Size structures of microplankton biomass and production in Jiaozhou Bay, China

Seasonal investigations of size-fractionated biomass and productionwere carried out from February 1992 to May 1993 in JiaozhouBay, China. Microplankton assemblages were separated into threefractions: pico- (0.7–2 µm), nano- (2–20 µm)and netplankton (20–200 µm). The biomass was measuredas chlorophyll a (Chi a), paniculate organic carbon (POC) andparticipate organic nitrogen (PON). The production was determinedby ¹⁴C and ¹⁵N tracer techniques. The seasonal patterns in biomass,though variable, were characterized by higher values in springand lower values in autumn and summer (for Chi a only). Theseasonal patterns in production, on the other hand, were moreclear with higher values occurring in summer and spring, andlower values occurring in autumn and winter. Averaged over thewhole study period, the respective proportions of total biomassaccounted for by net-, nano- and picoplankton were 26, 45 and29% for Chi a, 32, 33 and 35% for POC, and 26, 32 and 42% forPON. The contributions to total primary production by net-,nano- and picoplankton were 31, 35 and 34%, respectively. Therespective proportions of total NH₄⁺–N uptake accountedfor by net-, nano- and picoplankton were 28, 33 and 39% in thedaytime, and 10, 29 and 61% at night. The respective contributionsto total NO₃^–-N uptake by net-, nano- and picoplanktonwere 37, 40 and 23% in the daytime, and 13, 23 and 64% at night.Some comprehensive ratios, including C/N biomass ratio, Chla/C ratio, C uptake/Chl a ratio, C:N uptake ratio and the f-ratio,were also calculated size separately, and their biological andecological meanings are discussed.     

Comparison of carbon-specific growth rates and rates of cellular increase of phytoplankton in large limnetic enclosures

Potential carbon-specific growth rates of phytoplankton wereestimated from a series of measurements of photosynthetic radio-carbonuptake over 4- and 24-h exposure periods in the light fieldsof three large limnetic enclosures (‘Lund Tubes’),each providing different limnological and trophic conditions.Photosynthetic behaviour and short-term, chlorophyll-specificcarbon-fixation rates conformed to well-established criteriabut, over 24 h, the net retention represented 23–82% ofthe carbon fixed during the daylight hours. Potential mean growthrates (k'_p, of the photo-autotrophic community were calculatedas the net exponential rates of daily carbon-accumulation relativeto derived, instantaneous estimates of the cell carbon-content.Apparent actual community growth rates (k'_D were calculatedas the sum of the exponential rates of change of each of themajor species present, corrected for probable rates of in situgrazing and sinking, and expressed relative to the fractionof total biomass for which they accounted. The correspondingvalues were only occasionally similar, k'_p generally exceedingK'_D by a factor of between 1 and 30 or 1 and 14, depending uponthe carbon:chlorophyll ratio used. The ratio, K'_p/K'_D was foundto vary inversely both to k'_D and to k_n, the net rate of changein phytoplankton biomass, suggesting that measured carbon fixationrates merely represent a capacity for cellular increase which,owing to other likely limitations upon growth, is seldom realized.Apparent rates of loss of whole cells do not account for theloss of carbon; that the ‘unaccounted’ loss rates(K'_p–K'_D varied in direct proportion to K'_p (i.e., losseswere least when chlorophyll-specific photosynthetic productivitywas itself limited) is best explained by physiological voidingof excess carbon (for instance, by respiration, photorespiration,excretion) prior to the formation of new cells.     

Effects of CO2 enrichment and intraspecific competition on biomass partitioning, nitrogen content and microbial biomass carbon in soil of perennial ryegrass and white clover

