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1.
Resistance to CO2 Fixation in the Submerged Aquatic Macrophyte Callitriche stagnalis Scop 总被引:1,自引:0,他引:1
The resistance to the photosynthetic carbon fixation in thefreshwater angiospcrm Callitriche stagnalis Scop was investigatedby gas exchange experiments in a closed water-flow system. Anelectrical analogue model was used to analyse uptake of carbonin terms of boundary layer resistance, cytoplasmic resistanceand carboxylation resistance. The most important rate-limitingfactor was the boundary layer resistance which was from 86%to 91 % of the total resistance of 8521221 s cm1.The cytoplasmic and carboxylation resistances during activephotosynthesis were of minor importance being 89 s cm1and 2430 s cm1, respectively. The calculated thicknessof the boundary layer surrounding the foliage of the shootswas 103155 µm or 23 times the total thicknessof the leaves. The physiological and morphological characteristicsof submerged aquatic macrophytes are discussed as adaptationsto the low availability of carbon due to the high boundary layerresistance. Key words: Aquatic macrophytes, Resistance to carbon fixation, Adaptations 相似文献
2.
Journal of Plankton Research, 11, 12731295, 1989. The values of P/U0 (Table I) and fluid velocity used to calculatethe energy required for sieving (pp. 12891290) and severalequations (footnote b of Table I; p. 1290, lines 34)are incorrect. The corrected table appears below: Table I. Filter setule measurements (mean and within specimenstandard deviation) of the gnathobases for the cladocerans studiedaGnathobaseof trunklimb number. bP = 8µU0/(b(1 21nt + 1/6(t2) - 1/144(t4))), whereP = pressure drop in dyn cm2, =3.1416, U0 = fluid velocityin cm s1, b = distance between setule centres in cm,t = ( x setule diameter)/b and µ = 0.0101 dyn s1cm2. Formula from Jørgensen (1983). The text (p. 1289, line 19 to p. 1290, line 10) should read: organism. Using a similar argument, a 0.5 mm Ceriodaphnia witha filter area of 0.025 mm2 (Ganf and Shiel, 1985) and pressuredrop P = 2757 dyn cm2 (with fluid velocity of 0.07 cms1) allocates only 2171 ergs h1 to filtrationof a total energy expenditure of 104 ergs h1 [filtrationenergy (ergs h1) = area (cm2) x pressure drop (dyn cm2)x 3600 (s h1) x 1/0.2 (efficiency of conversion of biochemicalinto mechanical work); total energy (ergs h1) = respiration(0.05 µl O2 ind1 h1 consumed; Gophen, 1976)x conversion factor (2 x 105 ergs µl1 O2). Withan estimated 0.034 mm2 in filter area, fluid velocity of 0.041cm s1 and respiration of 1.8 x 104 ergs h1 (calculatedfrom Porter and McDonough, 1984), a 0.5 mm Bosmina uses <4%of its metabolism to overcome filter resistance. The velocities used in the original examples (0.4 cm s1for Ceriodaphnia, 0.2 cm s1 for Bosmina) were derivedfrom literature values of appendage beat rate and estimatesof the distance travelled by the appendages during each beatcycle. This approach unnecessarily assumes that all water movedpasses through the filter. In the new calculations, the flowacross the filter needed for food to be collected by sieving(0.07 cm s1 for Ceriodaphnia and 0.041 cm s1 forBosmina) was determined from the maximum clearance rate/filterarea. The amended energy expenditures, although higher, do notrefute the sieve model of particle collection. 相似文献
3.
In this paper we report measurements concerning the conductivityof water and ions and the interaction between the two in excisedpieces of xylem of red maple stems under various conditions.We have also demonstrated that it is possible to detect theflow of solutions through the stems of maple by measuring thedegree of interaction between the flow of water and ions. Inthis technique we apply voltage pulses of ±V volts acrossa length of stem and detect the unequal current pulses resultingfrom the greater frictional drag when current (which is carriedprimarily by cations) is flowing against the water stream thanwhen flowing with the water stream. The hydraulic conductivityof recent maple sapwood ranges from 30 to 90 cm3 s1 cm2(J cm3)1 cm; in 2 mM KCl the electrical conductivityis roughly 3 x 104 mho cm1 and the electro-kineticcross coefficient is roughly 4x105 A cm2 (J cm3)1cm. 相似文献
4.
