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1.
Short-term temporal variation in coastal zooplankton communities: the relative importance of physical and biological mechanisms 总被引:2,自引:0,他引:2
Drogues were deployed off the coast of Northumberland (north-eastEngland), as they were tracked zooplankton were collected, byfour vertical hauls of a UNESCO WP-2 net (200 µm), adjacentto the drogue at hourly intervals Sampling covered a full tidalcycle, at least once each month from February to April, andin July and August 1993. Short-term changes in the communitystructure (in terms of species composition and abundance) wereinvestigated with respect to the local wind field and tidaladvection. It was observed, from a cluster analysis that duringhorizontal transport, the zooplankton maintained the same communitystructure for at least three consecutive hours on each samplingoccasion [Pearson correlation (r) 0.70; P0.01] even during periodsof high turbulent mixing, driven by wind stress Multiple regressionmodels including parameters of the wind field and the rate ofhorizontal transport only accounted for a maximum of 52% ofthe temporal variation in zooplankton community structure. Theunaccounted for variation provides the basis for the considerationof the zooplankton as active drifters rather thanpassive particles, this is discussed. 相似文献
2.
Diel vertical migration of zooplankton following optimal food intake under predation 总被引:2,自引:1,他引:1
A model is developed to investigate the trade-offs between benefitsand costs involved in zooplanktonic diel vertical migration(DVM) strategies. The venturous revenue (VR) isused as the criterion for optimal trade-offs. It is a functionof environmental factors and the age of zooplankter. Duringvertical migration, animals are assumed to check instantaneouslythe variations of environmental parameters and thereby selectthe optimal behavioral strategy to maximize the value of VR,i.e. taking up as much food as possible with a certain riskof mortality. The model is run on a diel time scale (24 h) infour possible scenarios during the animals life history.The results show that zooplankton can perform normal DVM balancingoptimal food intake against predation risk, with the profileof DVM largely modified by the age of zooplankter. 相似文献
3.
The Effects of Salinity upon Galactosyl-Glycerol Content and Concentration of the Marine Red Alga Porphyra purpurea (Roth) C.Ag. 总被引:2,自引:0,他引:2
REED ROBERT H.; COLLINS JULIAN C.; RUSSELL GEORGE 《Journal of experimental botany》1980,31(6):1539-1554
Changes in the major alcohol-soluble, low molecular weight carbohydratesof P. purpurea, O--D-galactopyranosyl-(1-2)-glycerol (floridoside)and O--D-galactopyranosyl-(1-1)-glycerol (isofloridoside),have been examined in response to salinity variation. Floridosideis shown to vary in absolute amount, increasing in hypersalineand decreasing in hyposaline media. Isofloridosidecontent per cell does not change in a similar manner. Responsesare almost identical under light or dark conditions, floridosidechanges being complete within 24 h. Decreasing the externalwater potential using ionic and non-ionic solutes has the sameeffect upon galactosyl-glycerol content. The amount of floridosidesynthesized, and degraded under hypersaline and hyposaline conditionsrespectively is shown to be insufficient to restore cell volumeto its original value. It is therefore suggested that the primaryfunction of floridoside increases in concentratedsea-waters is that of a compatible solute, serving to protectthe cell during periods when the external salt content is increaseddramatically. 相似文献
4.
