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1.
Response to nutrient enrichment by the plankton of Antarctic coastal lakes and the inshore Ross Sea 总被引:2,自引:0,他引:2
Summary Water samples from coastal lakes and ponds on Ross Island (77°S) and from the adjacent Ross Sea were analyzed to determine nutrient supply relative to the population size of planktonic algae and bacteria. An enrichment test was applied to each water to measure N and P accumulation by the seston as a guide to nutrient demand and deficiency. In all waters, including the sea, the dissolved inorganic N-to-P ratios were low, but inorganic nitrogen was generally present at concentrations that satisfied or exceeded the current growth requirements of the algae. None of the samples responded to added P, and only 3 of the 13 plankton assemblages tested responded positively to nitrogen enrichment. These waters are therefore characterized by an abundance of resources relative to demand. This apparently r-selecting coastal environment contrasts markedly in many ecosystem properties with the inland meromictic lakes of Antarctica. 相似文献
2.
In a coastal area of southern Chile (41° S), the major ammoniumassimilating enzyme glutamine synthetase (GS) was detected ina green dinoflagellate bloom during April 2003. High chlorophylla concentrations (1000 µg L1) attributable to Gymnodiniumcf. chlorophorum in surface waters were associated with highand very low nitrate reductase activities. Coincident with thebloom, dissolved inorganic nitrogen concentrations were nearthe detection limit (NO3 + NH4+ <0.5 µM). SinceGS correlates with the use of ammonium as an external nitrogensource, we suggest that GS activity seems to be a good indicatorof ammonium utilization in a period dominated by a single dinoflagellatespecies. 相似文献
3.
Ammonium release by zooplankton in suspensions of heat-killed algae and an evaluation of the flow-cell method 总被引:1,自引:0,他引:1
Vanderploeg Henry A.; Laird Gwenyth A.; Liebig James R.; Gardner Wayne S. 《Journal of plankton research》1986,8(2):341-352
The maximum excretion rate of NH4 (39 nmol mg dry wt1h1) was directly measured for Daphnia pulex by measuringNH4 accumulation in bottles containing D. pulex and dense, satiatingsuspensions of heat-killed algae. Ammonium release rates inthe algal suspensions were compared to those of individual animalsremoved from the suspension and placed in flow cells. Ammoniumrelease rate, R (nmol mg dry wt1 h1). in the flowcell decreased very rapidly with time, t (min), after removalaccording to the relation R = 26 + 25e0.16t. Ammoniumexcretion obtained by the flow cell method after extrapolationto time zero was not significantly different from that obtainedin the bottles. The considerable experiment-to-experiment variationin NH4 excretion was in large part correlated (r2 = 0.73) withthe feeding rate on the algae. 相似文献
4.
MARQUES I. A.; OBERHOLZER M. J.; ERISMANN K. H. 《Journal of experimental botany》1985,36(11):1685-1697
Marques, I. A., Oberholzer, M. J. and Erismann, K. H. 1985.Metabolism of glycollate by Lemna minor L. grown on nitrateor ammonium as nitrogen source.J. exp. Bot. 36: 16851697. Duckweed, Lemna minor L., grown on inorganic nutrient solutionscontaining either NH4+ or NO3 as nitrogen source wasallowed to assimilate [1-14C]- or [2-14C]glycollate during a20 min period in darkness or in light. The incorporation ofradioactivity into water-soluble metabolites, the insolublefraction, and into the CO2 released was measured. In additionthe extractable activity of phosphoenolpyruvate carboxylasewas determined. During the metabolism of [2-14C]glycollate in darkness, as wellas in the light, NH4+ grown plants evolved more 14CO2 than NO3grown plants. Formate was labelled only from [2-14C]glycollateand in NH4+ grown plants it was significantly less labelledin light than in darkness. In NO3 grown plants formateshowed similar radioactivity after dark and light labelling.The radioactivity in glycine was little influenced by the nitrogensource. Amounts of radioactivity in serine implied that thefurther metabolism of serine was reduced in darkness comparedwith its metabolism in the light under both nitrogen regimes.In illuminated NH4+ plants, serine was labelled through a pathwaystarting from phosphoglycerate. After [1-14C]glycollate feedingNH4+ grown plants contained markedly more radioactive aspartateand malate than NO3 plants indicating a stimulated phosphoenolpyruvatecarboxylation in plants grown on NH4+. Key words: Photorespiration, glycollate, nitrogen, Lemna 相似文献
5.
