摘要:

The invasion pattern on a barren plain on the eastern flank of Mount St. Helens, Washington, devastated by the 1980 volcanic eruption was monitored between 1988 and 1992. All vascular plants on a grid consisting of 400 contiguous 100‐square‐meter quadrats were recorded with a cover score. The substrate was initially homogeneous, but significant heterogeneity had developed by 1988. Vascular plant species richness increased from 24 in 1988 to 41 in 1992. Mean species richness per quadrat increased from 0.44 to 5.71, mean cover increased from 0.04% to 0.51%, and mean diversity index (H') increased from 0.08 to 1.56. A variance/mean test of species richness pattern showed that invasion occurred sporadically since plots tended to have either several or no species. By 1992, mean species richness was more evenly distributed. Most seedlings continue to result from long‐distance dispersal, but reproductive colonies of species are developing. Seedling distributions are controlled by microsites. Eleven common species strongly and similarly preferred safe‐sites created by small rocks, undulations, or rills. However, many apparent safe‐sites are empty, suggesting that seeds are scarce and that even the most favorable microsites are marginal. The niches of these species seem to overlap broadly. The Plains of Abraham is in the earliest stage of primary succession. The detailed invasion pattern permitted us to distinguish species still dependent on immigration from those now locally established. Pronounced microsite preferences emphasize that physical amelioration (e.g., nutrient input and erosion) must occur before further succession can commence. We have observed the early stages of succession where an inhospitable site is gradually and heterogeneously changed into a habitat where safe‐sites do not limit succession, but where stochastic factors remain important.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb15324.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

Permineralized branchlets of Early DevonianPsilophytonand related trimerophytes sustained wounds that suggest the activity of animals, perhaps arthropods, with chewing and sucking mouthparts. Plant responses to injury were multiplication of cells beneath the wound, enlargement and lysing of those cells in some cases, and/or the formation of a protective tissue, a periderm. These reactions demonstrate that the plants were alive when injured. Presumed coprolites provide indirect evidence of the coexistence of plants and animals although the latter are lacking in the material. Spores, but no hyphae, assignable to Zygomycota demonstrate the presence of fungi in the community. Vascular plants, animals (? arthropods), and fungi apparently interacted freely in early terrestrial ecosystems.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb15325.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

In clonal plants, vegetative reproduction and clonal architecture can produce unusual population structures including populations composed of a single genetic individual and mosaics of discrete or intermingled genets.Fragaria chiloensisis a rapidly and diffusely spreading, stoloniferous, perennial herb that forms relatively isolated populations on coastal sand dunes in California. We predicted that populations would consist of a few, large, intermingled genets; and that genetic and spatial distances would be more closely correlated for clonal fragments than for genets. Using allozyme markers from four enzyme systems (Est, LAP, PGI, and TO), we measured genotypic differences among fragments in a population on the central coast of California. Contrary to predictions, the population contained numerous genets, and most were found only within areas of 10 × 10 m. However, fragments of some genets did occur at least 80 m apart, and genets intermingled. Genetic and spatial distances were correlated for both genets and fragments. These results suggest that clonal growth and sexual reproduction are both important in structuring this population.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb15326.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

Techniques for the determination of viability of field‐collected vesicular‐arbuscular mycorrhizal spores must be valid for spores of different ages and of varying levels of peridium (outer wall of unispored sporocarp) development. The use of the dehydrogenase‐activated stain 3‐(4,5‐dimethylthiazol‐yl)‐2,5‐diphenyl‐2H‐tetrazolium bromide (MTT) for determining viability of endogonaceous spores was reassessed. Freshly isolated and stored spores of three isolates ofGlomus mosseae(Nicol.&Gerd.) Gerd.&Trappe were stained using two different protocols: Miller, Torres, and McClean (Mycological Research,in press) and An and Hendrix (Mycologia80: 259–261). Time course results from selected experiments were analyzed graphically, and pooled results from all experiments were analyzed by factorial analysis of variance to determine statistically significant differences among the protocols, storage regime of spores, control killing method, and the effect of added cobalt ions. Significant nondehydrogenase‐specific staining occurred in both types of controls of freshly isolated spores using Miller, Torres, and McClean's method, rendering it inadequate for viability determination. With An and Hendrix's protocol, fresh nonkilled spores stained significantly more than ethanol‐treated spores, although these results underestimated viability as determined by two other assessment procedures, and autoclaving of fresh spores was not a satisfactory control treatment. Addition of cobalt to the incubation solution effectively drove all formazan production to the blue color but did not change the total percentage of colored spores produced, regardless of protocol used. Results corroborate the use of An and Hendrix's protocol with stored spores if color interpretation was corrected to include both blue and red colors as indicators of viability, results were read before nonspecific staining starts, and timing was extended to 75 hours. Both staining methods work with uniformly stored spores using specific incubation times, but not with spores of mixed ages, which could include young spores, making MTT not useful as a viability stain for field‐isolated spores.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb15327.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

