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     

Density Effects on Plant Height Growth and Inequality in Sunflower Populations

Comparisons between competing and non-competing sunflower （Helianthus annuus L.） populations demonstrate pronounced effects of density on plant height growth, height-to-crown width ratio, and s popuiaUon＇s height inequality. In the present study, non-destructive measurements of height and the prolected crown area of sunflower plants were taken at seven times from emergence to fruit maturation in even-aged monospeclflc stands with initial densities of 1, 4, 16, and 64 plants/m^2. The mean height of populations Increased and then decreased with increasing population density; the height Inequalities of uncrowded populations decreased during stand growth, whereas the height inequaiiUes of crowded popuisUons decreased first and then increased during stand development. The interindlvidual relationships between the relative height growth rate and height within uncrowded populations became significantly negative during population growth, whereas these relationships were negative first and then became positive during the development of crowded populations. In the uncrowded populations, the static Interindlvldual relationship between height-to-crown width ratio and volume was positive, whereas for the crowded population these relationships became negative with increasing competition for light. The data suggest that the plastic responses of plant height and height-to-crown width ratio to light competition will become more Intense with increasing competition Intensity. The results of the present study argue strongly for the Importance of size-dependent Individual-level plastic responses due to size-asymmetric light competition In generating the variations in population height inequality.     

Microbial Inoculants with Multifaceted Traits Suppress Rhizoctonia Populations and Promote Plant Growth in Cotton

The suppressive effects of microbial inoculants on cotton seedling mortality were assessed in Rhizoctonia solani‐infested soil. Per cent mortality ranged from 16 to 32 (60–120 days after sowing, DAS) and significant differences were recorded at 120 DAS, especially after drenching with compost tea of Azotobacter sp. and Anabaena torulosa—Trichoderma viride‐biofilmed formulations. The activity of hydrolytic enzymes was reduced in diseased root tissues due to a majority of the microbially inoculated treatments, compared with healthy root tissues. Per cent changes in the amounts of glomalin‐related soil proteins (GRSPs) were 2 to 85% greater than those of the uninoculated experimental controls. These microbial inoculants altered the rhizosphere bacterial communities as evident from the Denaturing gradient gel electrophoresis (DGGE) banding patterns and, also reduced the population of R. solani. While the copy numbers of the internal transcribed spacer (ITS) gene of R. solani in the uninoculated (infested soil) were approximately 1.47 × 10¹¹ per g soil, they were 1.34–1.42 × 10⁵ per g soil after the application of A. torulosa, Anabaena laxa and A. torulosa–Bacillus sp. Increases in yield (ranging from 3 to 23%) due to various microbial inoculants relative to uninoculated controls illustrated their promise as plant growth‐promoting and disease‐suppressing agents. This study illustrates the modulation of rhizosphere ecology through microbial inoculants as a mechanism of disease suppression and sustaining plant growth.     

The Quantitative Role of 'Dark' Respiratory Processes in Heterotrophic and Photolithotrophic Plant Growth

The hypothesis that ATP and reductant generated in photosyntheticpartial reactions can be used in vivo for energy-requiring reactionsother than the photosynthetic carbon reduction cycle is supportedby much experimental evidence. When such direct use of photo-producedcofactors occurs, it might be expected that the alternativesource of ATP and reductant, i.e. ‘dark’ respiration,occurs to a smaller extent than in heterotrophic cells. Thispaper uses data from the literature to compute the CO₂/C ratio(CO₂ produced in ‘dark’ respiration processes perC incorporated into cell material) for photolithotrophic andheterotrophic growth of a range of unicellular algae and angiosperms.The minimum CO₂/C value observed for heterotrophic growth issimilar to, but rather higher than, that calculated using thestoichiometry of known respiratory, biosynthetic and transportreactions for the conversion of carbohydrate and the suppliedminerals into a plant of the appropriate composition. However,for unicellular algae the CO₂/C for photolithotrophic growthis much lower than either of these values for the heterotrophicCO₂/C value, and strongly supports the view that the directuse of photo-produced cofactors for processes other than thephotosynthetic carbon reduction cycle is an important aspectof energy metabolism in these organisms. The minimum CO₂/C observedis similar to that predicted when dark respiratory reactionsserve only to produce essential C skeletons. For angiosperms,the evidence is more equivocal, but is consistent with somedirect use of photo-produced cofactors for processes other thanCO₂ fixation. The spatial separation of energy-requiring processesfrom chloroplasts could partly account for this smaller emphasison nonrespiratory energy supply to processes other than CO₂fixation in angiosperms compared with unicellular algae.     