Differential filtration was used to apportion [32p]orthophosphate(P1) uptake to predominantly bacterial (<3 µm) or algal(>3 µm) components of Lake Kinneret microplankton.Bacteria generally showed preferential 32Pi uptake in comparisonwith algae. Nevertheless, in most cases, the relative proportionof 32P counts retained on 3 µm filters was greater thanthe proportion of 14C counts from heterotrophic bacterial incorporationof [14Clglucose, indicating that algae were competing for Piwith bacteria with some measure of success. Most time courseexperiments did not show any consistent transfer of 32P frombacteria to algae. The addition of a bacterial inhibitor (garamycin)caused a relative increase in the proportion of algal to bacterial32Pi uptake. Added organic P substrates lowered the amount of32Pi uptake and appeared to be preferentially utilized by bacteria.Apparent residence times for Pi in Lake Kinneret ranged from0.4 h (prior to overturn) to 17.4 h during bomothermy. Despitelow ambient Pi concentrations, P limitation in Lake Kinneretis not as extreme as in many other aquatic environments. 相似文献
6.
Enrichment cultures of littoral benthic algae from Mono Lake, California, and Abert Lake, Oregon, were grown under conditions of varied salinity and nutrient content. Field-collected inocula were composed mainly of diatoms and filamentous blue-green and green algae. The yield of long-term cultures (30 days) showed tolerance over a broad salinity range (50–150 g·L?1) for Mono Lake-derived algae. Algae from Abert Lake had a lower range of tolerance (25–100 g·L?1) Organic content and pigment concentrations of algae from both lakes were also reduced above the tolerated salinity level. Within the range of salinity tolerance for Mono Lake algae, initial growth rates and organic content were reduced by increased salinity. The effects of macro- and micronutrient enrichment on algal growth in Mono Lake water were also tested. Only nitrogen enrichment (either as ammonium or nitrate) stimulated algal growth. Although the benthic algae cultured here had wide optima for salinity tolerance, the rates of growth and storage were limited by increased salinity within the optimum range. Although the lakes compared had similar species composition, the range and limits of tolerance of the algae were related to salinity of the lake of origin. 相似文献
7.
We examined the NO3 and NH4+ uptake capabilities of thedinoflagellate Peridinium cinctum and of the accompanying nanoplanktonduring the spring P. cinctum bloom in Lake Kin-neret. Throughoutthe Peridinium season, the smaller algae had greater affinitiesand faster specific uptake rates for both NO3and NH4+It appears that P. cinctum cannot directly compete with nanoplanktonfor nitrogen nutrients. Other factors such as the ability ofdinoflagellates to swim freely in the water column and low grazingpressures may explain their dominance in the lake. 相似文献
8.
Priscu John C.; Vincent Warwick F.; Howard-Williams Clive 《Journal of plankton research》1989,11(2):335-351
The isotope 15N was used to examine nitrogen dynamics in LakesFryxell and Vanda, two permanently ice-covered Antarctic lakes.Half-saturation constants for NH4+. uptake in the shallow watersof both lakes were <10 µg N l1; uptake kineticexperiments on populations forming the deep-chlorophyll layersof these lakes showed zero-order kinetics and could not be fittedwith the Michaelis-Menten equation. Elevated uptake within thefirst few minutes following pulses of NH4+. and NO3 occurredin both lakes. NH4+ regeneration, determined from isotope dilutionexperiments, exceeded uptake at 4.6 m in Lake Fryxell, was lessthan uptake at 9 m in Lake Fryxell and was equal to uptake at10 m in Lake Vanda under the experimental conditions. NO3uptake was suppressed by NH4+ levels as low as 2 µg NH4+-N l1 in Lake Fryxell; the suppression was strongestin the near-surface populations. Substrate-saturated C:N uptakeratios (g:g) in Lake Fryxell decreased from 8.4 near the surfaceto 1.8 at the bottom of the trophogenic zone. Overall, the nitrogendynamics in these lakes are similar to other lakes and the openocean in that biological productivity during the austral summeris supported by regenerated nutrients. 相似文献
9.
