Primary and secondary seed dispersal by wind and water in Spergularia salina

The patterns of repositioning by wind and water following their initial dispersal from the parent plant, of winged and unwinged seeds of the heteromorphic halophyte Spergularia salina were Investigated experimentally in both dense vegetation and bare ground under field conditions in a sea shore meadow in eastern Sweden Seeds were placed in situ in the field, and after four days with wind as the sole dispersing agency, 19% of the seeds were repositioned After another 11 days, during which both wind and water acted as dispersing agencies, all seeds of both types had either become repositioned and were still visible (1/3 of the seeds), had penetrated into the ground at the point of release or after dispersal (1/3), or were not recovered (1/3) The probability to become lifted secondarily by water was similar in both seed types Of those seeds repositioned and recovered on the ground, more of the winged type had been transported any distance horizontally than the unwinged type The seed dispersal curve was strongly skewed to the left, and the winged seed type was transported slightly further than the unwinged type, both during primary and secondary dispersal All seeds were transported further when placed on bare soil than when placed in dense vegetation Vertical transportation was quicker in dense vegetation, and unwinged seeds disappeared more quickly into the ground In dense vegetation, unwinged seeds were more frequently encountered in the seed bank than winged seeds, whereas in the absence of vegetation cover, seeds of both types recovered in the soil were found in equal shares     

Seed weight and germination behavior of the submerged plant Potamogeton pectinatus in the arid zone of northwest China

Variation in seed weight is common within and among plant species, but few studies have attempted to document the pattern of seed weight and germination attributes for aquatic macrophytes at a large scale. This study examined within‐species variation in seed weight and germination attributes and the effects of environmental factors on seed traits of the submerged plant Potamogeton pectinatus in the arid zone of northwest China. Our results showed that the average seed weight was 0.24 g per 100 seeds with a coefficient of variation (CV) of 28.4% among the eight P. pectinatus populations. The total germination fraction of seeds of P. pectinatus was relatively poor, less than 35% in seven P. pectinatus populations, and the lowest germination percentage found was only 2%. There were significant differences in seed weight, time to onset of germination, and total germination fraction among the eight different populations. Hierarchical partitioning analysis showed a strongly positive correlation between seed weight and water temperature and pH. Seed weight and the maternal environmental factors significantly affected both time to initiation of germination and total germination fraction. Our results suggest that (1) seed weight variation in P. pectinatus primarily is the result of temperature variation during fruit development; (2) relatively poor germination fraction suggests that seeds are relatively unimportant in the short‐term survival of populations and that it may be another adaptive trait allowing plants to take place in the right place and at the right time, especially in harsh environment; and (3) variation in seed germination traits should be determined by local environmental and intrinsic factors that interact in a complex fashion.     

浙江楠种群表型变异

以探讨浙江楠(Phoebe chekiangensis)种群间和种群内的表型变异程度和变异规律为目的, 对其分布区9个种群的10个表型性状进行了研究。采用巢式方差分析、变异系数、多重比较和相关分析等多种分析方法, 对种群间和种群内的表型多样性及其与地理生态因子的相关性进行了讨论。研究结果表明: 浙江楠叶片、种子等表型性状在种群间和种群内均存在着丰富的变异, 10个性状在种群间、种群内的差异均达极显著水平; 种群内的变异(21.74%)大于种群间的变异(18.45%), 表型性状的平均分化系数为41.43%, 种群内变异是浙江楠表型变异的主要变异来源。各性状平均变异系数为12.78%, 变化幅度为6.50%-19.38%。种群间叶片的平均变异系数(16.99%)高于种群间种子的平均变异系数(8.58%), 表明种子的稳定性高于叶片。叶宽、叶面积与叶片其他性状间多呈显著或极显著相关, 种子千粒重与种子宽、种子体积显著正相关; 而种子和叶片的各性状间多无显著相关性。种子宽、种子体积和种子千粒重随着海拔的增加出现减小的趋势, 种子体积受纬度控制, 随着纬度的增大表现出增大的趋势。     

Seed mass versus seedling performance in Scots pine: a maternally dependent trait

