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1.
The action spectrum for promotion of elongation of protonemata of Onoclea sensibilis has peaks at 400–420, 580–600 and 640–660 nm. The largest growth increments at saturating light doses are produced by yellow and far-red light. Elongation induced by yellow and far-red irradiation persists in old as well as young filaments, while red-light promotion is found only in young filaments. The growth promotion caused by yellow light is partially reversed by red light down to the level of growth produced by red irradiation alone. Elongation of rhizoids is under reversible red, far-red control, while yellow light is inactive. A model is proposed and discussed in which the light-sensitive elongation of filaments is accounted for by the presence of three distinct photoreceptors: phytochrome; a pigment absorbing yellow light. P580; and a pigment absorbing blue light, P420. 相似文献
2.
Light and dark bottle experiments, carried out in three systemsin the Netherlands, were used to estimate the parameters ofmodels relating the oxygen production rate to incident lightintensity. The maximum production rate (PM) and the light saturationconstant (IS) were estimated using both gross and nett oxygenproduction data. In the latter case, the community oxygen consumptionrate (Rox was also estimated. Eight models were compared withrespect to goodness of fit, as has been accomplished previouslyby Jassby and Platt (Limnol. Oceanogr., 21, 540547, 1976)and many others. This study, however, emphasizes the problemof parameter correlation and the consequential usefulness ofthese type of experiments to identify the P/I curve parameters.The results show that at a 90% level of confidence, the modelscannot be distinguished with respect to goodness of fit. However,the models do show distinct differences in parameter correlation.Parameter correlation was shown to be related to the shape ofthe curve. P/I curves with high convexity were shown to be lesssensitive for parameter correlation. In particular, models showinglow convexity suffer from over-paraineterisation, which meansthat on the basis of the observed production rates it is difficultto discriminate between the parameters. Also, alternative modelformulations, using PM and the initial slope (), were investigated.These formulations produced less parameter correlation. However,for models with low convexity, showing high parameter correlationanyway, the reduction is limited. The use of nett oxygen productiondata does not show a significant difference in fit at a 90%confidence level. However, measured Rox from dark bottle experimentstends to be higher than the values found by estimating Rox fromnett oxygen production. 相似文献
3.
The reversibly photochromic pigment, phycochrome c, was extracted from the blue-green alga Nostoc muscorum strain A. Action spectra were determined for in vitro conversions of the pigment from the short wavelength to the long wavelength form and vice versa. The action peak for the absorbance decrease at 650 nm is at 630 nm. During this decrease there is only a slight increase of the absorbance in the green region. Green and yellow light (maximum efficiency at 580 nm) completely restores absorbance at 650 nm. The observations are explained by the existence of three spectrally different forms of phycochrome c: Pc630 and Pc650 which equilibrate in darkness and Pc580 which is reversibly photoconvertible to Pc630. We have also measured the absorbance changes brought about by saturating irradiations with light of various wavelengths (“photostationary state spectrum”). Extreme photostationary states were obtained with about 650 nm and 500 nm light. 相似文献
4.
A short-day duckweed, Lemna paucicostata 6746, was exposed tocontinuous darkness at 26?C, and the changes in the floral parameters(3) due to far-red and/or red light pulse given at various timesof the dark period were studied. Parameters a (vegetative growth rate) and (flowering ratio)were respectively decreased and increased with a far-red lightpulse given at the outset of the dark period. The decreaseda and the increased remained almost unchanged until the 7thhour, but returned to their initial levels thereafter. The far-redlight actions on a and were reversed by subsequent exposureto red light. Parameter P1 (pre-flower induction period) wasextended by 1 day when far-red and/or red pulse was given atabout the 7th hour of the dark period. A far-jed pulse givenat the outset of the dark period only affected parameter P2(flower induction period). Although the sensitivity of P2 tored light increased with time, its sensitivity to far-red lightremained constant and at about the 7th hour was equally sensitiveto far-red and red lights. Both red and far-red pulses givenlater than the 7th hour were increasingly ineffective on P2.The red/far-red reversibility occurred only for the action onP2 of the far-red pulse applied during the early dark period.Parameter P4 (flower production period) varied rhythmicallyin length with a far-red puke, the maximum shortening and extensionbeing induced by the pulse given at about the 7th and 19th hours,respectively. The sensitivity of P4 to red light also changedrhythmically with an inverse phase angle to the rhythmic responseto farred light, and the far-red and red light actions werereversed respectively by subsequent red and far-red lights. These findings suggested that multiple timing devices includingan hourglass-type clock and a circadian clock are involved induckweed flowering. (Received October 25, 1978; ) 相似文献
5.