Uptake capabilities for ammonium (NH4+) and urea by diatoms(Thalassiosira pseudonana and Skeletonema costatum) growingon oxidized forms of nitrogen were studied in short-term uptakeexperiments. Even when nutrient-saturated, an enhanced uptakecapability not coupled with the growth rate was present forNH4+ and urea. No such enhanced uptake ability was seen forNO2 or NO3 under either nutrient-saturated ornutrient-depleted conditions. The presence of NH4+ decreasedthe enhanced ability to take up urea, but the urea uptake ratein 5 min incubations remained greater than the growth rate evenwhen NH4+ was present. 相似文献
10.
Varela Marta M.; Barquero Susana; Bode Antonio; Fernandez Emilio; Gonzalez Nicolas; Teira Eva; Varela Manuel 《Journal of plankton research》2003,25(7):719-736
Ammonium regeneration and dissolved organic nitrogen (DON) releasewere studied experimentally in the euphotic zone of shelf andoceanic waters of NW Spain in relation to coastal upwellingdynamics and the size-structure of phytoplankton communities.Incubations of plankton labelled with [15N]ammonium were madeduring four cruises, two of which also included size-fractionateddeterminations of chlorophyll a and primary production, andexperimental determinations of production rates of dissolvedorganic carbon (DOC) using 14C. Inorganic nitrogen concentrationswere mainly related to nitrate enrichment by upwelling pulses,while ammonium concentrations were generally low in all situations.Ammonium did not accumulate in the study area, suggesting adaily time scale coupling between regeneration and uptake. Incontrast, DON largely exceeded inorganic nitrogen in all situationsand generally increased from spring to autumn. Ammonium regenerationwas positively correlated with DON release and both rates showedthe largest variation in summer, with minimum values duringactive upwelling and maximum values when upwelling relaxed.Comparison of DON stocks and rates in different shelf areassuggests that DON release near the coast during summer was morepersistent in the water than DON release in off-shelf and oceanicareas. The carbon:nitrogen ratio of DOC and DON release rateswas highly variable, revealing a large excess of DOC comparedwith DON. This excess can be attributed to either an underestimateof total DON release (as only release from ammonium was measured)or to an enhanced production of carbon-rich organic substancesby diatoms in coastal areas. By considering a broad range oftrophic situations, this study reveals a fundamental differencebetween short term release of DOC and DON by plankton. Physiologicalprocesses (such as carbohydrate exudation by diatoms) seem tobe the cause of large DOC excess, whereas trophic processes(such as grazing) are more likely the cause of enhanced DONrelease. 相似文献
11.
In highly eutrophic ponds, buoyancy of the gas-vacuolate blue-green alga Anabaenopsis Elenkinii (Miller) was regulated by complex interactions between chemical and physical parameters, as well as by biological interactions
between various trophic levels. Algal buoyancy and surface bloom formation were enhanced markedly by decreased light intensity,
and to a lesser extent by decreased CO2 availability and increased availability of inorganic nitrogen. In the absence of dense populations of large-bodied Cladocera,
early season blooms of diatoms and green algae reduced light availability in the ponds thus creating conditions favorable
for increased buoyancy and bloom formation by A. Elenkinii. The appearance of blue-green algal blooms could be prevented by a reduced density of planktivorous fish, which allowed development
of dense cladoceran populations. The cladocerans limited the growth of precursory blooms of diatoms and green algae, and given
the resulting clear-water conditions, buoyancy of A. Elenkinii was reduced, and blue-green algal blooms never appeared. 相似文献
12.