Seedlings of perennial ryegrass (Lolium perenne L. cv. Parcour)and white clover (Trifolium repens L. cv. Karina) grown at fivedifferent plant densities were exposed to ambient (390 ppm)and elevated (690 ppm) CO₂ concentrations. After 43 d the effectsof CO₂ enrichment and plant density on growth of shoot and root,nitrogen concentration of tissue, and microbial biomass carbon(C_mic) in soil were determined. CO₂ enrichment of Lolium perenneincreased shoot growth on average by 17% independent of plantdensity, while effects on root biomass ranged between -4% and+ 107% due to an interaction with plant density. Since tilernumber per plant was unaffected by elevated CO₂, the small responseof shoot growth to CO₂ enrichment was atributed to low sinkstrength. A significant correlation between nitrogen concentrationof total plant biomass and root fraction of total plant drymatter, which was not changed by CO₂ enrichment, indicates thatnitrogen status of the plant controls biomass partitioning andthe effect of CO₂ enrichment on root growth. Effects of elevatedCO₂ and plant density on shoot and root growth of Trifoliumrepens were not significantly interacting and mean CO₂-relatedincrease amounted to 29% and 66%, respectively. However, growthenhancement due to elevated CO₂ was strongest when leaf areaindex was lowest. Total amounts of nitrogen in shoots and rootswere bigger at 690 ppm than at 390 ppm CO₂. There was a significantincrease in C_mic in experiments with both species whereas plantdensity had no substantial effect. Key words: CO₂ enrichment, intraspecific competition, biomass partitioning, Lolium perenne, Trifolium repens, grassland     

Carbon-specific phytoplankton growth rates: a comparison of methods

Measurements of biomass and growth rate of two axenic algalcultures were carried out using three different methodologicalapproaches: the specific ¹⁴C-labelling of chlorophyll a, [³H]adenineincorporation into DNA and net organic carbon assimilation.Time-course experiments revealed that the specific activitiesof chlorophyll a were significantly higher than the specificactivity of total algal carbon in six of seven experiments.When the specific activity of chlorophyll a is used to calculatethe carbon biomass and growth rate, the carbon biomass of thealgae will thus be underestimated and the specific growth ratewill be too high. Determination of growth rates from incorporationof [³H]adenine gave lower values than those obtained from netorganic carbon assimilation and from ¹⁴C incorporation intochlorophyll a. Problems with adenine saturation are suggested.When [³H]adenine is used to measure growth rates in dense algalcultures, additions of >1 µM [³H]adenine are oftenrequired to maximally label the extracellular and intracellularadenine pools and hence DNA.     

Vitamins, phytoplankton and bacteria: symbiosis or scavenging?

The conclusion that over 25% of global primary production dependson direct algal/bacterial symbiosis involving vitamin B₁₂ [Croftet al., (2005) Algae acquire vitamin B₁₂ through a symbioticrelationship with bacteria. Nature, 438, 90–93] is patentlyfalse, for it is based on a misconception of the probable levelof the vitamin B₁₂ requirement in marine pelagic algae. A reviewof the various published attempts at measuring this requirementsuggests that it is likely to be so low that oceanic and coastalconcentrations of the vitamin would usually be sufficient tosustain the populations that occur without the assistance ofdirect algal/bacterial symbiosis. The levels measured are discussedin relation to method (batch or continuous culture) and protocolsused. Requirement values considered by the author to be acceptablerange from 0.1 to 0.3 pM for the vitamin growth saturation constant(K_S) and from 30 to 100 µL algal biomass pmol^–1vitamin for the yield.     

Influence of subantarctic Macrocystis bed metabolism in diel changes of marine bacterioplankton and CO2 fluxes

The significance of bacterial communities in the fluxes of carbonand energy in giant kelp beds (Macrocystis pyrifera) in KerguelenArchipelago, subantarctica, was estimated by measuring bacterioplanktonbiomass and production over diel cycles in surface seawaterslocated inside and outside of Macrocystis beds. Several physicochemicalparameters [temperature, solar radiation, tide level, dissolvedoxygen, total inorganic carbon (TCO₂), partial pressure of CO₂(pCO₂) and dissolved organic carbon (DOC)] were simultaneouslyrecorded in order to establish possible relationships with observedchanges in bacterial parameters. Bacterial biomass and productionwere significantly higher inside the kelp bed than in the surroundingarea. Furthermore, the results showed large and clear diel variationsof all parameters measured inside the kelp bed. Changes in dissolvedoxygen, TCO₂ and pCO₂ paralleled those of solar radiation, andwere obviously related to the metabolic activity of the kelp.Mean cell volumes and saprophytic bacterial abundance variedover the diel cycles in the same way as photosynthetic activity,while DOC, bacterioplankton production and the frequency ofdividing cells varied in an opposite way with maximal valuesat night-time.     