Extracts of small and mature-size lupin pods yielded four substancesaffecting the growth of wheat-coleoptile sections: one acidpromotor (A), two acid inhibitors(B and X), and one neutralinhibitor(Y). Inhibitor B was extremely active, however, coleoptile sectionsshowed no signs of toxic effects; they resumed growth at a rapidrate after rinsing them and adding ß-indolylaceticand (IAA) to the medium. 1 µg of IAA was required to counteractthe effect of B extracted from 230 mg. Of tissue.On an equal fresh weight basis the inhibiting action of Bin lupin pods was 5001,500 times more potent than thatof inhibitor ß in etiolated pea seedlings. Small pods of plants infected with pea-mosaic virus yielded3 times the amount of A of healthy plants (equivalentto 1 µg. IAA 0.3 µg. IAA per 25 g. of tissue respectively),and approximately the amount of B. Mature podsof virus-infected plants again yielded moreA,but also 2? times more B than pods of healthyplants. Healthy pods yielded more A than virus-infectedpods, and there was no difference in X. A lupin abscission test was developed and the effects of proximaland distal application of -naphthyl acetic acid (NAA) are presented,and discussed with respect to results of other abscission tests. A accelerated abscission when applied proximally,and delayed or prevented it when applied distally. Bstrongly accelerated abscission when applied in either way.A possible mechanism explaining the abscission-inducing effectof developing pods on later flowers is discussed in terms ofthe substances A and B. The partlyprevented abscission observed on virus-infected plants was foundto agree well with the proposed mechanism. 相似文献
5.
Hansen B.W.; Hygum B.H.; Brozek M.; Jensen F.; Rey C. 《Journal of plankton research》2000,22(3):569-588
The significance of nauplii versus copepodite stage V of Calanusfinmarchicus grazing and their effects on the structure of thefood web were investigated during two sampling periods of 78days in March and April in experimental mesocosms held in aNorwegian fjord over a 2 month period. The mesocosms were manipulatedby the addition of two different levels of inorganic nutrients(control versus enriched). During the naupliarperiod in March, the phytoplankton was characterized by a diatombloom while during the copepodite period in April,it was in a post-bloom phase characterized by small-celled species,mainly Phaeocystis pouchetii. Phytoplankton, bacterial and protozooanbiomass and production rates were measured in addition to copepodbiomass. Copepod grazing was estimated by three different methods:(i) gut fluorescence; (ii) chlorophyll clearance from the water;and (iii) growth method measured as body carbon increase. Thetwo latter methods gave similar results for nauplii, but allthree gave different results for the copepodites. Independentsomatic growth, based on changes in abundance and individualcarbon content, and grazing estimates revealed an overall growthefficiency of 0.66 ± 0.20 (mean ± S.E.) for copepodites.Empirical carbon flow models were constructed, which indicatedthat the nauplii could not control either phytoplankton or protozoangrowth in either the control or in the enriched system. Ignoringrecycling and sedimentation, the fate of the primary productionfor the nauplii-dominated community was to be grazed by a diverseand abundant protozooplankton community. In the copepodite-dominatedcommunity, the copepods grazed >100% of the daily primaryproduction, and also grazed heavily on a protozooplankton communityof low biomass and diversity and presumably on detritus. Thefate of the primary production in the two different copepodscenarios followed predicted routes for low meso-zooplanktonand for high meso-zooplankton biomass systems,as suggested by Wassmann (Wassmann, 1998). 相似文献
6.
Factors structuring zooplankton communities in areas with 24h of sunlight are not well understood. In stratified temperatelakes with fish, zooplankton generally undergo a diel verticalmigration (DVM) to avoid predation. Zooplankton abundance mayalso be linked to the quality and quantity of food. To explorefactors that determine vertical structure of zooplankton whereDVM does not occur, we obtained time-series data on the verticaldistribution of the two dominate copepods, Cyclops scutiferand Diaptomus pribilofensis, in Toolik Lake, Alaska, a sitewithin the Arctic Long Term Ecological Research area. Thesetwo species compose 8090% of pelagic mesozooplanktoncommunity density. Temperature plays a large role in the verticaldistribution of these two species. During the summers of 2002and 2003, C. scutifer underwent a seasonal vertical migrationfrom the epilimnion to the hypolimnion as water temperaturesincreased. Diaptomus pribilofensis exhibited a strong preferencefor warmer water and were not present in the water column untilepilimnetic temperatures reached 9°C. During both yearsof this study, C. scutifer and D. pribilofensis segregated verticallyin the water column along thermal gradients when the two speciesoverlapped temporally. 相似文献
7.
