Phenology and life cycle of the annual, <Emphasis Type=Italic>Chamaesyce maculata</Emphasis> (L.) Small (Euphorbiaceae), with multiple overlapping generations in Japan

The phenology of germination, vegetative growth and sexual reproduction in the annual Chamaesyce maculata (L.) Small (Euphorbiaceae) were investigated in a natural population in western Japan. Seedlings emerged from mid-June to early October, with three peaks: mid-June, late July and late August. Plants that emerged in June commenced sexual reproduction from late July, and thereafter both vegetative growth and sexual reproduction occurred together until early November, the plants showing no switching from vegetative growth to sexual reproduction. Seedlings that emerged in June and July suffered high mortality, but most seedlings that emerged from August onward survived until the reproductive stage. The minimum size for reproduction was largest for plants that emerged early in the season, and it decreased with a delay in seedling emergence. The late emergence of seedlings that resulted in low reproductive output may be to some extent compensated for by the increased probability of survival in the seedling stage. A transplant experiment clarified that C. maculata can repeat a maximum of three overlapping generations within a year. Multiple generations per year were attained by non-dormant seeds produced in the first and second generations and clearly resulted in an increased reproductive output per year. The life cycle with multiple overlapping generations may have been acquired in habitats where unpredictable disturbance results in temporally unsuitable conditions for germination, vegetative growth and sexual reproduction of annual plants, but where suitable conditions frequently continue over a period longer than the single generation time of annual plants.     

Seasonally different modes of seed dispersal in the prostrate annual, <Emphasis Type="Italic">Chamaesyce maculata</Emphasis> (L.) Small (Euphorbiaceae), with multiple overlapping generations

The modes of seed dispersal in the prostrate annual, Chamaesyce maculata, with multiple overlapping generations were investigated. We found that C. maculata has two modes of seed dispersal; autochory in the summer and myrmecochory in the autumn. Seasonally different modes of seed dispersal have not been known in other plant species. The large proportion of seeds produced in the summer was positioned further than the expanse of the parent plants by automatic mechanical seed dispersal. Therefore, autochory would be effective for avoiding competition between parent and offspring plants. No autochory occurred in the seeds produced in the autumn. The seeds of C. maculata without an elaiosome were dispersed by seed-collecting ants in the autumn. Although 18 ant species in total visited the plants of C. maculata at the 50 sites investigated, only two ant species, Tetramorium tsushimae and Pheidole noda frequently carried the seeds of C. maculata. The low frequency of seeds carried out of the nest by P. noda suggests that the workers of P. noda carry the seeds as food into their nest. So, P. noda might be a less effective seed disperser for C. maculata, corresponding to the effectiveness of seed dispersal by harvester ants. However, T. tsushimae ants frequently carried the seeds into and out of their nest, suggesting that T. tsushimae do not regard the seeds of C. maculata as a food resource. Thus, T. tsushimae may be an effective seed disperser for C. maculata.     

Effect of defoliation on leaf growth,sexual expression and reproductive success of Cnidoscolus aconitifolius (Euphorbiaceae)

Several studies on herbivory have shown that plants may have different responses to foliar damage. Most studies have been done using hermaphroditic species, here we present, using a defoliation experiment, different types of response to foliar damage by the monoecious Cnidosculus acontifolius. We evaluated four treatments: natural herbivory (control), and 25%, 50% and 100% artificial defoliation. The results suggest that this species is capable of showing the following compensatory responses: (a) undercompensation in total production of flowers and in fruit set (damage >25%); (b) full compensation in seed weight (all levels of damage); and (c) overcompensation in leaf growth and in the proportion of female flower production (damage 25%). The results show that C. aconitifolius can exhibit a very fast and plastic response depending on the intensity of damage and the time since defoliation. The increase in foliar growth suggests a long-term tolerance response to hervibory, whereas the change in the proportion of female flowers produced does not appear to have a long-term effect due to the decrease of fruit production in all levels of damage. We suggest that the response in foliar growth and the change in sexual expression by C. aconitifolius, are associated with the high resource availability conditions prevalent in the population studied.     

