A Canopy Photosynthesis Model for the Dynamics of Size Structure and Self-thinning in Plant Populations

A dynamic model for growth and mortality of individual plantsin a stand was developed, based on the process of canopy photosynthesis,and assuming an allometric relationship between plant heightand weight, i.e. allocation growth pattern of plant height andstem diameter. Functions G(t, x), for the mean growth rate ofindividuals of size x at time t, and M(t,x), for the mortalityrate of individuals of size x at time t, were developed fromthis model and used in simulations. The dynamics of size structurewere simulated, combining the continuity equation model, a simpleversion of the diffusion model, with these functions. Simulationsreproduced several well-documented phenomena: (1) size variabilityin terms of coefficient of variation and skewness of plant weightincreases at first with stand development and then stabilisesor decreases with an onset of intensive self-thinning; (2) duringthe course of self-thinning, there is a power relationship betweendensity and biomass per unit ground area, irrespective of theinitial density and of the allocation-growth pattern in termsof the allometric parameter relating plant height and weight.The following were further shown by simulation: (a) competitionbetween individuals in a crowded stand is never completely one-sidedbut always asymmetrically two-sided, even though competitionis only for light; (b) plants of ‘height-growth’type exhibit a greater asymmetry in competition than plantsof ‘diameter-growth’ type, (c) the effect of competitionon the growth of individuals in a crowded stand converges toa stationary state, even when the stand structure still changesgreatly. All of these theoretical results can explain recentempirical results obtained from several natural plant communities.Finally, a new, general functional form for G(t, x) in a crowdedstand is proposed based on these theoretical results, insteadof a priori or empirical growth and competition functions. Canopy photosynthesis, competition mode, continuity equation, self-thinning, simulation, size distribution     

Effects of Density and Extinction Coefficient on Size Variability in Plant Populations

The effects of density and extinction coefficient on size variability,as measured by the coefficient of variation of plant weightin even-aged monocultures, were investigated theoretically usinga diffusion model of growth and size distribution and a canopyphotosynthesis model over the range of densities at which self-thinning(size-dependent mortality) does not occur. Size inequality (thecoefficient of variation of plant weight) increases with increasingdensity or leaf area index at each growth stage. Plants witherect leaves are prone to lower size inequality than plantswith horizontal leaves. These results agree well with existingobservations on even-aged plant monocultures and suggest thatcompetition between plants is mainly one-sided (competitionfor light). One sided competition affects size variability througha G(t, x) function (mean growth of plants of size x at timet per unit time). Two-sided competition (including competitionfor nutrients) affects size variability through a D(t, x) function(variance of growth of plants of size x at time t per unit time).In this case, size inequality decreases with increasing density.The importance of studying size variability is emphasized. Helianthus annus L., size variability, size inequality, coefficient of variation, competition, density effect, extinction coefficient, diffusion model, canopy photosynthesis model     

Effect of concentration on albumin diffusion in lung interstitium

The transport of macromolecules through the lung interstitiumdepends on both bulk transport of fluid and diffusion. In the presentstudy, we studied the diffusion of albumin. Isolated rabbit lungs wereinflated with silicon rubber via airways and blood vessels, and twochambers were bonded to the sides of a 0.5-cm-thick slab that encloseda vessel with an intersititial cuff. One chamber was filled with eitheralbumin solution (2 or 5 g/dl) containing tracer¹²⁵I-albumin or with tracer¹²⁵I-albumin alone; the other wasfilled with Ringer solution. Unbound ¹²⁵I was removed from the tracerby dialysis before use. The chamber with Ringer solution was placed inthe well of a NaI(Tl) scintillation detector. Diffusion oftracer through the interstitium was measured continuously for 60 h.Tracer mass (M) showed a time(t) delay followed by an increase toa steady-state flow(dM/dtconstant). Albumin diffusion coefficient(D) was given byL²/(6T),where T was the time intercept of thesteady-stateM-t line at zero M, andL was interstitial length.Interstitial cuff thickness-to-vessel radius ratio(Th₀/R)was estimated by using Fick's law for steady-state diffusion. BothD andTh₀/Rwere independent of albumin concentration.D averaged 6.6 × 10⁷cm²/s, similar to the freeD for albumin. Values ofTh₀/Raveraged 0.047 ± 0.024 (SD), near the values measuredhistologically. Thus pulmonary interstitial constituents offered norestriction to the diffusion of albumin.

