摘要:

The effect of the leachate of the noxious weedPluchea lanceolatawas explored using mustard and tomato seedling growth bioassays of four soil types (sandy loam, clay loam, silty loam, and sand). The objectives of the present study were: 1) to determine how soil chemistry changes after addition of leachate and leaves of the weed; 2) to determine what level of input to the soil does not cause significant differences from those of weed‐associated soils under field conditions; and 3) to determine whether soil texture affects bioassay results. Leaf leachates of the weed were added to four soil types in different dilutions, and soils were analyzed for pH, electrical conductivity, organic matter, Cl, PO4, exchangeable Cu+ +, Zn++, Na+, K+, Mg++, and Ca++, and total phenolics. These results indicated that the leachates of the weed altered chemical characteristics of each soil type. Concentration of phenolics in treatment of each soil type was dilution‐dependent. Leachates were more inhibitory on sandy loam and clay loam than on silty loam and sand. Present study indicated that in allelopathic bioassays, amended soils that are nonsignificantly different from weed‐associated soils should be taken. Further, present investigations confirmed the significance of good control soil with nonsignificantly altered chemical characteristics from those of natural soils, as well as soil texture to establish allelopathy of ecological relevance.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb15560.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

We experimentally manipulated fire season in a longleaf pine sandhill community in north Florida in 1990 and 1992. We determined the size and demography of shoots, rhizomes, and clones ofPityopsis graminifoliafrom late 1990 to early 1993. In addition, we examined shoot responses to seasonal variation in canopy/litter removal and soil fertility in 1992. May fires caused a higher short‐term rate of increase in shoot density than did either January fires or August fires. The combination of canopy/litter removal and mineral nutrient addition as part of the clipping experiment revealed a similar effect on shoot density in May. Fire season influenced clone structure. May fires resulted in greater numbers of shoots/clone than did January or August fires. January‐burned plots had clones and rhizomes that contained larger (but fewer) shoots than did May‐burned or August‐burned plots. We suggest that such variation in clone structure may indicate a greater capacity of clones to grow laterally following May fires than following either January or August fires. This capacity is positively associated with the likelihood that longleaf pine savannas will be burned by lightning fires at different times during the year.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb15561.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

For over 100 years the association betweenYucca(Agavaceae) andTegeticula(Lepidoptera: Incurvariidae) has been accepted as a quintessential example of an obligate mutualism. The yucca moth is purported to be the sole pollinator ofYucca, whileYuccaflowers provide courtship and mating arenas, andYuccaseeds provide food for developingTegeticulalarvae. We studiedYucca glaucain northern Colorado, comparing the reproductive ecology and breeding systems ofYuccain plains populations, the “preferred” habitat ofYucca, with “marginal” sites at the edge of the local elevational distribution.Tegeticulaare abundant at plains sites, and fruit set is significantly higher than in the foothills, where fruit set is limited by the paucity of moths. The low frequency of moths at high elevation, coupled with behaviors of adult femaleTegeticulawhich lead to self‐pollination, failure to pollinate, and periodic overloading of fruits with eggs, may help explain whyYucca glaucaappears to maintain alternative pollinators. Some fruits lack evidence ofTegeticulainfestation, suggesting that larvae die before completing development, or that fertilization ofYuccasometimes occurs without the intervention ofTegeticula.Biochemical analyses of nectar and observations of floral visitors revealed that it is highly likely that the flyPseudocalliopesp. nov. (Lauxaniidae), which congregates and mates onYucca glaucablossoms, acts as a secondary pollinator. Autogamy appears to occur infrequently in natural populations. We therefore propose that the yucca‐yucca moth symbiosis be viewed as a facultative mutualism.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb15562.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