The Effect of Vapour Pressure Deficit on Carbon Isotope Discrimination in the Desert Shrub Larrea tridentata(Creosote Bush)

Larrea tridentata (creosote bush) seedlings were subjected tothree regimens of atmospheric humidity in a growth chamber experiment.Relative humidity was varied to achieve daytime vapour pressuredeficits (VPD) during growth of 29, 48 and 77 kPa. Photosyntheticgas exchange, carbon isotope composition and biomass productionwere measured after 8–10 weeks of treatment. Whereas stomatalconductance (g) declined linearly with increasing ambient VPD,CO₂ assimilation rate (A) was not measurably affected by changesin ambient VPD. This resulted in a decrease in intrinsic wateruse efficiency (ratio of CO₂ assimilation to stomatal conductance;A/_g) with increasing VPD. Leaf carbon isotope discrimination(A) was negatively correlated (r² = 088) with A/g ratios. Carbonisotope discrimination also correlated positively with ratiosof internal (C₁) to ambient (c_a) CO₂ levels determined by gasexchange measurements (c₁/c). The ratio of c₁ to c_a was lowerat higher VPD levels. Leaf biomass decreased with increasingambient VPD and correlated positively with. Root to leaf biomassratio increased at higher VPD levels and correlated negativelywith. Key words: Larrea tridentata, vapour pressure deficit, carbon isotope discrimination, intrinsic water-use efficiency     

The Growth and Yield Responses ofFragaria ananassato Elevated CO2and N Supply

Strawberry plants (Fragaria ananassaDuchesne var. Elsanta) weregrown in pots at two concentrations of carbon dioxide (partialpressures of 39 and 56 Pa) and with three rates of nitrogensupply (0.04, 0.4 and 4 mMas nutrient solution) to study theirindividual and interactive effects on plant growth and fruityield. Nitrogen deficiency reduced total dry biomass and relativegrowth rate (RGR), mainly through reductions in leaf area ratio(LAR) and plant N concentration (PNC), although both the netassimilation rate (NAR) and root weight ratio (RWR) increased.Elevated CO₂increased the N productivity (NP) but reduced theLAR. High CO₂increased the fruit yield by 42% at high N supplyand by 17% at low N supply. The CO₂yield enhancement occurredthrough an increase in the flower and fruit number of individualplants. This resulted in an increase in the fruit weight ratio(FWR) of plants at high CO₂. Nitrogen deficiency reduced thefruit yield by about 50% through decreases in fruit size, fruitset and the number of fruits. However, N deficiency increasedthe proportion of total plant dry biomass allocated to fruits.There were no significant interactions between CO₂and N supplyon yield.Copyright 1998 Annals of Botany Company Nitrogen; carbon dioxide; strawberry (Fragaria ananassaDuchesne); fruit yield.     

Simulating Growth and Root-shoot Partitioning in Prairie Grasses Under Elevated Atmospheric CO2and Water Stress

We constructed a model simulating growth, shoot-root partitioning,plant nitrogen (N) concentration and total non-structural carbohydratesin perennial grasses. Carbon (C) allocation was based on theconcept of a functional balance between root and shoot growth,which responded to variable plant C and N supplies. Interactionsbetween the plant and environment were made explicit by wayof variables for soil water and soil inorganic N. The modelwas fitted to data on the growth of two species of perennialgrass subjected to elevated atmospheric CO₂and water stresstreatments. The model exhibited complex feedbacks between plantand environment, and the indirect effects of CO₂and water treatmentson soil water and soil inorganic N supplies were important ininterpreting observed plant responses. Growth was surprisinglyinsensitive to shoot-root partitioning in the model, apparentlybecause of the limited soil N supply, which weakened the expectedpositive relationship between root growth and total N uptake.Alternative models for the regulation of allocation betweenshoots and roots were objectively compared by using optimizationto find the least squares fit of each model to the data. Regulationby various combinations of C and N uptake rates, C and N substrateconcentrations, and shoot and root biomass gave nearly equivalentfits to the data, apparently because these variables were correlatedwith each other. A partitioning function that maximized growthpredicted too high a root to shoot ratio, suggesting that partitioningdid not serve to maximize growth under the conditions of theexperiment.Copyright 1998 Annals of Botany Company plant growth model, optimization, nitrogen, non-structural carbohydrates, carbon partitioning, elevated CO₂, water stress,Pascopyrum smithii,Bouteloua gracilis, photosynthetic pathway, maximal growth     