A laboratory-held specimen of Tonna zonatum was fed holothurianprey over a period of 21 weeks. At first, the Tonna consumedHolothuria cinerascens, H. insignis and H. fuscocinerea, butsubsequently consumed only H. leucospilota. Prey size chosenwas in the range 54200 g total weight with approximately1 holothurian being eaten each week by extension of the proboscis.Consumption time was 25 minutes and records of rejectionof living prey showed that food is not cut up in the proboscisby the jaws or the radula but is engulfed whole. Holothurians reacted violently to the hunting Tonna, typicallyby taking in large quantities of water to increase in size,particularly in diameter. Holothuria fuscocinerea fledthe predator while H. scabra and H. leucospilota became buoyantand, writhing, effected simple swimming. Calculations of consumption show that this adult specimen consumed2% (wet weight) or 1% (dry weight) of its body weight. day1.This is much lower than figures for other predatory gastropods,i.e. 5%. day1. Analysis of faeces production, correlatedwith consumption, suggests a residence time in the gut of 4days and an assimilation efficiency of 80.02%. This study andliterature data suggest that the Tonnidac are highly specialized,exclusive, predators of holothurians. (Received 16 November 1989; accepted 22 January 1990) 相似文献
8.
When nitrate, ammonium, or urea were the sole nitrogen sourcesfor the growth of Platymonas striata there was a short initiallag period, after which uptake/assimilation occurred at a constantrate. Glycine uptake was however non-linear withtime. Addition of ammonium or urea markedly inhibited nitrateuptake whereas although glycine was initiallytotally inhibitory, nitrate uptake recommencedabout 1 h after addition, but at a greatly reduced rate. Ammoniumtotally inhibited urea uptake, but did not inhibitglycine uptake. When ammonium, urea, or glycinewere present at the same time as nitrate the total rate of nitrogen'uptake/assimilation was within 40% (or closer) of that of nitratenitrogen uptake alone. In the first two casesthis reflected a total switching off of nitrate uptakewhilst the new substrate was assimilated at a rate similar tothe initial nitrate rate, whereas in the case of glycine, bothsubstrates were used simultaneously. Once the concentrationof any of the inhibitory nitrogen sources had been reduced toa low level the uptake/assimilation of nitraterecommenced. It is suggested that the ability of P. striatato maintain a more or less constant rate total nitrogen uptake/assimilationirrespective of the mixture of utilizable nitrogen sources presentedto it, is not due to controls at the level of the entry of substrateinto the cell, but to intracellular actions at the enzyme level.The relative constancy of, and high rate of uptake,irrespective of nitrogen source and over a wide range of extracellularconcentrations, is tentatively considered to be due to saturationof the assimilatory mechanisms under the conditions employed;all the sources lead, either directly or indirectly, to theproduction of amino groupings for entry into nitrogenous metabolism.This homeostasis of nitrogen uptake/assimilationwould clearly be of considerable benefit to the alga in nature,enabling it to maximize growth in changing environmental conditions. Platymonas striata, nitrogen update, nitrogen assimilation 相似文献
9.
The chrysophyte genera Poterioochromonas and Ochromonas andtheir heterotrophic analogons, i.e. the Spumella-likeflagellates, account for a significant and often dominatingfraction of the pelagic nanoplankton. Even though several osmotrophicallyand autotrophically grown strains of Ochromonas and Poterioochromonasare assumed to produce toxins, the potential toxicity has beeninvestigated neither for its association with bacterivorousnutrition nor within the related exclusively heterotrophic Spumella-likeflagellates. We investigated the toxic potential of severalflagellate strains using cultures of flagellates, cell extractsand filtrate of flagellate cultures. The effect on potentialpredators was exemplarily tested for the cladoceran Daphniamagna and the rotifer Platyias sp. All tested heterotrophicand mixotrophic flagellate strains were toxic to zooplanktonat abundances exceeding 104 flagellates mL1. For therotifers, survival on any of the flagellate strains was significantlylower than that in the control treatment (P < 0.001) alreadyafter 24 h. We conclude that (i) Spumella-likeflagellates can be toxic to zooplankton, (ii) all tested flagellates,i.e. heterotrophic and mixotrophic flagellates, feeding phagotrophicallycan be toxic to zooplankton and (iii) sublethal effects maybe observed at typical field abundances, even though acute toxicityseems to be restricted to flagellate abundances observed onlyat peak events. 相似文献
10.