Most organs of sugar-beet (<Emphasis Type="Italic">Beta vulgaris</Emphasis> L.) plants at the vegetative and reproductive stages of development are polysomatic

Polysomaty was studied using flow cytometry in different organs of diploid, triploid and tetraploid sugar-beet (Beta vulgaris L.) plants, in the first (at harvest) and the second (at the height of the blooming period) year of development. Of the organs/parts of organs of the vegetative plant that developed during the first year, only the leaf lamina did not contain endopolyploid cells; in all others, one to three endocycles had occurred. The second-year seed-crop plant was also highly polysomatic; even in reproductive organs such as the flower and pericarp the endopolyploid cells were present (up to 8C and 32C, respectively). At this stage of development no endocycles occurred in the leaf lamina, flower bract, and inflorescence bract. The parts of the plant with no endopolyploid cells are recommended for ploidy estimation, and as a material suitable for micropropagation and genetic manipulations. Endoreduplication, up to 32C (64Cx), was organ-specific and correlated negatively with plant ploidy. The highest mean C-value, over 7, was in the diploid, in the basal part of the oldest leaf petiole in the first-year plant, and in the storage parenchyma of the root in the second-year seed-crop plant. The results confirm that higher endopolyploidy occurs in plants with a smaller 2C DNA amount than in those with a larger one. The significance of endopolyploidization in development of sugar-beet plant organs is discussed.     

Effect of long photoperiod on the reproductive and bulbing processes in garlic (Allium sativum L.) genotypes

Garlic (Allium sativum L.) genotypes differ considerably in scape length, flowering ability, and seed production. In bolting clones reproductive processes are facilitated by a combination of specific temperature and photoperiod regimes. However, it is yet unclear whether the phase-specific photoperiod effect on florogenesis is universal for all garlic genotypes. We investigated the effect of ambient day length interruption by 10 or 30 days of long photoperiod in ten garlic accessions belonging to four bio-morphological groups. It was evident that garlic genotypes vary significantly in response to long photoperiod, and that in some clones the treatment enhances florogenesis, flower stalk elongation and bulbing. The competition for resources by the simultaneously developing bulb and inflorescence sinks differentially determines the fate of stalk elongation and flower development in the investigated genotypes. It is concluded that florogenesis in garlic can be promoted by exposure to proper environmental stimuli, during pre-planting storage and sprouting to the later growth stages. The genetic variability acquired from sexual reproduction and vegetatively preserved collections can serve in genetic and physiological studies as well as in breeding programs.     

Growth and reproductive characteristics of an aquatic macrophyte Ottelia alismoides (L.) Pers. (Hydrocharitaceae)

Life history and reproductive traits of a submerged aquatic weed, Ottelia alismoides (L.) Pers., were studied in irrigation ponds in southwestern Japan. In addition, growth and seed production were investigated in relation to nutrient condition and water depth. The size of plants was very variable but reproductive allocation was nearly constant irrespective of the plant size at reproductive stage, amounting to more than 30% at maximum. Bagging experiments confirmed autogamy of the species. Ottelia alismoides grew best in nutrient-rich water with mud substratum. The optimal water depth for the growth of the species was approximately 50 cm compared with 20 and 90 cm. However, the reproductive allocation and seed set rate did not change much in different nutrient and water depth conditions. The seeds were produced by cleistogamous flowers in a depth of 90 cm. Morphological and ecological plasticity revealed in the present study was considered to be adapted to unstable environments such as rice fields and irrigation ponds liable to water-level fluctuation. The conditions required for the restoration of the populations of O. alismoides are discussed based on the present results.     

