摘要:

Responses in net photosynthesis (A), stomatal conductance to water vapor (g), and leaf xylem pressure potential (ψ) were measured in the deciduous treeQuercus macrocarpaduring alternating periods of sun (photosynthetic photon flux, PPF>1,500μmol m‐2sec‐1) and shade (ca. 350μmol m‐2sec‐1simulating cloud cover). Measurements were made on trees growing at the gallery forest‐prairie edge on the Konza Prairie Research Natural Area in northeast Kansas. The region is near the westernmost extension of the range ofQ. macrocarpawhere this species experiences significant seasonal water stress (minimumψ<‐2.9 MPa).Quercus macrocarpawas chosen for study because it has relatively high A (15μmol m‐2sec‐1) and g (300 mmol m‐2sec‐1) in contrast to the deciduous and evergreen subalpine trees previously studied. Both trees and large saplings ofQ. macrocarparesponded to alternating several minute periods of sun and shade with relatively rapid changes in A and g. Reductions in g (110 mmol m‐2sec‐1) during shade periods lowered transpirational water losses (E) by 13% (and reduced A by 5%) relative to estimates of A and E made assuming g remained constant. Partial stomatal closure during shade was correlated with moderate enhancement inψ(0.31 MPa) inQ. macrocarpa. However, greater increases inψwere measured in adjacent prairie grasses exposed to similar periods of shade (0.72 MPa inAndropogon gerardii, 0.61 MPa inSorghastrum nutans). Reduced variability inψin tree growth forms may reflect greater buffering of water relations associated with the large size of trees, the amount of tissue devoted to water storage, and differences in hydraulic resistance relative to herbs. Nonetheless, the gas exchange and water relations responses inQ. macrocarpawere much more similar to those previously measured in herbaceous subalpine and grassland species than to those documented for subalpine trees. Thus, rapid gas exchange responses to variable PPF may also occur in tree growth forms.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1992.tb14601.x

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

Synchysidendron, gen. nov., is segregated fromDiaphorodendronDiMichele emend. Both genera are determinate, rhizomorphic, arborescent lycopsids that share identical reproductive organs but differ radically in growth architecture and consequently in the timing of reproduction. Cones inSynchysidendron(two species) are borne on late‐formed crown branches; inDiaphorodendron(three species) cones are borne on deciduous lateral branches, produced over much of the life of the tree. The two genera also differ in several characteristics of the stele and periderm. We hypothesize thatDiaphorodendrongave rise toSynchysidendronwithin their shared Late Carboniferous coal‐swamp habitat, by heterochronic suppression of lateral branching during ontogeny. Together, these genera form a highly apomorphic clade, here recognized as the new family Diaphorodendraceae, that is distinguished primarily by siphonostelic axes, a bifacial periderm, distinctive megasporangia, and gulate megaspores.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1992.tb14602.x

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

The extent of rejuvenation that occurs during in vitro culture and propagation ofBetulawas determined. Comparisons were made between half‐sib seedlings and micropropagated, grafted, and cutting‐propagated mature‐phase birch plants grown under similar conditions. To measure relative levels of juvenility, three clones were examined at 1, 4, and 8 mo postpropagation, for differences in stem and leaf morphology and the presence or absence of reproductive structures. Numerous morphological indicators of phase change inBetulawere identified. Micropropagated plants are not initially morphologically identical to conventionally propagated mature plants and display many features characteristic of seedlings. Micropropagated plants that exhibited juvenile morphology developed mature morphology more rapidly than did plants grown from seed. However, some mature‐phase morphological characteristics did not return to micropropagated plants during the time frame of the study. Rejuvenation ofBetulaappears to occur during in vitro micropropagation, but the level of juvenility that is regained may not be equivalent to that of a seedling. Not all morphological indicators of phase change are affected equally by in vitro rejuvenation.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1992.tb14603.x