Studies on the Movement of Water Through Apple Trees 总被引:12,自引:0,他引:12
Resistances to the flow of water through young potted appletrees were estimated by measuring the transpiration rate oftrees with and without root systems. Root system resistanceswere obtained by difference. Whole-plant resistances were ofthe order 10 x 1013 Pa s m3 and there was some evidencethat root resistances (Rr) varied with transpiration rate; theratio Rr:Rx (where Rx is resistance to water flow in the stemsystem) altered from 2:1 at relatively high transpiration ratesto 1:1 at lower rates. The trunk of a 9-year-old orchard tree (trunk diameter {smalltilde}7 cm, height {small tilde}2.5 m) was cut under water andestimates of the flow resistances in this tree were obtained.These were much lower than the resistances to flow in the pottedtrees. Capacitance (defined as the change in stored water content perunit change in plant water potential) values were calculatedfor the small trees and the large tree from measurements ofweight and water potential changes after the trees were removedfrom water. They were very similar on a weight basis (approx.2.0 x 108 kg kg1 Pa1). Leaf capacitancevalues ({small tilde}1 x 108 kg Pa1 m2)were also obtained. Stomatal conductances decreased with water potential and increasedwith short-wave radiation, but the relationships were not definitive.Estimates of boundary layer conductance in a greenhouse (verylow wind speeds) were of the same order ({small tilde}5 mm s1)as values obtained previously. 相似文献
5.
PRANGE ROBERT K.; ORMROD DOUGLAS P.; PROCTOR JOHN T. A. 《Journal of experimental botany》1983,34(9):1108-1116
Experiments were conducted in a gas exchange system to examinethe effect of a water stress, induced by 200 kPa polyethyleneglycol (PEG), on carbon dioxide and water vapour flux, fronddiffusive resistance, intercellular carbon dioxide concentration,carbon dioxide residual resistance and frond water potentialin the ostrich fern (Matteuccia struthiopteris (L.) Todaro).Measurements were taken 1 d after the application of PEG. Themeasurements were made on young fronds (8 d old) and maturefronds (2024 d old) at PPFD's (Photosynthetic PhotonFlux Density) from 01400 µmol m22 s1.Water stress decreased the net photosynthesis rate in maturefronds at PPFD's of 210 µmol m2 s1 or greaterand increased the net photosynthesis rate below 210 µmolm2 s1 in young fronds. The increase in net photosynthesisin stressed young fronds was associated with a significant reductionin the dark respiration rate. Water stress and decreasing PPFD'sincreased frond diffusive resistance. Carbon dioxide concentrationin the intercellular spaces decreased with increasing frondage and PPFD's up to 200 µmol m2 s1. Theresidual resistance to carbon dioxide flux was not significantlyaffected by either frond age or water stress. Frond water potentialwas significantly lower in mature fronds than in young fronds. Key words: Matteuccia struthiopteris, Water relations, Photosynthesis, Dark respiration 相似文献
6.
The theory and practice of applying the thermodynamics of irreversibleprocesses to mass-flow theories is presented. Onsager coefficientswere measured on cut and uncut phloem and cut xylem strandsof Heracleum muntegazzimum. In 0.3 N sucrose + 1 mN KC1 theyare as follows. In phloem, LEE = 5 ? 104 mho cm1,LpE = 9 ? 106 cm3 s1 cm2 volt1 cm,and LPP = 0.16 cm3 s1 cm2 (J cm3)1cm. In uncut phloem strands LEE is about 1 ? 103 mhocm1. In xylem in 2 x 103 N KCI, Lpp = 50 to 225,LPE = 2 ? 104, and LEE = 4 ? 103. The measurementsare tentative since the blockage of the sieve plates is an interferingfactor, but if they are valid they lead to the conclusion thatneither a pressure-flow nor an electro-kinetic mechanism envisaginga long distance current pathway can be the majormotive force for transport in mature phloem. Measurementsof biopotentials along conducting but laterally detached phloembundles of Heracleum suggest, nevertheless, that there may bea small electro-osmotic component of at least 0.1 mV cm1endogenous in the phloem. 相似文献
7.
