摘要:

The net photosynthetic (A), stomatal conductance to water vapor (g), water use efficiency (WUE = A/transpiration), and leaf water potential (ψ) responses of cultivated oats (A vena saliva) were determined under an experimental regime of alternating full sun (photosynthetic photon flux density, PPFD>1,700μmol · m‐2‐sec‐1) and shade (300‐400μmol · m‐2· sec‐1PPFD). Less extensive measurements were made on winter wheat (Triticum aestivum) to test the generality of crop species' responses. The rates of stomatal opening/closing after changes in PPFD inA venaandTriticumwere compared with previously determined rates for native grasses and forbs to assess how domestication might have altered stomatal dynamics. Characteristics ofAvenaunder alternating sun and shade were 1) rapid fluctuations in A between full sun (~27μmol · m‐2· sec‐1) and shade rates (~12 ‐13μmol · m2sec1); 2) slower changes in g, causing progressive stomatal closure during the measurement sequence and possible stomatal limitation of A; 3) no change in leaf ψ; and 4) a net reduction in WUE.Triticumhad similar sun/shade A, g, and WUE dynamics, except thatTriticumstomata returned to full‐sun g between shade periods. The rates of change of g inAvenaandTriticumwere lower than for some desert and subalpine native species, but were similar to rates for species in adjoining native habitat. The basic stomatal dynamics ofAvenaandTriticummay typify many cultivated C, species, and these data indicate that crop stomatal behavior has not diverged significantly from that of native species.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb15380.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

A method is described by which seeds of terrestrial orchids are sown and retrieved in the field under almost natural conditions. For the first time it is possible to conduct a quantitative study of orchid germination in situ and observe seasonal growth and mortality of seedlings. The technique has also enabled us to investigate the relation between the site where the seeds are sown, the availability of an appropriate fungus to infect the seeds, and seedling establishment in the soil. Five local species were studied.Corallorhiza odontorhiza, Goodyera pubescens, andGalearis spectabilisall began to germinate in May–June, after 23‐30 weeks in the soil. These species differed in their dependency on infection at germination time, but none of the seedlings developed beyond the point of rupturing the testa except when infected. Seeds ofLiparis lilifoliaandTipularia discolordid not germinate within the first 12 months of the experiment. The implications and potential uses of this field sowing technique for further studies and for other kinds of minute seeds are discussed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb15381.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

The factors influencing reproductive success in a haplo‐diploid marine alga,Gracilaria verrucosa, have been determined through single‐male crosses in the laboratory. Crossing success was assessed by measuring its early components, fertility, and abortion rate. The effects of the male or female parent identity, of the male × female interaction, and of the geographical distance between mates were tested in crosses within or between populations at different geographical scales. The identity of the female parent has a predominant effect on crossing success. Interparent distance has no effect in within‐population crosses; this strongly suggests an absence of inbreeding depression, expected in a species where the haploid phase is individualized and isomorphic to the diploid one. Crossing success tends to increase with distance between mates in between‐population crosses. This heterosis effect seems to indicate that the marine environment could allow genetic divergence between populations, even at short distances (about 100 m).

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb15382.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

The effects of light and nutrient availability on chasmogamous and cleistogamous flower and fruit production were investigated in an understory tropical herb,Calathea micans(Marantaceae). I censused chasmogamous and cleistogamous flower and fruit production at five permanently marked demographic study sites in Costa Rica, characterized by different successional stages. Using a transplant experiment, I examined whether an increase in light and/or nutrients would increase chasmogamous and/or cleistogamous flower production. In natural populations as well as in the experiment, chasmogamous reproduction increased with light; nutrient availability significantly increased chasmogamous reproduction in the transplant experiment. Field observations indicated that very few plants reproduced and low investment in reproduction might have been due to poor environmental conditions. Larger plants had a higher probability of reproducing, but plant size did not have an effect on the mode of reproduction, chasmogamy vs. cleistogamy. However, the production of new vegetative shoots increased the probability of producing chasmogamous inflorescences. Cleistogamy may allow the plant to reproduce even in conditions of poor habitat quality and assures some seed set even in conditions unfavorable to plant growth.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb15383.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