Rates of microbial degradation of dissolved organic carbon from phytoplankton cultures

Dissolved organic carbon (DOC) decay was measured for samplesfrom cultures of the diatoms Chaetoceros gracilis and Phaeodactylumtricornutum, the flagellate Isochrysis galbana, the dinoflagellateAlexandrium tamarense, and a natural algal assemblage from theNorthwest Arm, Nova Scotia, Canada, by a high-temperature catalyticoxidation (HTCO) method. Decay rate constants were determinedusing first-order reaction kinetics in the multi-G model ofBerner (In Early Diagenesis, a Theoretical Approach, PrincetonUniversity Press, 1980). Decay rates as high as 0.37 day^–1wereobtained, which demonstrated that DOC released by phytoplanktonmight be highly labile to bacterial utilization and could bedegraded significantly within hours. Decay rates for most speciestested followed much the same pattern, with K₀₁ values around0.3–0.4, K₀₂ values around 0.03, and K₀₃ and K₀₄ valuesaround 10^–3 day^–1. DOC released by the senescentcells of A.tamarense was found to be essentially bacteria resistant,in contrast to that of the other species tested. The decay ofDOC was directly temperature dependent over the 10–20°Crange. Six methods for DOC preservation were tested. Acidificationwith HCl and refrigerated storage was demonstrated to be themost convenient and practical method. This method can be usedfor both short- and long-term preservation of DOC samples containinghighly labile organic compounds.     

Clonal integration affects growth, photosynthetic efficiency and biomass allocation, but not the competitive ability, of the alien invasive Alternanthera philoxeroides under severe stress

Background and Aims: Many notorious alien invasive plants are clonal, but littleis known about some roles and aspects of clonal integration.Here, the hypothesis is tested that clonal integration affectsgrowth, photosynthetic efficiency, biomass allocation and competitiveability of the exotic invasive weed Alternanthera philoxeroides(Amaranthaceae). Methods: The apical parts of Alternanthera were grown either with orwithout the lawn grass Schedonorus phoenix (tall fescue) andtheir stolon connections to the basal parts grown without competitorswere either severed or left intact. Key Results: Competition greatly reduced the maximum quantum yield of photosystemII (F_v/F_m) and growth (biomass, number of ramets and leaves,total stolon length and total leaf area) of the apical Alternanthera,but not the biomass of S. phoenix. Stolon connections significantlyincreased F_v/F_m and growth of Alternanthera. However, such effectson growth were smaller with than without competition and stolonconnections did not alter the relative neighbour effect of Alternanthera.Stolon connections increased Alternanthera's biomass allocationto roots without competition, but decreased it with competition. Conclusions: Clonal integration contributed little to Alternanthera's competitiveability, but was very important for Alternanthera to exploreopen space. The results suggest that the invasiveness of Alternantheramay be closely related to clonal integration.     

Modelling interactions between phytoplankton and bacteria under nutrient-regenerating conditions

The interactions of phytoplankton and bacteria in a nitrogen-limitedsteady-state system with an organic nitrogen compound or ammoniumas the sole nitrogen source were modelled. The effects of variousalgal excretion rates and two different mathematical representationsof excretion were examined. The model predicted that higherexcretion elevated the bacterial steady-state biomass, and loweredthe algal biomass. Bacterial respiration, which directly determinednitrogen regeneration, had an important effect on the system.The bacterial growth yield in the model was mainly a functionof the growth rate, and not of the nitrogen:carbon ratio ofthe substrate. In one version of the model, where the excretionof organic carbon increased with decreasing growth rate, themodel started to oscillate when the multiplication product ofmaximum specific excretion of excreted organic carbon (EOC)and the bacterial yield on EOC exceeded the dilution rate, irrespectiveof the form of nitrogen (ammonium or dissolved organic nitrogen)in the medium. The model results were compared with chemostatexperiments with the alga Emiliania huxleyi and a bacterialisolate in pure and mixed culture at two different dilutionrates. The carbon and nitrogen biomass of the bacteria was {smalltilde}1.5 times higher in mixed culture than in pure culture.In the experiments with low dilution rate, the recovery of nitrogenin the form of biomass, ammonium or amino acids was low, suggestingthe excretion by the algae of a refractory nitrogen-containingproduct which the bacteria could not use.     

