摘要:

To help evaluate root distribution patterns, elongation rates of individual roots were measured as a function of soil temperature forEncelia farinosa(a C3species),Pleuraphis rigida(C4), andAgave deserti(CAM), sympatric codominants in the northwestern Sonoran Desert. Measurements were made at current and doubled CO2concentrations under winter and summer conditions of air temperature (day/night temperatures of 17 C/10 C and 33 C/22 C, respectively). The three species had different optimal temperatures for root elongation (Topt) under winter conditions (25 C forE. farinosa, 35 C forP. rigida, and 30 C forA. deserti);Toptincreased by 2‐3 C under summer conditions for all three species. The limiting temperatures for elongation also acclimated from winter to summer conditions. The rate of root elongation atToptwas higher under summer than winter conditions forE. farinosa(9 vs. 6 mm d−1) andP. rigida(20 vs. 14 mm d−1), reflecting conditions for maximum photosynthesis; no difference occurred forA. deserti(9 vs. 10 mm d−1). Decreased elongation rates at extreme temperatures were associated with less cell division and reduced cell extension. The doubled CO2concentration increased average daily root elongation rates forA. desertiunder both winter (7%) and summer (12%) conditions, reflecting increased cell extension, but had no effect for the other two species. Simulations of root elongation as a function of soil temperatures showed that maximum elongation would occur at different depths (16‐20 cm forE. farinosa, 4‐8 cm forP. rigida, and 0‐4 cm forA. deserti) and during different seasons (winter to spring forE. farinosa, spring to summer forP. rigida, and all year forA. deserti), contributing to their niche separation. Shading of the soil surface moderated daily variations in soil temperature, reducing seasonal root elongation for winter and spring and increasing elongation for summer. Shading also altered root distribution patterns, e.g., optimal rooting depth forA. desertiand especiallyP. rigidaincreased for a hot summer day.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb12688.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

The selective degradation of proteins, an essential process of any developmental program, may entail conjugation of the protein to be destroyed to the polypeptide ubiquitin. Experiments were designed to localize ubiquitin as a first step in determining whether this molecule is crucial for certain developmental processes in plant tissues and cells. Antibodies to ubiquitinated protein were detected on tissue prints of cross sections of bean petioles (Phaseolus vulgaris, Fabaceae), cotton hypocotyls (Gossypium hirsutum, Malvaceae), andColeusstems (Coleus x hybridus, Lamiaceae). For most of the material investigated, there appears to be an accumulation of ubiquitin antibodies in vascular tissues, but not preferentially in the abscission zone of bean petioles. Vascular localization was confirmed using immunohistochemical methods on fixed and sectioned internodal tissues ofColeus.Antibodies to ubiquitin are detected in parenchyma cells of the cortex and pith, but are most concentrated in the xylem, especially secondary xylem, and in the cambial region, and in the phloem. Thus, ubiquitin accumulates in certain vascular tissues, some of which may be undergoing programmed cell death. Ubiquitin can also be detected in nondifferentiating cells, and its level is elevated in rapidly dividing cambial cells.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb12689.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

The pollen‐pistil interaction has been examined in kiwifruit (Actinidia deliciosa). In this species a large number of seeds are produced in each fruit and a great many pollen grains germinate and grow to reach the ovules. This growth is assisted by an abundant secretion that is present all along the pistilar tract. At anthesis, the stigma is covered by a secretion where the pollen grains germinate and grow. The stylar transmitting tissue is initially rich in starch reserves, but the starch gradually disappears and, concomitantly, an abundant secretion that stains for carbohydrates appears in all of the intercellular spaces. Pollen tube growth relies on this secretion since it is depleted after pollen tube passage, while in unpollinated flowers it remains unaltered throughout the flower life‐span. In the ovary a similar situation occurs. The placental surface, where the pollen tubes grow before reaching the ovules, is covered by a number of obturators. At anthesis, these obturators are rich in starch reserves and have an abundant secretion on their outer surface. As time passes, starch disappears while the secretion increases. It is in this secretion that the pollen tubes grow on their way toward the ovules. These observations are discussed in terms of the support given by the pistil to pollen tube growth to achieve the highly successful reproductive performance of this species.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb12690.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