Sexual allocation theory assumes trade‐offs and negative genetic correlations between male and female allocation in hermaphrodite plants. We tested this assumption by studying variation in male and female fertility in two experimental populations ofPinus sylvestris. In these populations, the genotypes have been vegetatively replicated, which allowed separation of the genetic and environmental components of variation. The genetic components of variation accounted for 36% of the total variation in pollen production in the two populations, and for 54% of cone production. As assumed by sexual allocation theory, the genetic correlation of pollen and cone production was negative in both populations (‐0.59 and ‐0.15). However, positive environmental correlations between these traits (0.43 and 0.45) resulted in no phenotypic correlation in one population and a positive phenotypic correlation in the other.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb15328.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

At the northern limit of its distribution, arctic dwarf birch,Betula glandulosa,shows nearly complete absence of sexual reproduction (i.e.,<;0.5% viable samaras) and maintains its populations vegetatively. To investigate the possible role of pollination dynamics in the loss of sexual reproduction, pollination biology of arctic dwarf birch was compared at two locations: Tarr Inlet on Baffin Island, Northwest Territories near the northern limit of the species, and Kuujjuaq, Quebec in the center of its distribution where sexual reproduction is the primary mode of reproduction. Relative production of staminate and pistillate flowers, pollen rain, pollen viability, and stigmatic pollen loads throughout pollen dispersal were compared. Plants at Tarr Inlet produced 15%–30% of pollen produced at Kuujjuaq, both as a result of a lower density of staminate catkins and less pollen per catkin. Potential seed productivity is limited at the northern limit because pistillate catkins produce 50% fewer flowers in the north than in the south. While stigmatic pollen loads were similar at both sites, lower pollen viability (68% vs. 93%) and a higher probability of geitonogamous pollen due to clonal growth pattern reduced fertilization success at the northern site. These data suggest that lack of sexual reproduction inB. glandulosaat its northern limit is in part due to pollen limitation.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb15329.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

Complete nuclear‐encoded (18S) small subunit rRNA gene sequences were determined for four charophycean green algae,Chlorokybus atmophyticus, Coleochaete orbicularis, Klebsormidium flaccidum,andNitellasp.Chlorokybus atmophyticusandColeochaete orbicularishave been previously suggested to represent the most basal and most derived taxa within the charophytes, respectively. However, parsimony analysis of our 18S rDNA sequences along with a selection of other complete green algal and land plant 18S rDNA sequences yields a gene tree topology in whichChlorokybusis the most basal taxon, followed by the branching ofColeochaeteandKlebsormidium. Two “sister” clades then diverge, one includingNitellaand the land plants, and the second, members of the Chlorophyceae and Pleurastrophyceae. Despite producing slightly diiferent gene tree topologies than those inferred from parsimony, distance analyses of the 18S rDNA sequences also do not indicate a strong affinity between the land plants andColeochaete. Rather,KlebsormidiumandColeochaeteare virtually equidistant from the land plant taxa. Other data are needed in order to assess the unexpected findings reported here, particularly the position ofColeochaete.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb15330.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