Physiological Responses of Phytoflagellates to Dissolved Organic Substrate Additions. 2. Dominant Role of Autotrophic Nutrition in Pyrenomonas salina (Cryptophyceae)

The enhancement of algal growth by organic substrate assimilationis a common laboratory observation, yet few studies have addressedthe interaction of dissolved organic compounds and environmentalfactors for controlling the relative contribution of heterotrophyand autotrophy to the nutrition of these algae. The effectsof light intensity and glycerol addition on the growth, cellvolume, pigmentation, and carbon uptake of the facultative heterotroph,Pyrenomonas salina Santore, were examined. Glycerol additionto cultures growing at a limiting light intensity increasedthe growth rate, increased the average cell volume and cellularstarch content, decreased the cellular phycoerythrin to chlorophyll ratio, and had no effect on the CO₂ fixation rate cell^–1.Glycerol addition to cultures growing at a moderate light intensitythat was saturating for photo-autotrophic growth increased theaverage cell volume and cellular starch content but had no effecton the CO₂ fixation rate cell^–1. The results indicatethat autotrophy was the major process for carbon acquisitionduring the growth of P. salina, but that carbon acquisitionfrom glycerol catabolism also was used to partially supportgrowth of the alga at the limiting light intensity. In addition,glycerol presumably was used to fulfill the energy and/or reductantrequirements of the alga, and to increase the reserve carbohydrate(starch). ¹ Current address and address for correspondences: Horn PointEnvironmental Laboratories, University of Maryland, PO Box 775,Cambridge, Maryland 21613, U.S.A. (Received October 29, 1990; Accepted May 31, 1991)     

Short-term changes of protozoan control on autotrophic picoplankton in an oligo-mesotrophic lake

In May 1994, we investigated the short-term development of theplanktonic community in the epi- and metalimnion of an oligo-mesotrophiclake (Piburger See, Tyrol), focusing on trophic links betweenprotists and picoplankton, but also including phyto- and zooplankton.Uptake experiments with fluorescently labelled bacteria (FLB)and picocyanobacteria (FIC) were performed in order to comparethe importance of both prey types as carbon sources for bacterivorousprotists. Heterotrophic nanoflagellates (HNF) were responsiblefor {small tilde}90% of total protozoan picoplanktivory (FLB+ FLC); ciliates accounted for {small tilde}10%. A selectivityindex related to prey density showed that both HNF and ciliatesclearly preferred FLC over FLB. The mean cell size of autotrophic(prokaryotic) picoplankton (APP) was nearly three times larger(0.323 µm³) and much less variable than mean bacterialcell volume (0.122 µm³). Although APP biomass was on averageonly 8.6% of total picoplankton biomass, pico-cyanobacteriaaccounted for a mean 15.9% of total HNF carbon uptake. We calculatedthat total HNF grazing could match potential APP maximum growthrates at the beginning of the study period. A strong decreasein HNF individual clearance rate (CR) on APP was clearly relatedto a fall in the percentage of choanofiagellates (from 75 to{small tilde}10% of the HNF community). A simultaneous decreasein HNF biomass and CR was followed by a steep increase in APPabundance; APP abundance and HNF biomass were highly negativelycorrelated both in the epi- and the metalimnion (r_{1 EM} = –0.879,r_{1 META} = =0.907; P = 0.001). Total rotifer abundance increasedby a factor of 50 within 2 weeks and was also negatively correlatedwith HNF biomass (r_{1 EM} = –0.852, P < 0.001; r_{1 META}= –0.659, P < 0.05). HNF grazing was found to exerta strong short-term control on picocyanobacteria and this linkwas probably broken by an increase in metazooplankton, especiallydue to rotifer predation on HNF.     