     

Growth of Individuals in Plant Populations

Relationships between individual plant weight and net photosynthesisper day (G(t, x) function of plant weight) in plant populationsof various stand structures were simulated based on a canopyphotosynthesis model. The G(t, x) functions of plant weightare determined mainly by LAI (leaf area index), the relationshipbetween individual plant weight and leaf area, canopy structureand extinction coefficient. The concave relationship betweenindividual plant weight and leaf area at small LAI (<2),at small extinction coefficient (< 0.5), or at the canopystructure having the maximum leaf area density at the bottomproduces a concave G(t, x) function, which generates negativeskewness of plant weight. The linear relationship between individualplant weight and leaf area at large LAI (> 2) produces aconvex G(t, x) function, which generates positive skewness ofplant weight. These simulation results coincide with G(t, x)functions obtained experimentally and with the well-known phenomenonof stand dynamics in which skewness of plant weight becomesnegative in the early growth stage and then increases to a positivevalue as a stand grows and becomes crowded. Helianthus annuus L., individual plant size, mean growth rate, canopy photosynthesis model, skewness, stand structure     

Effects of Temperature and CO2 Concentration on Induction of Carbonic Anhydrase and Changes in Efficiency of Photosynthesis in Chlorella vulgaris 11h

The increase in carbonic anhydrase (CA) activity and the decreasein apparent K_m(CO₂) for photosynthesis induced by reducing CO₂concentration during the growth of Chlorella vulgaris 11h cellswere followed under different temperatures. Both changes wereaccelerated by raising the temperature and reached an optimumat 32–37?C. When the CO₂ concentration was lowered from3 to 0.04%, the rate of photosynthetic O₂ evolution at limitingCO₂ concentrations increased and reached a stationary levelafter 3 h. Under such conditions, the concentration of CO₂ dissolvedin the algal suspension decreased logarithmically (t_1/2=10 min)and reached a concentration in equilibrium with 0.04% CO₂ inair after ca. 2 h. When high-CO₂ cells grown with 3% CO₂ in air were transferredto various lower CO₂ concentrations, CA activity and apparentK_m(CO₂) for photosynthesis changed depending on the CO₂ concentration.The CO₂ concentration which gives one-half the maximum valuefor K_m(CO₂) and one-half minimum value foi CA activities wasabout 0.5%. The inverse relationship observed for the changesin CA activity and the affinity for CO₂ in photosynthesis supportsthe theory that CA loweres the apparent K_m(CO₂) for photosynthesisin Chlorella vulgaris 11h. (Received August 27, 1984; Accepted February 8, 1985)     

Competitive Asymmetry Reduces Spatial Effects on Size-Structure Dynamics in Plant Populations

The growth of each individual in plant populations was simulatedby a spatial competition model for five density levels and fourdifferent spatial distribution patterns of individuals, varyingfrom highly clumped to regular. The simulation results wereanalysed using the diffusion model for evaluating the effectsof density and distribution pattern on the size-structure dynamicsin relation to the degree of competitive asymmetry. At low densities,changes in statistics of plant weight over time such as mean,coefficient of variation, skewness, and Box-Cox-transformedkurtosis differed greatly among spatial patterns, irrespectiveof the degree of competitive asymmetry. In completely symmetriccompetition, the spatial effect on size-structure dynamics remainedrelatively large irrespective of densities, although mean plantweight became similar among the spatial patterns with increasingdensity. However, the spatial effect diminished with increaseddensity in strongly asymmetric competition, when similar sizedistributions were realized irrespective of the spatial patterns.Therefore, it was concluded that: (1) irrespective of the degreeof competitive asymmetry, spatial pattern is important for size-structuredynamics at low densities; (2) spatial pattern is nearly immaterialunder strongly asymmetric competition at high densities; and(3) under crowded conditions, neighbourhood effects are muchmore apparent at the population level in less asymmetric competition.These processes and outcomes are linked to the forms of thefunctions of mean growth rate of individuals [G(t,x) function]and variance in growth rate [D(t,x) function]. These functionsare variable depending on the spatial pattern under symmetriccompetition, but are rather stable under strongly asymmetriccompetition at high densities irrespective of the spatial patterns.Therefore, size structure under strongly asymmetric competitioncan be regarded as a stable system, whereas that under symmetriccompetition is regarded as a variable system in relation tothe spatial pattern and process. From this, it was inferredthat: (1) the goodness-of-fit of spatial competition modelsfor crowded plant populations is higher in less asymmetric competition;and (2) higher species diversity in plant communities is associatedwith the lower degree of competitive asymmetry.Copyright 1994,1999 Academic Press Asymmetric competition, diffusion model, neighbourhood effect, size-structure stability, spatial competition model, spatial distribution pattern, species diversity, symmetric competition     

