摘要:

Seeds of seven dune species were collected from sand dunes of Lakes Erie and Huron and buried to various depths in a natural sand dune habitat along Lake Huron. The seed samples were then retrieved after varying lengths of time and examined for their germinability and dormancy. Results showed that buried seeds remained viable for at least 2.5 years and had the potential to form a persistent seed bank. Seed banks were larger and longer lasting at greater depths of burial than those at shallow burial depths. The results suggested that failure to verify the existence of effective seed banks in previous studies may be due to insufficient number of samples, shallow sample depth, local population variations, and fruiting events. Several species also possessed a temporary, aboveground seed reserve formed by retention of a small proportion of viable seeds on the previous year's inflorescences. In some species, seeds retained aboveground were dormant and thus capable of forming a persistent seed bank when they entered the soil.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb15461.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

The eruptions of 1977–1978 on Mount Usu in northern Japan resulted in the almost complete destruction of vegetation by a 1–3‐m‐thick accumulation of volcanic deposits. Erosion created gullies that removed these deposits and frequently exposed the old original soil. I previously confirmed that seedlings of 14 species (eight annual and six perennial herbs) emerged from seeds buried in the original topsoil. To clarify the role of the seed bank on volcanic succession, I monitored seedlings of seed bank species from 1983 to 1992. Nearly all the annuals, such asPolygonum longisetumandRorippa islandica, originated from the seed bank. However, seed supply from the seed bank declined with time. Because seedling mortality was extremely high and reproductive success was low, due mostly to the instability of ground surface, these annuals emerged for several years but disappeared after 1989. The nitrogen‐fixing and stoloniferous perennials,Trifolium repensandLotus corniculatusvar.japonicus, were derived only from the seed bank. They have gradually increased in cover and have become large enough to flower. The other perennials derived from the seed bank, most of which produce short rhizomes, did not increase in cover annually and thus contributed less to revegetation than nitrogen‐fixing stoloniferous species. The fate of perennials seems to be dependent on the types of rhizome and stolon systems. Although recruitment from the seed bank was restricted to gullies, the seed bank was the major source of annuals and of nitrogen‐fixing perennials in the gullies. Succession in the gullies was substantially different from that which occurred outside the gullies where plants mostly originated from seed immigration and vegetative reproduction from surviving plants, and annual and nitrogen‐fixing plants were absent.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb15462.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

Age, height, number of shoot endings, neighbor density, and overhead cover from local neighbors were recorded for over 1, 400 young sugar maple trees under 200 cm tall and growing in open vs. closed (shaded) habitats from two sites. Up to about age 5 yr, seedlings increase in height but rarely branch. Once branching starts, there begins a general decrease with age in the number of centimeters of height added for every new shoot ending that is produced. The pattern of this allometric relationship, however, is plastic—in the closed habitats, this switch to increased branching relative to height growth is delayed compared with trees from the open habitats. Within the closed habitats, branching is also delayed for trees having dense cover from local neighboring understory vegetation compared with trees that are not overtopped by understory vegetation. The oldest and tallest unbranched seedlings were recorded from the closed habitats. Seedlings displaying the first branch, however, were younger in the open habitats than in the closed habitats, and at one site they were shorter in the open habitat than in the closed habitat. These results suggest that the allometric relationship between height and degree of branching can display adaptive plasticity depending on light availability: As competition for light decreases (with greater light availability), there is an increasing premium on lateral growth (branching) to maximize light interception. Conversely, as competition for light increases (under decreasing light availability), there is an increasing premium on vertical growth (through strong and persistent apical dominance) to minimize the chances of being overtopped by neighbors.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb15463.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

We present a mathematical model of the diffusive flux of methane throughPeltandra virginica.Data on the diurnal changes in both the petiolar [CH4] gradient and the values of the radial bulk exchange coefficient, Er, are entirely consistent with this model and the assertion that changes in stomatal conductance regulate the rate of methane efflux inP. virginica.The differences between the values of Ercalculated for daytime and nighttime conditions are ‐40% for the submerged condition and ‐54% for the emergent condition. The axial diffusivity of CH4through the petiole ofP. virginicais estimated in vitro to be 0.771 cm2min‐1. Using our model, we estimate the equilibrium rate of methane efflux under daytime (97 ng CH4min1petiole‐1) and nighttime (65 ng CH4min‐1petiole‐1) emergent conditions. Numerical solutions of the model equations in the time domain offer a way of providing a dynamic model of the gas exchange responses ofP. virginicato changing environmental conditions.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb15464.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