Kobayashi Hiroaki; Yamada Masahiro; Taniguchi Mitsutaka; Kawasaki Michio; Sugiyama Tatsuo; Miyake Hiroshi 《Plant & cell physiology》2009,50(1):129-140
In C4 plants, bundle sheath (BS) chloroplasts are arranged inthe centripetal position or in the centrifugal position, althoughmesophyll (M) chloroplasts are evenly distributed along cellmembranes. To examine the molecular mechanism for the intracellulardisposition of these chloroplasts, we observed the distributionof actin filaments in BS and M cells of the C4 plants fingermillet (Eleusine coracana) and maize (Zea mays) using immunofluorescence.Fine actin filaments encircled chloroplasts in both cell types,and an actin network was observed adjacent to plasma membranes.The intracellular disposition of both chloroplasts in fingermillet was disrupted by centrifugal force but recovered within2 h in the dark. Actin filaments remained associated with chloroplastsduring recovery. We also examined the effects of inhibitorson the rearrangement of chloroplasts. Inhibitors of actin polymerization,myosin-based activities and cytosolic protein synthesis blockedmigration of chloroplasts. In contrast, a microtubule-depolymerizingdrug had no effect. These results show that C4 plants possessa mechanism for keeping chloroplasts in the home position whichis dependent on the actomyosin system and cytosolic proteinsynthesis but not tubulin or light. 相似文献
6.
P2Z/P2X7 receptor-dependent apoptosis of dendritic cells 总被引:6,自引:0,他引:6
Coutinho-Silva Robson; Persechini Pedro M.; Bisaggio Rodrigo Da Cunha; Perfettini Jean-Luc; Neto Ana Cristina Torres De Sa; Kanellopoulos Jean M.; Motta-Ly Iris; Dautry-Varsat Alice; Ojcius David M. 《American journal of physiology. Cell physiology》1999,276(5):C1139
Macrophages andthymocytes expressP2Z/P2X7nucleotide receptors that bind extracellular ATP. These receptors playa role in immune development and control of microbial infections, but their presence on dendritic cells has not been reported. Weinvestigated whether extracellular ATP could triggerP2Z/P2X7receptor-dependent apoptosis of dendritic cells. Apoptosis could beselectively triggered by tetrabasic ATP, since otherpurine/pyrimidine nucleotides were ineffective, and it wasmimicked by the P2Z receptoragonist, benzoylbenzoyl ATP, and blocked by magnesium and theirreversible antagonist, oxidized ATP. RT-PCR analysis confirmed themRNA expression of theP2Z/P2X7receptor and the absence of P2X1.Caspase inhibitors and cycloheximide had only a partial effect on theapoptosis, suggesting that a caspase-independent mechanism may also beoperative. Brief treatment with ATP led to an increase in theintracellular calcium concentration and permeabilization of the plasmamembrane to Lucifer yellow, which diffused throughout the dendriticcell cytosol. Other small extracellular molecules may thus attain a similar intracellular distribution, perhaps activating endogenous proteases that contribute to initiation of apoptosis. 相似文献
7.