Different growth responses of C3 and C4 grasses to seasonal water and nitrogen regimes and competition in a pot experiment

Understanding temporal niche separation between C₃ and C₄ species(e.g. C₃ species flourishing in a cool spring and autumn whileC₄ species being more active in a hot summer) is essential forexploring the mechanism for their co-existence. Two parallelpot experiments were conducted, with one focusing on water andthe other on nitrogen (N), to examine growth responses to wateror nitrogen (N) seasonality and competition of two co-existingspecies Leymus chinensis (C₃ grass) and Chloris virgata (C₄grass) in a grassland. The two species were planted in eithermonoculture (two individuals of one species per pot) or a mixture(two individuals including one L. chinensis and one C. virgataper pot) under three different water or N seasonality regimes,i.e. the average model (AM) with water or N evenly distributedover the growing season, the one-peak model (OPM) with morewater or N in the summer than in the spring and autumn, andthe two-peak model (TPM) with more water or N in the springand autumn than in the summer. Seasonal water regimes significantlyaffected biomass in L. chinensis but not in C. virgata, whileN seasonality impacted biomass and relative growth rate of bothspecies over the growing season. L. chinensis accumulated morebiomass under the AM and TPM than OPM water or N treatments.Final biomass of C. virgata was less impacted by water and Nseasonality than that of L. chinensis. Interspecific competitionsignificantly decreased final biomass in L. chinensis but notin C. virgata, suggesting an asymmetric competition betweenthe two species. The magnitude of interspecific competitionvaried with water and N seasonality. Changes in productivityand competition balance of L. chinensis and C. virgata undershifting seasonal water and N availabilities suggest a contributionof seasonal variability in precipitation and N to the temporalniche separation between C₃ and C₄ species. Key words: Chloris virgata, competition, growth, Leymus chinensis, nitrogen seasonality, water seasonality Received 19 November 2007; Revised 29 January 2008 Accepted 4 February 2008     

Sinking losses of phytoplankton in closed limnetic systems

Specific algal recoveries from sediment traps of two differentdesigns and from mud surface deposits of large experimentalenclosures (Lund Tubes) were monitored during 1978 and are analyzedin relation to the vertical and temporal distribution of tendominant phytoplankton populations. Sedimentation accounts fordiffering proportions of the total loss of biomass for differentalgae: between 28 and 100% of diatoms; 15–95% of Eudorina;<4% of populations of small algae (spp. ofAnkyra, Chromulina,Cryptomonas). Rates of diatom loss are also derived from thecomparison of net rates of change (k_n) and the silica uptake-derivedgrowth rate (k¹); intrinsic sinking behaviour may be specificallyregulated in relation to growth conditions. Implications inthe calculation of sedimentary losses and their impact uponthe seasonal periodicity of phytoplankton are briefly discussed.     

The Influence of Nitrate and Ammonium Nutrition on the Growth of Wheat (Triticum aestivum) and Maize (Zea mays) Plants

