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Summary The effects of leaf hairs (pubescence) on leaf spectral characteristics were measured for the drought-deciduous desert shrub Encelia farinosa. Leaf absorptance to solar radiation is diminished by the presence of pubescence. The pubescence appears to be reflective only after the hairs have dried out. There are seasonal changes in leaf absorptance; leaves produced at the beginning of a growing season have high absorptances, whereas leaves produced during the growing season are more pubescent and have lower absorptances. The decrease in leaf absorptance is the result of an increase in pubescence density and thickness. Between 400 and 700 nm (visible wavelengths), pubescence serves as a blanket reflector. However, over the entire solar spectrum (400–3000 nm), the pubescence preferentially reflects near infrared radiation (700–3000 nm) over photosynthetically useful solar radiation (400–700 nm). Leaf absorptance to solar radiation (400–3000 nm) varies between 46 and 16%, depending on pubescence; whereas leaf absorptance to photosynthetically useful radiation (400–700 nm) may vary from 81 to 29%.C.I.W.-D.P.B. Publication No. 612  相似文献   

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Because leaf pubescence of the desert shrub Encelia farinosa increases in response to drought and influences photosynthesis and transpiration, we hypothesized that differences in water availability across the range of this species may result in genetic differentiation for pubescence and associated productivity traits. We examined maternal family variation of pubescence-moderated light absorption (absorptance) in three populations of E. farinosa. Absorptance was always greatest for plants from the high-rainfall environment and lowest for those from the driest site, but the rate of absorptance change in response to drought was similar among all populations. Similar patterns were found when we compared families within populations-all genotypes had similar initial leaf absorptances, differentiated very early in seasonal growth, then had concordant changes in absorptance thereafter. However, family-level variance was greatest for plants from the driest site, a region with highly heterogeneous precipitation patterns, whereas low variance was found for plants from the wettest, least heterogeneous site. The concordance of leaf absorptance changes, within and among populations, may be due to integration with other drought-related traits; however, the differences in absorptance values within and among populations suggest that variation of leaf pubescence results from selection associated with geographical and local patterns of water availability.  相似文献   

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Pleistocene glaciations have had a profound influence on the genetic structure of plant species throughout the Northern Hemisphere because of range contractions, fragmentations, and expansions. Phylogeographic studies have contributed to our knowledge of this influence in several geographic regions of North America, however, very few phylogeographic studies have examined plant species in the Sonoran, Mojave, and Peninsular deserts. In this study, we used sequence data from the chloroplast DNA psbA–trnH intergenic spacer to obtain information on phylogeographic patterns among 310 individuals from 21 populations of Encelia farinosa (“brittlebush”; Asteraceae) across its range. We applied several population and spatial genetic analyses that allowed us to interpret our data with respect to Pleistocene climate change. These analyses indicate that E. farinosa displays patterns of genetic differentiation and geographic structuring consistent with postglacial range expansion. Populations of E. farinosa are characterized by distinct haplotype lineages significantly associated with geography. Centers of genetic diversity for the species occur in southwestern Arizona, the plains of Sonora, and Baja California Sur, all of which are putative sites of glacial refugia as predicted by analyses of macrofossil and pollen data. Nested clade analysis suggests that genetic structure in E. farinosa has been affected by past fragmentation followed by range expansion. Range expansion in several locations is further supported by significant departures from neutrality for values of Fu’s FS and Tajima’s D, and mismatch analyses.  相似文献   

