Characterization of the Germination Responses of Silene dioica (L.) Clairv., Populations from Europe

Germination tests were done on 20 populations of Silene dioicacollected in different parts of Europe. Seeds collected fromwild plants and from their progeny growing at R.B.G. Kew, weretested using both freshly harvested and stored seeds. Responseswere compared from tests done on thermo-gradient bars and inincubators to examine germination and after-ripening processesbetween c. 2-c. 45 °C. The responses of different populations were characterized byidentifying variations due to the proportions of dormant seeds,the maximum and minimum temperatures favouring germination,and the time course of germination at particular temperaturesof freshly shed and stored seed. Germination and after-ripeningresponses of different populations displayed marked qualitativesimilarities, but differences in the degree of their expressionresulted in statistically significant quantitative differenceswhich could sometimes be correlated with features of the geographicaldistribution of the populations. The results are discussed in relation to the occurrence of thisspecies in a well-defined natural habitat in Europe, and itis concluded that they represent a situation in which fundamentallysimilar control patterns underlying the responses of every populationexamined are modulated quantitatively to produce variationsin the number of seeds germinating at particular seasons orremaining dormant within the soil.     

The parallel expression of metal tolerance in pollen and sporophytes of Silene dioica (L.) Clairv., S. alba (mill.) krause and Mimulus guttatus DC

Summary The purpose of this paper was to determine if heavy metal tolerance was expressed in pollen and if its expression was correlated with the tolerance of the pollen source. Clones of Silene dioica, tolerant to zinc, closely related but nontolerant S. alba and clones of Mimulus guttatus tolerant and sensitive to copper were grown in the greenhouse in either standard potting soil or nutrient culture. Pollen was collected shortly after dehiscence, hydrated, and tested over a broad range of metal concentrations. The tolerance of the pollen source was determined by comparing root growth in solutions with and without heavy metals. In both Silene species and M. guttatus, the tolerance of the parental clone was expressed in its pollen. Pollen from tolerant individuals was able to germinate and grow at concentrations of metals which markedly inhibited pollen from nontolerants.     

Adaptation to shade of the light-harvesting apparatus in Silene dioica

Abstract. The physiological characteristics and photo-system composition of the photosynthetic apparatus of Silene dioica , a woodland plant, grown in sun and natural shade are examined. As expected, shade leaves exhibited lower chlorophyll a/b ratios, light saturated rates of CO₂ assimilation (A_sat), dark respiration (R_d,) and light compensation points ( Г ), with both sun and shade leaves having similar absorptances and quantum yields of CO₂ assimilation (φ). Shade leaves were able to utilize far-red light for electron transport and carbon assimilation and reach the compensation point. Sun leaves in far-red light had a rate of carbon assimilation equivalent to their dark respiration rate. Chlorophyll fluorescence kinetics from leaves at 77 K together with analyses of thylakoid contents of photosystems (PS) I and II and the light-harvesting cholorphyll a/b protein complex associated with PSII (LHCII) demonstrated that the antenna size of PSII was similar in thylakoids of sun and shade leaves, but shade leaves contained ca. 20% more PSII and ca. 12% less PSI complexes. The increased PSII/PSI ratio in shade leaves accounted for their ability to achieve the compensation point in far-red light. An important feature of photosynethic shade adaptation in S. dioica is an increase in the PSII/PSI ratio and not an increase in the antenna size of PSII. The adaptive response of sun leaves when placed in a shade environment was rapid and had a half-time of ca. 18h.     

Changes in Germination Responses of Silene secundiflora in Relation to the Climate of its Habitat

Silene secundiflora is a Mediterranean species restricted in range to the southern coasts of Spain and the Balearic Islands. Germination tests were made in incubators and on thermo-gradient bars to evaluate changes in temperature-responses at intervals after seed harvest. Results were compared to average temperatures occurring in the region and interpreted in relation to the climatic characteristics of the area. Germination of freshly harvested seed was restricted to a narrow temperature band between ca. 7 and 16°C. After-ripening during the first four months resulted in a progressive widening of the temperature band favouring germination, but this remained below average summer temperatures. Exposure of imbibed seed to high temperatures (31°C) reduced the subsequent temperature maximum for germination by about 4°C, but did not induce a fully effective secondary dormancy. The results appeared to be well correlated with a situation in which germination normally occurs in September at the start of the winter growing season.     

