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1.
Quantification of track and grain density autoradiography and evaluation of 14C loss on preservation
Sources of error in quantifying autoradiography were determinedwith unialgal cultures and natural assemblages. Carbon-14 activityof cells as recorded by track autoradiography was generallynot significantly different from scintillation counts. Differenceswhich did occur were apparently due largely to filter-retainedextracellular 14C. An analysis of 37 preparations confirmedthat tracks per cell for healthy log-phase populations followeda Poisson distribution. Quantification and analysis of intraspecificdistributions for the grain density technique were relativelydifficult. 14C loss on preservation was lower and more consistent(021 %) than previously reported. Autoradiographs indicatedthat this loss consisted of unfixed filter-retained 14C or anextracellular release product rather than carbon within algalcells. Thus, track autoradiography was more reliable for quantifyingspecies-specific net productivity than other studies have indicated.
1Present address: Division of Environmental Studies and Instituteof Ecology, University of California, Davis, CA 95616, USA 相似文献
2.
Filter types, filtration and post-filtration treatment in phytoplankton production studies 总被引:1,自引:0,他引:1
Acid rinsing, used to decontaminate filters in 14C productionstudies, caused cell rupture and resulted in elevated 14C countsin the filtrates of six out of seven phytoplankton samples.Large volume (50 ml) rinses using only water caused some, butlesser, damage. Comparing the recovery of 14C-labelled cellsand chlorophyll a on glass-fibre, polycarbonate and celluloseester filters revealed unaccountable losses at times with allthree filter types. These losses could not be explained by cellrupture, attachment to the filter funnel wall, filter treatmentor self-absorption during scintillation counting. Compared tothe whole sample acid bubbling method, recovery on the glass-fibrefilters was highest. Results for the polycarbonate filters weremore variable, while, in all cases, recovery on cellulose esterfilters was much lower. 相似文献
3.
The photosynthesis of cellular materials by phytoplankton isaccompanied by release of organic molecules from the algal cellsinto the water. The patterns of carbon fixation in particulateand dissolved pools were investigated in Skeletonema costatumcultured under 12 h light/12 h dark cycles. The short-term production(115 min) of particulate organic carbon (POC) and extracellularorganic carbon (EOC) compounds was studied by measuring theuptake of 14C-labelled sodium bicarbonate and its subsequentincorporation and release into organic compounds. Slightly modifiedtraditional 14C radiotracer protocols were used, including separationby electrophoresis and thin-layer chromatography and detectionby autoradiography. Results indicated that there was a distinctdifference between radiolabelled compounds in the POC and EOCpools. Several metabolites found in the EOC pool were not presentin the POC pool, indicating the active release of these productsfrom the cells into the ambient water during short-term incubations,and indicating that inorganic carbon fixation pathways in marineautotrophs might be partly extracellular. 相似文献
4.
Fish-induced changes in zooplankton grazing on phytoplankton and bacterioplankton: a long-term study in shallow hypertrophic Lake Sobygaard 总被引:1,自引:0,他引:1
Jeppesen Erik; Sondergaard Martin; Jensen Jens Peder; Mortensen Erik; Sortkjaer Ole 《Journal of plankton research》1996,18(9):1605-1625
The impact of fish-mediated changes on the structure and grazingof zooplankton on phytoplankton and bacterioplankton was studiedin Lake Søbygaard during the period 198492 bymeans of in vitro grazing experiments (14C-labelled phytoplankton,3H-labelled bacterioplankton) and model predictions. Measuredzooplankton clearance rates ranged from 025 ml l1h1 on phytoplankton to 033 ml l1 h1on bacterioplankton.The highest rates were found during thesummer when Daphnia spp. were dominant. As the phytoplanktonbiomass was substantially greater than that of bacterioplanktonthroughout the study period, ingestion of phytoplankton was26-fold greater than that of bacterioplankton. Multiple regressionanalysis of the experimental data revealed that Daphnia spp.,Bosmina longirostris and Cyclops vicinus, which were the dominantzooplankton, all contributed significantly to the variationin ingestion of phytoplankton, while only Daphnia spp. contributedsignificantly to that of bacterioplankton. Using estimated meanvalues for clearance and ingestion rates for different zooplankters,we calculated zooplankton grazing on phytoplankton and bacterioplanktonon the basis of monitoring data of lake plankton obtained duringa 9 year study period. Summer mean grazing ranged from 2 to4% of phytoplankton production and 2% of bacterioplankton productionto maxima of 53 and 88%, respectively. The grazing percentagedecreased with increasing density of planktivorous fish caughtin August each year using gill nets and shore-line electrofishing.The changes along a gradient of planktivorous fish abundanceseemed highest for bacterioplankton. Accordingly, the percentagecontribution of bacterioplankton to the total ingestion of thetwo carbon sources decreased from a summer mean value of 8%in Daphnia-dominated communities at lower fish density to 0.71.1%at high fish density, when cyclopoid copepods or Bosmina androtifers dominated. Likewise, the percentage of phytoplanktonproduction channelled through the bacteria varied, it beinghighest (58%) at high fish densities. It is argued thatthe negative impact of zooplankton grazing on bacterioplanktonin shallow lakes is highest at intermediate phosphorus levels,under which conditions Daphnia dominate the zooplankton community. 相似文献
5.