Macduff, J. H., Hopper, M. J. and Wild, A. 1987. The effectof root temperature on growth and uptake of ammonium and nitrateby Brassica napus L. CV. Bien venu in flowing solution culture.II. Uptake from solutions containing NH4NO3.J. exp. Bot.38: 5366 The effects of root temperature on uptake and assimilation ofNH4+ and NO3 by oilseed rape (Brassica napus L. CV. Bienvenu) were examined. Plants were grown for 49 d in flowing nutrientsolution at pH 6?0 with root temperature decrementally reducedfrom 20?C to 5?C; and then exposed to different root temperatures(3, 5, 7, 9, 11, 13, 17 or 25?C) held constant for 14 d. Theair temperature was 20/15?C day/night and nitrogen was suppliedautomatically to maintain 10 mmol m3 NH4NO3 in solution.Total uptake of nitrogen over 14 d increased threefold between313?C but was constant above 13?C. Net uptake of NH4+exceeded that of NO3 at all temperatures except 17?C,and represented 4765% of the total uptake of nitrogen.Unit absorption rates of NH4+ and of 1?52?7 for NO3suggested that NO3 absorption was more sensitive thanNH4+ absorption to temperature. Rates of absorption were relativelystable at 3?C and 5?C compared with those at 17?C and 25?C whichincreased sharply after 10 d. Tissue concentration of N in theshoot, expressed on a fresh weight basis, was independent ofroot temperature throughout, but doubled between 325?Cwhen expressed on a dry weight basis. The apparent proportionof net uptake of NO3 that was assimilated was inverselyrelated to root temperature. The results are used to examinethe relation between unit absorption rate adn shoot:root ratioin the context of short and long term responses to change ofroot temperature Key words: Brassica napus, oilseed rape, root temperature, nitrogen uptake 相似文献
13.
Influence of nitrate on uptake of ammonium by nitrogen-depleted soybean: is the effect located in roots or shoots? 总被引:4,自引:1,他引:3
Saravitz Carole H.; Chaillou Sylvain; Musset Joanne; Raper C. David Jr.; Morot-Gaudry Jean-Francis 《Journal of experimental botany》1994,45(11):1575-1584
In non-nodulated soybean [Glycine max (L.) Merrill cv. Ransom]plants that were subjected to 15 d of nitrogen deprivation inflowing hydroponic culture, concentrations of nitrogen declinedto 1.0 and 1.4mmol Ng1 dry weight in shoots and roots,respectively, and the concentration of soluble amino acids (determinedas primary amines) declined to 40µmol g1 dry weightin both shoots and roots. In one experiment, nitrogen was resuppliedfor 10 d to one set of nitrogen-depleted plants as 1.0 mol m3NH4+ to the whole root system, to a second set as 0.5 mol m3NH4+ plus 0.5 mol m3 NO3 to the whole root system,and to a third set as 1.0 mol m3 NH4+ to one-half ofa split-root system and 1.0 mol m3 NO3 to theother half. In a second experiment, 1.0 mol m3 of nitrogenwas resupplied for 4 d to whole root systems in NH4+ : NO3ratios of 1:0, 9:1, and 1:1. Nutrient solutions were maintainedat pH 6.0. When NH4+ was resupplied in combination with NO3 to thewhole root system in Experiment I, cumulative uptake of NH4+for the 10 d of resupply was about twice as great as when NH4+was resupplied alone. Also, about twice as much NH4+ as NO3was taken up when both ions were resupplied to the whole rootsystem. When NH4+ and NO3 were resupplied to separatehalves of a split-root system, however, cumulative uptake ofNH4+ was about half that of NO3. The uptake of NH4+,which is inhibited in nitrogen-depleted plants, thus is facilitatedby the presence of exogenous NO3, and the stimulatingeffect of NO3 on uptake of NH4+ appears to be confinedto processes within root tissues. In Experiment II, resupplyof nitrogen as both NH4+ and NO3 in a ratio of either1:1 or 9:1 enhanced the uptake of NH4+. The enhancement of NH4+uptake was 1.8-fold greater when the NH4+: NO3-resupplyratio was 1:1 than when it was 9:1; however, only 1.3 timesas much NO3 was taken up by plants resupplied with the1 :1 exogenous ratio. The effect of NO3 on enhancementof uptake of NH4+ apparently involves more than net uptake ofNO3 itself and perhaps entails an effect of NO3uptake on maintenance of K+ availability within the plant. Theconcentration of K+ in plants declined slightly during nitrogendeprivation and continued to decline following resupply of nitrogen.The greatest decline in K+ concentration occurred when nitrogenwas resupplied as NH4+ alone. It is proposed that decreasedavailability of K+ within the NH4+-resup-plied plants inhibitedNH4+ uptake through restricted transfer of amino acids fromthe root symplasm into the xylem. Key words: Ammonium, Glycine max, nitrate, nitrogen-nutrition, nitrogen stress, split-root cultures 相似文献
14.
Seedlings of Ricinus communis L. cultivated in quartz sand weresupplied with a nutrient solution containing either 1 mol m3NO3 or 1 mol m3 NH+4 as the nitrogen source. Duringthe period between 41 and 51 d after sowing, the flows of N,C and inorganic ions between root and shoot were modelled andexpressed on a fresh weight basis. Plant growth was clearlyinhibited in the presence of NH+4. In the xylem sap the majornitrogenous solutes were nitrate (74%) or glutamine (78%) innitrate or ammonium-fed plants, respectively. The pattern ofamino acids was not markedly influenced by nitrogen nutrition;glutamine was the dominant compound in both cases. NH+4 wasnot transported in significant amounts in both treatments. Inthe phloem, nitrogen was transported almost exclusively in organicform, glutamine being the dominant nitrogenous solute, but theN-source affected the amino acids transported. Uptake of nitrogenand carbon per unit fresh weight was only slightly decreasedby ammonium. The partitioning of nitrogen was independent ofthe form of N-nutrition, although the flow of nitrogen and carbonin the phloem was enhanced in ammonium-fed plants. Cation uptakerates were halved in the presence of ammonium and lower quantitiesof K+, Na+ and Ca2+ but not of Mg2+ were transported to theshoot. As NH+4 was balanced by a 30-fold increase in chloride in thesolution, chloride uptake was increased 6-fold under ammoniumnutrition. We concluded that ammonium was predominantly assimilated inthe root. Nitrate reduction and assimilation occurred in bothshoot and root. The assimilation of ammonium in roots of ammonium-fedplants was associated with a higher respiration rate. Key words: Ricinus communis, nitrogen nutrition (nitrate/ammonium), phloem, xylem, transport, partitioning, nitrogen, carbon, potassium, sodium, magnesium, calcium, chloride 相似文献
15.