Relationship between Plant Weight and Growing Period for Vegetable Crops in the United Kingdom

A generalized equation is derived that relates total dry matterproduction to time from emergence for crops grown in the fieldwith adequate water and nutrients. It is: w+K₁lnw+W₀=K₂t where w is the plant dry weight in t ha^–1, t is time indays after emergence, K₂ and K₁ are constants and W₀ equals–(w₀+K₁lnw₀) where w₀ is the value of w at the start ofthe growing period. The increases in the dry matter of 18 different types of vegetablecrop were measured at intervals during growth in the field.In every case the data fitted the equation very satisfactorilywith K₁ set equal to 1 t ha^–1. The fitted values of K₂were similar for many crops; those of W₀ varied considerablybut were always similar to the values calculated from the individualseed weight and the plant population. Good fits were also obtainedwhen time in days was replaced with cumulative evaporation froman open water surface. It is concluded that the growth-time curves of many differentvegetable crops can be described by the same simple equationand that the variation between curves can be largely attributedto differences in seed weight and plant population.     

Adenine nucleotide-creatine-phosphate module in myocardial metabolic system explains fast phase of dynamic regulation of oxidative phosphorylation

Computational models of a large metabolic system can be assembled from modules that represent a biological function emerging from interaction of a small subset of molecules. A "skeleton model" is tested here for a module that regulates the first phase of dynamic adaptation of oxidative phosphorylation (OxPhos) to demand in heart muscle cells. The model contains only diffusion, mitochondrial outer membrane (MOM) permeation, and two isoforms of creatine kinase (CK), in cytosol and mitochondrial intermembrane space (IMS), respectively. The communication with two neighboring modules occurs via stimulation of mitochondrial ATP production by ADP and P_i from the IMS and via time-varying cytosolic ATP hydrolysis during contraction. Assuming normal cytosolic diffusion and high MOM permeability for ADP, the response time of OxPhos (t_mito; generalized time constant) to steps in cardiac pacing rate is predicted to be 2.4 s. In contrast, with low MOM permeability, t_mito is predicted to be 15 s. An optimized MOM permeability of 21 µm/s gives t_mito = 3.7 s, in agreement with experiments on rabbit heart with blocked glycolytic ATP synthesis. The model correctly predicts a lower t_mito if CK activity is reduced by 98%. Among others, the following predictions result from the model analysis: 1) CK activity buffers large ADP oscillations; 2) ATP production is pulsatile in beating heart, although it adapts slowly to demand with "time constant" 14 heartbeats; 3) if the muscle isoform of CK is overexpressed, OxPhos reacts slower to changing workload; and 4) if mitochondrial CK is overexpressed, OxPhos reacts faster. systems biology; computational model; creatine kinase; phosphocreatine shuttle; regulatory module; mitochondrial membrane permeability; oxygen consumption     

Leaf Characteristics and Net Gas Exchange of Diploid and Autotetraploid Citrus

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 5–15% 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 (A_CO2) wasbased on leaf area, 4x orange leaves had 24–35% lowerA_CO2than their diploids. There were no significant differencesin A_CO2between 2x and 4x orange or lemon leaves when expressedon a per cell basis. Overall, lower A_CO2per 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     

Dynamics of Competition in Populations of Carrot (Daucus carota)