Studies were conducted over a 13 month period at four pelagicsites in eutrophic Lake Okeechobee, Florida (USA), in orderto quantify carbon (C) uptake rates by size-fractionated phytoplankton,and subsequent transfers of C to zooplankton. This was accomplishedusing laboratory 14C tracer methods and natural plankton assemblages.The annual biomass of picoplankton (<2 µm), nanoplankton(220 µm) and microplankton (<20 µm averaged60, 389 and 100 µg C 11 respectively, while correspondingrates of C uptake averaged 7, 51 and 13 µg C11h1. The biomass of microzooplankton (40200 µm)and macrozooplankton (<200 µm averaged 18 and 60 µgC 11, respectively, while C uptake rates by these herbivoregroups averaged 2 and 3 µg C 11 h1. Therewere no strong seasonal patterns in any of the plankton metrics.The ratio of zooplankton to phytoplankton C uptake averaged7% over the course of the study. This low value is typical ofthat observed in eutrophic temperate lakes with small zooplanktonand large inedible phytoplankton, and indicates ineffectiveC transfer in the grazing food chain. On a single occasion,there was a high density (<40 11) of Daphnia lumholrzii,a large-bodied exotic cladoceran. At that time, zooplanktoncommunity C uptake was <20 µg C 11 h1and the ratio of zooplankton to phytoplankton C uptake was near30%. If D.lumholrzii proliferates in Lake Okeechobee and theother Florida lakes where it has recently been observed, itmay substantially alter planktonic C dynamics. 相似文献
6.
A study of the phytoplankton in Concarneau Bay (Bretagne, France)was carried out on 68 June, 1978. Autotrophy was measuredby the 14C method and heterotrophic activity was estimated by14C labelled glucose and protein hydrolysate uptake. The measurementswere made on the whole of the sample as well as on the bacterialfraction, isolated by size-fractionation on Nuclepore 3 µmfilters. Moreover, a study of the relationships between naturalphytoplanktonic and bacterial populations was possible becauseof cell counts. The phytoplankton shows coastal characteristicsand diatoms are dominant. The distribution of the genus Chaetoceros,Nitzschia and Leptocylindrus seems to have an influence on therelationship between algae and bacteria so that environmentalconditions not only interfere directly at the bacterial levelon heterotrophic activity, but also through the specific compositionand abundance of the phytoplankton. 相似文献
7.