Using the long‐styled, self‐compatible speciesLobelia cardinalis, I examined the relative abilities of self pollen and two outcross pollen sources to fertilize ovules when these three kinds of pollen were applied simultaneously to stigmas. Paternity was determined electrophoretically for 712 progeny of 25 seed parents. Two hypotheses were tested. First, it was hypothesized that self pollen would be less effective than outcross pollen at fertilizing ovules, as a means of reducing the selfing rate. Outcross pollen outperformed self pollen in eight of the 25 seed parents, self outperformed outcross in five, and they were competitively indistinguishable in 12. The mean proportion of offspring produced by self pollen was not significantly different from the value expected under random tube growth and fertilization. The rate of self‐fertilization is therefore determined by prepollination events. Second, to test one stage of the sexual‐selection process, it was hypothesized that the pollen of some individuals would outcompete that of others, across a range of maternal plants. The 25 maternal parents were divided into five groups of approximately five individuals. Each member of a group received pollen from the same two outcross pollen sources (as well as from itself). With offspring pooled across seed parents, one outcross pollen parent outcompeted the other in two of the five groups. In two other groups, pollen sources were competitively superior or inferior depending on the maternal parent. Overall, pollen donors were competitively indistinguishable in 13 of 25 maternal parents. There is thus no evidence for strong postpollination sexual selection. If such selection is present, it is weak, and its importance to the evolution of style length inLobelia cardinalisrequires other kinds of study.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb15384.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

Two hypotheses have been proposed concerning possible fitness advantages of multiple paternity. According to the Elbow Room hypothesis, the magnitude of resource partitioning is positively correlated with the genetic diversity of competitors. This leads to the prediction that the mean fitness of competing half‐siblings will exceed the mean fitness of competing full‐siblings. The Lottery hypothesis suggests that in a patchy environment a genetically diverse sibship increases the probability that a mother will produce winning phenotypes for each of several different microsites. Both hypotheses were tested in a greenhouse experiment with wild radish,Raphanus sativus.Progeny derived from factorial crosses were raised in competition as full‐ or half‐siblings. To simulate environmental variation, the experiment was replicated across a gradient of nutrient concentrations. After 9 weeks, the aboveground biomass of all plants was harvested and oven‐dried. Although dry weights were strongly influenced by nutrient level, within nutrient classes there were no significant differences in the mean dry weight of full‐ and half‐sib competitors. Thus, there was no evidence for the Elbow Room hypothesis. In addition, there were no significant differences in numbers of winning phenotypes in the two competition regimes. Therefore, there was also no support for the Lottery hypothesis. Although competition regime did not influence the mean fitness of competing progeny, it significantly affected variation in dry weight of seedlings within pots. Higher coefficients of variation in half‐sib pots suggest that interference competition may be greater in genetically diverse sibships.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb15385.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

Stomatal density, stomatal aperture length, area/leaf, and number of stomata/leaf were measured after the annual C3agronomic grasses oats (Avena sativa) and wheat (Triticum aestivum), the C, woody legume honey mesquite (Prosopis glandulosa), and the perennial C4grass little bluestem (Schizachyrium scoparium) were grown across a subambient carbon dioxide concentration ([CO2]) gradient from near 200 to 350μmol/mol in a growth chamber. The purpose was to determine if the size and density of stomata vary in response to atmospheric [CO2] during growth, across a subambient [CO2] range representative of the doubling that has occurred since the last ice age. Changes in stomatal density and aperture length with increasing [CO2] were small when detected. Stomatal density decreased on adaxial flag leaf surfaces of wheat, and aperture length increased slightly with [CO2], Leaf area and number of stomata/flag leaf increased by similar proportions with [CO2] in two wheat cultivars. No consistent relationship between [CO2] and stomatal density or size was detected in mesquite, oats, or little bluestem. We conclude that individual plants of these species lack the plasticity to significantly alter stomatal density and aperture length in response to increasing atmospheric [CO2] in a single generation (annuals) or growing season (perennials).