The so‐called copper mosses include a number of rare species that exhibit very broad intercontinental geographic distributions comprised of highly disjunct occurrences. In one species,Scopelophila cataractae,only the haploid gametophyte generation exists in the United States, although sporophytes occur in tropical America and in Asia. Gametophytic plants were sampled from all U.S. populations to determine what factors limit sexual reproduction. More than 50% of the plants in every population were devoid of gametangia, and no population contained plants with both male and female gametangia. Morphological differences between plants from putative male and female populations (when each was interpreted to be unisexual) suggested gametophytic sexual dimorphism, but generalized sexual differences were not maintained under common garden conditions. Experimental growth of plants on soils with low, moderate, or high concentrations of metals demonstrated extensive morphological variability, and thus genetic polymorphism, among five asexual populations. Morphological traits were also significantly plastic in response to differing soil types, but there was no evidence of differences in patterns of plasticity between sexes or populations. All populations produced higher cover area and individual plants formed larger leaves on the most highly metal‐contaminated soil. Populations varied significantly in growth on less contaminated soil, again suggesting genetic variability.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb15331.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

The internal transcribed spacers and the 5.8S coding region of nuclear ribosomal DNA were sequenced and analyzed to address questions of generic relationships in Winteraceae. The molecular data generated a single tree that is congruent with one based on morphological data. The sequences of ITS 1 in the family range from 235 to 252 bases in size and of ITS 2 from 213 to 226 bases. The size of the 5.8S coding region is 164 bases. The range of ITS 1 and ITS 2 sequence divergence between pairs of genera within Winteraceae is relatively low in comparison to other plant families. Two types of ITS 1 and ITS 2 sequences were observed in the same individual for some taxa. Sequence variations between the two arrays are 4.7%–6.3% for ITS 1 and 5.1%–7.0% for ITS 2. Both arrays of sequences, however, generate the same phylogenetic relationships. Rates of nucleotide substitutions for the internal transcribed spacers are 3.2–5.2 × 10‐10substitution per site per year estimated in ITS 1 and 3.6–5.7 × 10‐10in ITS 2.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb15332.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

To circumscribe Saxifragaceae sensu stricto better, as well as to elucidate generic relationships within this group, we sequenced the chloroplast generbcLand its 3' flanking region (yielding 1,471 bp) from 19 genera considered to represent core members of Saxifragaceae. In addition, we conducted a restriction site analysis of chloroplast DNA (cpDNA) for 21 core genera using 23 restriction endonucleases. Phylogenetic analyses using both data sets corroborate the results obtained from surveying the distribution of the loss of the intron in the chloroplast generp/2 in delimiting a well‐defined Saxifragaceae sensu stricto. Within the Saxifragaceae s.s. clade, a number of poorly resolved, basal phylogenetic branches supports the hypothesis that Saxifragaceae s.s. radiated rapidly very early in its evolutionary history. Molecular data also indicate the presence of several strongly supported groups of genera, such as theBoykiniagroup (Boykinia,Suksdorfia, Bolandra, Sullivantia, Jepsonia,andTelesonix), theHeucheragroup (Heuchera, Bensoniella, Conimitella, Eìmera, Lithophragma, Mitella, Tellima, Tiarelia,andTolmiea) theLeptarrhena/Tanakaeagroup, and theDarmeragroup (Darmera, Astilboides, Mukdenia, Bergenia,andRodgersia). Significantly, molecular data suggest that the very large, taxonomically complex genusSaxifragamay not be monophyletic. DNA data have also helped to resolve the generic relationships of problematic taxa, indicating, for example, thatTelesonixand the enigmaticJepsoniaare sister taxa. In addition to its phylogenetic implications, this study provides insight into basic trends in morphological, chemical, and cytological evolution within Saxifragaceae s.s. The molecular‐based phylogenies suggest multiple origins and/or losses of several classes of flavonoid compounds, as well as several independent instances of reduction in stamen and petal number, hypanthium‐ovary fusion, and aneuploidy. This study also illustrates the ability ofrbcLsequence data to resolve generic‐level relationships in some taxonomic groups.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb15333.x

出版商:Wiley    

年代:1993

数据来源: WILEY