Changes in the distribution of 14C between free and bound aminoacids in wheat grains (Triticum aestivum L. cv. Arkas) at 10and 20 d post-anthesis are described. After 14CO2, labellingof the flag leaf, 14C was initially more rapidly transferredto the grains of 20 d post-anthesis plants than for 10 d post-anthesisplants. However, after a 460 min chase period in the light theamount of 14C in the grains of the younger and older plantswere similar. In the younger, more rapidly growing grains, agreater proportion of the 14C was incorporated into structuraltissue and starch. 14C accumulation in the grains continuedduring the dark in the younger grains but not in the older grains. Although the overall 14C distribution between the free aminoacid and protein pools of the grain was similar for both treatments,the distribution within the albumin, prolamin and globulin fractionsand between the individual non-bound amino acids differed. Ofthe protein fractions, the albumins were initially the mostheavily labelled but after 460 min chase the prolamins containedmore 14C. The majority of the 14C in the albumin and globulinfractions after 280 min chase was in hydrolysable, non-aminoacid compounds. In both tissues, the free amino acid pools lostradioactivity in the dark but the solid residues and proteinscontinued to function as 14C sinks. Daily fluctuations in the radioactivity in free and bound alanineare consistent with the role of free alanine as a diurnal metabolicnitrogen pool. Wheat, Triticum aestivum14CO2, amino acids, proteins, carbon metabolism 相似文献
8.
The distribution of IAA-2-14C or IAA-5-3H applied to the apexin the upper and lower (with respect to gravity) halves of geotropicallystimulated stems of cucumber and pea was examined and the resultsobtained are as follows: 1. A larger amount of IAA-2-14C or IAA-5-3H was detected inthe lower than upper half of cucumber hypocotyls with 3-hr geostimulation. 2. A larger amount of IAA-2-14C was distributed in the lowerthan upper epidermis of pea epicotyls with 1-hr geostimulation. 3. Freezing autoradiography revealed that IAA-2-14C was concentratedin the vascular bundles and epidermis of cucumber hypocotyls,the distribution being affected by geostimulation only in thelatter. 4. Application of 1% TIBA in lanolin inhibited the distributionof IAA-2-14C in the lower epidermis of pea epicotyls, causingsuppression of geotropic curvature. 5. From these results, we concluded that IAA which accumulatedin the lower epidermis of the stem upon geostimulation causedthe negative geotropic curvature of the stem. (Received October 13, 1975; ) 相似文献
9.
Data are presented on primary productivity, cell size distributionsand the standing stocks of living and detrital paniculate organiccarbon (POC) in the waters of the SW Tasman Sea. Primary productivitywas measured by both standard 4- and 12-h incubations as wellas time-series incubations. Data are presented for 14C uptakeand loss in 12L/12D methods. The importance of time zero anddark controls is demonstrated. The uptake of 14C in the lightwas linear and the loss of label in the following dark periodranged from zero to 39%. The loss of label in the dark was correlatedwith the particle size distribution, being greatest in oligotrophicwaters dominated by small cells (2530%) and least inspring bloom areas (020%) dominated by large diatoms.Kinetic data were strongly supportive of a major grazing impactby microphagous organisms. The data were an experimental confirmationof recent theoretical models of 14C uptake and grazing. Sizedistributions of phytoplankton and detritus were measured byHIAC and by microscopic counting. The phytoplankton consistedof a ubiquitous group of picoplankton, and variable contributionsfrom small flagellates and diatoms. The distribution of totalcell volume was dominated by large cells in spring bloom areas.Chlorophyll concentrations were strongly correlated with themean cell size of the phytoplankton. Comparison of the resultsof 14C uptake experiments with the results of experiments todetermine changes in POC, by counting particles, gave good correlation.In detail, the comparison of the methods revealed systematicerrors with the greatest discrepancy between the methods atlow apparent growth rates. The detritus showed constant sizedistributions in surface waters. The mean size of detritus particlesreduced rapidly with depth and declined in a way suggestingbiological reprocessing and removal by grazing. These resultsare discussed in the context of the patterns of carbon metabolismin the photic zone, the role of living and detrital POC andthe balance of new versus regeneratedproduction in surface waters. 相似文献
10.