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Canonical variate analysis of plants raised in a uniform environment was used to study the pattern of geographical variation in leaf shape ofCrepis tectorum (Asteraceae). The diversity in leaf shape was much greater among populations confined to areas with exposed bedrock in the Baltic region than among weed populations scattered throughout Europe and Canada. A Ward's clustering linked outcrop populations from the archipelago of SW. Finland and the islands of Öland (Sweden) and Saaremaa (Estonia) due to the deeply lobed leaves characterizing these populations, while outcrop populations along the coast of E. Sweden were grouped due to their weakly lobed, narrow and dentate leaves. Most of the weed populations were grouped together but there was no tendency for the variation in this group to be related to habitat or geographical location. A mosaic of variation reflected in sharp (random) differentiation among local populations was superimposed on the large-scale ecogeographical pattern.—Crossing data indicated that most of the variation in degree of leaf dissection is governed by one major gene with deeply lobed leaves dominant over weakly lobed leaves. I suggest that the simple pattern of inheritance may have favoured rapid evolutionary changes in leaf shape, particularly in the Baltic area which emerged relatively late from the sea. Genetic correlations may have constrained the pattern of variation at higher taxonomic levels, since some of the trait associations detected in a segregating F2 generation were also found at the among-population level.  相似文献   

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To help evaluate root distribution patterns, elongation rates of individual roots were measured as a function of soil temperature for Encelia farinosa (a C3 species), Pleuraphis rigida (C4), and Agave deserti (CAM), sympatric codominants in the northwestern Sonoran Desert. Measurements were made at current and doubled CO2 concentrations under winter and summer conditions of air temperature (day/night temperatures of 17 C/10 C and 33 C/22 C, respectively). The three species had different optimal temperatures for root elongation (Topt) under winter conditions (25 C for E. farinosa, 35 C for P. rigida, and 30 C for A. deserti); Topt increased by 2-3 C under summer conditions for all three species. The limiting temperatures for elongation also acclimated from winter to summer conditions. The rate of root elongation at Topt was higher under summer than winter conditions for E. farinosa (9 vs. 6 mm d−1) and P. rigida (20 vs. 14 mm d−1), reflecting conditions for maximum photosynthesis; no difference occurred for A. deserti (9 vs. 10 mm d−1). Decreased elongation rates at extreme temperatures were associated with less cell division and reduced cell extension. The doubled CO2 concentration increased average daily root elongation rates for A. deserti under both winter (7%) and summer (12%) conditions, reflecting increased cell extension, but had no effect for the other two species. Simulations of root elongation as a function of soil temperatures showed that maximum elongation would occur at different depths (16-20 cm for E. farinosa, 4-8 cm for P. rigida, and 0-4 cm for A. deserti) and during different seasons (winter to spring for E. farinosa, spring to summer for P. rigida, and all year for A. deserti), contributing to their niche separation. Shading of the soil surface moderated daily variations in soil temperature, reducing seasonal root elongation for winter and spring and increasing elongation for summer. Shading also altered root distribution patterns, e.g., optimal rooting depth for A. deserti and especially P. rigida increased for a hot summer day.  相似文献   

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Summary Members of the shrub genus Encelia occur in the arid coastal regions of western North America and South America along gradients of precipitation extending from less than 50 mm annually to somewhat over 350 mm. At moist ends of the gradient species possess glabrate, green leaves. Proceeding to drier regions, the species possess progressively more pubescent, whiter leaves. Leaf absorptance to solar radiation decreases with precipitation in an identical pattern along gradients in both North and South America.  相似文献   

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Encelia farinosa is one of the most abundant and highly studied species of the Sonoran Desert, yet characteristics of its leaf development and long-term photosynthetic capacity are relatively unknown. The net CO2 uptake rate and the Rubisco activity per unit leaf area for E. farinosa in a glasshouse increased in parallel for about 18 days after leaf emergence (leaf area was then 5 cm2), after which both were constant, suggesting that Rubisco levels controlled net CO2 uptake. Instantaneous net CO2 uptake rates at noon for well-watered E. farinosa in the glasshouse at different temperatures and light levels correctly predicted differences in daily net CO2 uptake at four seasonally diverse times for transplanted plants under irrigated conditions in the field but overpredicted the daily means by 13%. After this correction, seasonally adjusted net CO2 uptake per unit leaf area multiplied by the estimated monthly leaf area predicted that 42% of the net carbon gain was incorporated into plant dry weight over a 17-month period. The ecological success of E. farinosa apparently reflects an inherently high daily net CO2 uptake and retention of a substantial fraction of its leaf carbon gain.  相似文献   