The effects of NO^-₃ and NH⁺₄ nutrition on hydroponically grownwheat (Triticum aestivum L.) and maize (Zea mays L.) were assessedfrom measurements of growth, gas exchange and xylem sap nitrogencontents. Biomass accumulation and shoot moisture contents ofwheat and maize were lower with NH⁺₄ than with NO^-₃ nutrition.The shoot:root ratios of wheat plants were increased with NH⁺₄compared to NO^-₃ nutrition, while those of maize were unaffectedby the nitrogen source. Differences between NO^-₃ and NH⁺₄-fedplant biomasses were apparent soon after introduction of thenitrogen into the root medium of both wheat and maize, and thesedifferences were compounded during growth. Photosynthetic rates of 4 mM N-fed wheat were unaffected bythe form of nitrogen supplied whereas those of 12 mM NH⁺₄-fedwheat plants were reduced to 85% of those 12 mM NO^-₃-fed wheatplants. In maize supplied with 4 and 12 mM NH⁺₄ the photosyntheticrates were 87 and 82% respectively of those of NO^-₃-fed plants.Reduced photosynthetic rates of NH⁺₄ compared to NO^-₃-fed wheatand maize plants may thus partially explain reduced biomassaccumulation in plants supplied with NH⁺₄ compared to NO^-₃ nutrition.Differences in the partitioning of biomass between the shootsand roots of NO^-₃-and NH⁺₄-fed plants may also, however, arisefrom xylem translocation of carbon from the root to the shootin the form of amino compounds. The organic nitrogen contentof xylem sap was found to be considerably higher in NH⁺₄- thanin NO^-₃-fed plants. This may result in depletion of root carbohydrateresources through translocation of amino compounds to the shootin NH⁺₄-fed wheat plants. The concentration of carbon associatedwith organic nitrogen in the xylem sap of maize was considerablyhigher than that in wheat. This may indicate that the shootand root components of maize share a common carbon pool andthus differences induced by different forms of inorganic nitrogenare manifested as altered overall growth rather than changesin the shoot:root ratios.Copyright 1993, 1999 Academic Press Triticum aestivum, wheat, Zea mays, maize, nitrogen, growth, photosynthesis, amino acids, xylem     

Excretion of glycolate during synchronous culture of Ankistrodesmus braunii in the presence of disalicylidenepropanediamine or hydroxypyridinemethanesulfonate

The rate of excretion of glycolate by the unicellular greenalga Ankistrodesmus braunii changes during its life cycle. Itis high in the main growth phase during the light period witha maximum 6 hr after the start of illumination, and low duringthe period of cell division in the dark. The glycolate excretion is stimulated by DSPD and HPMS, whilethe total ¹⁴CO₂-fixation is inhibited by DSPD and enhanced byHPMS. Changes in the effects of DSPD and HPMS on glycolate excretionas well as on photosynthetic ¹⁴CO₂-fixation during the courseof the algal life cycle were followed using the technique ofsynchronous culture. How far the change of glycolate excretion is due to a changeof glycolate oxidase activity during the life cycle and to achange of C₂-supply from the carbon reduction cycle is discussed.The effect of DSPD on glycolate excretion suggests a participationof ferredoxin in the glycolate pathway. (Received August 10, 1968; )     

Changes of algal biomass as carbon, cell number and volume, in bottles suspended in Lake Constance

Changes of algal biomass, as carbon, cell numbers and volumewere determined for phytoplankton of Lake Constance suspendedin situ in 2 l glass bottles. Phytoplankton placed at the 6%surface penetrating light level (photosynthetically availableradiation) were close to the compensation depth for growth estimatedas total particulate carbon and total cell volumes. Cell countsof individual alga] species however, showed appreciable growthof diatoms offset by the decline of flagellates. Bottles suspendedat two shallower depths in a separate experiment showed somegrowth of all species and indicated a vertical niche separationof growth of Rhodomonas minuta Skuja and R. lens Dascher andRuttner in accordance with their vertical distribution. ^*This paper is the result of a study made at the Group for AquaticPrimary Productivity (GAP) First International Workshop heldat the Limnological Institute, University of Konstanz, in April1982.     

Biomass-pigment relationships in potamoplankton

During most of the growing season of 1994, pigment content,as determined by HPLC analysis of algal sample extracts, wasfollowed in the River Meuse (Belgium) potamoplankton. The concentrationof some algal pigments (chlorophylls a and b, fucoxanthin, lutein,echinenone and alloxanthin) was related to biomass estimatesof total phytoplankton and of major taxonomic components (diatoms,green algae, cyanobacteria and cryptomonads). Highly significantlinear regressions were obtained for chlorophyll a-total biomass,fucoxanthin-diatoms, lutein-green algae, chlorophyll b-greenalgae. However, no relationship was found for cyanobacteriaor cryptomonads and their specific pigments, which may be attributedto poor accuracy of biomass estimates for these non-dominantalgae. In conclusion, the good relationship found for dominantalgae and their specific pigments confirms the value of pigmentsas quantitative markers of phytoplankton, as detected in othermarine and freshwater environments.