摘要:

Forty‐five percent of the Hawaiian pteridophyte flora were examined for mycorrhizae. Vesicular‐arbuscular mycorrhizae were present in 66 of the 89 species examined. Nonmycotrophy was significantly higher in Hawaiian pteridophytes than in non‐Hawaiian pteridophytes. The highest mycorrhizal colonization occurred in the leptosporangiate families Dicksoniaceae, Dryopteridaceae, and Lindsaeaceae. Mycotrophy was lower in the eusporangiate families. Substrate strongly influenced the presence of mycotrophy. Mycorrhizae were present in 83% of terricolous species, in 86% of epilithic species, in 55% of epiphytic species, and absent from aquatic species. A phylogram of pteridophyte families is constructed incorporating the intensity of mycorrhizal colonization as one criterion for classification.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1992.tb13665.x

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

Endemic, indigenous, naturalized and cultivated angiosperms growing in a variety of habitats in Hawaii were examined for mycorrhizae. Of 147 species (representing 61 families) examined, 122 were mycorrhizal, and 98% of the latter formed vesicular‐arbuscular mycorrhizae (VAM). Ericoid, orchid, and ectomycorrhizae also were found. Mycorrhizae were most frequent in endemic species (90.3%) and least in indigenous species (71.9%). The incidence of mycotrophy in Hawaiian endemic species was significantly greater than in mainland species. In addition, VAM often were found in species belonging to families that typically lack mycorrhizae (Aizoaceae, Brassicaceae, Caryophyllaceae, Cyperaceae, Hydrophyllaceae, Juncaceae, Pandanaceae, and Urticaceae). Naturalized weedy species were highly mycorrhizal. The high incidence of mycorrhizae in endemic species suggests that VAM fungi and obligately mycotrophic plant species may have been present in the Hawaiian Islands from the earliest stages of the development of the angiosperm flora.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1992.tb13666.x

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

Seeds from four plant pairs collected from contrasting elevations in Hawaii were grown in greenhouses at the University of Maryland at UV‐B radiation levels that approximated a 20% and 40% stratospheric ozone depletion anticipated at sea level in Maui. In general, increases in UV‐B radiation resulted in earlier reproductive effort, increased dark respiration and maintenance of relative water content (RWC), photosynthesis, and apparent quantum efficiency (AQE) in plants from higher elevations where natural UV‐B radiation is already high. In contrast, plants collected from low elevational ranges showed a significant decline in average plant and floral dry biomass, a decline in AQE and RWC, and a reduction in light‐saturated photosynthetic capacity. Increases in UV‐B‐absorbing compounds (e.g., flavonoids), were noted for low elevation but not high elevation plants. However, plants from high elevations produced a consistently larger amount of these compounds even in the absence of UV‐B radiation. This study suggests that plants growing in a naturally high UV‐B environment may have developed or maintained mechanisms related to reproductive phenology and carbon uptake which may maintain productivity in a high UV‐B environment. This would also suggest that ecotypic differentiation may have occurred in response to increasing UV‐B radiation over an elevational gradient. The range of adaptability to increased UV‐B also implies changes in species and community dynamics that might be anticipated in natural plant populations if stratospheric ozone depletion continues.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1992.tb13667.x

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

Antennaria arcuata(Asteraceae: Inuleae) is a rare sexual diploid species that occurs in three disjunct regions of Idaho, Nevada, and Wyoming. Isozyme diversity in six populations of the species from the three regions utilized 26 putative loci to provide clues to its population genetic structure. Results show that, in general, the amount of genetic diversity inA. arcuatais very low in comparison to other sexual species ofAntennaria.The values of several genetic statistics such as mean number of alleles per locus, proportion of loci polymorphic, and observed heterozygosity, are significantly lower than populations of any of 17 other sexual species ofAntennariathat have been studied previously. It is likely that the unusual disjunct and restricted distribution ofA. arcuatais partially the result of its unusual ecology, as it occurs in moist basins having high concentrations of salts that are frequently disturbed by large grazing animals. Canonical correspondence analysis shows strong relationships between several edaphic, environmental, and geographic features and the genetic variation in the populations. The migration ofA. arcuatato other regions since the end of the Wisconsinan might have been inhibited by the fact that suitable habitats occur as small isolated islands in a sea of inhospitable terrain, the dry sagebrush steppe.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1992.tb13668.x

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

Germination of dormant achenes of wild buckwheat (Polygonum convolvulusL.) was promoted at 25 C if they were stratified at low temperatures. Preincubation at either 2 C or 10 C promoted subsequent germination at 25 C equally, although the period of time to reach maximum germination was shorter for the 2 C treatment. Moreover, a preincubation treatment of a daily alternating cycle 2 C for 20 hr and 10 C for 4 hr promoted germination at 25 C more than either temperature alone. Removing portions of the hard pericarp and testa did not promote germination of dormant achenes at 25 C except when the portion of those structures covering the tip of the radicle was removed. This suggests that the structures covering the embryo do not prevent germination by restricting the movement of water or gases but rather restrict growth mechanically. Complete removal of the pericarp promoted germination, but much higher germination was obtained when the testa was also removed, indicating that the pericarp may not be the main factor in dormancy. Thus the role of low temperature in the loss of dormancy in wild buckwheat achenes may be to promote the production of hydrolytic enzymes that lower the mechanical resistance of pericarp and testa and/or increase the embryo growth potential beyond some threshold level and thereby enable the radicle to overcome the resistance to growth imposed by the structures covering the embryo.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1992.tb13669.x