Light-induced absorbance changes in the region around the redabsorption band of chlorophyll a were measured in cells andlamella fragments of Anacystis nidulans. In both materials,absorbance decreases were observed at 702 mµ and 682 mµ.(The pigments are designated as P700 and P680.) The nature ofP680 was investigated with special reference to its relationshipto P700. In the cells, light absorbed by chlorophyll a causedan absorbance decrease at 682 mµ; Simultaneous illuminationwith light absorbed by phycocyanin caused a partial recoveryof the absorbance decrease. Similar results were observed withthe light-induced absorbance change at 702 mµ. This indicatesthat P680 is also an electron carrier in the electron transportchain and occupies a place between the two photoreactions. Inlamella fragments, both the light-induced reversible absorbancechanges of P680 and P700 appeared in the presence of an electrondonor system; i.e., ascorbate and 2,6-dichlorophenolindophenolor N,N,N',N'-tetramethyl-l,4-phenylenediamine. The experimentsin which the oxidation-reduction potential of the reaction mediumwas changed showed that both P680 and P700 are one-electroncarriers, having a normal oxidation-reduction potential of 0.44v (assuming that the normal oxidation-reduction potential ofthe ferricyanide-ferrocyanide system is 0.409 v). A possibilitywas suggested that the absorbance change observed at 682 mµis another expression of the oxidation-reduction reaction ofP700). (Received October 30, 1968; ) 相似文献
8.
Effect of 17days of bed rest on peak isometric force and unloaded shortening velocity of human soleus fibers 总被引:6,自引:0,他引:6
Widrick J. J.; Romatowski J. G.; Bain J. L.W.; Trappe S. W.; Trappe T. A.; Thompson J. L.; Costill D. L.; Riley D. A.; Fitts R. H. 《American journal of physiology. Cell physiology》1997,273(5):C1690
The purpose of this study was to examine the effect of prolongedbed rest (BR) on the peak isometric force(Po) and unloaded shorteningvelocity (Vo)of single Ca2+-activated musclefibers. Soleus muscle biopsies were obtained from eight adult malesbefore and after 17 days of 6° head-down BR. Chemicallypermeabilized single fiber segments were mounted between a forcetransducer and position motor, activated with saturating levels ofCa2+, and subjected to slacklength steps. Vowas determined by plotting the time for force redevelopment vs. theslack step distance. Gel electrophoresis revealed that 96% of the pre-and 87% of the post-BR fibers studied expressed only the slow type Imyosin heavy chain isoform. Fibers with diameter >100 µm made uponly 14% of this post-BR type I population compared with 33% of thepre-BR type I population. Consequently, the post-BR type I fibers(n = 147) were, on average, 5%smaller in diameter than the pre-BR type I fibers(n = 218) and produced 13% lessabsolute Po. BR had no overalleffect on Po per fibercross-sectional area(Po/CSA), even though halfof the subjects displayed a decline of 9-12% inPo/CSA after BR. Type Ifiber Voincreased by an average of 34% with BR. Although the ratio of myosinlight chain 3 to myosin light chain 2 also rose with BR, there was nocorrelation between this ratio andVo for either thepre- or post-BR fibers. In separate fibers obtained from the originalbiopsies, quantitative electron microscopy revealed a 20-24%decrease in thin filament density, with no change in thick filamentdensity. These results raise the possibility that alterations in thegeometric relationships between thin and thick filaments may be atleast partially responsible for the elevatedVo of the post-BRtype I fibers. 相似文献
9.