It is generally accepted that larger seeds give rise to seedlings with better performance. On the other hand, the size that a seed reaches is genetically determined by at least two different traits ; the genetic variability of the developing embryo and the genetic variability of the maternal plant. Thus, the relative contributions of these two traits affect seedling performance by influencing seed size. In this paper, I investigate the effect of seed size on seedling performance in the Scots pine ( Pinus sylvestris ). From eight maternal plants, 50 seeds were planted in each of two soil types (800 seeds in total), and seedling performance was monitored for 1 yr. Seed mass proved to be highly constant within maternal plants. Soil type influenced emergence and survival; however, the effect of soil type differed depending on maternal origin. Seed mass was positively correlated with seedling emergence, although this relationship was not found for seedling survival or date of emergence. The initial growth of the shoot was also positively correlated with seed mass. However, after one growing season, seed mass had no effect on seedling performance, which depended exclusively on maternal origin. Nevertheless, the mean mass of seeds produced by plants was positively correlated with mean values of growth parameters. Thus, first-year seedling performance seems to be a maternal trait indirectly associated with seed size.     

Seed weight and seed number affect subsequent fitness in outcrossing and selfing Primula species

Using the outcrossing Primula farinosa and its autogamous selfing relatives P. scotica , P. scandinavica and P. stricta , we compared the fitness of light and heavy seeds. Heavy seeds germinated in greater numbers and more quickly. In competition with seedlings grown from lighter seeds, heavy seeds produced larger rosettes. In P. farinosa such seedlings went on to produce more seeds, and in two populations heavier seeds, than plants from lighter seeds. After transplantation to natural populations, seedlings of P. farinosa derived from heavy seeds produced larger rosettes, more flowers and seeds than those from lighter seeds in certain populations so that seedlings born of heavy seeds were much fitter than seedlings from lighter seeds. Average seed weight varied in inverse proportion to seed number per capsule. The autogamous species produced on average about twice as many seeds per capsule as P. farinosa . In P. scotica and P. stricta this difference appears to be due in part to assured fertilization, but this high fecundity did not cause disadvantageously light seeds. As these species produced fewer capsules per scape, their overall seed production was on average no greater than for P. farinosa . P. farinosa traded-off fitness between capsules with large seed numbers, which donated more offspring to the next generation, and those with small seed numbers, whose heavy seeds would be more likely to reproduce themselves in the next generation. We conclude that low fecundity in outcrossing species might at times be advantageous.     

Within and Between Plant Variation in Seed Number, Seed Mass and Germinability of Primula elatior: Effect of Population Size

Abstract: In this study, natural variation of seed mass and seed number between and within individual plants of P. elatior, a common forest herb on rich soils in Flanders, was investigated for both small (< 50 flowering individuals) and large (> 1000 flowering individuals) populations. The relationship between seed number and seed mass at both the between and within population level was also quantified. We also investigated how population size affected germinability of seeds through the effects of seed mass. Seed number varied by a factor of twenty, whereas seed mass spanned, on average, a 3.5 range. In both cases variation was highest among populations, indicating that population size has important effects on seed number and seed mass. Next, seed number-seed mass tradeoffs were significantly influenced by population size, with small populations showing strong negative relationships whereas in large populations seed mass was only marginally influenced by seed number. As to germination, larger seeds showed larger germination percentages only for the smallest population. In all other populations, seed mass had little effect on germination.     

Patterns of Seed Size,Germination and Seed Viability of Tropical Tree Species in Southern India1

Seed weight, days to germination and seed viability were observed for 99 species growing in the Western Ghats of Karnataka, India. Seed size was strongly correlated with days to germination; smaller seeds germinated faster than larger seeds. Species which flowered during the rainy season had lighter seeds than species which flowered during the dry season. It was also found that seed size and viability of seeds were related to the season of fruiting. Species which fruit during the rainy season had heavier seeds and shorter viability than species which fruit during the dry season. These flowering and fruiting patterns and varying seed sizes are argued to be adaptations to the time of dispersal, time of moisture availability in the habitat and seedling survival.     