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb15386.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

Flowers of the organ number (meristic) mutantclavata1‐1ofArabidopsis thaliana(Brassicaceae) were studied to examine timing and patterns of floral organogenesis as compared to the wild type. Allclavata1‐1flowers examined had four‐ instead of two‐loculed gynoecia; half showed increased numbers of stamens; and 10% formed increased numbers of sepals. An inflorescence plastochron index was used to establish the timing of developmental events during flower organogenesis.clavata1‐1flowers initiate faster but grow more slowly than in the wild type. The stages of sepal and stamen initiation were prolonged compared to those of the wild type. Although gynoecial initiation was not prolonged, the preceding stage was and it was characterized by a proliferation of meristematic cells above the initiating stamens. Theclavata1‐1flower apex did not become wider than that of the wild type until after the establishment of the gynoecium. We propose thatclavata1‐1is a heterochronic mutant, where flower organ number increases are due partly to prolongation of organ initiation stages.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb15387.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

The pollen‐collecting hairs (PCHs) ofCampanulahave been a subject of intense debate for the past two centuries. Although several morphological studies have been made on these hairs, detailed comparative studies among species are still lacking, their function and adaptive significance being an unsolved question. The present study comprises two microscopy techniques: scanning electron microscopy and confocal scanning laser microscopy. The aim of the present study is to elucidate: 1) the variation in morphology of the PCHs, 2) the variation in presence/absence of the PCHs by the time of spreading of the stigmatic lobes, 3) the variation in the retractive mechanism of the PCHs, and 4) the correlation between pollination and the retraction of the PCHs. In several species PCHs of various lengths are found. Despite the variations in length of the hairs, the same retractive mechanism is found in all species studied. In most species the hairs retract into basal cavities within the style late in anthesis. The cells into which the hairs retract differ in length among species. Pollen grains are often found within the cavities together with the retracted hairs, a mechanism considered to prevent self‐pollination. Pollen germination within the cavities was not observed. In a few species, the PCHs are still present at stigma receptivity. Differences in the shape and size of the cells surrounding the PCHs are documented. The diameter of the pits and the pollen grains vary among species. Other types of hairs on the style are recognized in some species, being of various lengths. These other types do not retract at stigma development and should not be regarded as pollen‐collectors. They possibly facilitate for visiting insects to reach the nectar glands, present at the top of the ovary.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb15388.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

A peculiar and often discussed feature in the genusCampanulais the presence and function of the pollen‐collecting hairs (PCHs), covering the style and the dorsal surface of the stigmatic lobes on the pistil. The hairs sweep up the pollen as the anthers dehisce, and this “stylar brush” serves as a secondary pollen presentation mechanism, facilitating the transfer of pollen from the flower to visiting insects. The adaptive significance of the hairs in relation to pollination has been variously interpreted by several authors during the past two centuries, but a satisfactory explanation for the floral mechanism is still lacking. The aim of the present investigation is to elucidate the function of the PCHs by experimental manipulations of the male phase. Comparisons are made 1) among species with various degrees of protandry and different mating systems, and 2) between annuals and perennials. The results clearly show that the hairs serve not only as pollen‐collectors, but also as an important and efficient mechanism controlling stigma spreading and promoting cross‐pollination. A tactile stimulation of the hairs causes a shortening of the length of the male phase and accelerates stigma maturation. The more frequently the hairs are treated, the shorter the male phase. Similar trends were found in all species regardless of differences in the degree of protandry, life span, or mating system. Geographically well‐separated populations in two species showed differences in length of the male phase, depending on mating system and/or weather conditions. The relevance of the method used in this study compared to pollinator activity and its effect on the PCHs is discussed. The consequences of the retraction of the hairs with respect to self‐pollination are briefly discussed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb15389.x

出版商:Wiley    

年代:1993

数据来源: WILEY