The quantum yields of O2 evolution (o2), CO2 fixation (co2)and of photosystem II measured by fluorescence analysis (PSII),were determined in a mutant of tobacco (C3) and a mutant ofmaize (C4) having large deficiencies in light harvesting chlorophyll,but having similar capacities for photosynthesis on a leaf areabasis as the wild-type plants. The heterozygous dominant mutantof tobacco (aurea, Su/+) having 30% chlorophyll content of thewild-type, and of maize (oil yellow, Oy/+) having 60% chlorophyllcontent of the wild-type, maintain high leaf absorptances. Themaximum o2 on an absorptance basis, measured under limitingred light and saturating CO2 were the same in the mutant versuswild-type plants. PSII and co2 decreased in a similar mannerwith increasing light intensity, while the ratio of PSII/co2under varying light remained reasonably constant, in mutantversus wild-type seedlings. The results indicate that theseC3 and C4 mutants which have high capacities for photosynthesisdespite large deficiencies in chlorophyll content, maintaina high leaf absorptance, and a balanced utilization of absorbedquanta in photochemistry.
1Present address: Botany Dept., University of California, Davis,CA, 95616, U.S.A. 相似文献
10.
Protonemata of the fern Adiantum capillus-veneris grown undercontinuous red light for 6 days were kept in darkness for 15h and subsequently centrifuged 3 times in different directions,so that oil droplets and other cytoplasm were removed from theapical region of the protonemata. Electron micrographs clearlydemonstrated that cell wall, plasma membrane, ectoplasm andmicrotubules remained in the apical and subapical regions afterthe centrifugal treatments. A brief local exposure of the flankof the subapical region of the centrifuged protonemata to amicrobeam of red light effectively induced a phototropic responsetoward the irradiated side, suggesting that phytochrome is locatedin the ectoplasm and/or plasma membrane. When the flank of thecentrifuged protonema was irradiated with linearly polarizedred or far-red light, red light with an electrical vector parallelto the cell surface was more effective than that perpendicularto the cell surface. The direction of the electrical vectorof far-red light for reversion of the preirradiated red lighteffect, however, was opposite. These results suggest that differentdichroic orientations of PR and PFR exist in the plasma membraneor ectoplasm. (Received May 26, 1983; Accepted September 1, 1983) 相似文献
11.
Effects of temperatures ranging from 16 to 31?C on inductionand production of flowers in Lemna paucicostata 6746 were studiedin uninterrupted and interrupted darkness. In uninterrupted darkness, the growth rate (a) and floweringratio () increased and the flower production period (P4) decreasedas the temperature rose. On the contrary, the pre-flower inductionperiod (P1) and the flower induction period (P2) were independentof temperature except that P2 was remarkably extended at 31?C.Thus, a, and P4 may be rate-limited by chemical reactions andP1 and P2 by physical reactions. P2 started at the onset ofdarkness. A red light pulse given 7 hr after the start of the dark periodextended P1, P2 and P4 without modifying a and at any temperature.The pulse extended P1 by one day irrespective of temperature,and the sensitivity of P1 to the pulse was constant at all temperatures.The red light pulse caused obvious extensions of P2 and P4 at2126?C, but no extension at lower and higher temperatures.Thus, the extension of P1 by red light seems to be rate-limitedby a physical reaction and those of P2 and P4 by chemical reactions. (Received September 26, 1978; ) 相似文献
12.
The vertical distribution of the cyanobacterium Planktothrir(Oscillazoria) rubescens in Lake Zrich was investigated fromMarch 1993 to June 1995 by collecting filaments on filters andmeasuring them by epifluorescence microscopy and computer imageanalysis. The initial population, which began to stratify inApril, decreased by up to 99% by June. During the summer, thepopulation peaked at depths of 815 m; it reached a maximumareal filament-volume concentration of -60 cm 3 of lakesurface in early September and was then entrained in the deepeningsurface layer. It became mixed progressively deeper, to thelake bottom in the cold winter of 199394, but less completelyin the milder winter of 199495. Most of the filamentsremained viable during the winter. At the end of the mild winterof 19945, 70% of filaments in the water column retainedbuoyancy, but after the cold winter of 19967 only 22%were buoyant. Few remained buoyant below 80 m, where the hydrostaticpressure caused gas vesicle collapse. The proportion that remainbuoyant decreases with the depth and duration of winter mixing,and increases with the critical collapse pressure (Pc) of thegas vesicles, which provide buoyancy. Strains of P.rubescensisolated from Lake Zrich differed in mean (Pc) of their gasvesicles, from 0.9 to 1.1 MPa, the highest values in freshwatercyanobacteria. Allowing for a turgor pressure of 0.2 MPa. thesestrains would remain buoyant at depths down to 70 and 90 m,respectively. Natural selection for gas vesicles of high (Pc)will operate by increasing the proportion of filaments thatremain buoyant in the upper parts of the water column aftercirculation to various depths during the winter because onlybuoyant filaments will form the inoculum for the following season. 相似文献
13.