The thesis that the minimum cell-phosphorus content of planktonalgae is a light- and temperature-independent species constantwas investigated using the marine plankton diatom Thalassiosirarotula. To what extent the maximum cell-phosphorus content isalso a constant, light- and temperature-independent quantityhas been tested in parallel. At 2.5C and 3.03 nE cm2s1 the minimum and maximum cell-phosphorus contents aregreater than the values for 16C and 8.93 nE cm2 s1by a factor of 5.7. The light intensities were kept near thelight saturation for the growth rate for all experimental temperatures(2.5, 6, 12 and 16C). The light dependence of the phosphoruscontent was tested at 12C. For 1.43 nE cm2 s1the minimum phosphorus content was lower by a factor of 2.5than for 64.28 and 80.36 nE cm2 s1 respectively.The maximum P-content for 2.86 nE cm2 s1 was 3.9times higher than for 64.28 nE cm2 s1 T. rotulais, on the basis of the stored P-content, only capable of betweenthree and five cell divisions. The N/P atomic ratios were, dependingupon light and temperature, between 56:1 and 226:1 for the minimumcell-phosphorus content, which implies a pronounced phosphorusdeficiency. 相似文献
8.
The Boundary Layer over a Populus Leaf 总被引:6,自引:0,他引:6
Air flow over a Populus leaf was investigated using a hot-wireanemometer. When the air flow in the wind tunnel was laminar,the boundary layer was often turbulent at a wind speed of only1.5 m s1, particularly when encouraged by uneven topographyand roughness of the surface, as on the lower side of the leaf.The smoother upper surface behaved in a similar way to a flatplate when at low wind speeds, and the profiles of wind speedcould be shown to be equivalent to those expected from laminarboundary layer theory. Nevertheless, the boundary layer becameturbulent at Reynolds numbers much lower than those requiredto cause the transition to turbulence in a flat plate. Turbulentair flow in the wind tunnel greatly increased boundary layerturbulence but had only a small effect on evaporation from amodel of the leaf. The evaporation rates observed were 2.5 timeshigher than expected from theory, irrespective of the turbulenceregime. 相似文献
9.
Measurement of the rate of water loss and the gradient in water-vapourconcentration from the evaporating surface to the air enabledcalculation of the resistance to water loss from the leaf mesophyllof leek (Allium porruni) and from green blotting-paper. Theadditional resistance found in the case of mesophyll estimatesthe mesophyll cell-wall resistance (wall resistance). Wall resistancewas, however, small, less than 0.09 sec cm1 in turgidmesophyll and only 0.15 sec cm1 greater when the mesophyllwater deficit was 50 per cent. Results are discussed in relationto the evidence of other workers indicating greater resistancesto water loss in the mesophyll. 相似文献
10.
In-Phase Cycling of Photosynthesis and Conductance at Saturating Carbon Dioxide Pressure Induced by Increases in Water Vapour Pressure Deficit 总被引:2,自引:1,他引:1
Bunce, J. A. 1987. In-phase cycling of photosynthesis and conductanceat saturating carbon dioxide pressure induced by increases inwater vapour pressure deficit.J. exp. Bot. 38: 14131420. The leaf to air water vapour deficit was increased suddenlyfrom about 1·0 to 2·5 IcPa for single leaves ofsoybean (Glycine max L. Merr.) plants held at 30 °C, 2·0mmol m 2 s1 photosynthetic photon flux density(PPFD) and carbon dioxide pressures saturating to photosynthesis.After a lag of about 10 min, photosynthetic rate and stomatalconductance to water vapour began to decrease, and then cycledin phase with each other. The period of the cydes was about20 min. During these cycles the substomatal carbon dioxide pressurewas constant in the majority of leaves examined, and was alwaysabove saturation for photosynthesis. Epidermal impressions showedthat most stomata changed in aperture during the cycles, andthat very few were ever fully closed. Water potential measuredon excised discs changed by at most 0·1 MPa from theminima to the maxima in transpiration rate. In contrast, forleaves of sunflower (Helianthus animus L.) grown at low PPFD,the increase in VPD led to leaf wilting and decreased photosynthesis,followed by recovery of turgor and photosynthesis as stomatalconductance began to decrease. In these leaves photosynthesisand conductance then cycled approximately 180° out of phase.It is suggested that in soybeans decreased leaf conductanceinduced by high VPD provided a signal which decreased the rateof photosynthesis at carbon dioxide saturation by a mechanismthat was not related to a water deficit in the mesophyll. Key words: Photosynthesis, stomatal conductance, cycling, vapour pressure deficit 相似文献
11.