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Stefan Andersson 《Oecologia》1989,80(4):540-545
Summary Populations of the monocarpic plant Crepis tectorum were grown in a series of uniform environments to test the hypothesis that weedy populations are more r-selected than populations from a more natural habitat. Weedy populations exhibited a combination of r- and K-selected traits. The relatively rapid growth, the potential for a summer annual habit, and the relatively high fecundity that characterized at least one of the two weed populations studied were considered as r-selected traits favored in habitats of unpredictable duration. However, high levels of competition from other weedy species or from the crop in arable fields may explain at least some presumably K-selected traits observed in the weedy populations, e.g. relatively large seeds and late flowering in the summer. Results indicated that stress due to abiotic factors (strong winds, desiccation and nutrient deficiency) has been a more important selective factor than r- or K-selection, in non-weedy populations from calcareous grasslands (alvars) on the Baltic islands.  相似文献   

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For tenBlandfordia grandiflora populations spanning about 90% of the species' range, univariate and multivariate analyses on 14 vegetative and reproductive characters separated plants into distinct coastal and tableland groups. Distinguishing characters were number of flowers and leaves, leaf length and width, and inflorescence stalk height and diameter; coastal plants were larger than tableland plants. In a transplant experiment, coastal and tableland plants retained their phenotypic distinctness, indicating that vegetative morphology was genetically determined. Coastal plants exhibited clinal variation with latitude. Compared to tableland plants, coastal plants had higher pollen: ovule ratios, and produced fewer but heavier seeds per flower. Tableland and coastal plants are phenotypically distinct, indicating that separate subspecific status is warranted.  相似文献   

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Few integrative analyses of the structure of agamospermous plant populations have been conducted. Erigeron compositus occurs in montane western North America and comprises both sexual and agamospermous populations. Sexual E. compositus has previously been characterized as outcrossing and predominantly diploid (2n = 18). Agamic E. compositus is usually hexaploid (2n = 54), though counts herein range from 2n = 36 to 2n = 80. Starch-gel electrophoresis, cytology, and analysis of pollen production were used to evaluate variation within and among agamospermous populations. Fifteen enzyme loci were used to identify 24 unique multilocus genotypes in seven populations, an average of 3.4 genotypes per population. Proportion of distinct genotypes per population sample size (GIN) and measures of genetic diversity (D) and evenness (E) are 0.10, 0.48, and 0.61, respectively, which indicate that E. compositus maintains levels of diversity similar to other agamospermous taxa. Most agamospermous populations are mosaics comprising groups of genetically distinct individuals that are frequently distinguished by cytotype and capacity for pollen production. The geographical and ecological separation of sexual and agamospermous populations make it unlikely that gene flow from sexual populations is a direct source of genetic variation in agamospermous populations. Instead, crossing between genetically distinct facultative agamosperms probably accounts for most variation. Genetic and morphological evidence document one such putative crossing event. Agamospermous E. compositus is very similar genetically to sexual E. compositus. Allozyme analysis further shows that genetic variation in agamospermous populations is partitioned among a few highly heterozygous genotypes, whereas sexual populations maintain numerous genotypes of relatively low heterozygosity.  相似文献   

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This study examines the relationship among traits distinguishing populations of C. tectorum and the extent to which existing trait associations reflect underlying (genetic) tradeoffs. Highly consistent trait associations were found in a comparison of 52 populations representing the western part of the geographical range of the species. In addition to a tight integration of traits reflecting plant stature and inflorescence development, there were consistent links between vegetative and reproductive traits; populations characterized by individuals with large leaves and tall stems with terminal branches usually had larger heads, flowers and fruits (achenes) than those whose individuals had small leaves and a short stem branched from the base. There was a weak negative relationship between the extent of leaf dissection and plant stature; short and compact plants had more deeply lobed leaves than tall plants with terminal branches. Few of these associations were present among families representing a single population of C. tectorum , but there was remarkable similarity between the correlations at the between-population level and those obtained in two segregating F2 progenies of crosses between contrasting populations. Hence, provided that the F2 correlations have a strong genetic basis, it appears that the course of population divergence has been constrained by the underlying correlation structure, although some trait associations may also be a result of selection operating in a correlated fashion on functionally related traits, perhaps leading to linkage disequilibrium of parental traits in the first segregating generation of a cross between ecologically differentiated populations.  相似文献   