Flowering (number of flowers) of a short-day duckweed, Lemnapaucicostata 6746, in continuous darkness at 26?C was affectedby a red light pulse in various ways depending on the time ofapplication. A conspicuous inhibition and a slight promotionwere respectively caused by the pulse given at the 7th and 19thhours of the dark period. Of the recently introduced floral parameters (4), a (vegetativegrowth rate) and (flowering ratio) were almost unchanged bythe pulse given at any time. P1 (pre-flower induction period)was extended by one day when the pulse was given at about the7th hour of the dark period. The pulse greatly extended P2 (flowerinduction period) when given at about the 7th hour of the darkperiod. A pulse given earlier or later was increasingly ineffectiveon P2. P4 (flower production period) changed rhythmically (i.e.,was extended or shortened) with the time of the red light pulse,the maximum extension and shortening being induced by the pulsegiven at about the 7th and 19th hours, respectively. Differenttiming mechanisms were suggested as controlling the sensitivitiesto the red light pulse of P1 and P2 or P4. The floral response (number of flowers) vs. the red light pulseapplication time curve was explained in terms of the sum ofthe responses of P2 and P4 to the pulse. Floral parameters P1and P2 were defined more clearly. (Received September 4, 1978; ) 相似文献
14.
Anwaruzzaman ; Sawada Shinichi; Usuda Hideaki; Yokota Akiho 《Plant & cell physiology》1995,36(3):425-433
The mechanism of the regulation of the activation of ribulose1,5-bisphosphate carboxylase/ oxygenase (RuBisCO) by inorganicphosphate (Pi) in the presence of limiting concentrations ofCO2 was explored. The activation state of RuBisCO increasedsigmoidally following a biphasic kinetics against the concentrationof Pi in the activation mixture with an intermediary plateauat 2 to 3 mM Pi when the enzyme was activated for 30 min. Theintermediary plateau could not be seen when the preincubationtime was 10 min and the activation was completed at 10 mM Pi.RuBisCO from Euglena also showed a quite similar activationkinetics. The activation was not due to the contaminating CO2included in the stock Pi solution or in the activation buffercontaining the enzyme. The experiments with 2-carboxyarabinitol1,5-bisphosphate showed that the Pi stimulated activation wasdue to the promotion of binding of the activator CO2 to theactivation sites. It was also found that Pi increased the affinityof RuBisCO for the activator CO2 5.4-fold accompanied by a decreaseof the half-saturating concentration of CO2 to 1.6 µMat 20 mM MgCl2. Physiological significance of the effects ofPi on the activation of RuBisCO is discussed.
2Present address: Laboratory of Plant Molecular Physiology,Research Institute of Innovative Technology for the Earth (RITE),9-2 Kizugawadai, Kizu-cho, Soraku-gun, Kyoto, Japan. 相似文献
15.
Action spectra studies have shown that in the short day plant(SDP) Lemna paucicostat441 there are at least two actions ofphytochrome in the induction of flowering. At the beginningof the dark period far-red light inhibited flowering, and theaction spectrum corresponded to the absorption spectrum of PFR,while at the middle of the inductive dark period both red andfar-red light were inhibitory. The action spectrum for the redlight corresponded to that of PR absorption, but there was activityin the region beyond 720 nm which exactly coincided with theabsorption by PFR observed at the beginning of the dark period,indicating that at the middle of the dark period there was absorptionby both PR and PFR. The difference in quantum efficiency betweenthe red and far-red light effects was about 60-fold. These resultsare consistent with there being a stable pool of PFR necessaryfor the induction of flowering and another pool of phytochromein a different cellular environment which participates in thenight-break reaction as PR.
