldiatoms (Nilzschia f. seriaia, Chaeloceros socialis), smallflagellates (<30 µm) and small gymnodinid forms (<30µm) was observed. In the nutrient-depleted upper layer,several autotrophic and large heterotrophic dinoflagellatesdominated. It is suggested that the ratio between the velocityof upward water movement and the depth of the stratified upperlayer (flushing rate, day^–1) is the critical parameterwhich triggers active phytoplankton growth. It can be concludedthat upward water velocities of {small tilde}2.5 m day^–1and a stratified upper layer of 10 m depth (flushing rate 0.25day^–1) are the main physical constraints for red tidedevelopment.     

Effets des fluctuations rapides de la lumiere sur la photosynthese du phytoplancton

[¹⁴C]-assimilation rates were measured on cultures of two unicellulargreen algae (Chlamydomonas sp. and Oocystis sp.) as a functionof light intensities (saturation curves), under steady lightand also under rapidly alternating high and low light intensities.Assimilation rates vary according to the frequency of the intermittentlight regime and it falls under two categories: (1) at 0.1 and0.2 Hz, the assimilation rate is equal to the average of therates observed at high and low light intensities under steadylight, and (2) under 1.0, 1.6 and 10 Hz the assimilation rateis equal to the rate observed under a mean steady irradiance.Moreover, the range of assimilation rates at a given frequencydepends on the difference between the high and the low intensities.Batch cultures of Oocystis sp. have been grown under intermittentlight of 0.1, 1.0 and 10.0 Hz (same mean intensity). Growthrate under intermittent light of 0.1 Hz is –40% lowerthan the control under steady light. Photosynthetic potential(P^B_max)and efficiency () change with the growth stages of thecultures. At the end of the logarithmic growth phase, both photosyntheticparameters are maximum at 1.0 Hz and minimum at 0.1 Hz. Averagecell concentrations of chlorophyll a increase as the frequencyof the light regime decreases. During the log phase, concentrationof carotenoids relative to chlorophyll a increases at 1.0 Hz,decreases at 0.1 Hz, and remains constant at 10.0 Hz. Underclear sky conditions, wave-induced light fluctuations in thephotic layer may therefore enhance primary production, especially(1) in the lower part of the photic layer, where low frequencylight changes might cause cell chlorophyll a to increase, and(2) at a depth of 1–4 m, where the main frequencies (ofthe order of 1.0 Hz), might cause a significant increase ofboth the photosynthetic potential (P^B_max)and efficiency (). ¹Contribution au programme du GIROQ (Groupe interuniversitairede recherches océanographiques du Québec) ²Adresse actuelle: Centre de recherches en nutrition, UniversitéLaval, Québec, Qué. G1K 7P4, Canada     

Acclimation in Seedlings of a Tropical Tree, Bischofia javanica, Following a Stepwise Reduction in Light

Acclimation of fully developed leaves of Bischofia javanicaBlume to shadelight was examined. Seedlings were grown undersimulated daylight (1000 µmol m^–2 s^–1), thentransferred to a simulated shadelight (40 µmol m^–2s^–1). When a high-light leaf was transferred to low light, large negativenet photosynthetic rates (P_m) were recorded. This decrease wasrapid, but within 7 d the rate increased and became equal tothe low-light control leaf. These changes in photosynthesisdid not follow the pattern of changes in stomatal conductance(g_s). Transfer to the low light resulted in a dramatic decreasein leaf weight per unit area (L_w), and most of the decreasesin L_w occurred within 3 d of transfer when the P_m of the transferredleaf was well below that of the low-light control leaf. There was a significant decrease in chlorophyll a in the transferredleaf without an appreciable change in chlorophyll b resultingin a large decrease in the chlorophyll a to chlorophyll b ratio.Leaf chlorophylls per unit area were higher in the transferredleaf than the low-light control leaf. Maximum photosyntheticrate in the transferred leaf was decreased by 40% compared tothat for the high-control leaf, but was almost at the same extenthigher than the low-light control leaf The results are discussedin the context of carbon gain capacity of its seedlings underlight-limiting forest understorey habitats. Bischofia, chlorophylls, light, photosynthesis, shade acclimation, tree seedlings, tropical tree     

Liquid-Tissue Mechanics in Amphibian Gastrulation: Germ-Layer Assembly in Rana Pipiens