This study compares the establishment success of cleistogamous (CL, obligately selfed) and chasmogamous (CH, potentially outcrossed) seeds of the neotropical understory herb,Calathea micans(Marantaceae). In this species, CH and CL seeds are morphologically identical and are both dispersed by ants. I measured dispersal distances and analyzed seedling recruitment and seedling size for ant‐planted CH and CL seeds, a protocol made possible by the fact that the seed coat ofC. micanscan be indelibly marked and remains attached to the base of the seedling for a few months. Seeds were taken by ants from experimental depots placed in natural conditions. In a second experiment, I planted CH and CL seeds in gap and understory sites to determine the effects of seed type and light on germination percentage, date of emergence, and seed and seedling survivorship. Ant‐planted CH and CL seedlings did not differ in dispersal distance. CH and CL seeds did not differ significantly in recruitment probability and seedling size in either experiment. However, for the ant‐planted seedlings, CH recruitment was higher in the understory than in the gap, while CL recruitment was uniform across light environments. In conclusion, I found a difference in the establishment success of CH and CL seeds in this understory herb, only after dispersal by ants in field conditions.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb12691.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

This 2‐yr study of gender and its relation to the sizes of pin and thrum plants inLithospermum croceumwas performed in central Michigan. The population was composed of 51‐52% thrums, 42‐43% pins, and ≈6% homostyles in 1988 and 1989. Pins produced more flowers and fruits than thrums, and a greater proportion of their ovaries produced more than one nutlet. However, the number of fruits produced by pins and thrums in 1988 did not differ when plant size is a covariate in ANCOVA. The number of seeds produced by plants in 1989 is also unaffected by floral morph when size is a covariate. Instead, plant size is the most important predictor of fecundity in both years. The average percent fruit sets (fruits/ovaries) of the morphs did not differ in either year. Herbivory was more common in 1988 than in 1989, but there was no difference in the frequency with which pins and thrums were attacked. Furthermore, the effect of herbivory on fecundity did not differ for the morphs. The fecundity of neither morph was limited by pollen in 1989. Apparent gender specialization was a consequence of subtle differences in the vegetative sizes of the morphs.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb12692.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

Variation in flowering time ofArabidopsis thalianawas studied in an experiment with mutant lines. The pleiotropic effects of flowering time genes on morphology and reproductive yield were assessed under three levels of nutrient supply. At all nutrient levels flowering time and number of rosette leaves at flowering varied among mutant lines. The relationship between these two traits depended strongly on nutrient supply. A lower nutrient supply first led to an extension of the vegetative phase, while the mean number of leaves at flowering was hardly affected. A further reduction resulted in no further extension of the vegetative phase and, on average, plants started flowering with a lower leaf number. At low nutrients, early flowering affected the timing of production of siliques rather than the total output, whereas late flowering was favorable at high nutrients. This may explain the fact that many plant species flower at a relatively small size under poor conditions. Flowering time genes had pleiotropic effects on the leaf length, number of rosette and cauline leaves, and number of axillary flowering shoots of the main inflorescence. Silique production was positively correlated with the number of axillary shoots of the main inflorescence; the number of axillary primordia appeared to have a large impact on reproductive yield.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb12693.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

Annually burned tallgrass prairie is purported to be a nitrogen‐limited system, especially when compared to unburned prairie. To test the hypothesis that legumes, potential nitrogen‐fixers, would increase in relative abundance in annually burned sites, we assessed their density and biomass for two seasons on upland and lowland soils in annually burned and unburned watersheds. Total legume density was significantly higher in burned (8.0 ± 1.0 [SE] stems/m2) than in unburned watersheds (3.0 ± 0.3 stems/m2). Species with higher (P<0.05) densities in burned than in unburned prairie includedAmorpha canescens, Dalea candida, Dalea purpurea, Lespedeza violacea, Psoralea tenuiflora, andSchrankia nuttallii. Desmodium illinoensewas the only legume that responded negatively to annual fire. Total legume biomass did not differ between burned (11.3 ± 1.3 g/m2) and unburned prairie (10.5 ± 0.9 g/m2). Biomass productions ofDalea candidaandPsoralea tenuiflorawere higher (P<0.05) in burned than in unburned sites, but biomasses of other legumes were similar between burn treatments. Average individual stem masses ofAmorpha canescensandBaptisia bracteatawere significantly greater in unburned than in burned prairie. Legumes were affected differentially by topographic location. Total legume density was higher (P<0.05) on lowland soils (6.6 ± 1.0 stems/m2) than on upland soils (4.3 ± 0.5 stems/m2). However, total legume biomass was not different between lowland soils (12.0 ± 1.2 g/m2) and upland soils (9.9 ± 1.0 g/m2). Densities and biomasses ofAmorpha canescens, Desmodium illinoense, andLespedeza capitatawere higher on lowland sites than on upland sites, whereas densities and biomasses ofBaptisia bracteataandDalea purpureawere higher on upland than on lowland soils. Most legume species are either fire tolerant or exhibit a positive response to fire and their persistence in annually burned prairie suggests that they may play an important role in the nitrogen budget of this ecosystem.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb12694.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