同一生境中强脚树莺鸣声的个体差异及多样性

在杭州市郊小和山森林公园内约85hm2范围内,用SHARP-CE-15l型录音机(频响30—l4000Hz)和强指向麦克风(频响40—14000Hz),对夏季繁殖期连续分布的同一生境中不同个体的强脚树莺(Cettiafor-tipes)的鸣声进行了记录,并通过计算机声谱分析系统从句型结构、音图结构、时域和频域特征及短时能量等方面进行了分析和比较,发现在同一生境一个小范围内同一种鸟就有6种不同类型的鸣声。这些鸣声的音调各不相同,鸣声的结构差异很大,大多声学参数之间也存在显著或极显著差异。形成这种鸣声多样性的原因可能是繁殖竞争在声行为上的体现。     

Seed Production in Leafless and Conventional Phenotypes of Pisum sativum L. in Relation to Water Availability Within a Controlled Environment

Water requirements in relation to seed production was studiedin near-isogenic lines of leafless (afafstst) and conventional(++++) pea plants (Pisum sativum). The plants were grown toseed maturity in pots in a controlled environment under conditionsof high, medium and low irrigation levels. When each genotypewas irrigated independently and on demand and the soil moisturecontent maintained at 65–80 per cent of full capacitythere was no significant phenotypic difference in water useefficiency (WUE), defined as g d. wt seed per kg H₂O utilized.There existed genotypically-controlled upper and lower limitsto yield between which the total dry weight of seed per plantcan be determined by water availability. There was no significantdifferential effect of genotype or of irrigation treatment onthe number of pods, number of seed, unit seed dry weight andbiological yield per plant. There was significant interactionon stem length, and leaf area at specified nodes. When the wateractually required in relation to the water available was takeninto account, the leafless phenotype consistently utilized 33–38per cent less water and produced a correspondingly lower totaldry weight of seed than the conventional counterpart. Independentlyof regime the total dry weight seed per phenotype remained anear constant proportion of the above-ground biomass. Pisum sativum L., garden pea, leafless peas, seed production, water availability     

Differences in response to defoliation between males and females of Silene dioica

Summary The response by male and female plants to herbivory was studied by experimental defoliation of the dioecious perennial herb Silene dioica in a green-house. Male and female plants were defoliated prior to and during the early flowering phase at two intensities (50% and 100% of leaf-area removed) in two consecutive years. Defoliation resulted in a decrease in the number of flowers initiated in both sexes, while a larger delay of peak flowering and a higher mortality was observed in males compared to females. In female plants, severe defoliation resulted in a reduction in seed number per capsule and in seed size compared to control. Females showed a negative correlation between the production of flowers in the first and second season in all treatments, while flowering in males the first season was not correlated with flowering in the second season. Females also showed a lower frequency of flowering than males during the two seasons studied. However, during the flowering period, males allocated significantly more biomass to flowers than did females. This outcome supports the idea that females may have a higher total reproductive expenditure than males, but males have a higher reproductive effort during flowering. Male rosette leaves were significantly preferred by the generalist herbivore Arianta arbustorum in experiments. This preference was most pronounced in trials with leaves from fertilized plants compared to nonfertilized plants. A greater storage of resources in aboveground leaves during winter by males compared to females may explain the higher preference for male leaves and the higher male mortality following early defoliation. Furthermore, males are smaller than females and may have a lower ability than females to replace lost resources needed for reproduction when defoliated early in the season.     

The Relation Between Seed and Fruit Development in the Peach (Prunus persica L.)

The ontogeny of the peach seed and its organs correlates wellwith the stages of growth of the pericarp of peach fruit. Theinitial stages of rapid f.wt (FW I) and d.wt (DW I) increasecoincide with the period of rapid f.wt increase of the wholeseed and rapid size increase of the endosperm respectively.The period of slow f.wt increase of the fruit (FW II) coincideswith the period of rapid size increase of the embryo. The seed and pericarp compete strongly for assimilates throughoutfruit development and the seed is the weaker competitor. Thereis no period however when the growth of the seed or one of itsorgans inhibits the sink strength of the pericarp to allow theseed to develop. The data presented indicate that the periodsof high nutrient demand (DW I and DW III) are created in thepericarp in response to a stimulatory signal from the seed andthe period of low nutrient demand (DW II) results from the absenceof this signal after the endosperm reaches full size.     