During amphibian gastrulation, migrating subsurface germ layersmay flow past one another like immiscible viscous liquids inresponse to tissue surface tension forces. We describe heretwo physical tests for liquid-tissue morphogenesis in culturedaggregates of subsurface ectoderm (E), mesoderm (M) and endoderm(N) excised from mid-yolk-plug Rana pipiens gastrulae. (i) Liquidsare coherent substances in which subunits can slip past oneanother to relax internal shear stresses. We find, in cross-sectionsof cell aggregates fixed during compression, that cells withinflattened aggregates are intially deformed, but do, as predicted,gradually reassume their original, undistorted shapes, (ii)Surface tensions ('s) govern ordinary liquid-droplet spreading;e.g., if equal-sized droplets A and B fuse in medium O, B spreadsaround A when _{AO BO}. When pairs of subsurface aggregates arecultured together, N surrounds M and E, and M surrounds E. Tosee if _EO > _MO > _NO. we flatten aggregates with quartzfibers calibrated to measure the force of compression. As predicted,under the same flattening force, E aggregates are rounder thanM aggregates, which are rounder than N aggregates. Furthermore,a second surface tension relationship can account for the autonomousinvolution of M between E and N; and these surface tension relationshipscan also explain the inversion of E, M and N by coated ectodermto produce normal gastrular germ-layer arrangements. We concludethat, combined with active cell shape changes in solid-likesurface cell layers and also with autonomous elongation of dorsallip mesoderm, tissue surface tension control of liquid-tissueflow in subsurface germ layers is a key morphogenetic mechanismin amphibian gastrulation which might be regulated by changesin intercellular adhesiveness.     

Relationships between the hydrological structure, chlorophyll and zooplankton biomasses in the Gulf of Guinea

In the deep-sea part of the Gulf of Guinea, zooplankton dryweights (D.W.)are negatively correlated with the top of thenitrate gradient (D_NO3) or the shallowest undersaturated oxygenlevel (D_ox). This is the consequence of a two-fold relation:the integrated chlorophyll, Chl a_i, vs. D_NO3 or D_ox relationin typical tropical structures (i.e. with no nitrate in themixed layer) and the linear relation between D.W. and Chl a_i,for offshore oligotrophic areas and the equatorial divergenceas well. However this D.W.-Chl a_i relation is not valid anymore in the Mauritanian coastal upwelling. This point is discussedtogether with that of the respective vertical distributionsof zooplankton and chlorophyll and the limits of the studiedrelations.     

Hydraulic and osmotic properties of oak roots

Hydraulic and osmotic properties of root systems of 2.5–8-months-oldoak seedlings (Quercus robur and Q. petraea) were measured usingthe root pressure probe. Root pressures of excised roots rangedbetween 0.05 and 0.15 MPa which was similar to values obtainedfor herbaceous species. Root hydraulic conductivity (Lp_r; perunit of root surface area) was much larger in the presence ofhydrostatic than in the presence of osmotic pressure differencesdriving water flow across the roots. Differences were as largeas a factor of 20 to 470. Roots of the young seedlings of Q.robur grew more rapidly than those of Q. petraea and had a hydraulicconductivity which was substantially higher. Nitrogen nutritionaffected root growth of Q. robur more than that of Q. petraea,but did not affect root Lp_r of either species. For Q. robur,Lp_r decreased with root age (size) which is interpreted by aneffect of suberization during the development of fine roots.Root hydraulic conductance remained constant for both species.For Q. robur, this was due to the fact that the overall decreasein Lp_r was compensated for by an increase in root surface area.Root reflection coefficients (_sr) were low and ranged between_sr=0.1 and 0.5 for solutes for which cell membranes exhibitreflection coefficients of virtually unity (salts, sugars etc.).Solute permeability was small and was usually not measurablewith the technique. When root systems were attached to the rootpressure probe for longer periods of time (up to 10d), solutepermeability increased due to ageing effects which, however,did not cause a general leakiness of the roots as Lp_r decreased.Hence, values were only used from measurements taken duringthe first day. Transport properties of oak roots are comparedwith those recently obtained for spruce (Rdinger et al., 1994).They are discussed in terms of a composite transport model ofthe root which explains low root _sr at low solute permeabilityand reasonable rootLp_r The model predicts differences betweenosmotic and hydraulic water flow and differences in the transportproperties of roots of herbs and trees as found. Key words: Composite transport, hydraulic conductivity, nitrogen nutrition, Quercus, reflection coefficient, root transport, water relations     