Phytoplankton rate processes in the oligotrophic waters of the central North Pacific Ocean 总被引:1,自引:0,他引:1
Sharp Jonathan H.; Perry M.J.; Renger Edward H.; Eppley Richard W. 《Journal of plankton research》1980,2(4):335-353
The central North Pacific is one of the more oligotrophic regionsof the world oceans. There the particulate organic nitrogen:cabonratio of surface waters is variable and less than the Redfieldratio of 16N:106C by atoms. The phytoplankton P/B ratio basedupon both C and N assimilation rate varied directly with theparticulate matter PON:POC ratio as did the productivity index[mg C (mg chl a)1h1]. At steady state the doublingtime of the phytoplankton, the turnover time of the limitingnutrient supplied via herbivore grazing, and the time for herbivoresto filter a unit volume of water would be equivalent. They appearto be of the order of 59 days based on present methodologyand straightforward interpretation of its results. The rate measurements involved incubation of water samples forseveral hours in bottles. In the central N. Pacific the valueswere similar using bottles of different sizes. Addition of chelatorsdid not enhance the rates implying no poisoning of the planktonby heavy metal contaminants. The observed specific activitiesof 14C and 15N of the particulate matter in the rate measurementsare inconsistent with the notion of an active, rapidly growingand recycling microplankton food web within the incubation bottlesand support the idea that phytoplankton are growing slowly. 相似文献
11.
Phytoplankton composition, density, vertical distribution andprimary production were investigated in the Sea of Okhotsk andin the adjacent northern north Pacific in JulyAugust1994, together with measurements of density and distributionof planktonic microheterotrophs: bacteria, nanoheterotrophsand ciliates. Different phases of phytoplankton seasonal successionwere encountered during the period of investigation in variousregions of this sea. Primary production measured at 144 stationswas found to be greatest (1.54 g C m-2day-1) in areasof spring-phase succession along the Sakhalin shelf and theKashevarov bank. Periodic relapses of the spring blooms of heavydiatoms during the whole growth season were recorded over thisbank. The summer phase of the phytoplankton minimum prevailedin the central and eastern parts of the sea, manifested by thedominance of nanoflagellates in terms of phytoplankton biomass.Primary production was 0.51 g C m-2 day-1. The earlyautumn phase of succession was typical of the Kurile straitarea and the adjacent north Pacific. Primary production therevaried from 0.7 to 2 g C m-2 day-1. The integrated phytoplanktonbiomass in the water column varied from 912 g m-2 inzones supporting the summer minimum assemblage to 1520g m-2 in zones of early autumn recovery of phytoplankton growth,and up to 4070 g m-2 in areas of remnant or relapseddiatom blooms. The numerical density of bacterioplankton wasbetween 1 x 106 and 3 x 106 cells ml-1 and its wet biomass wasbetween 100 and 370 mg m-3. In deep waters it was 815mg m-3. The integrated bacterioplankton biomass in the upperwater column varied from 6 to 29 g m-2. The numerical densityof zooflagellates varied in the upper layer between 0.8 x 106and 4 x 106 l-1 and their biomass was between 20 and 50 mg m-3.In deep waters they were still present at a density of 0.05x 106 to 0.2 x 106 cells l-1. The biomass of planktonic ciliatesvaried between stations from 20 to 100 mg m-3. The joint biomassof planktonic protozoa in the water column was between 3 and12 g m-3 at most of the stations. 相似文献
12.
Slawyk Gerd; Minas Monique; Collos Yves; Legendre Louis; Roy Suzanne 《Journal of plankton research》1984,6(2):249-257
The stable carbon isotope 13C has been used in the open oceanto estimate the inorganic carbon uptake by phytoplankton andthis technique has been compared with the 13C tracer method.An overall correlation coefficient of 0.806 and a regressionslope of 1.29 were calculated from 50 sample pairs gatheredduring three cruises in widely different oceanic areas rangingin production rates from 0.01 to 6 mgC m3 h1.However, significant differences between the two methods wereapparent for cruises located in nutrient-depleted areas. Possibleexplanations lie either in a volume effect, the high silicatecontent of the 14C solution which could stimulate the 14C uptakeor in errors associated with the particulate carbon measurementswhich are necessary to convert specific uptake rates to absoluteuptake rates and to yield compatible units for the comparison,in laboratory cultures the 14C technique overestimated the netparticulate carbon increase by 16%.
+Present address: Laboratoire marin CNRS-IFREMER, L'Houmeau,17137 Nieul-sur-Mer, France.
*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. 相似文献
13.