1 Present address: School of Applied Biology, Faculty of Science,Lancashire Polytechnic, Preston PR1 2TQ, U.K.
2 2 Present address: Division of Environmental Biology, NationalInstitute for Environmental Studies, Yatabemachi, Tsukuba, Ibaraki305, Japan.
3 Present address: Division of Plant Biological Regulation,The Riken Institute for Frontier Research Program, Hirosawa,Wako-shi, 351-01, Japan. (Received December 13, 1986; Accepted July 17, 1987) 相似文献
16.
温度对黄瓜幼苗光合生理弱光耐受性的影响 总被引:3,自引:0,他引:3
以不耐弱光的津研2号和较耐弱光的戴多星黄瓜(Cucumis sativus L.)为试材,在人工气候室内研究适温25 ℃/18 ℃(昼/夜)、亚适温15 ℃/9 ℃和低温9 ℃/7 ℃对弱光(75~85 μmol·m-2·s-1)耐受性的影响.结果表明:弱光下黄瓜叶片的SPAD、净光合速率(Pn)、气孔导度(Gs)、蒸腾速率(Tr)、水分利用效率(WUE)、实际光化学效率(ΦPSⅡ)、光化学猝灭(qP)等指标下降,下降程度随温度的降低而加剧,而超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)活性上升.逆境解除后的恢复过程中,光合和荧光参数逐渐恢复,荧光参数恢复速度快于气体交换参数.弱光下温度越低对黄瓜幼苗叶片光合机构造成的伤害越重,低温降低了叶片对弱光的耐受性.在低温、弱光处理过程中,津研2号Pn、ΦPSⅡ、qP等下降程度较戴多星明显,而在随后的恢复过程中其回升速度较戴多星迟缓,表明弱光下戴多星对低温的耐受性强于津研2号. 相似文献
17.
The relationship between germination and PFR level in sporesof the fern Lygodium japonicum was investigated. Percent PFRestimated from direct spectrophotometric measurement of sporesincreased with the logarithm of total fluence of 660 nm-light.The transformation from PR to PFR was saturated by giving ca.200 Jm2 of 660 nm-light and half-saturated by ca. 55J2 of 660 nm-light. Clear positive correlation was observedbetween % PFR levels and germination rates in spores irradiatedwith 660 nm and/or 730 nm-light, or with 686 or 700 nm-light.The PFR percentage in spores was raised to 1634% by blue(415 nm) light irradiation. This PFR level was enough to causesome germination when produced by monochromatic light of redto far-red region, but blue light did not cause any germination. After 660 nm-light irradiation, the PFR level decreased graduallyin darkness (25±1°C) and PFR completely disappearedin 8 h, but 730 nm-light given even 16 h after 660 nm-lightirradiation inhibited germination.
4Present address: Tropical Botanic Garden and Research Institute,Navaranga Road, Trivandrum 695 011, India. (Received March 15, 1983; Accepted June 4, 1983) 相似文献
18.
