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The correlation between pollen/ovule (P/O) ratio and breeding system has generally been accounted for either on the basis that P/O reflects pollination efficiency, or in terms of the sex allocation theory. The following were assessed for taxa belonging to genus Astragalus subgenus Epiglottis: 1) Degree of correlation between P/O and the breeding system, measured by means of autofertility; 2) The absence or existence of correlation between P/O and pollen grain size; and 3) The ability of various theories to account for the results obtained. Results showed a minimal correlation between P/O and autofertility, and between P/O and pollen grain size in the taxa studied. Analysis of these results in terms of the sex allocation theory enabled this correlation to be explained as a function of the variation existing between taxa with respect to the resources invested in each pollen grain and in each ovule. The predictive capacity of this theory, which has moreover proven valuable in explaining the structural peculiarities of the androecium in these taxa, was also highlighted. The type of self-pollination applicable was also discussed, as was the phenotypic model of selection of self-fertilization considered most plausible for these taxa. 相似文献
24.
Hydraulic properties of sphagnum peat moss and tuff (scoria) and their potential effects on water availability 总被引:2,自引:0,他引:2
The importance of macrostructure to root growth of ryegrass (L. perenne) seedlings sown on the soil surface was studied in two soils in which the macrostructure had resulted mainly from root growth
and macro-faunal activity. Sets of paired soil cores were used, one of each pair undisturbed and the other ground and repacked
to the field bulk density.
Undisturbed and repacked soils were first compared at equal water potentials in the range −1.9 to −300 kPa. At equal water
potential, the undisturbed soil always had the greater strength (penetration resistance), and root growth was always greater
in the repacked soil with no macrostructure than it was in the soil with macrostructure intact. At equal high strength (low
water potentials) it appeared that root growth was better when soils were structured. When strength was low (high water potentials),
root growth was better in the unstructured soil.
Soils were then compared during drying cycles over 21 days. The average rate at which roots grew to a depth of 60 mm, and
also the final percentage of plants with a root reaching 60 mm depth, was greatest in repacked soils without macrostructure.
The species of vegetation growing in the soil before the experiment affected root growth in undisturbed soil; growth was slower
where annual grasses and white clover had grown compared with soil which had supported a perennial grass.
It appears that relatively few roots locate and grow in the macrostructure. Other roots grow in the matrix, if it is soft
enough to be deformed by roots. Roots in the matrix of a structured soil grow more slowly than roots in structureless soil
of equal bulk density and water potential. The development of macrostructure in an otherwise structureless soil, of the type
studied, is of no advantage to most roots. However, once a macrostructure has developed, the few roots locating suitable macropores
are able to grow at low water potential when soil strength is high. The importance of macrostructure to establishing seedlings
in the field lies in rapid penetration of at least a few roots to a depth that escapes surface drying during seasonal drought.
ei]{gnB E}{fnClothier} 相似文献
25.
Paula Tatiana Lopes Seixas Antonio Jacinto Demuner Luiz Claudio Almeida Barbosa Cristiane Isaac Cerceau Daiane Einhardt Blank Marcelo Henrique Dos Santos Elizeu de Sá Farias Marcelo Coutinho Picanço 《Journal of Applied Entomology》2023,147(2):116-125
Aedes aegypti L. (Diptera: Culicidae) is a vector for serious diseases in tropical regions. This pest is mainly controlled by commercial larvicides but the application of such products has led to environmental problems. Essential oils (EO) have been consistently reported as molecules with insecticidal activity and can be used to produce more environmentally friendly larvicides in the control of A. aegypti. In this study, the larvicidal effect of essential oils (EO) from the leaves of three Artemisia species was evaluated against A. aegypti. The oils were obtained from steam distillation and their chemical composition was determined by gas chromatography–mass spectrometry. The EO of Artemisia camphorata was the most active in the screening bioassay and presented LC50 and LC95 of 64.95 and 74.18 μg ml−1, respectively. In addition, we found that germacrene D-4-ol was the constituent responsible for the toxicity of this EO. Artemisia camphorata EO and its major constituent, germacrene D-4-ol, are promising for the development of natural larvicides against A. aegypti. 相似文献
26.