Plankton in the River Rhine: structural and functional changes observed during downstream transport 总被引:6,自引:0,他引:6
de Ruyter van Steveninck E.D.; Admiraal W.; Breebaart L.; Tubbing G.M.J.; van Zanten B. 《Journal of plankton research》1992,14(10):1351-1368
The growth dynamics of phytoplankton, zooplankton and bacterioplanktonin the River Rhine were analysed simultaneously with a numberof environmental factors in order to identify environmentalsteering factors and to describe some of their interrelations.Observations on the metabolic activity (for algae and bacteria)and density (for all organisms) were carried Out three timesin 1990 using successive sampling of the same water parcel duringits transport in the lower 660 km reach of the river. High algaldensities (up to 170.5 µg chlorophyll a l1), rotifers(up to 1728 l1), crustaceans (up to 65 l1) andbacteria (up to 16x109 l1) were found. Algae and rotifersshowed a rapid successive development during transport, whilecrustaceans were only abundant in the tidal reach of the river.In May, a vigorous growth of phytoplankton, zooplankton andbacteria was found. The diatom-dominated phytoplankton depletedthe dissolved silicate in the river water and this led to acollapse of the populations, indicated by a decreased specificrate of photosynthesis (measured by the 14C method) and vigorousbacterial growth (measured by [3H]thymidine incorporation).Subsequently, the remaining phytoplankton diminished to verylow levels near the river mouth. In July and September, it seemedthat biological interactions within the plankton populationsor between plankton and benthos balance the population densitiesso that separate developmental stages, as in spring, were lessprominent. Estimates of the growth rates and loss rates of thephytoplankton were made. Phytoplankton exerted a substantialinfluence on the partitioning of nutrients (nitrogen, phosphorus,silicate) over water and suspended matter (as analysed by elementanalysis). It seems likely that only the reduction of phosphate,as planned under the Rhine Action Programme, and not that ofnitrogen, may restrict the peaks of plankton growth describedhere. 相似文献
14.
KENDALL A. C.; TURNER J. C.; THOMAS S. M.; KEYS A. J. 《Journal of experimental botany》1985,36(2):261-273
Spring wheat plants were grown in a cage with a glass roof untilthree days after anthesis and then subjected to treatments inconstant environment rooms with any one of all combinationsof four irradiances and two concentrations of carbon dioxide.The photoperiod was 16 h and day/night temperatures 19?C/14?C.Growth and yield of grain were saturated at the two brightestirradiances. Carbon dioxide enrichment from 350 to 1200 mm3dm3 increased shoot dry weight and grain yield at finalharvest at all irradiances, by averages of 10.5 (not significant)and 23.5 (significant) percent respectively. However, increasingthe irradiance from 150 to 613 µE m2 s1caused much larger yield increases (approximately 3-fold). Increasedgrain production by increased light was caused by both increasesin dry weight per grain and by increases in grain number perspikelet. The increase caused by CO2 enrichment was mainly becauseof increased dry weight per grain. Increase in ear dry weightcaused by CO2 enrichment took place between 30 and 60 d afteranthesis. The increase in shoot dry weight took place immediatelyafter exposure to increased CO2 from 3 to 15 d after anthesis.Net photosynthesis by flag leaves on the main shoots was almostdoubled 16 d after anthesis by the CO2 enrichment even thoughstomatal resistance was also doubled. However, this increasewas not reflected by a proportional increase in yield, probablybecause increased mutual shading by bigger stems and late tillersreduced total assimilation and because of increased respirationby the shoots. The increase in photosynthesis was not due toa decrease in photorespiration but to an increase in gross photosynthesis. Key words: CO2enrichment, Photosynthesis, Photorespiration 相似文献
15.