Effects of the Mode of Competition on Stationary Size Distribution in Plant Populations

The effects of the mode of between-individual competition onthe stationary size distribution in uneven-aged and continuallyreproducing tree populations were investigated theoretically,based on the diffusion and continuity equation models. The B(t,x) function, which gives a measure proportional to total leafarea of individual trees larger than dbh (trunk diameter atbreast height) x at time t, expresses the effect of one-sidedcompetition on the subject individual of dbh x. The effect oftwo-sided competition on individuals of any size is equallygiven by B(t, x₀), i.e. total leaf area of the stand (or LAI),where x₀ is the minimum dbh. The following two points, whichwere shown by Kohyama (1991) from results of model simulation,were theoretically derived: (1) the effect of the diffusionterm [D(t, x) function] of the diffusion model on the stationarysize distribution is small for the range of parameter valuesobtained empirically for the warm-temperate and tropical rainforests; (2) the shape of the stationary size distribution underone-sided competition is less changed by a change in the seedlingsupply rate than under two-sided competition. The followingtwo points were further shown theoretically: (3) one-sided competitionis likely to lead to a monotonically decreasing size distributionof dbh with the peak at x = x₀, which is a characteristic ofthe rain forest; (4) the slope of size distribution of dbh steepensas one-sided competition intensifies. Relationships betweenthe mode of competition and the stability of population structure,and general functional forms of one-sided and two-sided competitionare discussed. Diffusion model, one-sided competition, stability of population structure, stationary size distribution, two-sided competition     

Isotonic contractile and fatigue properties of developing rat diaphragm muscle

Postnatal transitions in myosin heavy chain (MHC) isoformexpression were found to be associated with changes in both isometric and isotonic contractile properties of rat diaphragm muscle(Dia_m). Expression of MHC_neo predominated inneonatal Dia_m fibers but was usually coexpressed withMHC_slow or MHC_2A isoforms. Expression ofMHC_neo disappeared by day 28. Expression ofMHC_2X and MHC_2B emerged at day 14 andincreased thereafter. Associated with these MHC transitions in theDia_m, maximum isometric tetanic force (P_o), maximum shortening velocity, and maximum power output progressively increased during early postnatal development. Maximum power output ofthe Dia_m occurred at ~40% P_o at days0 and 7 and at ~30% P_o in older animals.Susceptibility to isometric and isotonic fatigue, defined as a declinein force and power output during repetitive activation, respectively,increased with maturation. Isotonic endurance time, defined as the timefor maximum power output to decline to zero, progressively decreasedwith maturation. In contrast, isometric endurance time, defined as thetime for force to decline to 30-40% P_o, remained>300 s until after day 28. We speculate that with thepostnatal transition to MHC_2X and MHC_2Bexpression energy requirements for contraction increase, especiallyduring isotonic shortening, leading to a greater imbalance betweenenergy supply and demand.

     

Clouds, deep chlorophyll maxima and the nutrient supply to the mixed layer of stratified water bodies

A deep chlorophyll maximum (DCM) is common in the pycnoclineof the offshore tropical and subtropical oceans outside of divergencesas well as in temperate seas and lakes during summer. It trapsthe diffusive flux of nutrients into the depleted upper layers.When the DCM and the associated nutricline are situated in thetop of the pycnocline (e.g. as during early summer in temperateseas), cloudiness materially reducing photosynthesis in theDCM may lead to a nutrient flux into the mixed layer. For thewarm seas, with the DCM and the nutricline being usually deepin the stratified domain, it is shown here that even severecloud cover can only be expected to lead to enhanced nutrientflux into the upper parts of the pycnocline but not the mixedlayer. The same is likely for temperate seas and deep lakesduring the height of the summer. The implication of irregular,enhanced upward flux of nitrate for the ratio of new/regeneratedprimary production is noted.     

Elevated atmospheric CO2 concentration ameliorates effects of NaCl salinity on photosynthesis and leaf structure of Aster tripolium L.