Populations of carrot (Daucus carota) were raised over a widerange of densities (79–5763 plants m^-2) to examine thedynamics of competition in terms of yield–density relationshipsand size variability, and to investigate the effects of nutrientsupply on competition. While the relationship between shootyield and density was asymptotic, the relationship between rootand total yield and density tended to be parabolic. For a giventime and density series the relationship between yield per unitarea and density could best be described by the model: y=w_mD_(1+aD)^b wherey is the yield per unit area,D is density,w_m, a andb arefitted parameters. The parametersw_m anda increased over timebut nutrient availability affected onlyw_m. An extension of thebasic yield-density model is proposed to describe the dynamicsof the yield–density relationship over time: y=kD_{[1+cexp(-rt)]{1+}     

Simulation of the Structural Development of Warm-Temperate Rain Forest Stands

The change in all-sized dbh distribution with stand age wassimulated using data from secondary stands of different agesafter clear-felling in warm-temperate rain forests in YakushimaIsland, southern Japan. The cumulative basal area [cm² m^–2]of all trees larger than a given dbh x [cm] was used as an indexof onesided density effect, which primarily regulates the growthrate and mortality of the tree at x. The relative growth ratein dbh was expressed by a negative linear function of both thecumulative basal area and logarithmic dbh, irrespective of standage. Mortality was found to be positively related to the cumulativebasal area. From these empirical relations, the change in dbhdistribution during the course not only of stand developmentafter clear-felling, but also of gap regeneration within primaryforests, was successfully simulated using the continuity equation,eliminating ‘stand age factors’ from the model.Results of the simulation satisfied the —3/2 power lawof self-thinning. Competition, continuity equation, cumulative basal area, simulation, size distribution, stand dynamics, —3/2 power law, warm-temperate rain forest, Yakushima Island     

Effects of Priming and Endosperm Integrity on Seed Germination Rates of Tomato Genotypes: II. GERMINATION AT REDUCED WATER POTENTIAL

Seed germination rates (GR =inverse of time to germination)are sensitive to genetic, environmental, and physiological factors.We have compared the GR of tomato (Lycopersicon esculentum Mill.)seeds of cultivar T5 to those of rapidly germinating L. esculentumgenotypes PI 341988 and PI 120256 over a range of water potential(). The influence of seed priming treatments and removal ofthe endosperm/testa cap enclosing the radicle tip on germinationat reduced were also assessed. Germination time-courses atdifferent 's were analysed according to a model that identifieda base, or minimum, allowing germination of a specific percentage(g) of the seed population (_b(g)), and a ‘hydrotime constant’(_H) indicating the rate of progress toward germination per MPa.h.The distribution of _b(g) determined by probit analysis was characterizedby a mean base (_b) and the standard deviation in _b among seeds(_b). The three derived parameters, _b, _b) and _H, were sufficientto predict the time-courses of germination of intact seeds atany . A normalized time-scale for comparing germination responsesto reduced is introduced. The time to germination at any (t_g())can be normalized to be equivalent to that observed in water(t_g(0)) according to the equation t_g(0)=[l–(/_b(g))]t_g().PI 341988 seeds were more tolerant of reduced and had a morerapid GR than T5 seeds due to both a lower _b and a smaller _H.The rapid germination of PI 120256, on the other hand, couldbe attributed entirely to a smaller _H. Seed priming (6 d in–1.2 MPa polyethylene glycol 8000 solution at 20 ?C followedby drying) increased GR at all >_b(g), but did not lower theminimum allowing germination; i.e. priming reduced _H withoutlowering _b. Removing the endosperm/testa cap (cut seeds) markedlyincreased GR and lowered the mean required to inhibit germinationby 0.7 to 0.9 MPa. However, this resulted primarily from downwardadjustment in _b during the incubation of cut seeds at low inthe test solutions. The difference in _b between intact and cutseeds incubated at high was much less (0.l MPa), indicatingthat at the time of radicle protrusion, the endosperm had weakenedto the point where it constituted only a small mechanical barrier.In the intact seed, endosperm weakening and the downward adjustmentin embryo _b ceased at < –0.6 MPa, while the reductionin _H associated with priming proceeded down to at least –1.2MPa. Based on these data and on the pressure required to pushthe embryos from the seeds at various times after imbibition,it appears that the primary effect of priming was to shortenthe time required for final endosperm weakening to occur. However,as priming increased GR even in cut seeds, priming effects onthe embryo may control the rate of endosperm weakening. Key words: tomato, Lycopersicon esculentum Mill., water potential, germination rate, seed priming, genetic variation     