Primary and Secondary Induction Requirements for Flowering of Contrasting European Varieties of Lolium perenne 总被引:1,自引:0,他引:1
The flowering requirements of six European varieties of Loliumperenne L. were studied in controlled environments. In experimentson primary induction, flowering was recorded after transferto long days (LD) in a greenhouse at 1224°C. In experimentson secondary induction, primary induction was first accomplishedat 6°C/10 h daylength for 12 weeks. When evaluated by the50% heading criterion, the requirement for duration of primaryinduction at 6°C/8 h daylength was <3 weeks in Mediterranean,56 weeks in Central European and 78 weeks in Scandinavianvarieties. While Veyo (Italy) flowered profuselyregardless of temperature or daylength during primary induction,critical temperatures for primary induction in SD and LD were15 and 11°C in Baca (Czech Republic) and 11and 7°C in Falster (Denmark). The criticalphotoperiod for secondary induction at 15°C ranged from12 h in Veyo and 14 h in Baca to16.5 h in Falster and 17.5 in Kleppe(Norway). The critical number of LD cycles varied correspondingly.While the Central and North European varieties required fewerLD cycles for 50% heading at 18 than at 12°C, Veyoshowed the opposite response. It is concluded that the requirementsfor both primary and secondary induction of Lolium perenne increasewith increasing latitude of origin of the germplasm. In oneexperiment, 3987% of the inflorescences came from tillersthat were not visible on transfer from primary to secondaryinduction, thus it is also concluded that there is no juvenilestage in tillers of Lolium perenne. Copyright 2000 Annals ofBotany Company Daylength, flowering, juvenility, perennial ryegrass (Lolium perenne L.), primary induction, secondary induction, temperature, varieties, vernalization 相似文献
11.
Enantiomers of the earthy smelling odorant geosmin(t-1, 10-dimethyl-t-9-decalol) were tested on 52 human subjectsfor odor threshold ratio (+)/() variability. Thresholdconcentrations of (+) and () and their (+)/()ratios appeared to be monomodally distributed. For most subjects,the ratio varied within a predictable narrow range comparableto that found previously for carvone enantiomers and contraryto the large variability found for -ionone enantiomers (Polaket al., 1989). The natural occurring isomer, () geosminhad, on average an x11 lower threshold than (+). 相似文献
12.
The temperature dependence of the efflux kinetics of labelledwater in isolated maize roots has been studied. The purposeof these experiments was to obtain the energy of activation,E (kcal/mole), of the rate-limiting step in this radial exchangeprocess under various experimental conditions. Estimates ofE were obtained from linear relations between ln{D'w} and thereciprocal of the absolute temperature; values of the apparentdiffusion coefficient, D'w, of labelled water in the root werefound from an analytical treatment of the efflux data in termsof a cylindrical diffusion model. The energy of activation forlabelled-water exchange in normal roots was 14.9 kcal/mole.The corresponding value for dead (boiled) rootswas 3.9 kcal/mole. These values of E substantiate the view thatin normal roots the penetration of water across the membranesof the root cells constitutes the rate-determining step in theefflux whereas in dead roots extracellular diffusionof water is the source of rate-control. Similar temperature dependence studies were performed on theefflux kinetics from normal and dead roots treatedwith 105 M phenylmercuric acetate (PMA). The energiesof activation for labelled-water exchange in normal and deadroots under these conditions were respectively 15.5 and 5.3kcal/mole. Moreover, the results of the efflux experiments onPMA-treated roots were considered to indicate that this inhibitorproduces an alteration in some structural aspect of the rate-controllingmembranes. 相似文献
13.