Rideout James W.; Chaillou Sylvain; Raper C. David Jr; Morot-Gaudry Jean-Francois Jr 《Journal of experimental botany》1994,45(1):23-33
Soybean [Glycine max (L.) Merrill] plants that had been subjectedto 15 d of nitrogen deprivation were resupplied for 10 d with1.0 mol m3 nitrogen provided as NO3, NH4+, orNH4++NO3 in flowing hydroponic culture. Plants in a fourthhydroponic system received 1.0 mol m3 NO3 duringboth stress and resupply periods. Concentrations of solublecarbohydrates and organic acids in roots increased 210 and 370%,respectively, during stress. For the first day of resupply,however, specific uptake rates of nitrogen, determined by ionchromatography as depletion from solution, were lower for stressedthan for non-stressed plants by 43% for NO3- resupply, by 32%for NH4+ + NO3 resupply, and 86% for NH4+ resupply. Whenspecific uptake of nitrogen for stressed plants recovered torates for non-stressed plants at 6 to 8 d after nitrogen resupply,carbohydrates and organic acids in their roots had declinedto concentrations lower than those of non-stressed plants. Recoveryof nitrogen uptake capacity of roots thus does not appear tobe regulated simply by the content of soluble carbon compoundswithin roots. Solution concentrations of NH4+ and NO3 were monitoredat 62.5 min intervals during the first 3 d of resupply. Intermittenthourly intervals of net influx and net effluxoccurred. Rates of uptake during influx intervals were greaterfor the NH4+ -resupplied than for the NO3 -resuppliedplants. For NH4+ -resupplied plants, however, the hourly intervalsof efflux were more numerous than for NO3 -resuppliedplants. It thus is possible that, instead of repressing NH4+influx, increased accumulation of amino acids and NH4+ in NH4+-resupplled plants inhibited net uptake by stimulation of effluxof NH4+ absorbed in excess of availability of carbon skeletonsfor assimilation. Entry of NH4+ into root cytoplasm appearedto be less restricted than translocation of amino acids fromthe cytoplasm into the xylem. Key words: Ammonium, nitrate, nitrogen-nutrition, nitrogen-stress, soybean 相似文献
16.
The significance of nitrogen for algal growth was studied in Lake Vesijärvi in 1979 and 1980 by algal bioassay, using Selenastrum capricornutum and Anabaena cylindrica as test organisms. Nitrogen limited the growth of Selenastrum for the major part of the investigation period, while phosphorus seemed to be the most limiting factor for Anabaena. This difference was reflected in the in situ succession of phytoplankton. As the ratio of inorganic nitrogen to phosphate phosphorus became smaller, nitrogen-fixing blue-green algae became dominant. Nitrogen fixation was greatest at the beginning of July, coinciding with maximum heterocyst numbers. 相似文献
17.
In studies of Trifolium repens nitrogen nutrition, the controlof nutrient solution pH using dipolar buffers, was evaluatedin tube culture under sterile conditions. Five buffers; MES,ADA, ACES, BES and MOPS with pK2s (20 °C) of 6.15, 6.60,6.90, 7.15 and 7.20 respectively, at a concentration of 2.0mol m3, were provided to inoculated Trifolium repensgrowing in nutrient solution containing 7.13 mol m3 nitrogenas (NH4)2SO4. Initial pH of each solution was adjusted to theappropriate buffer pK2 Two buffers, ADA and ACES completelyinhibited plant growth. The remaining buffers had little effectin limiting pH change, although plant dry matter was higherand nodule numbers lower in the presence of these buffers. MESand MOPS were supplied to nutrient solutions with and without7.13 mol m3 (NH4)2SO4, at concentrations ranging from012 mol m3. MES at 9 mol m3 and 12 molm3 reduced growth of plants reliant on the symbiosisfor providing nitrogen. The provision of MES to plants providedwith NH4+ significantly increased plant yield and reduced nodulenumber at all concentrations. MOPS did not affect plant yieldor nodule number. The use of dipolar buffers in legume nitrogennutrition studies is considered in terms of buffering capacity,and the side effects on plant growth and symbiotic development. Key words: Ammonium, Dipolar buffer, Nitrogen nutrition, pH control, Symbiosis, Trifolium repens 相似文献
18.