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

The pattern of protein production during rejuvenation of in vitro culturedBetulawas determined. Comparisons were made between half‐sib seedlings and micropropagated, grafted, and cutting‐propagated mature‐phase birch grown under similar conditions. Three clones were examined at 1, 4, and 8 mo postpropagation, for differences in total denatured protein and peroxidase and esterase isozymes. Polyacrylamide gel electrophoresis was employed to produce protein banding patterns representative of each type of plant at each time postpropagation. Evaluation of total denatured protein banding patterns indicated that micropropagated plants are initially more like seedlings than mature plants. Peroxidase and esterase isozyme analyses detected differences in isozyme activity and composition between the variously propagated plants and supported evidence provided from the denatured protein patterns. The type of plant part that is evaluated is critical in determining if isozyme banding patterns can be seen. Specific proteins or enzymes that mediate phase change in birch could not be detected consistently between clones or tissue types.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1992.tb14604.x

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

Cross‐comparisons of nectar production data are complicated because different workers use bags made of various materials to exclude animal visitors. Using clonal populations ofAsclepias syriacaandA. exaltatain northern Virginia, we carefully measured the effects of four bagging treatments (bridal veil, pellon, paper, plastic) on microenvironment (temperature, relative humidity) and nectar production (volume, concentration, sucrose amount) over the course of a day. In general, bridal veil bags changed the microenvironment least relative to unbagged controls. Plastic bags resulted in higher temperatures and constantly higher relative humidities. Temperature and relative humidity were also elevated, though less dramatically, in paper and pellon bags. Under more humid conditions, flowers contained larger volumes of more dilute nectar. Therefore, researchers who wish to obtain nectar production data that reflect natural field conditions should use bridal veil, or a material with similar properties, to bag inflorescences. We also performed a watering experiment, involving the addition of the equivalent of a 10‐cm rain to theA. syriacaplot. After watering, nectar volumes and sucrose amounts were increased approximately twofold.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1992.tb14605.x

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

White clover (Trifolium repensL.) is a stoloniferous clonal legume. Dynamics of white clover populations are controlled by the recruitment of both seedlings (genets) and node production (ramets). To understand the role of seedling dynamics in natural populations of white clover, the recruitment and mortality of seedlings in a lawn and pasture clover population were followed and the roles of biotic and abiotic factors in seedling recruitment and survival were assessed. Seedling recruitment was several orders of magnitude less than vegetative recruitment in both lawn and pasture populations. However, at least several new genets are added to these populations on a yearly basis. In both locations, physical disturbances may open sites for seed germination, as disturbed sites had higher seed germination rates than undisturbed sites. However, these sites were not favorable for long‐term establishment due to such factors as frost upheaval. Therefore, there are trade‐offs in safe site attributes for seed germination and establishment that strongly limit recruitment in natural populations of white clover.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1992.tb14606.x

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

The evolution of inbreeding in plants has often been attributed to selection for the ability to set seed in the absence of mates or pollinators. Mechanisms of reproductive assurance in five populations of mixed matingMimulus guttatus, three populations of inbreedingM. platycalyx, and two populations of inbreedingM. nasutuswere examined in a pollinator‐free greenhouse. Reproductive assurance was manifested in all populations by autofertility, vegetative reproduction, or both. The inbreeding taxa had significantly greater levels of autofertility and less vegetative reproduction. Three modes of autofertility were identified: 1) due to corolla abscission only, occurring in threeM. guttatuspopulations; 2) due to both corolla abscission and direct anther‐stigma contact by curling of the lower stigmatic lobe into the anthers, occurring in twoM. guttatuspopulations; and 3) direct stigma‐anther contact by stigma curling alone prior to corolla abscission, found in eachM. platycalyxandM. nasutuspopulation. Stigma‐anther distance and its interaction with stigma curling contributed to differences in autofertility among populations. Significant levels of intrapopulation quantitative genetic variation were found for seven of ten traits examined; average levels were similar between inbreeding and mixed mating populations. Genetic variation within populations for autofertility per se was not detected, but significant levels controlling stigma‐anther distance were found in twoM. guttatuspopulations. These results show that evolution of inbreeding by natural selection for reproductive assurance is possible inMimulus, and illustrate the complex changes in floral dynamics and morphology it may involve.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1992.tb14607.x