Very few studies have evaluated the effects of UV‐B radiation on trees. especially deciduous species. In this study we evaluate the effects of supplemental UV‐B radiation on the growth and photosynthetic capacity of sweetgum (Liquidambar styracifluaL.). Sweetgum seedlings were grown for 2 years in the field under either ambient or supplemental UV‐B radiation. Artificial UV‐B radiation was supplied by fluorescent lamps at a maximum daily supplementation of either 3.1 or 5.0 kJ of biologically effective UV‐B radiation. Over the 2‐year period, supplemental UV‐B radiation had little effect on total plant biomass or photosynthetic capacity. However, subtle changes in leaf physiology, carbon allocation, and growth were observed. Supplemental UV‐B radiation reduced photosynthetic capacity only during the first year, while leaf area and biomass were reduced in the second year. Alterations in carbon allocation included an increase in branch number and root to shoot ratio. While these data do not indicate that the productivity of sweetgum would likely be compromised by an increase in solar UV‐B radiation, they do suggest that the UV‐B portion of the solar spectrum contributes to the regulation of sweetgum growth and development. Therefore the possibility of significant consequences to sweetgum due to possible increases in UV‐B radiation cannot be ruled out.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb15563.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

Root hairs are specialized epidermal cells that are thought to play an important role in plant nutrition by facilitating the absorption of water and nutrients. Three maize mutants with abnormal root hair morphologies (rthl, rth2, andrth3) have been isolated fromMutatortransposon stocks. All three root hair mutant phenotypes are controlled by single recessive alleles. Therthlmutant initiates normal‐looking root hair primordia that fail to elongate. The normal‐looking root hair primordia of therth2mutant elongate to only approximately one‐fifth to one‐fourth the length of wild type root hairs. Likerth1primordia,rth3primordia undergo little elongation. However, unlike the relatively normal‐lookingrth1primordia,rth3primordia are distinctly abnormal when viewed through a scanning electron microscope. Therth1mutant exhibits pleiotropic nutrient deficiencies, while therth2andrth3mutants grow vigorously. This finding suggests that under some environmental conditions, root hairs are less important to plant growth than has been previously thought. Therthl, rth2, andrth3genes have been mapped to chromosomes 1L, 5L, and 1S, respectively, via crosses with BA translocation stocks. Therth2allele exhibits reduced transmission through the male gametophyte, but a normal rate of transmission through female gametophytes;rth1andrth3are transmitted at normal rates.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb15564.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

Sixteen sour orange tree (Citrus aurantiumL.) seedlings were grown out‐of‐doors at Phoenix, Arizona, in eight clear‐plastic‐wall open‐top enclosures maintained at four different atmospheric CO2concentrations for a period of 2 years. Over the last year of this period, the trees were coppiced five times. The amount of dry matter harvested at each of these cuttings was a linear function of the atmospheric CO2concentration to which the trees were exposed. For a 75% increase in atmospheric CO, from 400 to 700 microliter per liter (μLliter1), total aboveground biomass rose, in the mean, by a factor of 3.19; while for a 400 to 800 μL liter1doubling of the air's CO2content, it rose by a factor of 3.92. The relative summer (mean air temperature of 32.8 C) response to CO2was about 20% greater than the relative winter (mean air temperature of 16.4 C) response.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb15565.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

Gender phenotypes ofThymelaea hirsuta(L.) Endl. were surveyed in six major habitats in the western Mediterranean region of Egypt. Five gender phenotypes were observed at all sites: subandroecious (male), subgynoecious (female), protogynous, protandrous, and gender‐labile individuals. Patterns of vegetative growth, reproductive effort, and sex‐size relationships were also determined. Females and males were comparable in overall abundance (35.5% and 30.2%, respectively). However, the frequency of sex forms varied significantly among habitats. Plant size (canopy volume) was used as a measure of environmental quality for the species: the coastal dunes were by far the most favorable habitat, followed by the nonsaline depressions, inland plateau, and inland siliceous deposits. The smallest plants were associated with the inland ridges and saline depressions. Protandrous individuals, and female shrubs at the more favorable habitats (e.g., the coastal dunes and nonsaline depressions), had greater canopy volume than males. In contrast, males were larger than females at the less favorable habitats (e.g., the inland plateau and saline depressions). Advantageous growth conditions at the coastal dunes are demonstrated by the greater rate of increase in crown diameter and crown volume noted there, for each size class and sex form. The greatest rates of increase were present in smaller‐sized individuals. Size differences between the sex forms were considered in terms of trade‐offs between individual growth rate (GR) and reproductive effort (RE); evidence of a trade‐off was mixed. Indeed, in a comparison of GR and RE at two extremes of habitat (coastal dune vs. inland plateau), females had greater GRandgreater RE at the relatively benign coastal dunes, while at the more harsh, inland plateau site males showed greater GR and RE than females. Peak reproductive effort varied significantly with gender phenotype and habitat type.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb15566.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