Impedance spectroscopy was used in studying frost hardinessof leaves of two diploid rhododendron cultivars, RhododendronL. PJM and R. Cunningham's White,and their tetraploid derivatives, R. Northern Starburst(NSB) and CW4. After the growing season and initial hardeningin a greenhouse, plants were subjected to an acclimation regimein a phytotron: 3 consecutive weeks at +5, +1 and -2°C each.Hardiness was studied with controlled freezing tests beforeeach decrease in temperature and at the end of the experiment,based on data of extracellular resistance reand relaxation time of the frost-exposed leaves. The correlation of the two estimateswas 0.92. Generally, the diploid clones had better frost hardinessthan the tetraploid clones. At the end of the experiment, frosthardiness of the diploid PJM was -28.7°C andthat of the tetraploid NSB -20.6°C. Leaves of the diploidCunningham's White and of the tetraploid CW4 hardenedto -32.0°C and -20.9°C, respectively. Frost hardinessestimated by impedance spectroscopy correlated well with earlierresults based on visual scoring (r = 0.810.86) and electrolyteleakage tests (r = 0.840.90), but results from impedancespectroscopy indicated weaker hardiness than the other tests.The difference between the results from impedance spectroscopyand the other tests was smaller and more coherent within theCunningham's White clones than within PJMand NSB. Changes in extracellular and intracellular resistanceof non-frozen leaves during the acclimation correlated withthe changes in frost hardiness of Cunningham's Whiteclones, but not with those of PJM and NSB, whichbelong to another subspecies.Copyright 2000 Annals of BotanyCompany Cold resistance, evergreen, frost hardiness, impedance spectroscopy, polyploid, Rhododendron, tetraploid 相似文献
14.
Diel vertical migration (DVM) of zooplankton is considered less prominent at high latitudes where diel changes in irradiance are minimal during periods of midnight sun and polar night, leaving zooplankton without a temporal refuge and thus eliminating a key advantage of DVM. One of the shortcomings of previous DVM studies of zooplankton based on net sampling is that the depth resolution often has been too coarse to detect vertical migrations over short distances. We investigated DVM of zooplankton during August 2010 in drifting sea ice northeast of Svalbard (~81.5°N, ~30.5°E). Classical DVM behaviour (midnight rising, midday sinking) was observed between 20 and 80 m in young copepodite stages (CI–III) of Calanus finmarchicus and Calanus glacialis. The copepods Microcalanus spp., Pseudocalanus spp., Oithona atlantica, Oithona similis and Triconia borealis, alongside Eukrohnia hamata, Limacina helicina, and Fritillaria spp., all displayed signs of DVM. We conclude that zooplankton exhibit DVM in ice-covered waters over rather short distances to optimise food intake in the presence of predators. 相似文献
15.
The chlorophyll content of a water column (WCC), which is commonlyused as an index of the phytoplankton abundance, is affectedby the choice of the sampling depths and by the variations ofthe vertical structure of density. For instance, the thicknessof the water layer, between two sigma-t values, which containsthe deep chlorophyll maximum, can vary with internal waves.The resulting noise often dominates the mesoscale variationsof the observed water-column chlorophyll (OWCC). Sigma-t dependentstatistics (mean, standard deviation) of the chlorophyll concentrationare computed using the observations at 29 casts from a 22-day-longfixed station in an oligotrophic environment at 15S, 173°E.For each cast, these statistics, the sampling depths, and thewater density at these sampling depths, allow the estimationof a station-dependent expected water-column chlorophyll(EWCC). The ratio of EWCC to the overall likelihood of WCC duringthe fixed station (i.e. the mean of all OWCC) is a measure ofthe effect of sampling and variable density structure at eachcast. When this effect is removed, the noise in WCC estimatesdecreases significantly. The time variations of WCC during thefixed station then show a trend with relatively high valuesduring the first days, followed by a 12-day-long period withlow values. A regular increase occurred from 1 October, whichwas accompanied by high carbon fixation rates and was mainlydue to an increase of the chlorophyll concentration betweenthe surface and the deep chlorophyll maximum. New productionduring this active phase was estimated to be 535 mgC m2day1, corresponding to 62% of the total production. Breakingof internal waves which were recorded at the beginning of thegrowth phase and vertical mixing of nutrients can explain theobservation. 相似文献
16.