Light rather than iron controls photosynthate production and allocation in Southern Ocean phytoplankton populations during austral autumn 总被引:2,自引:0,他引:2
van Oijen T.; van Leeuwe M. A.; Granum E.; Weissing F. J.; Bellerby R. G. J.; Gieskes W. W. C.; de Baar H. J. W. 《Journal of plankton research》2004,26(8):885-900
The role of iron and light in controlling photosynthate productionand allocation in phytoplankton populations of the Atlanticsector of the Southern Ocean was investigated in AprilMay1999. The 14C incorporation into five biochemical pools (glucan,amino acids, proteins, lipids and polysaccharides) was measuredduring iron/light perturbation experiments. The diurnal Chla-specific rates of carbon incorporation into these pools didnot change in response to iron addition, yet were decreasedat 20 µmol photons m2 s1, an irradiancecomparable with the one at 2045 m in situ depth. Thissuggests that the low phytoplankton biomass encountered (0.10.6µg Chl a L1) was mainly caused by light limitationin the deep wind mixed layer (>40 m). Regional differencesin Chl a-specific carbon incorporation rates were not foundin spite of differences in phytoplankton species composition:at the Antarctic Polar Front, biomass was dominated by a diatompopulation of Fragilariopsis kerguelensis, whereas smaller cells,including chrysophytes, were relatively more abundant in theAntarctic Circumpolar Current beyond the influence of frontalsystems. Because mixing was often in excess of 100 m in thelatter region, diatom cells may have been unable to fulfil theircharacteristically high Fe demand at low average light conditions,and thus became co-limited by both resources. Using a modelthat describes the 14C incorporation, the consistency was shownbetween the dynamics in the glucan pool in the field experimentsand in laboratory experiments with an Antarctic diatom, Chaetocerosbrevis. The glucan respiration rate was almost twice as highduring the dark phase as during the light phase, which is consistentwith the role of glucan as a reserve supplying energy and carbonskeletons for continued protein synthesis during the night. 相似文献
16.
Fitzwater Steve E.; Knauer George A.; Martin John H. 《Journal of plankton research》1983,5(6):935-938
The effects of short-term, acute Cu exposure (6 h) on the adenylateenergy charge (ECA) of open-ocean phytoplankton populations(northeastern equatorial Pacific) were investigated. Energycharge remained at {small tilde}0.77 over the range of Cu additions(0.025 5.µg l1), even though 14C uptakeand total adenylate levels (ATP + ADP + AMP) were reduced byas much as 60%. These findings suggest that ECA alone is nota sensitive indicator of acute sublethal metal effects on phytoplankton.
1This research was supported by the NSF Biological OceanographyProgram grant #OCE 81-17286. 相似文献
17.
The contribution of picophytoplankton to community structure in a Mediterranean brackish environment 总被引:3,自引:0,他引:3
The seasonal composition of phytoplankton communities was investigatedin a Mediterranean brackish area (Varano lagoon). Twelve stationswere sampled monthly from March 1997 to February 1998. Numbersof prokaryotic and eukaryotic picophytoplankton cells were estimatedby epifluorescence microscopy, while larger phytoplankton (nanoand micro fractions) were enumerated by the Utermöhl settlingtechnique. Picophytoplankton densities ranged from 0.7 to 448.6cells x 106 l1. Nano- and microphytoplankton abundancesvaried between 0.2 and 7.9 cells x 106 l1. The picoplanktonfraction was represented mainly by cyanobacteria and the Utermöhlfraction by nano-sized phytoflagellates (56.2%) and diatoms(20.1%). The phytoflagellates had a greater abundance over timewhile diatoms reached the highest densities in summer and fall.In Varano lagoon, phytoplankton development is related to nitrogen-poor'waters and to phosphorus availability. Suspension-feeding bivalves(Mytilus galloprovincialis) are sufficiently abundant to filtera volume equivalent to the volume of Varano lagoon at leastonce daily. These observations suggest that grazing exerts animportant influence on phytoplankton dynamics, mainly on themicro fraction, and that diatoms seem to play an important rolein the food web dynamics of this coastal fishery. 相似文献
18.