Peperomiahas species that may be C3, show Crassulacean acid metabolism (CAM), or CAM‐cycling. Species that show CAM progress from C3to CAM through CAM‐cycling during leaf development. In CAM and CAM‐cycling species, CAM metabolism is predominately in the upper multiple epidermis and lower spongy mesophyll, whereas C3metabolism is localized mostly in the palisade mesophyll. Using specific protein and cDNA probes prepared from P‐enolpyruvate carboxylase (PEPc) and ribulose‐1,5‐bisphosphate carboxylase (Rubisco), we have now studied the differential distribution of photosynthetic metabolism inPeperomialeaves using the technique of tissue printing. The tissue printing studies detected Rubisco protein in leaves of C3P. orba, but not PEPc. Young C3leaves ofP. scandensandP. camptotrichashowed Rubisco protein, but not PEPc; however, the mature leaves of these two species that have CAM showed PEPc protein and RNAs in both the multiple epidermis and spongy mesophyll. In contrast, Rubisco protein and RNAs were present throughout the leaf. The tissue printing data are consistent with our previously published data showing the differential distribution of photosynthetic metabolism in leaves ofPeperomia.Although the tissue printing technique is qualitative, coupled with quantitative data it has proven useful for the study of function related to structure.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb15465.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

Two critical innovations had a profound influence upon the evolutionary history of plants: the nutritionally dependent embryo and apoplastic phloem loading processes. Both depend upon the ability of the plant cell membrane to transport sugars. The evolutionary origin of sugar transport by plants is, therefore, of special phylogenetic importance. Recent evidence suggests that hexoses such as glucose are the main form of sugar transported apoplastically across the placental junction between gametophyte and sporophyte of the mossPolytrichum(Renault et al., 1992,Plant Physiology100: 1815–1822). There is also considerable evidence that hexose transport may be involved in apoplastic phloem loading inArabidopsisand other flowering plants. Results of numerous molecular, biochemical, immunofluorescence, and ultrastructural studies indicate that bryophytes and charophycean algae are related to the ancestors of vascular plants. This report demonstrates that the charophyteColeochaete orbicularisexhibits enhanced growth in the presence of glucose under conditions in which inorganic carbon sources are limiting. Computer image analysis was used to demonstrate that nonaerated cultures ofC. orbicularisgrown for 7 weeks in an inorganic medium supplemented with 1% glucose produce as much as 13.6 times the biomass of clonal cultures grown for the same length of time in the same medium without glucose. Furthermore, addition of 1% glucose to nonaerated cultures yielded chlorophyll a concentration 20 times higher after 4 weeks growth than cultures grown under the same conditions without added glucose. This and other evidence derived from comparative growth measurements strongly suggest thatColeochaetetakes up (or loads) glucose. Experimental results also suggest that hexose uptake by charophytes (such asColeochaete) that typically grow in low alkalinity waters might provide a supplementary source of organic carbon when dissolved carbon dioxide levels are low. This capability could have served as an evolutionary precursor to hexose import by plant embryos, as well as leptom and phloem loading in bryophytes and vascular plants.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb15466.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

Reproductive allocation was investigated in female and hermaphrodite plants of gynodioeciousSidalcea oreganassp.spicata.Total reproductive investment and partitioning of that investment was documented at the level of whole plants in terms of four ecologically relevant currencies: biomass, nitrogen, phosphorus, and potassium. Nutrient augmentations in the field confirmed that nutrients were limiting plant vegetative growth and propensity to flower; thus the use of these nutrients as currency was appropriate. Once the effects of plant size were removed, the sex morphs allocated similar total amounts of biomass, nitrogen, phosphorus, and potassium to reproduction, but partitioned those differentially. For any given individual size, females allocated larger proportions of their reproductive resource budgets to seeds. Hermaphrodites' reproductive investment in pollen and flowers was allocated at the expense of allocation to seeds. These data are relevant to the evolution of gynodioecy from hermaphroditism and support the hypothesis that females reallocate resources not spent on pollen to seeds.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb15467.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

We tested whether nonrandom mating can occur across a range of conditions in wild radish by performing experimental crosses on plants grown under three greenhouse and one field regime. Variation in maternal condition among treatments was sufficient to alter components of reproduction. Effects of pollen donor identity on total seed mass per fruit were significant overall and stronger in the greenhouse than the field treatment. Mating was nonrandom in the field and in some, but not all greenhouse treatments. Selective filling of multiply sired fruits tended to occur in all treatments but was most pronounced in the low‐water and defoliation treatments as performed in the greenhouse. Our results demonstrate that nonrandom mating is possible in the field, so patterns of nonrandom mating found in previous studies of wild radish are not likely to be artifacts of greenhouse conditions. However, we also discovered that there may be limits to the range of maternal conditions under which these processes occur.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb15468.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

Aster furcatusis 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 furcatusappears to be evolving self‐compatibility as a result of bottleneck‐induced losses of S‐alleles.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb15469.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

The association between dioecy and generalist mode of pollination suggested about 20 years ago has been recently questioned. It is argued that there is evidence to indicate that a disproportionate number of dioecious species have relatively smaller flowers and a more generalist mode of pollination than hermaphroditic taxa. This trend seems to hold at the community level as well as within genera containing dioecious and hermaphroditic species. Like other correlations among characters, correlations among dioecy, small flower size, and pollination systems provide important insights into mechanisms of plant evolution.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb15470.x

出版商:Wiley    

年代:1994

数据来源: WILEY