Food and suspended sediment influences on the naupliar and copepodid durations of freshwater copepods: comparative studies on Tropodiaptomus and Metadiaptomus

Post-embryonic durations of Tropodiaptomus spectabilis (Kiefer)and Metadiaptomus colonialis(van Douwe) were determined at 20°Cin laboratory factorial experiments involving four algal foodenrichment levels (0, 100, 500 and 2500 µg l^–1 Cof Selenastrum added to 20 µm filtered water from respectivesource-lakes) and three suspended sediment levels (filtered,natural, and 2- to 3-fold sediment-enriched lake water). Foodeffects (30, 75, 225 and 600 (µg ^–1 C of Scenedesmus)were tested alone at 20°C for Metadiaptomus meridianus (vanDouwe). Total naupliar (D_n) and total copepodid (D_c) developmenttimes [summed to give total post-embryonic duration (D_t)] andmetasome lengths at maturity were measured In all taxa, foodsupply maximally affected D_c values 2- to 3-fold, whereas itsmaximal influence on D_n values was relatively slight (generally25%). The measured effect of food supply on D_t, was as strongas the predicted influence of temperature over an appropriateannual range. Food supply influenced size at maturity, and probablythereby fecundity, thus exerting additional demographic influences.Sediment effects were inconsistent, and quantitatively weakerthan food effects Total development of T.spectabilis was 20%raster, and that of M.colonialis 15% slower in sediment-enrichedthan in natural sediment level treatments; contrasting baselinesediment levels (2–3 times higher for the latter species)and different enrichment procedures confound interpretation.Unexpectedly, and inexplicably, development almost invariablyfailed in sediment-free water, implying an apparent dependencyon inorganic particles in these taxa This contrasts with thegenerally adverse influences of high sediment concentrationsupon zooplankton. Minimal male and female D_t values at 20°Cwere comparable and significantly longer in M.colonialis (15.5and 17 7 days) and M meridianus (16.5 and 21.5 days) than inT.spectabilis (11.7 and 12 2 days). These differences in durationare ecologically incongruous in relation to expected r –K life history strategies of genera characteristic of temporaryor semipermanent waters and permanent waters respectively.     

Restricted postexercise pulmonary diffusion capacity and central blood volume depletion

Hanel, Birgitte, Inge Teunissen, Alan Rabøl,Jørgen Warberg, and Niels H. Secher. Restricted postexercisepulmonary diffusion capacity and central blood volume depletion.J. Appl. Physiol. 83(1): 11-17, 1997.Pulmonary diffusion capacity for carbon monoxide(DL_CO),regional electrical impedance(Z₀), and the distribution oftechnetium-99m-labeled erythrocytes together with concentration ofplasma atrial natriuretic peptide (ANP) were determined before andafter a 6-min "all-out" row in nine oarsmen and in six controlsubjects. Two and one-half hours after exercise in the upright seatedposition,DL_CO wasreduced by 6 (2 to 21; median and range) %, thethoracic-to-thigh electrical impedance ratio(Z_{0 thorax}/Z_{0 thigh})rose by 14 (1 to 29) %, paralleled by a 7 (3 to 11) % decrease and a 3 (5 to 12) % increase in the thoracic and thighblood volume, respectively. These responses were associated with adecrease in the plasma ANP concentration from 15 (13-31) to 12 (9-27) pmol/l (P < 0.05).Similarly, in the supine position,Z_{0 thorax}/Z_{0 thigh}increased by 10 (5 to 28) % whenDL_CO wasreduced 12 (6-26) % (P < 0.05), whereasDL_CO remained stable in the control group. The increase inZ_{0 thorax}/Z_{0 thigh} and the corresponding redistribution of the blood volume in both bodypositions show that approximately one-half of the postexercise reduction ofDL_CO isexplained by a decrease in the pulmonary blood volume. The role of areduced postexercise central blood volume is underscored by the lowerplasma ANP, which aids in upregulating the blood volume after exercisein athletes.