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

Internal geitonogamy (IG) is a unique self‐fertilization system that occurs in the genusCallitriche.In IG self‐fertilization is effected by pollen tube growth through vegetative tissues from the staminate to pistillate flowers. IG occurs in seven of the 22 species ofCallitrichein the New World (C.heterophylla, C. heteropoda, C. lechleri, C. nubigena, C. rimosa, C. trochlearis, C. verna).Callitriche vernaoccurs in both the New and Old Worlds and represents the only known instance of IG in the latter region. IG is correlated with the amphibious growth habit and polyploidy, although not all polyploid amphibious species ofCallitrichehave IG. Correlations between IG and geographic distribution are not apparent. There is a tendency for species that possess IG to occur at higher elevations than those that lack this system.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1992.tb13670.x

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

To examine the breeding system and components of male and female reproductive success in the hermaphroditic plantLobelia cardinalis, we performed three crossing experiments with plants taken from natural populations. The experiments were designed to determine if the crossing success of plants as pollen and ovule parents was affected by the distance among mates, including self‐pollinations and pollinations between populations; to determine if plants differed in their abilities to sire or mature seed; and to determine if there was a correlation between a plant's success at siring and maturing seed. Selfpollinations resulted in significantly fewer seeds per fruit and significantly smaller seeds. There were no significant differences in germinability between selfed and outcrossed seeds. Distance among parents within a population did not affect any of the traits. Outcrosses within and between population produced similar numbers of seeds per fruit, similar seed weights, and similar germination success. There were highly significant differences among maternal plants in all three experiments in the number of seeds they matured, mean seed weight, and seed germinability. The maternal parent was the most important factor determining seed production, but there were also significant differences among paternal plants in the number of seeds they sired (all three experiments), in the germinability of the seeds they sired (two experiments), and in the sizes of seeds they sired (one experiment). Our results indicate that differences in success ofLobeliaplants as male parents cannot be due solely to their relatedness to the female parent.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1992.tb13671.x

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

The sexual and asexual portions of the life cycle ofGlenodiniopsis steiniiwere examined at both the light and scanning electron microscopic levels. Asexual reproduction by cell division occurs every 2 to 3 d under optimal conditions. Gamete formation and sexual reproduction can be induced by either nitrogen deprivation or aging of cultures. Fusion of gametes peaks about 10 hr into the light cycle and requires about 10 hr for completion. Cells remain motile during fusion but the zygote loses motility. The cell then undergoes changes that give it a thick‐walled, warty appearance.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1992.tb13672.x

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

The various primary vascular systems of shoots ofAnagallis arvensisL. (Primulaceae) can be distinguished in relation to the number of leaves (two, three, or four) at each node. In this study, shoot segments (single intemodes and the nodes above them) were examined. The arrangement of segments within shoots was also recorded. The vasculature forms a closed system with the number of sets of bundles usually equal to twice the number of leaves. Irregularities are found in the following features of the system: the number of bundles composing leaf half‐traces; occurrence of anastomosing bundles; the number of intemodes through which bundles extend; levels of leaf attachment to the stem at the node; and distribution of parenchyma within the vascular cylinder, which determines the number of bundles in sets and the number of bundle sets. The irregularities occur with different frequencies for segments exhibiting different phyllotactic patterns. Comparison of these frequencies leads to the following conclusions: anastomosing bundles occur only in decussate or trimerous shoot segments, whereas sets of bundles united within intemodes and displaced leaves occur only in tetramerous or trimerous ones; decrease of the number of bundles per leaf and displacement of leaves at the nodal level are correlated; variation between segments exhibiting the same phyllotactic pattern is greatest for trimerous, less for tetramerous, and least for decussate segments; the vascular system of decussate shoot segments is more stable than that of the other systems; and trimerous segments seem to be intermediate between the other two segment types.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1992.tb13673.x

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

The stem unit is defined as the smallest portion of a stem that can duplicate the stem in toto through regular rotations and dilations over successive plastochrons. In stems exhibitingk(m,n) contact parastichy phyllotaxis, the stem unit is delimited vertically and tangentially by the boundaries of four successive leaf primordia along them‐, n‐, and(m + n)‐parastichies and radially by these boundaries extended to the centroid of the stem. With the stem unit concept, node refers only to the region of actual leaf insertion, rather than the entire transverse level of insertion. Many of the conflicting and complicating aspects of the traditional node‐intemode subdivisions of stems are demonstrated, and the utility of the stem unit in circumventing these is illustrated. The stem unit is proposed as a more useful analytic subunit of the stem with which to examine stem growth and tissue differentiation processes than the more traditional node‐intemode subdivisions of stems.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1992.tb13674.x

出版商:Wiley    

年代:1992

数据来源: WILEY