摘要:

We used15N to quantify rates of N translocation from aerial to belowground tissues, foliar leaching, and turnover and production of root and rhizome biomass in the plant‐sediment system of shortSpartina alternifloraareas of Great Sippewissett Marsh, Massachusetts. Decay of belowground tissues in litterbag incubations at 1‐ and 10‐cm depths resulted in 80% remineralization of the original plant (15N‐labeled) N and 20% burial after 3 years. Translocation of15N from plant shoots in hydrologically controlled laboratory lysimeters maintained under field conditions was 38% of the aboveground pool while leaching of N was 10% from June to October. Most of the translocated N was not retranslocated to new aboveground growth in December but appeared to be either remineralized or buried in the sediment. Injection of15N into field stands of grass showed initially high incorporation into plants followed by a continuous decline over the next 7 years yielding a gross tumover time of 1.5–1.6yr. Correcting the gross N turnover for recycling of label via translocation and uptake of remineralized label during this period, a net root and rhizome turnover time of 1.0–1.1 yr was obtained. Combining the turnover time with independent estimates of seasonal belowground biomass yielded an estimate of belowground production of 929–1,022 g C m−2yr−1, similar to measurements by traditional biomass harvest, CO2based budgets and models for comparable areas of this marsh. Integration of the production and nitrogen balance estimates for shortSpartinamarsh yielded translocation, 1.4 g N m−2yr−1, leaching, 0.4 g N m−2yr−1, remineralization, 14.9–16.3 g N m−2yr−1, and burial, 3.7–4.1 g N m−2yr−1.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb11443.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

Interspecific correlations between plant height and basal stem diameter (the allometry of height) and between stem length distal to where diameter is measured (the allometry of stem taper) were determined for a total of 265 species with self‐supporting stems and for the shoots of five conifers and 15 angiosperm vine species. The allometric equations obtained for these data are proposed as a method to predict the heights of fossil plants for which basal stem diameters are either known or inferred, and to predict the missing lengths of fragmented stems based on the most proximal stem diameters observed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb11444.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

The frequency of wood‐anatomical characters in the eastern North America dicotyledonous tree flora shows spatial variance that can be related to climate (40% of the variation in 18 characters is explained by temperature and precipitation). Percent of taxa with rings varies with mean annual temperature, but the relationship is weak and the difficulties in making determinations as to presence or absence of rings make this character a problematic climatic indicator. Significant climate sensitivity is seen among characters pertaining to: a) vessel size and density (in diffuse‐porous woods); 2) vessel arrangement; 3) parenchyma types; and 4) rays. Overall, the anatomical variables can be used to represent 82% of the variance in total precipitation and 91% of the variance in mean annual temperature within the study area. These results demonstrate the possibility of deriving a multivariate representation of the response of wood to climate that will be useful in climate reconstruction and comprise a source of information similar to that obtainable from leaf morphology and permitting estimates of precipitation as well as temperature.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb11445.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

We estimated rates of self‐fertilization and inbreeding depression in the hermaphroditic perennialArabis fecunda.Crosses were made on mesh‐bagged wild plants, yielding 12 plants producing self‐, outcross‐, and naturally fertilized seeds that were then grown in a greenhouse. Analysis of variance indicated aboveground dry weight at 160 days differed among pollination treatments, but mean seed weight, number of seeds per fruit, and days to germination did not. For dry weight, selfed progeny have 9.4% reduction and naturally pollinated progeny a 3.7% reduction compared to outcrossed progeny, suggesting a 39% selling rate inArabis.Significant inbreeding depression and a mixed mating system are evidence that the deleterious effects of self‐fertilization are maintained through high rates of mildly deleterious mutation. Significant maternal‐parent‐by‐pollination‐treatment interactions for mean seed weight and dry weight are consistent with inbreeding depression caused by deleterious recessives and varying past maternal inbreeding.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb11446.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

To determine how the capability of pollen is affected by lengthy exposure to field conditions, we obtained pollen samples (fromErythronium grandiflorum) that were fresh (from newly dehisced anthers) or aged, from 6 to 24 hr. Without pretreating the collected grains, we compared their abilities 1) to retain viability, as indicated by the Heslop‐Harrison fluorochromatic reaction (FCR) test; 2) to retain germinability, as indicated by pollen‐tube growth in vitro on Brewbaker‐Kwack medium; 3) to sire seeds when used as a pollen donor on recipient flowers in the field; and 4) to sire seeds competitively when mixed with another donor pollen in competitive pollinations. FCR scores declined drastically with pollen age. Germinability typically declined with age, but less drastically; the correlation between FCR and germinability ranged from strong to nil in different trials. The sharp decline in FCR was probably due to nonlethal, reversible desiccation. Seed‐siring success, both in competitive and noncompetitive trials, bore no relation to pollen age or to germinability. Any loss in seed‐siring ability inE. grandiflorumpollen over 24 hr is apparently overwhelmed by other sources of variation. The lack of correlation between seed‐siring ability and FCR or germinability scores means that those tests should not be used to estimate overall pollen competence in this species. They should be so used in other species only if experiments have demonstrated their greater reliability.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb11447.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