Not all phyloplankton behave as ideal water tracers. Longitudinaldispersion experiments were conducted in a large flume withseawater of constant depth and velocity. The transport of thepassive, fluorescent tracer, Rhodamine B dye, was compared withunialgal cultures of a large, fast-sinking diatom (Odontellachinensis) and a small, slow-sinking diatom (Skeletonema costatum).Horizontal dispersion rates, proportional to variance per distance,were linear for the dye and Skeletonema but nonlinear for Odontella.Results are explained by the interaction of Odontella sinkingand advection. Longitudinal dispersion coefficients for thedye and Skeletonema were between 6080 cm2 s1 andas high as 280 cm2 s1 for Odontella. This may have implicationsfor nutrient uptake in natural phytoplankton populations. 相似文献
12.
The Diffusive Conductivity of the Stomata of Wheat Leaves 总被引:2,自引:0,他引:2
A leaf chamber (described in detail) was used alternately witha resistance porometer to measure resistance to viscous flowof air through the leaf, and with a diffusion porometer to measurethe differential diffusive flow of hydrogen and air (VHVA)through the leaf and the component of hydrogen flow (V'H) movingstraight across the leaf. The resistance of the mesophyll isneeded for interpretation: estimates by three different methodsfor viscous flow did not agree very well, but two differentmethods for diffusive flow gave good agreement. For wheat leaves,only very large errors are important. Formal analysis is in three appendixes: I. Interpretation ofviscous and diffusive flow in small pores involves some problemsin molecular physics, complicated by the particular geometryof the wheat stoma. With some uncertainty, formal expressionsare derived for the viscous resistance of a single stoma, rv,and for the resistances to diffusion of hydrogen and air, andof water vapour and carbon dioxide, all expressed as rs persquare centimetre of leaf surface. The analysis for hydrogen/airis the most uncertain; that for water vapour and carbon dioxideis more reliable. II. An indication is given of the flow characteristicsof the leaf-chamber system, from which rv can be derived, andof the basis for estimating mesophyll resistance. III. The methodof converting estimates of rs into estimates of VHVAand V'H is given. The results presented are expressed as nearly as possible interms of the quantities which were measured. For five leavesthe dependence of VHVA on V'H agrees well with theoreticalpredictions; the dependence of VHVA (and V'H) on rv,on average, agrees well with prediction, but involves the assumptionthat the stomata get shorter as they close. The agreement isgood enough to suggest that the formal expressions for rs interms of stomatal dimensions and molecular gas constants arereliable enough to be carried forward into future transpirationand assimilation studies. The minimum value of ra for watervapour (c. 3 sec cm+1) is close to values found elsewhere bydifferent techniques. At very small stomatal openings there was a large deviationfrom predicted behaviour, such as would occur if the imposedexcess air pressure further closed the stomata during viscousflow experiments. 相似文献
13.
Growth of Ceratium hirundinella in a subtropical Australian reservoir: the role of vertical migration 总被引:3,自引:0,他引:3
Whittington John; Sherman Bradford; Green Damian; Oliver Roderick L. 《Journal of plankton research》2000,22(6):1025-1045
A study into the photophysiology, growth and migration of Ceratiumhirundinella in Chaffey Reservoir in subtropical northern NewSouth Wales, Australia, revealed that a proportion of cellsformed subsurface accumulations at depths that optimized lightintensity (212552 µmol photons m2 s1)for photosynthesis and cell growth. At high incident irradiance,Ceratium migrated downwards from the near-surface waters, avoidinghigh-light-induced, slow-recovering non-photochemical quenchingof photosystem II. Overnight deepening of the surface mixedlayer by convective cooling produced homogeneous distributionsof Ceratium with a significant proportion of the populationbelow the depth where light saturation of photosynthesis occurred.Ceratium migrated towards the surface from suboptimal lightintensities, at a velocity of 1.62.7 x 104 m s1.Subsurface accumulations occurred under a variety of turbulenceintensities; however, accumulation was significantly reducedwhen the turbulent velocity scale in the mixed layer was >5x 103 m s1, beyond which turbulent diffusion dominatedadvection by swimming. The formation of subsurface accumulationswith increased computed water column integral photosynthesisby 35% compared to a uniform cell distribution. 相似文献
14.