This study investigated the interaction of NaCl-salinity andelevated atmospheric CO₂ concentration on gas exchange, leafpigment composition, and leaf ultrastructure of the potentialcash crop halophyte Aster tripolium. The plants were irrigatedwith five different salinity levels (0, 25, 50, 75, 100% seawatersalinity) under ambient and elevated (520 ppm) CO₂. Under salineconditions (ambient CO₂) stomatal and mesophyll resistance increased,leading to a significant decrease in photosynthesis and wateruse efficiency (WUE) and to an increase in oxidative stress.The latter was indicated by dilations of the thylakoid membranesand an increase in superoxide dismutase (SOD) activity. Oxidativestress could be counteracted by thicker epidermal cell wallsof the leaves, a thicker cuticle, a reduced chlorophyll content,an increase in the chlorophyll a/b ratio and a transient declineof the photosynthetic efficiency. Elevated CO₂ led to a significantincrease in photosynthesis and WUE. The improved water and energysupply was used to increase the investment in mechanisms reducingwater loss and oxidative stress (thicker cell walls and cuticles,a higher chlorophyll and carotenoid content, higher SOD activity),resulting in more intact thylakoids. As these mechanisms canimprove survival under salinity, A. tripolium seems to be apromising cash crop halophyte which can help in desalinizingand reclaiming degraded land. Key words: Aster tripolium, cash crop halophyte, elevated CO₂, gas exchange, oxidative stress, photosynthesis, salt tolerance, ultrastructure, water use efficiency Received 29 July 2008; Revised 8 October 2008 Accepted 9 October 2008     

Changes in levels of Proteases and Their Inhibitors during Development of the Seeds of Job's Tears (Coix lacryma-jobi L. var. Ma-yuen Stapf) and Their Localization and Interactions

Changes in levels and localization of proteases and a trypsininhibitor (JBTI) in the developing seeds of Job's tears (Coixlacryma-jobi L. var. Ma-yuen Stapf) were followed, and theirinteractions were examined. The JBTI was induced from the middlestage of development (12 DAF, i.e., 12 days after flowering)and increased until the late stage of development (24 DAF),and was localized in the germ. Two groups of proteases (A, thosewith molecular weights of 55–70 kDa; and B, those withmolecular weights greater than 94 kDa) were detected by activestaining of substrate-containing SDS-polyacrylamide gels. Thegroup of larger proteases seems to consist of three members(B₁, B₂₎ B₃, with increasing molecular weights). Band A wasobserved only in the early stage of development (until DAF 9),band B₂ persisted during all stages, while bands B, and B₃ werepresent only during early and late stages, respectively. Thegroup A proteases and one of the group B proteases (probablyB₁) were inhibited by diisopropyl-fluorophosphate (DFP), bytrypsin inhibitors from soybean and rice, and by JBTI. The proteasesthat were present in the seeds of Job's tears at a late stageseemed to be localized in the germ. (Received September 9, 1988; Accepted April 19, 1989)     

Effect of light regime upon growth rate and chemical composition of a clone of Skeletonema costatum from the Trondheimsfjord, Norway

Nutrient-saturated cultures of Skeletonema costatum were grownat 15C and 42 combinations of photon flux density (PFD) anddaylength. The growth rate increased with the daylength andPFD up to 460–630 µE m^–2 s^–1 (maximum2.5 doublings day At 2000 µE m^–2 s^–1 the growthrate was reduced by 45%. The chlorophyll (chl) content of thecells and the rate of production of carbon per unit chlorophylland ambient light increased for declining light regimes as didcellular nitrogen and carbon. The N/C ratio, cellular phosphorusand ratios between in vivo fluorescence, with and without DCMU,and chlorophyll varied negligibly. The ATP/C ratio was linearlyrelated to the growth rate. The results were described mathematically.The chl/C ratio was low both in strong light and in marginallylow light, corresponding to low cellular chlorophyll and highcellular carbon, respectively. The observed increase in cellularnitrogen and carbon at shade adaptation probably represent anincrease in the size of internal stores of organic nitrogenand may imply that Skeletonema cells become enriched with organicnitrogen when staying in nitrate-rich subsurface layers, e.g.in or below a nutricline. However, close to zero growth in marginallight the cells become greatly enriched with respect to everymeasured factor. Such cells may be physiologically resting stageswhich may ensure survival during dark periods and promote rapiddevelopment during the initial phase of blooms. Cultures andnatural blooms of Skeleronema in the Trondheimsfjord exhibitvery similar patterns of variation.     