Numerical analysis of infraspecific variation in European Silene alba and S. dioica(Caryophyllaceae)

Infraspecific variation among European populations of Silene alba and S. dioica was analysed by non-metric multidimensional scaling, which was applied to K-dissimilarity matrices based either on 16 seed characters or on 34 seed, flower and capsule characters. The material used for analysis consisted of 167 collections of wild seed, largely obtained from European botanic gardens, and 97 sets of mature greenhouse-grown progeny. S. alba was found to show topoclinal variation, primarily along an axis from the Iberian peninsula through central Europe to Romania. This pattern is not reflected in current taxonomic treatments. N. and N.W. European S. alba is morphologically heterogeneous and has probably been introduced from various southern sources. S. dioica shows less total variation between populations than S. alba , and consists of local ecogeographic races that intergrade at their margins. The two species are completely discriminated by seed, flower and capsule characters when used in combination, but S. alba populations from the eastern end of the cline closely approach S. dioica in seed morphology. This convergence is unlikely to be an effect of recent introgression.     

Distribution ofUrtica dioica L. andRubus fruticosus L. (+agg.) in relation to edaphic factors in cultivated poplar woods

Urtica dioica L. andRubus fruticosus L. (+agg.) are widely distributed in Belgian cultivated poplar woods. Using adjusted standardized residuals as an objective measure of preference of a species for ecoparameters, it seems possible to describe the distribution betweenUrtica andRubus as coincidental as regards ecological considerations. Both plant species behave obviously as antagonists.     

Seed Number, Seed Size and Seed Diversity in Washington Lupin (Lupinus polyphyllus Lindl.)

Over 20 000 seeds of the Washington lupin (Lupinus polyphyllusLindl.) were examined and measured in an experiment carriedout over a 10 year period (1989–1999). Four differentgroups of Washington lupin seeds were found: dark, patterned,grey and light seeds. During the 10 year experiment, the totalaverage number of seeds per plant decreased from 2654 (1990)to 1220 (1999), there was a slight decrease in seed weight perplant and an increase in the average weight per seed. Therewas a clear seed size/number trade-off at the intraspecificlevel. The relative proportions of each seed group also changedwith patterned seeds becoming dominant (50% at the beginningand 90% at the end of the experiment), grey seeds remained constant(constituting 10% of the total seeds) and the proportion ofboth dark (33% at the beginning and 5% at the end) and light(10% at the beginning and 5% at the end of the experiment) seedsdecreased. Six hundred and sixty nine seeds were found to havea different testa ornamentation; they were distributed amongthe different groups as follows: 48% patterned seeds, 29% darkseeds, 12% grey seeds and 11% light seeds. There were no significantdifferences in the physical dimensions of the ornamented seedscompared with all other seeds. The results suggest that theWashington lupin is a mixture of different species and botanicalforms; this is discussed in relation to possible selection pressuresto produce both smaller and larger seeds. The possibility thatchanges in testa ornamentation are influenced by genes controllingthe synthesis of the seed coat pigment is discussed. Copyright2001 Annals of Botany Company Lupinus polyphyllus Lindl., lupine, plant biotechnology, plant parameters, selection pressure, seed size/number trade-off, testa ornamentation     

DNA diversity in sex-linked and autosomal genes of the plant species Silene latifolia and Silene dioica

The relatively recent origin of sex chromosomes in the plant genus Silene provides an opportunity to study the early stages of sex chromosome evolution and, potentially, to test between the different population genetic processes likely to operate in nonrecombining chromosomes such as Y chromosomes. We previously reported much lower nucleotide polymorphism in a Y-linked gene (SlY1) of the plant Silene latifolia than in the homologous X-linked gene (SlX1). Here, we report a more extensive study of nucleotide diversity in these sex-linked genes, including a larger S. latifolia sample and a sample from the closely related species Silene dioica, and we also study the diversity of an autosomal gene, CCLS37.1. We demonstrate that nucleotide diversity in the Y-linked genes of both S. latifolia and S. dioica is very low compared with that of the X-linked gene. However, the autosomal gene also has low DNA polymorphism, which may be due to a selective sweep. We use a single individual of the related hermaphrodite species Silene conica, as an outgroup to show that the low SlY1 diversity is not due to a lower mutation rate than that for the X-linked gene. We also investigate several other possibilities for the low SlY1 diversity, including differential gene flow between the two species for Y-linked, X-linked, and autosomal genes. The frequency spectrum of nucleotide polymorphism on the Y chromosome deviates significantly from that expected under a selective-sweep model. However, we detect population subdivision in both S. latifolia and S. dioica, so it is not simple to test for selective sweeps. We also discuss the possibility that Y-linked diversity is reduced due to highly variable male reproductive success, and we conclude that this explanation is unlikely.     