Breeding biology, resource partitioning and reproductive effort of a dioecious shrub, Clutia pulchella L. (Euphorbiaceae)

 The flowering of Clutia pulchella was studied in a coastal scarp forest community in southern KwaZulu-Natal, South Africa. Sex dependent differences in the frequency and magnitude of floral output were recorded, with male individuals producing 4.32 times more flowers per leaf axis than females. Increased node production, as a manifestation of significantly increased branching, allowed for prolific flower production in males. Energy investment per flower was marginally greater in females (0.045 J/mg), despite copious pollen production and glandular secretion in males (0.035 J/mg). Differential flower production, reproductive organ dry mass and an unbalanced branching ratio revealed that “per plant” expenditure towards flowering was more pronounced in males (♀ flowering × 5.04). The elevated cost of fruit production (♀ flowering × 5.5), inclusive of imperfect fruit set, resulted in overall reproductive expense being slightly higher for females. Such sex-dependent reproductive investment was shown to have minimal influence on the population sex ratio, with sex frequencies and nearest neighbor distances yielding a non-significant male bias of 1.16. No evidence of spatial asymmetry was found. Received December 1, 1999 Accepted September 27, 2000     

Effects of genotype and temperature on pollen tube growth in perennial ryegrass (Lolium perenne L.)

Summary Low yield in seed crops of perennial ryegrass is related to low fertilization efficiency and low temperature during anthesis. To study the effect of genotype and temperature on pollen performance, we conducted greenhouse experiments at controlled temperatures. Individual florets of four genotypes that are known to differ in seed production were hand pollinated at four temperatures (14°, 18°, 22°, 26° C) both in vivo and via a semiin-vitro method involving excised florets on agar. Pollen germination and tube growth were determined with UV-fluorescence microscopy and scored in six classes at 2 h after pollination in vitro and after 0.5, 2 and 5 h in vivo. In vitro, both genotype and temperature had a significant effect on the performance of self-pollen. Pollen tube growth increased with temperature. In cross-pollinations, the pistil parent had a significant effect on pollen tube growth, and there was also a significant pistil-by-temperature interaction. In vivo, genotype and temperature significantly affected pollen performance. The genotype-by-temperature interaction was only significant 5 h after pollination. One genotype with low seed yield was pseudoself-compatible and was a relatively poor mother after cross-pollination. The effects of genotype and temperature on the growth of self-pollen might be exploited in a breeding programme.A.G. Stephenson was on a sabbattical leave at SVP in 1987     

Spatial distribution of soil nutrients and ephemeral plants underneath and outside the canopy of Porlieria chilensis shrubs (Zygophyllaceae) in arid coastal Chile

Soil nutrients and density and biomass of annual plants underneath and outside the canopy of Porlieria chilensis shrubs were measured at the end of the growing season in a protected arid coastal site in Chile. Levels of soil nitrogen, phosphorus and organic matter were significantly higher underneath than outside the canopies of shrubs. Almost 4 times as many plants occurred outside than underneath shrubs, but no significant differences in total aboveground biomass were found. Several species had higher densities and/or biomass outside rather than underneath shrubs, whereas others showed the oppsite trend. Species richness was lower underneath P. chilensis canopy. The spatial microdistribution of ephemeral species may be explained by differential water and nutrient requirements. Comparison of the patterns observed in our protected site versus surrounding unprotected areas supports the generalization that man, by removing shrubs and trees, has changed a previous heterogeneous spatial distribution of nutrients to a more homogenous one.This is a contribution of the Program of Arid Zone Studies of the Universidad de la Serena     

Consistent associations with beneficial bacteria in the seed endosphere of barley (Hordeum vulgare L.)

The importance of the plant microbiome for host fitness has led to the concept of the “plant holobiont”. Seeds are reservoirs and vectors for beneficial microbes, which are very intimate partners of higher plants with the potential to connect plant generations. In this study, the endophytic seed microbiota of numerous barley samples, representing different cultivars, geographical sites and harvest years, was investigated. Cultivation-dependent and -independent analyses, microscopy, functional plate assays, greenhouse assays and functional prediction were used, with the aim of assessing the composition, stability and function of the barley seed endophytic bacterial microbiota. Associations were consistently detected in the seed endosphere with Paenibacillus, Pantoea and Pseudomonas spp., which were able to colonize the root with a notable rhizocompetence after seed germination. In greenhouse assays, enrichment with these bacteria promoted barley growth, improved mineral nutrition and induced resistance against the fungal pathogen Blumeria graminis. We demonstrated here that barley, an important crop plant, was consistently associated with beneficial bacteria inside the seeds. The results have relevant implications for plant microbiome ecology and for the holobiont concept, as well as opening up new possibilities for research and application of seed endophytes as bioinoculants in sustainable agriculture.     