Occurrence of viable photoautotrophic picoplankton in the aphotic zone of Lake Biwa, Japan 总被引:1,自引:0,他引:1
Eguchi Mitsuru; Oketa Takemi; Miyamoto Nobukazu; Maeda Hiroto; Kawai Akira 《Journal of plankton research》1996,18(4):539-550
The distribution and abundance of photoautotrophic picoplankton(PPP. Synechococcus group) in the aphotic bottom sediments ofLake Biwa were investigated by direct counting and viable counting(most probable number, MPN) methods. In the surface layer ofbottom sediments (01 cm). where large PPP blooms occurredin the past 5 years, >105 cells cm3 of PPP were foundto be viable throughout the year. Furthermore, the density ofPPP deposited on the sediment surface (00.1 cm) was oneorder of magnitude higher (MPN = 1.3 x 106 cells cm3.direct count = 9.9 x 106 cells cm3) than that of bulkedsurface sediments (01 cm). Even in the deeper layer (1314cm) of bottom mud, viable PPP were still found (101 cells cm1.In winter, viable PPP in the aphotic bottom sediments were 104105times greater per Unit volume than those in the euphotic lakewater. Since the aphotic bottom sediments have high levels ofPPP, as well as high growth potential (high ratio of viablecount/total direct count), they are likely to seed PPP bloomsin the North Basin of Lake Biwa. 相似文献
15.
Apparatus is described for exposing plants to low concentrationsof SO2 (50500µg m3 in air) and for measuringeffects on photosynthesis, dark respiration, and transpiration.Temperature, humidity, and irradiance in the chambers were controlledindependently, and fans ensured that leaf boundary layer resistanceswere low. Experiments with plants of Vicia faba in clean andpolluted air showed that: (i) a depression of net photosynthesisby 50 µg m3 SO2 depended on boundary layer resistanceand on irradiance; (ii) stomatal resistance was increased ordecreased by 50 µg m3 SO2 when relative humidityin the chambers was low (35% r.h., 22 °C) or high (50% r.h.,22 °C) respectively. 相似文献
16.
Size, composition and distribution of particles related to wind induced resuspension in a shallow tropical lagoon 总被引:4,自引:0,他引:4
The size, composition and distribution of particles in the watercolumn were surveyed in a shallow area (1 m depth) of a tropicallagoon (Cte d'Ivoire) during a sequence of wind-induced resuspension.Water samples were collected hourly near the surface duringone tidal cycle. Three characteristic periods were distinguished:a calm period with low wind speed (average 1.2 m s1 awindy period with wind speed >3 m1 s (range between4 and 6 m s1) inducing sediment resuspension and a relaxationperiod during the decrease of wind velocity. From the analysisof several parameters (particle size and volume, bacteria. pico-and nanophytoplankton, ciliates and detritus), sediment resuspensioncaused a regular injection of particles from the bed. The finestparticles (1.56 µm: chlorophytes such as Chiorellaspp., picocyanobacteria such as Synechococcus) were the firstto be affected by wind-induced turbulence, whereas large particles(612 µm: diatoms. cyanobacteria such as Lyngbiaspp.) were dispersed into the water column at the highest windspeed. The fate of the different seston components differedaccording to their size. Therefore, wind-induced resuspensioncould greatly influence the food web organization through thequantity, quality and size of edible particles available ata given time. 相似文献
17.
The photosynthetic responses of eight tree and shrub speciesto simulated sunflecks was measured in the field. The net carbonexchange (NCE) of Corylus avellana and Ulmus glabra increasedwith irradiance up to the maximum irradiance of 230 µmolm2 s1. The NCE of Fraxinux excelsior, Hedera helixand the sun and shade forms of Rhododendron ponticum saturatedat about 120 µmol m2 s1 whereas the NCEof Ilex aquifolium, Daphne laureola and Fagus sylvatica hadeffectively saturated at 27 µmol m2 s1. In all cases the quantum efficiency of NCE could be predictedfrom measurements of chlorophyll fluorescence and the maximumvalue for NCE from measurements of stomatal conductance. Therelationships were combined into a model for predicting NCE/irradiancecharacteristics. Corylus avellana L., Daphne laureola L., Fagus sylvatica L., Fraxinus excelsior L., Hedera helix L., Ilex aquifolium L., Prunus laurocerasus L., Rhododendron ponticum L., Ulmus glabra Huds., gas exchange, stomatal resistance, water use efficiency, chlorophyll fluorescence, quantum efficiency 相似文献
18.
