摘要:

To investigate the origin of the tetraploid species ofLeymusHochst., we examined variation in 26 repeated nucleotide sequence families isolated from four species of Triticeae. The genome relationships were determined by calculating repeated nucleotide sequence identity (RSI) between species. RSI is the ratio of the number of diagnostic bands (DBs) and diagnostic hybridization intensities (DIs) in Southern blots of a diploid taxon encountered in a polyploid species divided by the total number of the DBs and DIs of the diploid taxon (DB is a band in Southern blot observed in a single diploid taxon, and DI is the intensity of hybridization higher by at least one order of magnitude in a diploid taxon than in any other diploid taxon). The RSIs ofPsathyrostachysNevski withLeymusranged from 0.92 to 0.95, which confirmed that the N genome ofPsathyrostachyswas involved in the phylogeny ofLeymus.Since RSIs of other genera of Triticeae withLeymusvaried from 0.00 to 0.17, it is unlikely that any of them contributed the second pair ofLeymusgenomes. RSIs were also calculated betweenLeymusand the lineage ofLophopyrumLöve‐ThinopyrumLöve or the lineage ofLophopyrum‐Thinopyrum‐Pseudoroegneria(Nevski) Löve‐AgropyronGaertn. The RSIs were close to zero, which made it unlikely that the second pair ofLeymusgenomes originated from even an extinct species in these major lineages of Triticeae. Several lines of evidence were obtained that indicated that the second pair ofLeymusgenomes is also fromPsalhyrostachys.The genomes of tetraploid species ofLeymuswere designated N1N1N2N2, rather than JJNN as proposed by other workers.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb14491.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

The mat‐forming succulent,Carpobrotus edulis(Aizoaceae), surrounds and grows over many native plant species in California coastal communities. Two shrub species,Haplopappus ericoidesandH. venetusvar.sedoides,were found to have shallow root systems that occupied the same soil depths as those ofC. edulis.In the presence ofC. edulis,the normal rooting profiles of the shrubs were displaced downward, although partial overlap withC. edulisremained. Removal ofC. edulisfrom around individuals of both shrub species resulted in higher predawn xylem pressure potentials in shrubs from the removal treatments as compared to controls, suggesting that the surroundingC. eduliswas utilizing water that would otherwise have been available to these shrubs. InH. ericoides,predawn xylem pressure potentials of removal treatment shrubs remained higher than those of the controls throughout the remainder of the dry season even though these shrubs showed a marked increase in canopy area after removal of surroundingC. edulis.Removal ofC. edulisfrom aroundH. venetusalso initially led to higher predawn xylem pressure potentials in the removal shrubs as compared to the controls and increased production of new leaves. After this initial period the predawn xylem pressure potentials of the removal shrubs were not significantly different from those of controls, suggesting that the demand for water by the increased leaf areas eventually matched the enhanced water availability resulting fromC. edulisremoval. Also, the morphology ofH. venetusshrubs changed to that more typical of unaffected individuals. Thus,C. edulissignificantly affected not only the water relations of these two shrub species but also their shoot sizes and overall morphologies.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb14492.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