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BACKGROUND AND AIMS: A wide variety of plants produce extrafloral nectaries (EFNs) that are visited by predatory arthropods. But very few studies have investigated the relationship between plant genetic variation and EFNs. The presence of foliar EFNs is highly variable among different aspen (Populus tremuloides) genotypes and the EFNs are visited by parasitic wasps and predatory flies. The aim here was to determine the heritability of EFNs among aspen genotypes and age classes, possible trade-offs between direct and indirect defences, EFN induction following herbivory, and the relationship between EFNs and predatory insects. METHODS: EFN density was quantified among aspen genotypes in Wisconsin on trees of different ages and broad-sense heritability from common garden trees was calculated. EFNs were also quantified in natural aspen stands in Utah. From the common garden trees foliar defensive chemical levels were quantified to evaluate their relationship with EFN density. A defoliation experiment was performed to determine if EFNs can be induced in response to herbivory. Finally, predatory arthropod abundance among aspen trees was quantified to determine the relationship between arthropod abundance and EFNs. KEY RESULTS: Broad-sense heritability for expression (0.74-0.82) and induction (0.85) of EFNs was high. One-year-old trees had 20% greater EFN density than 4-year-old trees and more than 50% greater EFN density than > or =10-year-old trees. No trade-offs were found between foliar chemical concentrations and EFN density. Predatory fly abundance varied among aspen genotypes, but predatory arthropod abundance and average EFN density were not related. CONCLUSIONS: Aspen extrafloral nectaries are strongly genetically determined and have the potential to respond rapidly to evolutionary forces. The pattern of EFN expression among different age classes of trees appears to follow predictions of optimal defence theory. The relationship between EFNs and predators likely varies in relation to multiple temporal and environmental factors.  相似文献   

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To explore the biogeographic history of Mediterranean/arid plant disjunctions, Old and New World Senecio sect. Senecio were analyzed phylogenetically using nuclear ribosomal DNA sequences (ITS). A clade corresponding to sect. Senecio was strongly supported. Area optimization indicated this clade to be of southern African origin. The Mediterranean and southern African floras were not distinguishable as sources of the main New World lineage, estimated to have become established during the middle Pliocene. Another previously suspected recent dispersal to the New World from the Mediterranean was confirmed for the recently recognized disjunction in S. mohavensis. The loss of suitable land connections by the Miocene means that both New World lineages must represent long-distance dispersal, providing the first evidence of repeat intercontinental dispersal in a Mediterranean group. In contrast, migration within Africa may have utilized an East African arid corridor. Recent dispersal to northern Africa is supported for S. flavus, which formed part of a distinct southern African lineage. Novel pappus modifications in both disjunct species may have enabled dispersal by birds. An estimated early Pliocene origin of sect. Senecio coincides with the appearance of summer-dry climate. However, diversification from 1.6 BP highlights the importance of Pleistocene climate fluctuations for speciation.  相似文献   

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Some recent systematic investigations have placed great reliance on micromorphological floral features in generic delimitation in the Senecioneae. In order to test the taxonomic value of those features, 31 species of New World “Cacalioid” and “Senecionoid” Senecioneae were examined for five micromorphological characters: 1) configuration and distribution of the stigmatic area on the style branches, 2) stylopodial structure, 3) cellular structure of the carpopodium, 4) configuration of the anther collar, and 5) form of the endothecial cells in the anther. LM or SEM photographs were made for each character for each species. Variation was found to exist with age and geographical range for each of these characters and sometimes between florets on one capitulum. Differences in these five microcharacters were found between the “Cacalioid” and “Senecionoid” genera, but they were no more consistent than the differences in traditional characters employed in generic delimitation.  相似文献   