山荆子腊叶标本表型性状变异分析

为了揭示山荆子表型性状的变异程度和规律,以150份山荆子腊叶标本为材料,选择20个表型性状,统计基本参数并进行聚类分析.结果表明:叶的平均变异系数(CV=32.67%)大于果的平均变异系数(CV=20.7%),果的性状稳定性较高,叶性状中叶柄长变异系数(CV=38%)最大,叶宽位/叶长变异系数(CV=13.29%)最小;果实性状中果径宽位/果柄长(CV=29.37%)变异最大,变异最小的性状是果长/果径(CV=13.10%);选用平均欧氏距离对各地方居群的20个表型性状进行UPGMA聚类,在距离5阈值处,可以划分为5类,在欧氏距离6阈值处,可划分为3大类.     

Genetic and ecological differentiation in the hybridizing campions Silene dioica and S. latifolia

Ecological differentiation is a major contributor to the generation and maintenance of biological diversity. We investigated habitat differentiation between and within sites in the fully cross-fertile and hybridizing Silene dioica and S. latifolia using amplified fragment length polymorphisms (AFLP) profiles and corresponding vegetation relevés around individual plants. Nineteen study sites in the Swiss Alps included pure sites and contact sites (both taxa present within 30 m). In pure sites and at contact sites, the two taxa showed consistently differentiated AFLP banding patterns across regions but few discriminating bands. This indicates that although the two taxa are weakly differentiated, current introgression has not led to genome-wide admixture. Only three putative early generation hybrids were detected at contact sites. The habitats of the two taxa differed between pure sites with S. dioica occurring in moister, colder, and less-disturbed sites than S. latifolia. However, asymmetric habitat overlap was evident within contact sites found in intermediate conditions that were more similar to S. latifolia sites. This situation might favor introgression from S. dioica into S. latifolia. Evidence for habitat-genotype associations within contact sites was weak making habitat-mediated selection against intermediate phenotypes of hybrids unlikely in the contact sites investigated. We suggest that other reproductive barriers together with dispersal limitation contribute to the rarity of early generation hybrids.     

Distribution ofUrtica dioica L. in relation to edaphic factors

Summary Soils withU. dioica (a soils) were compared with soils 1–6 m away (b soils) with seemingly identical conditions except for absence of Urtica. The a soils had a higher EDTA–Cu concentration than b soils. The values for mineralised N, anion exchanged P, CEC, conductivity, Zn, Ca, Mg, K, organic matter and pH were alike in a- and b soils. Inorganic P was a limiting factor for Urtica when the P level, in general, was low (in this material not roadside soils). In the roadside soils the level of inorganic P was, in general, high and the content in a- and b soils was alike.     

Habitat switching by dark-bellied brent geese Branta b. bernicla (L.) in relation to food depletion

Seasonal changes in the distribution and feeding behaviour of dark-bellied brent geese Branta b. bernicla (L.) and the biomass of their food plants were studied in three successive winters on the Norfolk coast. The data was used, in conjunction with published information, to show how depletion, productivity and mortality of food plants drive the pattern of habitat switching in this species. It is then possible to explain the habitat shifts observed over the last 35 years and predict future changes. On arrival, geese fed first on algal beds and then on salt marsh, grass and arable fields before returning to feed entirely on the salt marsh in spring. The biomass of green algae, and subsequently the salt marsh vegetation, declined during the autumn and this could be attributed to depletion through goose grazing and natural mortality. As depletion occurred the geese fed more intensively, for a greater percentage of time and with an increasing pace rate, the net result, however, was a declining intake rate (as measured by defaecation rate). The algal biomass at which the geese switched from the algal beds to salt marsh was consistent between years, with heavy storm-induced loss of algae in one year resulting in an earlier switch. That the timing of habitat switches may be explained by depletion of food plants was further supported by historical data: the number of brent geese wintering at the site has increased dramatically over the last 30–35 years and the time of switching from algal beds to salt marsh and from salt marsh to salt marsh and fields has become progressively earlier, as expected from the increased depletion. The expected further increase in brent goose numbers will increase the rate of depletion of intertidal vegetation so that the switches between habitats will be more rapid and the geese will move inland earlier and remain inland longer. The expected increase in the brent goose population will thus result in a disproportionate increase in the levels of conflict between brent geese and agriculture.