We studied the seed dynamics ofAbies balsameaandAcer saccharumin a sugar maple‐yellow birch forest of Québec, Canada. Seed rain was censused every week from spring to autumn in 1988 and 1989. The soil seed bank was sampled four times during the 1988 growing season.Abiesseed rain varied significantly between 1988 and 1989. A total of 92.5 ± 7.0 seeds nr‐2(mean ± 1 SE) were produced in 1988; 1989 seed production was null. Seed viability in 1988 averaged 31.5%. Dispersal during the winter period accounted for ca. 22% of the annual seed crop. The spatial dispersion pattern of the seed rain was contagious for the autumn period, but was not significantly different from random for the winter period. There was only a weak relationship in the spatial distribution of the seed rain between the autumn and winter periods.Abiesdid not maintain a persistent seed bank on the site; viable seeds were present on the soil only after seed dispersal had started. Postdispersal seed mortality was relatively high, ca. 70%.Acerseed rain started soon after the flowering period, but consisted at that time only of aborted, underdeveloped samaras. Viable seeds were disseminated from September through early winter. Dispersal during the autumn accounted for ca. 98% of the annual seed crop. There were significant differences between seed rain abundance of 1988 and that of 1989 (118.1 ± 9.5 samaras m‐2and 158.9 ± 16.3 samaras m‐2in 1988 and in 1989, respectively). Seed viability also varied significantly between the 2 years, i.e., 19% in 1988 and 5% in 1989. For both 1988 and 1989, samaras were contagiously dispersed over the site. There was a significant positive relationship between the spatial distribution of the seed rain in 1988 and that in 1989. Seed rain abundance was high mainly in the proximity of matureAcertrees. As forAbies, Acerdid not maintain a persistent seed bank in the soil; viable seeds were present only in the autumn seed bank sampling, after seed fall had started. Postdispersal seed mortality was relatively low, i.e., 20%.AbiesandAcerare quite similar in their regenerative traits, and these contrast sharply with those ofBetula alleghaniensis,a regular member of this forest community. Differences in regenerative traits may contribute to the coexistence of these tree species considering the gap regime of the system studied.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb14493.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Concurrent determinations of changes in hydraulic conductivity and tissue anatomy were made for roots ofAgave desertiexcised during drying and following rewetting in soil. At 30 d of drought, hydraulic conductivity had declined less than twofold for older nodal roots, tenfold for young nodal roots, and more than 20‐fold for lateral roots (“rain roots” occurring as branches on the nodal roots). These decreases were consistent with increases in cortical lacunae caused by cell shrinkage and collapse. Similarly, reduction of lacunae in response to rewetting after 7 d of drought corresponded to levels of recovery in hydraulic conductivity, with young nodal roots showing full recovery, lateral roots returning to only 21 % of initial conductivity, and older nodal roots changing only slightly. Increases in suberization in the exodermis, endodermis, and cortex adjacent to the endodermis in response to drying coincided with decreases in hydraulic conductivity. Measurements of axial hydraulic conductance per unit length before and after pressurization indicated that embolism caused reductions in axial conductance of 98% for lateral roots, 35% for young nodal roots, and 20% for older nodal roots at 7 d of drought. Embolism, cortical lacunae, and increasing suberization caused hydraulic conductivity to decline during drought in the three root types, thereby helping limit water loss to dry soil; the recovery in hydraulic conductivity for young nodal roots after rewetting would allow them to take up water readily once soil moisture is replenished.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb14494.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Leaves of six species selected to represent a broad range in internal structure were collected in the field and studied in the laboratory to determine primary and secondary effects of water content on leaf spectral reflectance. Primary effects were those that resulted solely from the radiative properties of water. Secondary effects were those that could not be explained solely by these properties. Decreased leaf water content generally increased reflectance throughout the 400‐2,500‐nm wavelength range. For the aquaticsEichhornia crassippesandNuphar luteum,the broadleaved treesLiquidambar styracifluaandMagnolia grandiflora,the cane‐grassArundinaria tecta,and the needle‐leavedPinus taeda,the sensitivity of reflectance to water content was greatest in the water absorption bands near 1,450, 1,940, and 2,500 nm. Sensitivity maxima occurred also between 400 and 720 nm, indicating secondary effects that resulted from decreased absorption by pigments. Secondary effects of water content on reflectance that were largely wavelength‐independent, together with any wavelength‐independent effects of leaf internal structure, were far less significant than primary and secondary effects resulting from decreased absorption by water and pigments, respectively.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb14495.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Six populations ofOxystylis luteaand nine populations representing three subspecies ofWislizenia refractawere analyzed for electrophoretic variation at 18 loci. Several marker alleles differentiateO. luteafromW. refracta,although mean pair‐wise genetic identity values (range, 0.53–0.64) are comparable to those found among many congeners.OxystylisandWislizeniashare two duplicated gene loci that are not present in outgroup species inCleomeandCleomella.Thus, they appear to be monophyletic sister taxa within a larger monophyletic group. Based on allozyme differentiation patterns, we infer a pre‐Pleistocene divergence prior to differentiation withinW. refracta.Subsequent anagenesis in theO. lutealineage and cladogenesis in theW. refractalineage have resulted in extensive morphological differentiation betweenOxystylisandWislizenia.Therefore,OxystylisandWislizeniaare phenetically and phylogenetically distinct, and we recognize them as genera. Geographic modes of speciation predominate in the group. Variation patterns withinW. refractaare consistent with recognition of three subspecies, and indicate that subsp.californicais not a historical introduction in the Central Valley of California.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb14496.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