Endogenous cytokinins in the vegetative and reproductive phases of development in the dioecious plant Rumex acetosella L.

The content of endogenous cytokinins has been analysed in leaf and inflorescence extracts of male and female R. acetosella plants, using gas chromatography. Plant parts were extracted at four stages of development: leaves of juvenile plants, leaves of adult plants at the time of flower initiation and in full bloom, and upper internodes of the inflorescence stalks. Cytokinins with characteristics similar to isopentenyl adenine and adenosin, zeatin, zeatin riboside, and a bound form of zeatin, were all found in the extracts. The total amount of cytokinins was higher in female than in male plants during all these stages.Reprint requests     

Individual resource allocation to vegetative growth and reproduction in subgenus <Emphasis Type="Italic">Cyclobalanopsis</Emphasis> (<Emphasis Type="Italic">Quercus</Emphasis>, Fagaceae) trees

The resource allocation for vegetative growth and female reproduction in three tree species of subgenus Cyclobalanopsis (Quercus, Fagaceae), i.e., Q. salicina, Q. sessilifolia, and Q. acuta, were examined on a per-individual basis in two consecutive reproductive seasons, in order to test whether these trees fit the predictions of the masting hypotheses about resource matching versus resource switching. Since the three Quercus species have a biennial fruiting habit, it takes 3 years for the observation of two reproductive events. Female flower and acorn production per tree were investigated by using a seed-trap method and a numerical analysis of seed dispersal. The net production of each individual was estimated as the sum of the annual increase in the dry mass of vegetative organs and reproductive investment per tree. In the data analyses, the three species were pooled, since all 12 sample trees of the subgenus apparently showed masting in the same year, with no exceptions. Female flower and acorn production per individual tree changed considerably between years. The net production per tree increased with tree size, but did not differ between years. Therefore, the reproductive allocation (proportion of a plant’s annual assimilated resources which are used for reproduction) differed dramatically between years. On the other hand, within a year, the reproductive allocation increased with increasing net production per tree. These results suggest that the switching of resource allocation between years within an individual are occurring in subgenus Cyclobalanopsis species, and the intensity of the switching increases with increasing tree size.     

Causes and consequences of extreme variation in reproductive strategy and vegetative growth among invasive populations of a clonal aquatic plant, <Emphasis Type="Italic">Butomus umbellatus</Emphasis> L. (Butomaceae)

The mode of reproduction may influence the spread of invasive species by affecting evolutionary potential and dispersal ability. We sampled 51 introduced North American populations of the clonal aquatic plant Butomus umbellatus L. (flowering rush) and found extreme variation in sexual fertility caused by polyploidy. Populations consisted of diploids that produced thousands of viable seeds or of sexually sterile triploids. Although a trade-off between sexual and clonal reproduction predicts that the sexual sterility of triploids would be compensated for by greater clonal reproduction, a greenhouse experiment involving eight diploid and 10 triploid populations showed that diploid plants not only invest substantially in sexual structures but also make hundreds of tiny clonal bulbils on both rhizomes and inflorescences. In contrast, triploids do not make bulbils and have very limited scope for clonal multiplication and dispersal. Diploid populations were more frequent than triploid populations, especially in the Great Lakes region. This is probably because of the difference between cytotypes in clonal rather than sexual reproduction, as genetic analyses indicate a general lack of sexual recruitment in North America. Although triploids were less common, they have a wider geographical distribution. This could be due to a greater ecological tolerance resulting from polyploidy. However, genetic evidence suggests that triploids have become widespread via their use in and escape from horticulture. North America is being colonized by two distinct forms of B. umbellatus that differ strongly in reproductive strategy as well as the vectors and pathways of invasion.     