ROMERO-ARANDA R.; BONDADA B. R.; SYVERTSEN J. P.; GROSSER J. W. 《Annals of botany》1997,79(2):153-160
The effect of tetraploidy on leaf characteristics and net gasexchange was studied in diploid (2x ) and autotetraploid (4x) Valencia sweet orange (Citrus sinensis (L.)Osb.) and Femminello lemon (Citrus limon (L.)Burm. f.) leaves. Comparisons between ploidy levels were madeunder high irradiance (I) in a growth chamber or low total Iin a glasshouse. Tetraploids of both species had thicker leaves,larger mesophyll cell volume and lower light transmittance thandiploids regardless of growth I. Mesophyll surface area perunit leaf area of 2x leaves was 515% greater than on4x leaves. Leaf thickness and mesophyll cell volume were greaterin high I leaves than low I leaves. In high I, average leafarea was similar for 2x and 4x leaves, whereas in low I it was30% greater in 4x than in 2x leaves. Nitrogen and chlorophyllconcentration per cell increased with ploidy level in both growthconditions. The ratio of chlorophyll a:b was 25% greater in2x than in 4x leaves. When net CO2assimilation rate (ACO2) wasbased on leaf area, 4x orange leaves had 2435% lowerACO2than their diploids. There were no significant differencesin ACO2between 2x and 4x orange or lemon leaves when expressedon a per cell basis. Overall, lower ACO2per unit leaf area oftetraploids was related to increase in leaf thickness, largermesophyll cell volume, the decrease in mesophyll area exposedto internal air spaces, and the lower ratio between cell surfaceto cell volume. Such changes probably increased the resistanceto CO2diffusion to the site of carboyxlation in the chloroplasts. Cell volume; chlorophyll; irradiance; leaf thickness; nitrogen; photosynthesis; ploidy; Citrus limon ; C. sinensis ; Valencia sweet orange; Femminello lemon 相似文献
17.
Hydrobiological studies in the Straits of Dover show a differencebetween the characteristics of the French coastal water andthe open sea water. A cruise between Boulogne-sur-mer and Dover(October 15, 1985) confirms the existence of a frontal area(4 miles off the French coast). This area is characterized byan increase of the salinity (1%) and decrease of the suspendedmatter content (from 27 to 20 mg l1), of primary production(from 15 to 3 mg C m3h1) and of chlorophyll aconcentration (from 4.5 to 1.5 mg m3). The presence ofdifferent zooplanktonic species in the two water masses alsocharacterizes this discontinuity. Oncaea sp., Corycaeus anglicus,Centropages typicus and Calanus helgolandicus are indicatorspecies of open sea water, while Cyciopina littoralis and Saphirellaare only present in coastal water. 相似文献
18.