A Method for Separating Cuticular and Stomatal Components of Gas Exchange by Amphistomatous Leaves: II. EXPERIMENTAL SOLUTION 总被引:1,自引:1,他引:0
The apparent cuticular component of transpiration of stomatabearing leaf epidermis was estimated by restricting stomataldiffusion by mass flow of air in the opposite direction. Thiswas achieved by applying an air pressure gradient across theamphistomatous leaf. Some assumptions of the previously suggestedmethod (antrcek and Slav?k, 1990) were experimentally verifiedusing maize leaves. The technique makes possible a quantitativeestimation of cuticular water loss including that of the externalperistomatal (i.e. vapour not passing through the pores) andthe respective conductance when the stomata are partially open. In addition to the fact that the cuticular portion of the totalleaf vapour loss (i.e. relative cuticular transpiration) dependson stomatal opening, even the absolute value of apparent cuticulartranspiration was (1) increased by lower vapour pressure deficitand (2) decreased with closing stomata. These changes, inducedby variations in a vapour pressure deficit of 2.45?0.35 kPa,ranged between 0.66?0.14µg cm 2 s1. Theabsolute value of apparent cuticular transpiration changed onaverage by a factor of 2.3 due to stomata opening or closingwhich was induced by turning the light on or by exogenous ABAapplication. Possible interference by residual vapour diffusingthrough the stomatal pore was evaluated by the model application.An attempt was also made to assess the cuticular component ofCO2-uptake rate. Experimental results are discussed in contextwith the feedforward response of stomata to air humidity. Key words: Cuticular transpiration, cuticular CO2-uptake, feedforward response, maize 相似文献
19.
Transpiration of Festuca arundinacea Schreb, strain S170, wasmeasured at two different wind speeds in a controlled-environmentwind tunnel. As a result of a wind increase from 1 m s1to 3.5 m s1 above the sward, transpiration graduallyincreased, especially at night-time. Similar effects were notedin three other grass species. The transpiration increase couldbe attributed to decreases in stomatal and cuticular resistances,as a result of leaf buffeting. 相似文献
20.
Stomatal Control of Photosynthesis of Eucalyptus globulus Labill. Trees under Field Conditions in Portugal 总被引:4,自引:0,他引:4
Pereira, J. S., Tenhunen, J. D. and Lange, O. L. 1987. Stomatalcontrol of photosynthesis of Eucalyptus globulus Labill. treesunder field conditions in Portugal.J. exp. Bot. 38: 16781688. Stomatal behaviour of adult leaves of Eucalyptus globulus treeswas studied under field conditions in Portugal. In the absenceof severe plant water stress stomata were open when the summedtotal of photosynthetically active photon flux density incidenton both leaf surfaces was above 100 µmol m2s1 and leafconductance to water vapour reached 245 mmol m 2 s1 on a total(both epidermes) leaf area basis. The stomata of both leaf epidermesresponded similarly to changes in solar radiation and waterstress. Water stress resulted in decreasing daily maxima inleaf conductance as predawn leaf water potential decreased.Maximal leaf conductance decreased to less than 50 mmol m 2s 1 when predawn leaf water potential decreased below 1·0MPa. At similar values of predawn leaf water potential stomatawere more closed as the leaf to air water vapour partial pressuredifference increased. The effect of increasing air dryness onstomata was greatest at high predawn leaf water potential. Dailymaxima in photosynthetic rates and in leaf conductance werelinearly related to one another in spring and summer. Both decreasedwith increase in leaf water stress. In autumn and winter, increasesin leaf conductance occurring under natural conditions duringthe course of the day were not necessarily accompanied by increasesin net photosynthesis. Stomata were more closed in the afternoonthan in the morning at the same rates of net photosynthesis,temperature or leaf to air water vapour partial pressure difference. Key words: Eucalyptus globulus,, photosynthesis, stomata, water stress. 相似文献