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

Perforations of vessel elements characteristically retain remnants of pit membranes (primary walls) in woods of species of more than 30 families of dicotyledons. Scanning electron microscopy is necessary to demonstrate presence and type of membrane remnant. Species with these remnants in perforations given in earlier literature as well as those newly reported here are listed. Perforation membrane remnants may take the form of flakes, strands, or webs, and particular types may characterize particular families (e.g., strands or bands in Illiciaceae). Some families have abundant perforation membrane remnants (e.g., Chloranthaceae, Illiciaceae). Where membranes are nearly intact, they are porose and closely resemble the porose pit membranes on end walls ofTetracentrontracheids. InTetracentron, however, tracheary elements are monomorphic, so vessel origin cannot yet be said to have occurred. Membrane remnants in perforations are regarded as a relictual primitive feature that should be added to the list of primitive character states claimed for vessel elements in angiosperms; alternative hypotheses are considered and discussed, and evidence from DNA phylogenies is needed. In vessel‐bearing dicotyledons with membrane remnants in perforations, many perforations are relatively clear, but an appreciable proportion of perforation plates do have membrane remnants.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1992.tb14608.x

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

Draba(Brassicaceae) is well known for its taxonomic complexity in arctic and alpine floras, and the polyploids in particular present vexing taxonomic problems. It has been suggested that polyploids inDrabamay have formed recurrently from different populations of the parental species (polytopy), and it is also possible that a given taxonomic species may actually comprise several polyploid races, each originating from different progenitor species (polyphyly). To unravel the taxonomic complexity of polyploidDrabain the Nordic area, we investigated three of the most morphologically variable species and their possible progenitors using enzyme electrophoresis and restriction site analysis of chloroplast DNA (cpDNA) and nuclear ribosomal RNA genes (rDNA):D. norvegica(6x),D. lactea(6x), andD. corymbosa(16x). Electrophoretic analyses of progeny showed high levels of fixed heterozygosity in all three polyploids, demonstrating that all are genetic alloploids. Electrophoretic and rDNA data indicate that polytopic and/or polyphyletic origins have contributed to the complexity of these polyploids. However, a lack of cpDNA variation among the species limited the usefulness of this molecule for analysis of polyploid origins. The considerable electrophoretic variation observed inD. norvegicanecessitates a minimum of three and probably 13 independent origins. Electrophoretic and rDNA data suggest thatD. lacteaandD. corymbosaare polyphyletic polyploids. Crossing data also support thatD. corymbosais polyphyletic. Given the widespread geographic distributions of these species and their possible progenitors, and that the populations analyzed represent only a small fraction of their geographic distributions, it is likely that these species have formed numerous times in different areas. As more molecular analyses of polyploids are completed, the data continue to suggest that multiple origins of polyploids are the rule rather than the exception.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1992.tb14609.x

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

The genusTriboliumDesv. consists of nine species, i.e.,T. utriculosum(Nees) Renv.,T. ciliare(Stapf) Renv.,T. echinatum(Thunb.) Desv.,T. hispidum(Thunb.) Desv.,T. acutiflorum(Nees) Renv.,T. obliterumsensu Davidse,T. glomeratumsensu Davidse,T. uniolae(L.f.) Renv., andT. brachystachyum(Nees) Renv. The genus has a basic chromosome number of 6, and from diploid to hexaploid specimens have been examined. Precocious segregation of metaphase I bivalents were observed in four species. Multivalent formation results in unequal chromosome segregation during anaphase I, and several cells with an 11–13 chromosome distribution have been observed. The presence of univalents and anaphase I bridges in allT. brachystachyumspecimens suggests a hybrid origin for the species. B‐chromosomes were present in specimens from four species. The B‐chromosomes are similar to the euchromosomes with the exception that they do not participate in meiosis. The B‐chromosomes have a possible isochromosome origin. The cytogenetic evidence presented supports the combination ofPlagiochloaandLasiochloaintoTriboliumand indicates that the genus is closely related toUrochlaena, whereas it is not closely related toPrionanthium.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1992.tb14610.x

出版商:Wiley    

年代:1992

数据来源: WILEY