     

Parallel airways inhomogeneity and lung tissue mechanics in transition to constricted state in rabbits

Toinvestigate whether changes of tissue resistance (Rti) duringmethacholine (MCh)-induced constriction correspond to an intrinsicmechanism or are an artifact of increased airways inhomogeneity, rabbits were studied after exposure to air(n = 7) or 1.5 parts/million O₃(n = 6). Animals were anesthetized andmechanically ventilated. Tracheal flow and pressure (Ptr) and fouralveolar capsule pressures (Pcap) were measured during 3 min afteradministration of an intrajugular bolus of 0.8 mg/ml MCh. By adjustmentof the equation of motion [P(t) = E · V(t) + R · dV(t)/dt + P₀] [whereP(t), V(t), and dV(t)/dt are pressure, volume, and flow as a function of time, respectively, Eis elastance, R is resistance, and P₀ is end-expiratorypressure] to Ptr, lung resistance(RL) and dynamic elastance(EL) were determined breath bybreath. Rti and airways resistance (Raw) were determined from Pcap in phase with rate of change of pulmonary expansion. Hysteresivity () was calculated. Parallel inhomogeneity wasestimated from the coefficients of variation (CV) of every Pcap at endinspiration and end expiration. Increase in CV significantly laggedRti, RL, and . A linearrelationship between EL and Rawwas observed. Our results suggest that changes in tissue mechanicsduring the transition to the constricted state are not artifactual.

     

Limitations on the Analysis of Acetylene Reduction by Soybean at Low Levels of Acetylene

The analysis of acetylene reduction at low concentrations ofacetylene involves a number of assumptions and both technicaland kinetic complexities. The major difficulty in convertingacetylene reduction rates to apparent N₂ reduction rates isdetermining the K_m for acetylene in the presence of N₂. Thissubstrate competition is dominant over diffusion limitationeffects, but both introduce equivalent deviations in the observedK_m. Because N₂ is a non-linear partial competitive inhibitorof acetylene reduction, correction for its presence is difficult.Two further complications are introduced by the non-linear responseof nitrogenase to acetylene concentration even in the absenceof N₂, and changes in the apparent K_m of acetylene and K₁ ofN₂ as a function of other variables in the enzyme assay. Itis proposed that transient analysis may be used for measurementof diffusion coefficients and calculations of possible diffusionlimitations. It is demonstrated that one proposed model forestimating diffusion limitation (Denison et al., 1983, PlantPhysiology 73, 648–51) confounds substrate competitionwith diffusion limitation. Acetylene reduction, nitrogen fixation, diffusion limitation     

Allometry and Competition between Saplings of Picea jezoensis and Abies sachalinensis in a Sub-boreal Coniferous Forest, northern Japan

The crown shape and the mode of competition between saplings(<2m in height) of the two conifers,Picea jezoensis andAbiessachalinensis, of a sub-boreal forest, northern Japan, wereinvestigated based on the diffusion model. A model for individualsapling growth considering both inter- and intraspecific competitionwas developed. The effect of species-specific crown shape onthe sapling growth and competition of the two species were examined.PiceajezoensisandAbies sachalinensissaplings had deep conic and shallowflat crowns, respectively.Picea jezoensishad more foliage massthanAbies sachalinensisof the same sapling mass. It was suggestedthat thePicea jezoensissapling has a high cost for assimilation–respirationbalance under dark conditions of closed canopies, whereas theAbiessachalinensissapling maintains effective assimilation even undersuppressed conditions. Widely spaced saplings, such as gap successors,ofPicea jezoensishad a greater relative growth rate (a₀) thanwidely spacedAbies sachalinensis. The crown shape of saplingsof the two species shows different adaptations for efficientpersistence in the sub-boreal forest. Saplings ofPicea jezoensisandAbies sachalinensiswere not uniformlydistributed, but aggregated in different sites as the saplingsgrew, indicating habitat segregation between the two speciesat the sapling stage. Intraspecific sapling competition wasone-sided in each of the two conifers. Interspecific saplingcompetition was one-sided in the direction only fromAbies sachalinensistoPiceajezoensis. Therefore, asymmetric competition prevailed at thesapling stage of the two species. These results contrast withweak symmetric competition or the almost absence of competitionbetween trees (2m in height) of the two species (Kubota andHara,Annals of Botany76: 503–512, 1995). The mode of competitionchanged with the life-history stage from the sapling (intenseand asymmetric) to the tree (weak and symmetric or almost absent). In conclusion (1) asymmetric and intense competition betweensaplings brought about habitat segregation between the dominantspecies,Picea jezoensisandAbies sachalinensis, in the earlystage of life-history; (2) therefore, the coexistence ofPiceajezoensisandAbies sachalinensisof the sub-boreal forest wasdetermined by the boundary conditions for the growth dynamicsof the trees, as segregation of establishment sites resultingfrom asymmetric and intense competition between saplings; (3)then the species composition of the forest was maintained byweak symmetric competition or the almost absence of competitionbetween trees. Crown shape; growth dynamics; species coexistence; habitat segregation; diffusion model     