In nodulated common bean (Phaseolus vulgaris L.), there is typicallya period of N stress between 15 and 20 d after emergence (DAE),due to a lack of synchronization between the depletion of Nin the cotyledons and the beginning of N2 fixation and transport.Screening trials identified some Rhizobium leguminosarum bv.phaseoli strains with which symptoms of N deficiency were notvisible (precocious strains). Cultivar Negro Argelwas then inoculated with two traditional strains(C-05 and CIAT 727) and two precocious strains(CNPAF 146 and CNPAF 512), and plants were harvested from 8to 30 DAE. There were no differences between the two groupsof strains in nodule dry weight or in the acetylene reductionrates between 8 and 16 DAE. However, nodules induced by theprecocious strains showed earlier onset of glutaminesynthetase (GS) (EC 6.3.1.2
[EC]
) and glutamate synthase (GOGAT)(EC 1.4.1.14
[EC]
) activities, and ureide synthesis. The N concentrationin the nodules formed by precocious strains variedfrom 4.2 to 4.5%, whereas with the traditionalstrains, it increased from 3.2% at 8 DAE to 65% at 18 DAE, atwhich time plants exhibited N-deficiency symptoms. By 21 DAE,GS and GOGAT activities in traditional noduleswere increased, as well as the ureide-N-concentration in thexylem sap, nodule N content declined to 4.5% and the leavesbecame green. These results suggest that the N stress with traditionalstrains is not a limitation in early N2 fixation activity butrather in the rates of expression of the processes of N assimilationand transport. Key words: Glutamate synthase, glutamine synthetase, nitrogen fixation, Phaseolus vulgaris, Rhizobium 相似文献
19.
The Nitrogen Content of Plants and the Self-thinning Rule of Plant Ecology: A Test of the Core-skin Hypothesis 总被引:3,自引:0,他引:3
The core-skin hypothesis postulates that secondarilythickened plants behave energetically as an inert corecovered by an active skin, the skinbeing two-imensional, the core three-dimensional.This would explain the self-thinning or3/2 rule of plant ecology, that is, the tendencyfor log (dry weight per plant) and log (number of plants perunit area) to progress along a straight line relationship, withslope = 3/2. The hypothesis was tested as follows. Plant nitrogen contentwas used as an estimate of the mass of skin perplant, and dry weight as an estimate of the mass of the core.As plants mature the slope of the relationship between y = log(mass of nitrogen per plant) and x = log (mass of dry matterper plant) is expected to decline from an initial value of 1.0towards a final value of 0.66. The intercept of the relationshipis expected to reflect the intrinsic content of skinper unit of core. Genotypic variation in thisparameter should cause genotypic differences in the maximumattainable yield of biomass per unit area. The expectations were investigated by fitting the function y= p+qx+r exp x to 30 sets of data on plant nitrogencontent, plant weight and time in 18 different vegetables. Simplelinear regressions of y on x were fitted to more limited setsof data on weights and nitrogen contents of mature trees. Theexpectations were, with some minor exceptions, confirmed. Nitrogen, yield, plant competition, self-thinning 相似文献
20.
A general modelling approach was used to predict the changesresulting from dehydration in the Young's modulus (E) of a tereteorgan with a simple anatomy (e.g. hypodermis of thick-walledtissue surrounding a parenchymatous core of ground tissue).Two general anatomical models were investigated: (1) an apoplastmodel in which each cross section through the organ wasconsidered as a composite elastic material consisting of a solid(cell wall) and liquid (protoplasm) phase; and (2) a core-rindmodel in which the organ consisted of a thick-walledand a thin-walled tissue. For each of these two anatomical models,two composite material models were considered, i.e. a Voigtor Reuss equation was used to predict the changes in E attendingdehydration. The predictions from the variants of the generalmodel were evaluated on the basis of observed changes in E ascylindrical segments of the pseudopetioles of Spathiphyllumwere allowed to desiccate at room temperature. Statistical comparisonsbetween predicted and observed values of E revealed that oneof the simple variants of the model, the Voigt apoplastmodel, was the most successful in predicting the observedtrend seen in the changes in E. However, when the Voigt andReuss apoplast models were combined, the hybridmodel provided estimates of changes in E that were statisticallyindistinguishable from those observed. Based on the hybrid model,it was estimated that roughly 76.7% of the tissues with a representativeSpathiphyllum pscudopetiole operated according to a Voigt apoplastmodel. Young's modulus, dehydration, plant tissues 相似文献