摘要:

The influence of soil waterlogging on the distribution and energy status ofSalix nigraandS. exiguawere studied in the field and laboratory. Differential flooding in natural stands ofSalixspp. and under controlled conditions in the greenhouse demonstrated thatS. nigrawas more tolerant of waterlogged soil conditions than wasS. exigua. Salix nigraexhibited a significantly higher leaf energy status and greater ability to oxidize waterlogged soil when flooded than didS. exigua.However,S. exiguaappeared to be more tolerant of moisture stress thanS.nigraas indicated by the significantly higher leaf resistances to water vapor exchange and higher leaf water potentials ofS. exigua.These data support the theory that the reason S.nigrainhabits lower elevation sites thanS.exiguain the Atchafalaya River Basin may be the differential tolerance of these two species to soil waterlogging on one extreme and moisture deficiencies on the other.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb05349.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

Several aspects of the spatial pattern of plants were investigated in six very different stands in the alpine tundra of the Colorado Front Range. Pattern was related to the internal structure of the stands, to interactions among the species, and to microhabitats within the stands.Evidence from species‐species associations and species ordinations clearly divided the stands into two groups. The first was characterized by thin, coarse, unstable soils, low plant cover, and nurse‐plant establishment. The second group was characterized by deeper, more mature, and more stable soils, higher plant cover, and more competition between species.Pattern evidence allowed some species to be categorized as competitors, ruderals, or stress‐tolerators in the context of the alpine vegetation. The two groups of stands also differed in the relative importance of species with these “strategies.”

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb05350.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

Successful fruit set by deerberry,Vaccinium stamineum(Ericaceae: Vaccinioideae) requires floral visitation by insects, and in particular by bees that collect its pollen by sonication of anthers (“buzz‐pollination”). A diversity of bees visit deerberry flowers, but most species are either 1) infrequent, 2) polylectic (broad host range for pollen), or 3) principally nectar‐seeking, and so are unimportant as pollen vectors. Both sexes of the solitary, oligolectic beeMelitta americana5(Melittidae) are abundant at flowering deerberry bushes in central New York State. FemaleM. americanasonicate the deerberry anthers while imbibing nectar, and carry virtually pure scopal loads of deerberry pollen, unlike the other common visitor,Xylocopa virginica(Anthophoridae). Comparative analyses of bee 1) abundances, 2) buzz‐pollination behaviors, 3) pollen fidelities, and 4) pollination efficiencies, all indicate thatMelitta americanais the primary pollinator ofVaccinium stamineum.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb05351.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

Fouquieria splendens, a desert plant native to the southwestern United States, was studied to determine the capacity for photosynthesis of green stem tissue. The plant is leafless most of the year because of drought, so the capacity for gas exchange by the stems is essential for their photosynthetic function. With secondary growth, sclerified leaf bases which cover the stem become separated, and a transparent cork forms in the furrows between them. A well‐developed chlorenchyma occurs beneath this cork as well as beneath the leaf bases. Chloroplasts of the stem have an unusually high degree of granal stacking, but are mostly typical. Light is transmitted through the leaf base on the young primary shoot and the furrow cork, but not through the older leaf base. Chlorophyll fluorescence studies indicated that the chloroplasts were fully competent and indeed stem tissue is capable of fixing14CO2if supplied to cut sections. Despite competent chloroplasts, no exogenous CO2uptake occurs because the cork is impermeable to CO2, and presumably water. The functional significance of competent chloroplasts in stems that do not transfer gas may be the production of high energy compounds for metabolism, the recycling of internally generated respiratory CO2, or it may simply be a relictual feature in this species of theFouquieriaceae.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb05352.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

Thickets of speckled alder (Alnus incanassp.rugosa(Du Roi) Clausen) consist of numerous discrete clumps of stems. Presumably all stems in a single clump are part of a single genetic individual, but a genet could comprise more than one clump. Starch‐gel electrophoresis was used to identify genetic individuals in four alder populations in central New York. A single genetic marker, a tetramer with three alleles, could discriminate five genotypes. Nearest neighbor analysis revealed that genotypes were distributed randomly. That is, the pattern of genotypes was statistically indistinguishable from a model where each clump is considered a unique individual and where clump genotypes are randomly distributed. Calculation of Morisita's index of dispersion confirmed that clumps of a single genotype were not aggregated. Although alder is capable of forming root suckers and offsets, lateral expansion of genets is apparently ineffective. Apparently, spatial distribution of genetic individuals within alder thickets is not influenced by clonal growth or by other factors acting to cause patterns in the genetic structure of plant populations.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb05353.x

出版商:Wiley    

年代:1985

数据来源: WILEY

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb05354.x

出版商:Wiley    

年代:1985

数据来源: WILEY

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb05338.x

出版商:Wiley    

年代:1985

数据来源: WILEY