The deciduous woody genusLiquidambarhas four morphologically similar species in eastern and western Asia, eastern North America, and Central America.Liquidambar styracifluais found in the eastern United States and Central America,L. orientalisis native only to southwest Turkey, andL. formosanaandL. acalycinaoccur in eastern Asia. This genus is one of many that contributes to the floristic similarities observed between these different regions. Allelic variation was scored at 22 isozyme loci from 41 populations. The level of genetic divergence between species on different continents is high. Nei's genetic identity was 0.431 betweenL. formosanaandL. styraciflua,0.485 betweenL. acalycinaandL. styraciflua,0.512 betweenL. orientalisandL. styraciflua,0.256 betweenL. formosanaandL. orientalis,and 0.305 betweenL. acalycinaandL. orientalis.Estimates of time of divergence from the isozyme data suggest that the current species diverged before or during the Miocene. The pattern of relationships portrayed by the isozyme data suggest a longer period of separation between the eastern and western Asian forms of this genus. In addition, the eastern North American and Turkish species appear to be the most closely related intercontinental pair of species providing evidence for a North Atlantic land bridge as late as the Miocene. It would appear, therefore, that the North American populations were in contact with the Asian populations over the North Pacific and North Atlantic possibly as late as the Miocene, but that the separation between the two Asian populations occurred much earlier. The time of divergence as measured from the isozyme data correlates with an independent assessment of the origin of these disjuncts as determined from the fossil record.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb14497.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Compounds inhibitory to the growth of neighboring plant species were found in significant concentrations in the leaves and stems of youngAilanthus altissimaramets. The surrounding soil also contained appreciable concentrations of similarly acting toxins. Individuals of neighboring plant species have either incorporated active portions of inhibitory compounds or responded toAilanthusby producing growth‐inhibiting substances. Under greenhouse conditions, individuals of neighboring plant species previously unexposed toAilanthusin the field were found to be more susceptible to theAilanthustoxins than individuals previously exposed. Moreover, seeds produced by unexposed populations were also more susceptible toAilanthustoxins than seeds produced by previously exposed populations. These differences demonstrated that the allelochemicals ofAilanthus altissimaexhibited a measurable impact upon neighboring plant species. Since the progeny of these populations displayed a differential response toAilanthustoxin, this phenotypic difference between the two populations may have a heritable basis.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb14498.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Thrips and/or aphids played an important role in the self‐pollination of two facultatively xenogamous herbs that inhabit wetlands in northwestern Iowa. In bothRanunculus sceleratusandPotentilla rivalisthe fruit set and/or successful pollination of plants that were sprayed with malathion to kill thrips and aphids and caged to exclude typical flower visitors was substantially and significantly lower than that of open‐pollinated and caged plants. We observed pollenbearing thrips and aphids on the flowers. The high fruit sets of emasculated flowers ofR. sceleratusshowed that insects moved pollen between flowers, and our observations of bees collecting pollen and moving between plants suggest that cross‐pollination can occur in both species.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb14499.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

We tested for the presence of an optimal outcrossing distance in a population ofImpatiens capensis,an annual herb that possesses a mixed mating system, by measuring fitness components for offspring of parents that were separated by distances of 2, 10, or 50 m. Heavier seed weights and later seed maturation enhanced probabilities of emergence and subsequent survival, but emergence and survival were unaffected by outcrossing distance. Path analysis showed that most characteristics of seeds and seedlings were positively correlated. Effects of maternal family were strong through the first month of growth. Analyses of covariance reveal that, as anticipated, the effects of maternal family, seed weight, and seed maturation date declined over time. Seeds that were produced late in the season were heavier than early seeds, and late seeds germinated at later dates than early seeds. Surprisingly, although late germination dates were associated with taller plants after 1 and 3 months of growth, late germination resulted in lighter dry weights at maturity. The distance between parents had a negative direct effect on seed weight but a positive effect on height after 1 month. Height at 1 month responded positively to outcrossing distance and negatively to the square of distance when seed weight, collection date, and maternal family were held constant. This implies an optimal outcrossing distance for height at 1 month, which we estimate as 29 m using a quadratic procedure. However, path analysis suggests that the apparent optimum is due to a negative correlation between the interparent distance and seed weight.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb14500.x

出版商:Wiley    

年代:1991

数据来源: WILEY