Quantitative data on sieve tubes in foliar terminal veins (vein endings) were added to the meager published information from only five dicot species. Correlations with other minor vein configurations were also explored. Leaf samples from ten species of dicots (Oxalis nelsonii, O. pes‐capri, O. rubra, O. stricta[Oxalidaceae],Caesalpinia pulcherrima. Glycine max, Trifolium repens[Leguminosae],Ampelamus albidus[Asclepidaceae],Eupatorium rugosum[Asteraceae], andPolygonum convolvulus[Polygonaceae]) were selected for two quantitative procedures: 1) a survey of the arrangement of terminal veins and distribution of sieve tubes in terminal veins in 100 areoles per species using stained leaf clearings; and 2) a search for correlations of sieve tube distribution with number and branching patterns of terminal veins, and with sizes of areoles using image analysis. TwoOxalisspecies (O. pes‐capriandO. stricta) had the smallest areoles and virtually no sieve tubes in any terminal vein.Polygonum convolvulus,at the other extreme, had sieve tubes extending to the tips of most terminal veins. The other species had various intermediate sieve tube configurations. The data indicate that species with few or no sieve tubes associated with their terminal veins, regardless of the number of terminal veins per areole, have smaller areoles. These results may have implications regarding the entry of leaf photosynthates into the vascular system.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb11448.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

Size‐dependent variations in the critical buckling heightHcritand actual heightHof plants were determined for a total of 111 species with self‐supporting stems ranging in diameter between 0.03 cm ≤D≤ 3.0m. For each species, experimentally determined values for the physical properties of stems (Young's elastic modulus and bulk tissue density) were used to computeHcrit.For small species (D<3 cm), empirically determined critical buckling loads were used to computeHcritby means of the Elastica equation and the more traditionally employed Greenhill formula; for larger species (D≖ 3 cm), Greenhill's formula was used exclusively to estimateHcrit.Within most of the size‐range examined, the predicted values ofHcritfrom the Elastica equation and Greenhill's formula were statistically indistinguishable. Regression analyses showed that the interspecific allometry ofHcritparallels that ofHsuch that the safety factor against the elastic mechanical failure of stems (i.e.,Hcrit/H) under their own biomass was roughly constant. Since the safety factor against elastic buckling is independent of plant size, a general allometric “rule,”Hcrit/H≈ 4, appears to govern the evolution of plant size.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb11449.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

Enzyme electrophoresis was used to estimate genetic variability within and among populations of five species of the genusLeucodon(L. atrovirens, L. luteus, L. nipponicus, L. sapporensis,andL. temperatus). All of these perennial, dioecious plants are epiphytic on tree trunks and produce numerous spores that are released in winter. Gene diversity within populations (HS) was low (0.070) inL. nipponicus,which grows in disturbed habitats, and high (0.169–0.202) in the other four species, which inhabit stable environments. Gene diversity between populations relative to total diversity (GST) was low inL. temperatus(0.042) andL. luteus(0.043), suggesting that extensive gene flow occurs among populations. GSTwas moderate inL. sapporensis(0.104) andL. atrovirens(0.114); these values are still less than those previously reported for terrestrial mosses. Since epiphytes could disperse their spores effectively by the wind, low genetic divergence among populations may be related to the epiphytic habit of the species. On the other hand, high GSTvalue (0.208) was found inL. nipponicus.It is probably explained by the genetic differentiation of populations by genetic drift, for the species forms geographically and ecologically isolated populations with small number of individuals. We also observed incongruity between morphological and genetic similarity among species.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb11450.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

An analysis of the levels and distribution of allozyme variation in theStreptanthus glandulosusspecies complex was undertaken to test paradigms of speciation processes in the context of serpentine endemism. Electrophoretic analysis of 21 putative enzyme loci in 1,224 individuals representing 56 populations revealed extensive intrapopulational variation and interpopulational divergence. Estimates of gene flow among populations within taxa are typically lower than is theoretically needed to counteract the effects of genetic drift (i.e.,Nmvalues are below 0.5), suggesting that drift may play a significant role in the evolution of the complex. A cluster analysis of genetic identities between populations using UPGMA demonstrates geographically structured groupings, some of which include neighboring populations of different taxa. Moreover, the genetic identity between two populations is correlated with the distance by which they are separated. The results are consistent with a hypothesis of a paleoendemic origin of the complex. The ancestor of the complex (perhapsS. glandulosusssp.glandulosus) probably was formerly distributed more continuously across serpentine and nonserpentine habitat throughout its range. Elimination of the nonserpentine populations allowed regional and population‐level divergence, following a model of geographic speciation.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb11451.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

Allozyme variation at 17 loci encoding ten enzyme systems was examined in 21, 22, and 15 populations across the ranges ofMagnolia fraseri, M. macrophylla,andM. tripetala,respectively, in the southeastern United States. All three species have regional distributions, and are insect‐pollinated outcrossing deciduous trees with seeds dispersed by birds, yet strikingly different levels of genetic variability were observed among them. In comparison with other woody angiosperm species,M. fraseripossesses a moderate amount of variation at the population level (A = 1.4, P = 39.2, Ho= 0.111, and He= 0.111), whereasM. macrophyllaandM. tripetalaare genetically depauperate in their populations (A = 1.2, P = 18.7, Ho= 0.47, and He= 0.055; A = 1.1, P = 11.0, Ho= 0.032, and He= 0.033). Examination of population structure revealed a small amount of inbreeding within populations and extensive intra‐ and interregional differentiation among populations of the latter two species. These two factors are perhaps partly responsible for the low genetic variability in populations of the twoMagnoliaspecies. Furthermore, the bottleneck effect caused by extinctions during cold periods of the Quaternary glaciations and human deforestation in the last two centuries as well as the founder effect in postglacial establishment of the populations might have also played significant roles in loss of genetic diversity inM. macrophyllaandM. tripetala.We suggest that historical factors are important determinants of genetic variation profile of a species, in addition to life history and ecological characteristics as generally recognized.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb11452.x

出版商:Wiley    

年代:1994

数据来源: WILEY