Interplant nutrient transfer may be an important ecological process in grasslands, and may significantly influence plant neighborhood interactions. We investigated the potential for phosphorus transfer between the dominant grassAndropogon gerardiiand several neighboring plant species in tallgrass prairie via a field32PO4labelling experiment. The mean amount of32P received from donor shoots differed significantly among neighboring species and decreased with increasing distance from the donor. In general, forbs and cool‐season C3grasses received more labelled32P than warm‐season C4grasses. Phosphorus transfer occurred over distances up to 0.5 m. The effects of species and distance on movement of phosphorus changed with increasing time after labelling. The relative mass of receiver and donor shoots did not affect amounts of32P transfer. A benomyl fungicide treatment, applied to suppress mycorrhizal activity, likely did not affect existing vegetative hyphae and did not affect the amount of32P transferred. These studies demonstrate that: (1) phosphorus is transferred among neighboring species in tallgrass prairie plant communities, (2) phosphorus may be transferred over significantly greater distances than reported in other grasslands, and (3) there is differential transfer among co‐occurring species. Hypothesized mechanisms accounting for these patterns in tallgrass prairie include mycorrhizal hyphal interconnections and/or extensive and differential root and rhizosphere overlap among neighboring species.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb12695.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

Eryngium cuneifoliumSmall. (Apiaceae) is a narrowly distributed endemic found only inCeratiola ericoides(Florida rosemary)‐dominated Florida scrub, a periodically burned, shrub‐dominated habitat. Multivariate analyses using 22 ∗∗∗microhabitat characteristics indicated significant microhabitat and time‐since‐fire effects on survival, growth, and fecundity of 1287 individuals over a 4‐yr period. Survival increased with distance to the nearest shrub, and plants in larger open patches had greater survival rates. Neighboring shrubs ofCeratiola ericoidesandCalamintha asheiwere associated with a higher mortality ofE. cuneifoliumthan other neighboring shrub species. Survival was reduced by two‐thirds over 4 yr (14% vs. 42%) forE. cuneifoliumnearC. ericoides.Sand accretion increased growth and fecundity. With greater time since fire, woody shrubs increasingly dominate and open patches shrink, significantly reducing survival, growth, and fecundity ofE. cuneifolium.Effects were particularly dramatic between 2 and 7 yr postfire, when annual mortality increased from30% (r =0.74). This herbaceous species is dependent on an open habitat maintained by periodic fire. Belowground competition or allelopathy from shrubs probably restrictsE. cuneifoliumto recently burned, open patches within the most xeric parts of Florida scrub.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb12696.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

Aqueous extracts ofAilanthus altissimabark and foliage were previously shown to be toxic to other plants. Using bioassay‐directed fractionation, I isolated the phytotoxic compound fromA. altissimaroot bark and identified it to be ailanthone, a quassinoid compound having molecular mass of 376. Ailanthone was highly phytotoxic, with concentrations of 0.7 ml/L causing 50% inhibition of radicle elongation in a standardized bioassay with garden cress (Lepidium sativum) seeds. Ailanthone exhibited potent pre‐ and postemergence herbicidal activity in greenhouse trials. Postcmergence activity was especially striking; even the lowest application rate (0.5 kg/ha) caused complete mortality of five of the seven plant species tested within 5 d of treatment. In contrast, the highest application rate (8 kg/ha) did not cause any detectable injury toA. altissimaseedlings, indicating the presence of a protective mechanism in the producer species to prevent autotoxicity. Ailanthone was rapidly detoxified in field soil as a result of microbial activity. Applications of ailanthone equivalent to 0.5 and 4.0 kg/ha completely lost their phytotoxicity within ≤5 d when incubated in the presence of nonsterile soil. When incubated with sterile soil under identical conditions, however, ailanthone remained highly phytotoxic throughout the 21‐d duration of the investigation. The high level of postemergence herbicidal activity in conjunction with its rapid biodegradation in soil suggest ailanthone may have potential for development as a natural‐product herbicide.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb12697.x

出版商:Wiley    

年代:1996

数据来源: WILEY