Dark Respiration of Several Varieties of Winter Wheat Given Different Amounts of Nitrogen Fertilizer 总被引:1,自引:1,他引:0
Carbon dioxide production in the dark by ears and by the restof the shoot of winter wheat grown in the field was measuredin 2 years during grain growth. The respiration rate per g d.wt of the ears was increased by nitrogen fertilizer. Ears ofthe semi-dwarf varieties Maris Fundin and Hobbit respired moreslowly than ears of Maris Huntsman and Cappelle-Desprez. Respirationrates of the rest of the shoot were unaffected by nitrogen orvariety. The amount of carbohydrate required to provide the CO2 respiredduring the whole period of grain growth varied from 163 to 443g m2, or 42 to 76 per cent of the dry weight of the grain.More than half the CO2 lost was respired by the ear. The additionof 180 kg N ha1, which increased grain yield by 78 percent in 1975, almost trebled the amount of CO2 lost by the ears.The semi-dwarf varieties lost less CO2 from ears and shootsthan did the taller ones, and had larger yields of grain. Respiration was also estimated from the difference between the14C contents of shoots sampled immediately after a 30 s exposureto 14CO2 and at maturity. When 14C was supplied 10 days afteranthesis, the loss by maturity amounted to 1628 per centof that initially absorbed by flag leaves and 40 per cent ofthat absorbed by the leaf below the flag leaf. Most of the lossoccurred in the first day. The loss of 14C by maturity was significantlyincreased by nitrogen fertilizer in 1975. Triticum aestivum L., wheat, respiration, nitrogen supply, fertilizer treatment 相似文献
19.
Carbon and nitrogen uptake response to light by phytoplankton during an upwelling event 总被引:5,自引:0,他引:5
Kudela Raphael M.; Cochlan William P.; Dugdale Richard C. 《Journal of plankton research》1997,19(5):609-630
The interactions between phytoplankton nutrition and the responseof carbon (C) and nitrogen (N) uptake to irradiance relationshipswere examined during September 1993 in Monterey Bay, California,an eastern boundary current upwelling regime. Measurements ofN uptake and C assimilation rates versus irradiance (V:I andP:I) experiments were performed using trace-level additionsof 15N-labeled NO3 and NH4+, and 14C-labeled bicarbonateto water collected from a depth of {small tilde}30% of surfacephotosynthetic photon flux density (PPFD). An upwelled watermass was sampled consecutively, with hydrographic stations locatedat the upwelling site, 48 h later down the horizontal axis ofthe upwelling plume, and a final time (24 h later) with watersconsisting of a mixture of 56 day aged upwelled waterand warmer surface water from outside the plume. As the wateraged, a pro gressive shift in the rates of C and N utilizationoccurred, with C assimilation increasing while N uptake ratesdecreased. At the same time, NH4+ dominated the nitrogenousnutrition in older upwelled water, even in the presence of highconcentrations of ambient NO3. Dark-uptake rates forall substrates were uniformly low at all stations; NH4+ uptakedemonstrated the least dependence on PPFD. The results of thisstudy demonstrate dramatic changes in the light-mediated responseof C and N uptake, resulting in assimilation ratios considerablydifferent from predicted values assuming phytoplankton C:N uptakerates will be proportional to Redfield C:N composition. Thesedata provide clear evidence of physiological changes in thenatural planktonic assemblage of this evolving upwelling ecosystem. 相似文献
20.
The Stability and Movement of Gibberellic Acid in Pea Seedlings 总被引:1,自引:0,他引:1
The stability and movement of gibberellic acid (GA) in intactdwarf pea seedlings growing in the light was studied by meansof both unlabelled GA and GA labelled with isotopic carbon (14C).After 14C-GA had been applied to the mature leaves of pea seedlingsmuch remained in association with the treated leaflets, but14C-GA was also extractable from the young shoots. The yieldwas approximately the same 5 to 96 hours after treatment. GApenetrated leaf surfaces only while the application solventwas moist (about 1 hour), but moved from the treated leafletsinto the shoots for at least 24 hours. Some hours after treatmentthere was an abrupt increase in the growth-rates of the plants,and crude estimates suggest that an effective dose of GA movedto the elongating tissue at about 5 cm/hr. The pattern of distributionof 14C was examined by autoradiography. The data suggest thatGA which enters the plant is redistributed from maturing leavesto immature leaves, passing through the elongating tissue, foras long as any of the substance is present. The hypothesis remainstenable that GA produces its growth effects by acting only uponexpanding tissue 相似文献