Establishment and reproduction of Aeschynomene virginica (L.) (Fabaceae) a rare,annual, wetland species in relation to vegetation removal and water level

Aeschynomene virginica is a rare annual plant found in freshwater tidal wetlands of the eastern United States. We hypothesized that standing vegetation and water inundation were two important environmental factors in its population dynamics. To test these hypotheses, we sowed seeds into plots with undisturbed vegetation or plots with all aboveground vegetation removed in 1998 and 1999. Presence/absence of seedlings was noted and seedling survival to reproduction, final size, and seed set were measured throughout both growing seasons. Seedling establishment from germination to the first true leaf stage increased with decreasing water depth. Vegetation removal plots had greater seedling establishment, higher seedling survival, and higher seed set per plant than non-removal plots. In a greenhouse study designed to test the effects of water level on seed germination and seedling establishment, no seedlings established in submerged soils, and seed germination and seedling establishment were lower in waterlogged soil than in wet soil. Physical stress associated with deeper water likely limits the distribution of A. virginica to higher elevations, where seeds that colonize patches with low vegetative cover are more likely to produce reproductive adults that produce more seeds relative to patches with established vegetation. A. virginica appears to be a fugitive species specializing on open habitat patches in tidal wetlands. This species may be dependent on disturbances for population establishment and maintenance.     

Differential allocation of protein resources to flight muscles and reproductive organs in the flightless wing-polymorphic bug, <Emphasis Type="Italic">Pyrrhocoris apterus</Emphasis> (L.) (Heteroptera)

Differences in the growth of dorsolongitudinal flight muscles and gonads in 1–28 days old long-winged (macropterous) and short-winged (brachypterous) adults of the firebug (Pyrrhocoris apterus L.) and the resource allocation to these organs were studied by means of total protein analysis. We found predominant allocation of food resources to flight muscles compared to reproductive organs in both macropterous males and females during the first 5 days of adult life. Subsequent histolysis of developed flight muscles coincided with increased total protein content in some reproductive organs. Initiation of intensive food intake after starvation or application of higher dose of methoprene on macropterous adults changed the resource allocation in favour of growth of reproductive organs and induced precocious histolysis of flight muscles. It indicates an involvement of juvenile hormone in wing morph-related differential allocation of resources in the bug. Increased total protein contents in the ovaries and accessory glands of starved macropterous females and males treated with methoprene, respectively, indicate that proteins derived from the methoprene-induced histolysis of the flight muscles are re-utilized for the growth of the reproductive organs. It is the first report of persistence of differential resource allocation to flight muscles and reproductive organs in the wing-polymorphic insects with non-functional macropterism.     

Variability in annual recruitment success as a determinant of long-term and large-scale variation in annual production of intertidal Wadden Sea mussels (<Emphasis Type="Italic">Mytilus edulis</Emphasis>)

To understand the background of the strong variation and recent decline of stocks and production of mussels (Mytilus edulis) on tidal flats of the Wadden Sea, we analysed long-term (twice-annual for 26 years) and multi-station (15 sites) estimates of numbers, mean individual weights, biomass, and annual production on Balgzand, a 50-km² tidal-flat area in the westernmost part of the Wadden Sea (The Netherlands). Somatic production was estimated from summed growth increments of soft tissues per half-year period and expressed in ash-free dry mass (AFDM). In adults, positive values in spring/summer regularly alternated with negative values in autumn/winter, when up to ∼25% (mean: 14%) of individual weight gains in the preceding season were lost. No weight losses were observed during the first winter of the life of mussels. The 26-year mean of net somatic tissue production P amounted to 5.5 g AFDM m⁻² a⁻¹ at a mean biomass B of 3.2 g AFDM m⁻²; the ratio P/B varied strongly with age composition of the mussel population and ranged between 0.5 and 3.0 a⁻¹ (mean: 1.7). Within the restricted areas of mussel beds, mean biomass and annual production values were two orders of magnitude higher. In the Wadden Sea, mussel beds cover a typical 1% of extensive tidal flat areas. Numerical densities of recruits showed straight-line relationships with subsequent life-time year-class production. Once recruits had reached an age of ∼10 months, their numbers predicted subsequent production within narrow limits. Production per recruit averaged 0.21 g AFDM for 10-mo recruits and was not related to recruit density. Local variation in annual production varied strongly, with maximal values between mid-tide and low-tide level, where recruitment was also maximal. Production per recruit was higher at low than at high intertidal levels. Frequently failing recruitment is indicated as the main cause of declining mussel stocks in the Wadden Sea. As in other bivalve species, a declining frequency of the occurrence of cold winters appears to govern declining recruitment success and consequently declining production.     