A Model for the Growth of Individuals in Plant Populations Cultivated at Different Concentrations of Fertilizer Solution

The growth of mean individual weight is the joint outcome ofthe growth of the individuals comprising a population. Fromthe growth data of individual weight in radish (Raphanus sativusL. var. radiculus Pers.) populations cultivated at differentconcentrations of ammonium sulphate solution, a deterministicmodel was proposed for integrating individual plant weight intomean weight per plant in a population. The model constructiondepended on the relation between mean individual weight andthe amount of fertilizer supplied to a population, and uponPearson's type VII distribution. The model related the weightof any individual to the amount of fertilizer. The fitness ofthe model to observed data was satisfactory, although the modelwas simple. Using the model, properties of the growth of componentindividuals of a population were examined in relation to thegrowth of mean individual weight. fertilizer, growth, individual, mean, Pearson's type VII distribution, plant weight, population, radish, Raphanus sativus L. var. radicula Pers     

Plant Domestication and Crop Evolution in the Near East: On Events and Processes

Reconstructing the evolutionary history of crop plants is fundamental for understanding their adaptation profile and the genetic basis of yield-limiting factors, which in turn are critical for future crop improvement. A major topic in this field is the recent claim for a millennia-long ‘protracted’ domestication process. Here we evaluate the evidence for the protracted domestication model in light of published archaeobotanical data, experimental evidence and the biology of the Near Eastern crops and their wild progenitors. The crux of our discussion is the differentiation between events or ‘domestication episodes’ and the later following crop evolutionary processes under domestication (frequently termed ‘crop improvement stage’), which are by definition, still ongoing. We argue that by assuming a protracted millennia-long domestication process, one needlessly opts to operate within an intellectual framework that does not allow differentiating between the decisive (critical) domestication traits and their respective loci, and those that have evolved later during the crop dissemination and improvement following the episodic domestication event. Therefore, in our view, apart from the lack of experimental evidence to support it, the protracted domestication assumption undermines the resolution power of the study of both plant domestication and crop evolution, from the cultural as well as from the biological perspectives.     

The Distribution of Plant Populations

In studying the distribution of plant species in sample quadratsit may be assumed that the individuals are aggregated into groupsshowing a Poisson distribution, while the number of individualsin each group follows a logarithmic distribution. The resultingcompound distribution of individuals per quadrat is the negativebinomial. Evidence is produced to show that the distributionscalculated on this basis agree with those actually obtainedin the cases examined.     

A Test for Non-randomness in Plant Populations

A simple test for non-randomness suitable for use in samplingplant populations is suggested. The criterion used is where n_i is the number of quadrats containing i shoots. A tablegiving significant points of for various values of N, the totalnumber of quadrats, is provided. The test is applied to four sets of experimental data and theresults agree with tests carried out on the complete distributions.It is suggested that this type of criterion could be used inother fields where similar forms of non-randomness also exist.     

Consequences of High-Intensity Magnetic Effects on the Early Growth Processes in Plant Seeds and the Development of Honeybees

The influence of magnetic field on the early growth processes in plant seeds and the postembryonic development of honeybees was studied. Some general trends in the effects of magnetic field and differences in the tolerance of plant seeds and developing honeybees to its action were revealed. Some factors that may be responsible for a low reproducibility of magnetobiological effects are discussed.     

Notes on Contagious Distributions in Plant Populations

Past experience has shown that the Poisson series is often inadequateas a model for describing plant populations. Various alternativetwo-parameter models have been suggested in place of the Poissonseries, but they all depend on assumptions which may or maynot hold. In this paper a different approach is put forwardin that attention is concentrated on the mean number of plantsper quadrat and an index of ‘clumping’ or ‘contagiousness’.Examples are given as to the use of these concepts to test fordifferences between the distribution of a plant in two localitiesor between two plants in the same locality.     

植物种群的繁殖对策

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Modelling the Time Course of Self-thinning in Crowded Plant Populations

A logarithmic model for the self-thinning of plants is proposed.This model describes the time course of self-thinning very welland fits data from forest stands and yield tables, which followthe 3/2 power law. An approximated expression of this modelshows that plant density decreases with age along a Gompertzcurve. This appears to be a basic property of the time courseof self-thinning in plants. Pinus strobus L., Pinus densiflora Sieb, et Zucc., stand development, self-thinning, 3/2 power law, logarithmic model, mortality     

Morphological Polyvariance of Ontogeny in Natural Plant Populations

The main patterns of expression of the morphological polyvariance of plants are discussed: diversity of biomorphs, pathways of ontogeny, and disturbances of morphogenesis. The diversity of biomorphs of tap root plants in different ecological conditions has been analyzed in detail. Promising directions of future studies have been formulated.     

Microsatellite Polymorphism in Natural Populations of the Wild Plant Arabidopsis Thaliana

Variation in repeat number at 20 microsatellite loci of Arabidopsis thaliana was studied in a worldwide sample of 42 ecotypes to investigate the pattern and level of polymorphism in repetitive sequences in natural plant populations. There is a substantial amount of variation at microsatellite loci despite the selfing nature of this plant species. The average gene diversity was 0.794 and the average number of alleles per locus was 10.6. The distribution of alleles was centered around the mean of repeat number at most loci, but could not be regarded as normal. There was a significantly positive correlation between the number of repeats and the amount of variation. For most loci, the observed number of alleles was between the expected values of the infinite allele and stepwise mutation models. The two models were rejected by the sign test. Linkage disequilibrium was detected in 12.1% of the pairwise comparisons between loci. In phylogenetic tree, there was no association between ecotype and geographic origin. This result is consistent with the recent expansion of A. thaliana throughout the world.