Variation in the DNA Content of Glycine Species

Nuclei were isolated from cotyledons of a range of accessionsfrom 14 species of Glycine. These were stained with ethidiumbromide and the relative fluorescence for each genotype wasmeasured by flow cytometry. The DNA content was estimated bycomparison of relative fluorescence with that from nuclei fromseedling leaves of Allium cepa, whose DNA content has been calculatedpreviously by chemical assay. The 4C amounts for diploid Glycineranged from 3.80 to 6.59 pg. Two groups of diploid species appearedfrom the analysis. The first consisted of species with amountsranging from 3.80 to 5.16 pg and included G. canescens (AA),G. argyrea (A₁ A₁), G. clandestina (A²A²), G. microphylla(BB),G. latifolia (B₁B₁), G. tabacina 2n=40 (B²B²), G. tomentella2n=38 (EE) and 2n=40 (DD), G. max and G. soja (GG), G. arenariaand G. latrobeana. A second group had higher DNA contents rangingfrom 5.27 to 6.59 pg, and consisted of G. curvata, G. cyrtoloba(CC), and G. falcata (FF). The polyploid species, G. tabacina2n=80 (AABB, BBB¹B¹), G. tomentella 2n=78 and 2n=80 (AAEE andDDEE, respectively) contained amounts approximating to the sumsof the respective parental diploid species thought to have givenrise to these allotetraploids. Intraspecific variation was detectedin the DNA content of G. canescens. Within the overall distributionof DNA amounts found in A genome species, each genome containeda range of DNA contents specific to that species. This phenomenonwas also detected amongst B genome species.     

Changes in levels of Proteases and Their Inhibitors during Development of the Seeds of Job's Tears (Coix lacryma-jobi L. var. Ma-yuen Stapf) and Their Localization and Interactions

Changes in levels and localization of proteases and a trypsininhibitor (JBTI) in the developing seeds of Job's tears (Coixlacryma-jobi L. var. Ma-yuen Stapf) were followed, and theirinteractions were examined. The JBTI was induced from the middlestage of development (12 DAF, i.e., 12 days after flowering)and increased until the late stage of development (24 DAF),and was localized in the germ. Two groups of proteases (A, thosewith molecular weights of 55–70 kDa; and B, those withmolecular weights greater than 94 kDa) were detected by activestaining of substrate-containing SDS-polyacrylamide gels. Thegroup of larger proteases seems to consist of three members(B₁, B₂₎ B₃, with increasing molecular weights). Band A wasobserved only in the early stage of development (until DAF 9),band B₂ persisted during all stages, while bands B, and B₃ werepresent only during early and late stages, respectively. Thegroup A proteases and one of the group B proteases (probablyB₁) were inhibited by diisopropyl-fluorophosphate (DFP), bytrypsin inhibitors from soybean and rice, and by JBTI. The proteasesthat were present in the seeds of Job's tears at a late stageseemed to be localized in the germ. (Received September 9, 1988; Accepted April 19, 1989)