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The only available ethnobotanical information on Pteronia incana has been recorded by the Montagu Museum in the Western Cape Province of South Africa. It was reported that the plant is used to treat influenza, fever, kidney ailments and backache. In common with other species of Pteronia, the plant contains an essential oil reminiscent of pine turpentine oil with β-pinene, limonene, 1,8-cineole, myrcene, spathulenol, p-cymene and methyleugenol as main compounds present in all or most of the samples, with smaller amounts of α-pinene, sabinene, γ-terpinene, terpinen-4-ol, biclogermacrene, globulol and α-bisabolol in some of the distillates. We investigated the oil composition of 11 individual plants collected at three geographically distant localities but found limited variation, both within and between populations. Leaf sections of P. incana showed that it is anatomically similar to P. divaricata in the presence of a secretory duct associated with the main vascular bundle (and often other bundles as well), in addition to glandular and non-glandular trichomes on both leaf surfaces. One yeast (Cryptococcus neoformans), two Gram-negative bacteria (Moraxella catarrhalis and Klebsiella pneumoniae) and one Gram-positive bacterium (Mycobacterium smegmatis) were selected for antimicrobial activity studies using the minimum inhibitory concentration (MIC) microtitre plate method. The results showed that methanol:dichloromethane (MeOH:CH2Cl2) extracts were active against M. smegmatis (lowest MIC values of 0.5–0.8 mg/ml) and C. neoformans (lowest MIC values of 0.5–2.0 mg/ml). The essential oil was most active against C. neoformans (lowest MIC value of 0.3 mg/ml). These results provide a scientific rationale for the use of P. incana in Cape herbal medicine.  相似文献   

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Aster furcatus is a rare species with extremely limited genetic variation at isozyme loci. We utilized crossing experiments and seed set data obtained from natural populations to verify that there is also little allelic variation at the self-incompatibility (S) locus. Seed set in several populations was limited by a low number of S-alleles. Associated with a low number of S-alleles in populations was the dissolution of the incompatibility system, manifest by individual variation in self-compatibility, and by complex dominance relationships among S-alleles. Plant self-compatibility was correlated with mean number of ovules per inflorescence. Thus, self-compatibility appeared to be under partial environmental influence. Computer simulations revealed that the shapes of seed set distribution curves of modeled self-incompatible plant populations depend on the number of incompatibility alleles in the populations. By varying the number of S-alleles in modeled populations, we generated seed set distribution curves similar to those of natural populations. Genetic bottlenecks reduce the number of S-alleles and the proportion of compatible matings in populations of multiallelic self-incompatible species. Self-compatible genotypes are at a selective advantage in populations that lack a sufficient number of S-alleles to produce compatible crosses. Aster furcatus appears to be evolving self-compatibility as a result of bottleneck-induced losses of S-alleles.  相似文献   

20.
Background: It is argued that coastal endemic taxa may evolve in parallel at the periphery of the distributional range of a widespread species.

Aims: We tested this hypothesis for the origins of three peripheral, coastal isolates of Senecio, S. glaucus ssp. glaucus (Israel), S. g. ssp. coronopifolius p.p. (Sicily), and S. hesperidium (Morocco), from widespread S. glaucus ssp. coronopifolius. We also determined the relative roles of selection vs. genetic drift in shaping phenotypic divergence in ssp. glaucus and S. hesperidium, using Lande’s test of neutral morphological change.

Methods: We surveyed morphological and/or allozyme variation in the three peripheral isolates and mainly inland populations of S. g. ssp. coronopifolius.

Results: Genetic data supported independent origins of the coastal taxa from nearby populations of ssp. coronopifolius. These descendant and ancestral populations showed pronounced morphological but weak genetic differentiation. Phenotypic similarities between ssp. glaucus (Israel) and S. hesperidium (Morocco) in plant height and floral traits may have resulted from parallel divergent selection from ssp. coronopifolius, though drift remains an alternative cause in S. hesperidium.

Conclusions: Our results indicate parallel ecotype formation and (sub)speciation in Senecio in which primarily selective vs. neutral determinants promoted the recurrent origin of coastal types in, respectively, Israel and Morocco.  相似文献   

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