Production of food bodies on the reproductive organs of myrmecophytic Macaranga species (Euphorbiaceae): effects on interactions with herbivores and pollinators

In protective ant–plant mutualisms, plants offer ants food (such as extrafloral nectar and/or food bodies) and ants protect plants from herbivores. However, ants often negatively affect plant reproduction by deterring pollinators. The aggressive protection that mutualistic ants provide to some myrmecophytes may enhance this negative effect in comparison to plant species that are facultatively protected by ants. Because little is known about the processes by which myrmecophytes are pollinated in the presence of ant guards, we examined ant interactions with herbivores and pollinators on plant reproductive organs. We examined eight myrmecophytic and three nonmyrmecophytic Macaranga species in Borneo. Most of the species studied are pollinated by thrips breeding in the inflorescences. Seven of eight myrmecophytic species produced food bodies on young inflorescences and/or immature fruits. Food body production was associated with increased ant abundance on inflorescences of the three species observed. The exclusion of ants from inflorescences of one species without food rewards resulted in increased herbivory damage. In contrast, ant exclusion had no effect on the number of pollinator thrips. The absence of thrips pollinator deterrence by ants may be due to the presence of protective bracteoles that limit ants, but not pollinators, from accessing flowers. This unique mechanism may account for simultaneous thrips pollination and ant defense of inflorescences.     

Growth and annual production of the brown alga Laminaria japonica (Phaeophyta, Laminariales) introduced into the Uwa Sea in southern Japan

The brown alga Laminaria japonica is distributed from southern Hokkaido to the northeastern Honshu in Japan. Recently, aquaculture of L. japonica has expanded to the southern coast of Japan and to China along the East China Sea. In order to elucidate the growth, biomass and productivity of L. japonica in a subtropical area, we cultivated and examined it in the Uwa Sea, in southwestern Japan over a period of 2 years. The seawater temperature ranged from 13.8 to 26.8 °C in 2001/2002 and from 13.1 to 27.2 °C in 2002/2003. In 2001/2002, the maximum density, maximum mean length and maximum mean wet wt. of L. japonica were 59.7 ± 28.0 ind. 50 cm^− 1 (mean ± S.D.), 187.5 ± 82.7 cm (360 cm in the largest individual) and 130.1 ± 94.6 g wet wt., respectively. In 2002/2003, these values were 94.7 ± 22.2 ind. 50 cm^− 1, 159.3 ± 74.4 cm (300 cm in the largest individual) and 95.2 ± 69.5 g wet wt., respectively. Thus, the length and weight increased when the density was low (2001/2002), and the length and weight decreased when the density was high (2002/2003). The maximum biomass was estimated to be 7200 ± 3400 g wet wt. 50 cm^− 1 in 2001/2002 and 7300 ± 2000 g wet wt. 50 cm^− 1 in 2002/2003. Annual production was estimated to be 33.3 kg wet wt. m^− 1 year^− 1 in 2001/2002 and 34.0 kg wet wt. m^− 1 year^− 1 in 2002/2003. The present study indicates that the annual production of L. japonica per rope of 1 m at Uwajima Bay, the Uwa Sea corresponded to 1.1-2.2 m² of that of Hokkaido in their native area. Thus, the present study indicates that L. japonica is highly adaptable because it is able to keep a high level of productivity when grown in water with a high temperature.