Dynamic Interactions between Root NH4+ Influx and Long-Distance N Translocation in Rice: Insights into Feedback Processes 总被引:3,自引:0,他引:3
Kronzucker Herbert J.; Schjoerring Jan K.; Erner Yair; Kirk Guy J.D.; Yaeesh Siddiqi M.; Glass Anthony D.M. 《Plant & cell physiology》1998,39(12):1287-1293
Ammonium influx into roots and N translocation to the shootswere measured in 3-week-old hydroponically grown rice seedlings(Oryza sativa L., cv. IR72) under conditions of N deprivationand NH4+ resupply, using 13NH4+as a tracer. Root NH4+ influxwas repressed in plants continuously supplied with NH4+ (at0.1 mM), but a high proportion of absorbed N (20 to 30%) wastranslocated to the shoot in the form of N assimilates duringthe 13-min loading and desorption periods. Interruption of exogenousNH4+ supply for periods of 1 to 3 d caused NH4+ influx to bede-repressed. This same treatment caused N translocation tothe shoot to decline rapidly, until, by 24 h, less than 5% ofthe absorbed 13N was translocated to the shoot, illustratinga clear priority of root over shoot N demand under conditionsof N deprivation. Upon resupplying 1 mM NH4+, root NH4+ influxresponded in a distinct four-phase pattern, exhibiting periodsin which NH4+ influx was first enhanced and subsequently reduced.Notably, a 25 to 40% increase in root influx, peaking at {smalltilde}2 h following re-exposure was correlated with a 4- to5-fold enhancement in shoot translocation and a repression ofroot GS activity. The transient increase of NH4+ influx wasalso observed in seedlings continuously supplied with NO3and subsequently transferred to NH4+. Extended exposure to NH4+caused root NH4+ influx to decrease progressively, while shoottranslocation was restored to {small tilde}30% of incoming NH4+.The nature of the feedback control of NH4+ influx as well asthe question of its inducibility are discussed. (Received August 7, 1998; Accepted September 21, 1998) 相似文献
19.
Changes in the growth rates of saline-lake diatoms in response to variation in salinity, brine type and nitrogen form 总被引:4,自引:0,他引:4
The growth rates of four saline-lake diatom taxa were measuredunder varying conditions of salinity (5, 8 and 11), brine type(sulfate- versus bicarbonate-dominated) and nitrogen form (NH4+versus NO3), using a full factorial design. With NO3as the nitrogen source, Cyclotella quillensis, Cymbella pusillaand Anomoeoneis costata exhibited lower growth rates in thesulfate versus bicarbonate media. The strain of Chaetoceroselmorei used in these experiments, isolated from a sulfate-dominatedlake, was unable to grow on NO3 alone. In the NH4+ treatments,neither salinity nor brine type affected the growth rates ofC.quillensis or C.elmorei. When supplied with NH4+, C.pusillaand A.costata had higher growth rates in the bicarbonate versussulfate media, although for C.pusilla the difference on NH4+was not as great as on NO3. The impact of brine typeon NO3 use is consistent with the theory that sulfateinhibits molybdate uptake, as molybdenum is required for NO3use but not NH4+. Cymbella pusilla was the only taxon affectedby changes in salinity. The four taxa used in these experimentsare frequently found in saline lakes and saline-lake sediments,hence they are used in paleoclimate reconstructions; the resultspresented here provide additional information that may enhancethese diatom-based reconstructions. 相似文献
20.
Takahashi Kazushi; Yoshioka Takahito; Wada Eitaro; Sakamoto Mitsuru 《Journal of plankton research》1990,12(4):799-808
Temporal variations in carbon isotope ratio of phytoplanktonand dissolved inorganic carbon (DIC) in Lake Suwa were reported.In summer, blooming of Microcystis spp. resulted in low concentrationsof DIC and high pH, and HCO3 was the prominent speciesof DIC. Chlorophyll-specific rates of photosynthesis were relativelyconstant irrespective of the algal biomass during summer. Carboxylationin photosynthesis of Microcystis spp. was mainly catalyzed byribulose bisphosphate carboxylase (RuBPCase). Carbon isotopediscrimination between 13C of phytoplankton and DIC was considerablysmall in early summer and appeared to be negatively correlatedto DIC concentration. We concluded that carbon fixation by phytoplanktonin Lake Suwa is controlled not by the switch of photosyntheticpathways, but by low DIC concentration and high pH, suggestingthat photosynthesis of Microcystis spp. in Lake Suwa is governedby uptake kinetics other than the carboxylation step. 相似文献