Previous study and our laboratory have reported that short-wavelength (blue and green) light and combination stimulate broiler growth. However, short-wavelength stimuli could have negative effects on poultry husbandry workers. The present study was conducted to evaluate the effects of human-friendly yellow LED light, which is acceptable to humans and close to green light, on broiler growth. We also aimed to investigate the potential quantitative relationship between the wavelengths of light used for artificial illumination and growth parameters in broilers. After hatching, 360 female chicks (“Meihuang” were evenly divided into six lighting treatment groups: white LED strips (400–700 nm, WL); red LED strips (620 nm, RL); yellow LED strips (580 nm, YL); green LED strips (514 nm, GL); blue LED strips (455 nm, BL); and fluorescent strips (400–700 nm, FL). From 30 to 72 days of age, broilers reared under YL and GL were heavier than broilers treated with FL (P < 0.05). Broilers reared under YL obtained the similar growth parameters with the broilers reared under GL and BL (P > 0.05). Moreover, YL significantly improved feeding efficiency when compared with GL and BL at 45 and 60 days of age (P < 0.05). In addition, we found an age-dependent effect of light spectra on broiler growth and a quantitative relationship between LED light spectra (455 to 620 nm) and the live body weights of broilers. The wavelength of light (455 to 620 nm) was found to be negatively related (R
2 = 0.876) to live body weight at an early stage of development, whereas the wavelength of light (455 to 620 nm) was found to be positively correlated with live body weight (R
2 = 0.925) in older chickens. Our results demonstrated that human-friendly yellow LED light (YL), which is friendly to the human, can be applied to the broilers production. 相似文献
19.
In Lemna paucicostata 6746, P2 (flower induction period) incontinuous darkness was largely extended by dilution of 1/2H1S medium (Hutner's medium supplemented with 1% sucrose) to1/10 strength. The dilution of 1/2 H1S medium to 1/10 strengthremoved completely the extension of P1 (pre-flower inductionperiod) and P2 due to a red light pulse given at the 7th h ofthe dark period, which was observed in 1/2 H1S medium. When iron and phosphate ions were added to 1/10 H1S medium upto the same concentration as in 1/2 H1S medium, the extensionof P2 was removed completely. The red light pulse-induced extensionof P1 was observed in 1/10 H1S medium only when iron ions wereadded. It is suggested that iron (Fe$ $) and phosphate ionsare important in determining the rate of photoperiodic flowerinduction in L. paucicostata 6746. (Received December 23, 1983; Accepted June 6, 1984) 相似文献
20.
Limitations on photosynthesis of competing individuals in stands and the consequences for canopy structure 总被引:7,自引:0,他引:7
The canopy structure of a stand of vegetation is determined by the growth patterns of the individual plants within the stand and the competitive interactions among them. We analyzed the carbon gain of individuals in two dense monospecific stands of Xanthium canadense and evaluated the consequences for intra-specific competition and whole-stand canopy structure. The stands differed in productivity, and this was associated with differences in nitrogen availability. Canopy structure, aboveground mass, and nitrogen contents per unit leaf area (Narea) were determined for individuals, and leaf photosynthesis was measured as a function of Narea. These data were used to calculate the daily carbon gain of individuals. Within stands, photosynthesis per unit aboveground mass (Pmass) of individual plants increased with plant height, despite the lower leaf area ratios of taller plants. The differences in Pmass between the tallest most dominant and shortest most subordinate plants were greater in the high-nitrogen than in the low-nitrogen stand. This indicated that competition was asymmetric and that this asymmetry increased with nitrogen availability. In the high-nitrogen stand, taller plants had a higher Pmass than shorter ones, because they captured more light per unit mass and because they had higher photosynthesis per unit of absorbed light. Conversely, in the low-nitrogen stand, the differences in Pmass between plants of different heights resulted only from differences in their light capture per unit mass. Sensitivity analyses revealed that an increase in Narea, keeping leaf area of plants constant, increased whole-plant carbon gain for the taller more dominant plants but reduced carbon gain in the shorter more subordinate ones, which implies that the Narea values of shorter plants were greater than the optimal values for maximum photosynthesis. On the other hand, the carbon gain of all individual plants, keeping their total canopy N constant, was positively related to an increase in their individual leaf area. At the same time, however, increasing the leaf area for all plants simultaneously reduced the carbon gain of the whole stand. This result shows that the optimal leaf area index (LAI), which maximizes photosynthesis of a stand, is not evolutionarily stable because at this LAI, any individual can increase its carbon gain by increasing its leaf area. 相似文献