Ultrastructural Investigation of Tension Wood Fibre in Fraxinus mandshurica Rupr. var. japonica Maxim.

The ultrastructure of the fibre wall in Fraxinus mandshuricaRupr. var. japonica Maxim. was investigated by electron microscopy.The trees had been inclined artificially at an angle of 30°to the vertical at the beginning of the initiation of cambialgrowth in early spring. The secondary walls of tension woodfibres were of the outer (S₁) layer and gelatinous (G) layertype. The microfibrils in the gelatinous (G) layer were orientedas a steep Z-helix relative to the fibre axis with a deviationthat ranged from 0° to 25° but was mainly between 5°and 10°. The cross-sectional surface of tension wood fibresrevealed the relatively strong attachment of the G-layer tothe S₁ layer. The G-layer stained weakly with potassium permanganate.The S₁ layer of tension wood fibres stained less strongly thanthat of the normal and opposite wood fibres. These results indicatethat the tension wood in F. mandshurica var. japonica is nottypical and is somewhat anomalous. The secondary walls of normaland opposite wood fibres were composed of two layers, S₁ andS₂, and lacked an S₃ layer. Microfibrils in the S₃ layer ofjuvenile stems were extremely variable in orientation and weresparsely distributed without forming a layer. By contrast, avery thin S₃ layer was present in the wood fibres of maturestems. The variations in the formation of the S₃ layer in thefibre walls were probably due to the differences in the cambialage of the stems of F. mandshurica Rupr. var. japonica.Copyright1995, 1999 Academic Press Fraxinus mandshurica Rupr. var. japonica Maxim., Japanese ash, tension wood, fibre wall, G-layer, microfibrillar orientation, normal and opposite wood, juvenile stem, field-emission scanning electron microscopy, low accelerating voltage     

Planktonic primary production in the German Wadden Sea

By combining weekly data of irradiance, attenuation and chlorophylla concentrations with photosynthesis (P) versus light intensity(E) curve characteristics, the annual cycle of planktonic primaryproduction in the estuarine part of the Northfrisian WaddenSea was computed for a 2 year period. Daily water column particulategross production ranged from 5 to 2200 mg C m^–2 day^–1and showed a seasonal pattern similar to chlorophyll a. Budgetcalculation yielded annual gross particulate primary productionsof 124 and 176 g C m^–2 year^–1 in 1995 and 1996,respectively. Annual amounts of phytoplankton respiration, calculatedaccording to a two-compartment model of Langdon [in Li,W.K.W.and Maestrini,S.Y. (eds), Measurement of Primary Productionfrom the Molecular to the Global Scale. International Councilfor the Exploration of the Sea, Copenhagen, 1993, pp. 20–36],and dissolved production in 1996, were both in the range of24–39 g C m^–2 year^–1. Annual total net productionwas thus very similar to particulate gross production (127 and177 g C m^–2 year^–1 in 1995 and 1996, respectively).Phytoplankton growth was low or even negative in winter. Inspring and summer, production/biomass (Pr/B) ratios varied from0.2 up to 1.7. Phytoplankton growth during the growth seasonalways surpassed average flushing time in the area, thus underliningthe potential of local phytoplankton bloom development in thispart of the Wadden Sea. The chlorophyll-specific maximum photosyntheticrate (P^B_max) ranged from 0.8 to 9.9 mg C mg^–1 Chl h^–1and was strongly correlated with water temperature (r² = 0.67).By contrast, there was no clear seasonal cycle in ^B, which rangedfrom 0.007 to 0.039 mg C mg^–1 Chl h^–1 (µmolphotons m^–2 s^–1)^–1. Its variability was muchless than P^B_max and independent of temperature. The magnitudeand part of the variability of P^B_max and ^B are presumably causedby changes in species composition, as evidenced from the rangeof these parameters found among 10 predominant diatom speciesisolated from the Wadden Sea. The ratio of average light conditionsin the water column (E_av) to the light saturation parameterE_k indicates that primary production in the Wadden Sea regionunder study is predominantly controlled by light limitationand that nutrient limitation was likely to occur for a few hoursper day only during 5 (dissolved inorganic nitrogen) to 10 (PO₄,Si) weeks in the 2 year period investigated.