Jennifer L. Wright Heather A. Stewart Ivette Candanedo Evan D'Alessandro Maria Estevanez Rafael J. Araújo 《Biotropica》2023,55(2):299-305
We conducted visual fish surveys in coexisting mangrove-coral (CMC) habitats in Panama to analyze the effect of coral presence in mangrove habitats on the fish assemblage. Our study revealed that CMC habitats harbor distinct fish assemblages compared to mangrove habitats without coral, with greater species richness and increased herbivore abundance. Abstract in Spanish is available with online material. 相似文献
27.
Coelho-Rocha Nina Dias de Jesus Luís Cláudio Lima Barroso Fernanda Alvarenga Lima da Silva Tales Fernando Ferreira Enio Gonçalves José Eduardo dos Santos Martins Flaviano de Oliveira Carvalho Rodrigo Dias Barh Debmalya Azevedo Vasco Ariston de Carvalho 《Probiotics and antimicrobial proteins》2023,15(1):160-174
Probiotics and Antimicrobial Proteins - Beneficial effects of Lactiplantibacillus plantarum strains have been widely reported. Knowing that the effects of probiotic bacteria are strain-dependent,... 相似文献
28.
James L. Patton Sergio F. dos Reis Maria Nazareth F. da Silva 《Journal of Mammalian Evolution》1996,3(1):3-29
Variation in the mitochondrial cytochrome b gene (nucleotide and amino acid sequences) is evaluated for 9 genera and 15 species of American opossums in the family Didelphidae, using the American caenolestid rat opossumLestoros and the New Guinean peroryctid bandicootEchimypera as outgroups. Phylogenetic analyses (parsimony and distance) strongly support the monophyly of the Didelphidae and delineate two major clades; (1)Didelphis andPhilander are strongly aligned sister taxa, withMetachirus weakly but consistently associated with them, and (2)Marmosa plusMicoureus, withMonodelphis falling outside that pair. The generaMarmosops, Caluromys, andGlironia exhibit varied relationships, depending upon the method of analysis and data (DNA or amino acid sequences) used, but generally are placed individually or in combinations near or at the base of the didelphid radiation. Some aspects of these relationships are consistent with current taxonomic views, but others are in marked contrast. Specifically, a clade comprised of the mouse opossumsMarmosa, Micoureus, andMarmosops is strongly rejected by log-likelihood analysis, contrary to expectations from some current classifications. Also, the woolly opossumsCaluromys andGlironia also do not form a sister-taxon relationship, as suggested by their placement in a subfamily separate from the remaining didelphids examined. However, such a relationship cannot be rejected from log-likelihood analyses. The relationships suggested fromcyt-b sequences are strongly concordant with those based on DNA-DNA hybridization analyses. In addition to systematic and phylogenetic properties, molecular evolution of the didelphid cytochrome b gene sequence is characterized according to nucleotide bias and rate differentials at each codon position and across the entire sequence.To whom correspondence should be addressed. 相似文献
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Four xylanase preparations that are commercially available, namely Cartazyme from Sandoz, Ecopulp from Alko-ICI, Irgazyme from Ciba-Genencor and Pulpzyme HB from Novo Nordisk, were tested in bleaching experiments of kraft pulps from Pinus radiata. The main objective of this study was to optimize a reduction in the consumption of chlorine dioxide in the bleaching sequences C90/D10EoDED, C70/D30EoDED and D100EDED. Enzymatic treatments led to savings of ClO2 between 3.5 and 3.9 kg per air-dried tons (ADT) in the three bleaching sequences, without affecting the target brightness of the pulps. In these assays, some minor although reproducible differences in the performance of the enzymes were observed. In most cases, xylanase treatment partially affected the beatability of the pulps, measured as the number of revolutions in the PFI mill required to reach the same tensile index as the respective controls. 相似文献