We describe the breeding system of an autotetraploid trioecious cactus,Pachycereus pringlei, provide estimates of the fitnesses of males and females relative to that of hermaphrodites, and discuss the role played by pollinators in the maintenance of three sexual morphs. Relatively high frequencies of females (45%) and males (26%) exist in coastal desert populations around Bahia Kino, Sonora, Mexico. They differ from hermaphrodites in flower size (females only), initiation of the flowering season, number of flowers produced per night and per season, sucrose content of nectar, and, in females, number of fruits produced per season under open pollination and in response to hand‐pollination. Major similarities between the sex classes include overall plant size, nectar volume per flower, percent fruit set in open‐pollinated flowers of females and hermaphrodites, seed mass and number of seeds per fruit, and pollen mass per flower in males and hermaphrodites. Hermaphrodites are self‐compatible, and the selfing rate is high (65%). Levels of inbreeding depression in selfed fruits and seeds appear to be low. Fruit set is strongly pollinator‐dependent in females but much less so in hermaphrodites. Relative fitness of males and females, as measured by annual production of pollen or seeds, is at least 1.5 times higher than that of the corresponding sex function in hermaphrodites. Given the high selfing rate and apparent lack of inbreeding depression, these fitness differences are insufficient to explain the occurrence of trioecy in this species.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb15567.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

Sieve cell differentiation in the primary phloem ofEphedra viridisis first indicated by an increase in thickness of the wall, which begins in the corners of the cell, and next by the proliferation of smooth tubular endoplasmic reticulum (ER). As differentiation proceeds, cisternae of rough ER form stacks along the wall, losing their ribosomes in the process. Concomitantly, all of the mitochondria, plastids, and ER become parietal in distribution, and the vacuoles collapse. Nuclear degeneration is pycnotic and accompanied by the formation of tubular invaginations of the nuclear envelope into the peripheral chromatin. At maturity, an anastomosing network of smooth ER borders the plasmalemma, interconnecting aggregates of smooth tubular ER located primarily opposite the sieve areas. In addition to ER, the mature sieve cell contains mitochondria, plastids, and remnants of the degenerate nucleus, all of which are parietal in distribution. P‐protein is lacking at all stages of sieve cell development. Sieve pore and compound median cavity development is similar to that reported for the sieve cells of conifers. Albuminous cells are associated with the sieve cells of the metaphloem throughout the shoot but with sieve cells of the protophloem only in the node. Among their cytoplasmic components are broad bundles of microfilaments spatially associated with a complex system of rough and smooth ER.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb15568.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

Fifty populations ofLiriodendron tulipiferawere sampled and scored for electrophoretic variation at 23 loci. The level of genetic polymorphism and population differentiation is greater inL. tulipiferathan is usual for an outbreeding species. Since this species exhibits a cline of morphological and ecological variation from north to south, the 50 populations were divided into seven geographically defined regional groupings: three from the Appalachian uplands, three from the southeastern coastal plains, and one from the Florida peninsula. Nei's genetic identity, I, was calculated for all within‐ and among‐population and region comparisons. The populations from the upland regions clustered closely together while the coastal plain populations were similar but measurably separated from the upland ones. The populations from the Florida peninsula were markedly divergent. A principal components analysis of the same data set revealed a nearly identical pattern of population clustering. Two hypotheses were explored to explain the pattern observed: 1) post‐Pleistocene differentiation and migration from a single refugium and; 2) sympatry of two previously isolated taxa during glacial maxima, followed by introgression and migration. The weight of evidence best supports the introgression hypothesis which is explained in terms of plant migration events during Pleistocene time. The level and distribution of electrophoretic variation inL. tulipiferais compared to that of other woody taxa in which historical events of the Pleistocene may have contributed to modern levels and patterns of variation.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb15569.x

出版商:Wiley    

年代:1994

数据来源: WILEY