祁连山青海云杉天然群体的种实性状表型多样性

 以系统揭示其表型变异程度和变异规律为目的,对祁连山青海云杉(Picea crassifolia )天然分布区的10个群体的8个种实性状进行了比较分析。采用方差分析、多重比较,相关分析、聚类分析等多种分析方法,对群体间和群体内的表型多样性进行了讨论。方差分析结果表明,各种实性状在群体间都存在极显著差异,除球果干质量和球果长/球果径外,其余性状在群体内都存在着极显著的差异;表型分化系数即群体间变异为27.18%,小于群体内的变异(72.82%);球果长、球果径、球果干质量、球果形状指数、种子长、种子宽、千粒重和种子形状指数的变异系数分别为：10.08%、5.80%、19.29%、9.66%、8.38%、15.34%、6.52%和13.94%;8个种实性状间多数呈极显著或显著的正相关,球果干质量、种子长、千粒重、球果长和球果径为青海云杉易测定和重要的种实性状;种实性状呈现出以经度变异为主的梯度规律性;通过表型性状的聚类分析可以将青海云杉10个群体划分为4类。     

晋西北丘陵风沙区不同种植年限柠条的种子形态特征

以晋西北丘陵风沙区不同种植年限(6、12、18、40和50 年)人工柠条的3种大小类型种子为对象,分析不同年限柠条种子形态特征,从繁殖策略的角度探讨人工植被恢复潜力。结果表明:人工柠条的结实量随着种植年限的增加总体呈上升趋势,在种植50年达到最大值(584粒·株^-1);种子长度、种子宽度、种子形状指数随着种植年限的增加总体呈下降趋势,在种植50年达到最小值(5.09 mm、2.76 mm、0.05);种子萌发率随种植年限的增加呈上升-下降-上升的波动变化趋势,在种植12年达到最大值(97.2%)。结实量与种子重量呈显著负相关。种子萌发率与种子重量密切相关,重量小的种子萌发率低,更易于形成持久种子库。相关分析表明,结实量与株高、地上生物量和地下生物量呈显著正相关;种子形状与新枝数呈显著负相关。这表明随着种植年限的增加,柠条繁殖对策由种植前期(6～12年)大种子较多的K策略向种植后期(18～50年)小种子逐渐为主的r策略转变,即柠条既要保证繁殖体数量,又要保证繁殖体的持久性,从而产生了数量更多的小而圆的种子。     

种子休眠机理研究概述

种子休眠是植物本身适应环境和延续生存的一种特性,是种子植物进化的一种稳定对策。野生植物特别是原产温带的植物,其种子大多有深而长的休眠期。关于种子休眠的概念有多种,这些概念引出了许多学说、假说和模型。种壳障碍、胚形态发育不完全和生理后熟以及种子中含有化学抑制剂等,都可导致种子休眠。根据不同的分类标准可将种子分成不同类型,一般将种子分为强迫休眠和机体休眠;机体休眠又可分为外部休眠、内部休眠和综合休眠。植物种类不同休眠特性也不同;同种植物的种子来源于不同的居群和植株时,若采集时期不同,其休眠也可能不同;甚至在同一果实中的不同种子,休眠特性亦可能有差异。影响休眠性状表达的基因既有核基因,也有质基因,休眠通常表现为一种受多基因控制的数量性状。种子休眠具有重要的生态学意义,能有效地调节种子萌发的时空分布。研究种子的休眠特性和机理及其解除方法,有助于农业生产和植物多样性保护。     

Geographic differentiation among populations ofArabis serrata Fr. & Sav. (Brassicaceae)

Geographic variation in morphological traits of thirteen populations ofArabis serrata was analyzed to characterize the life history of each particular population in the field. These localities varied in altitude, topography, soil type, humidity, vegetation structure and degree of disturbance. Twelve morphological characters were measured in each plant, and populations were compared using both univariate and multivariate analyses. Populations showed significant differences for most of the traits measured. Principal component analyses revealed a significant differentiation among populations although a continuous variation for some traits was noted. Length of capsules and leaf length of inflorescence's stalks were correlated with the number of frost free days and with temperature, precipitation and number of days of the growing season. The number of rosettes was also correlated with the same variables but negatively. Seed weight was correlated positively with altitude but negatively with temperature and length of the growing season. Populations were also differentiated according to soil conditions and disturbance regimes distinguishing different types of populations: I) populations with many small rosettes, and few heavy seeds per capsule in volcanic soils with low disturbance; ii) plants with many small seeds and few rosettes in very disturbed localities along asphalt roadways and mountain trails; and iii) large plants with intermediate seed size and intermediate number of seeds per plant in limestone and serpentine soils under different conditions of disturbance. Populations ofA. serrata displayed a complex pattern of differentiation in morphological and life history traits in relation to several biotic and abiotic factors. The quantitative nature of the differences among populations ofA. serrata observed in the field deserves further studies (e.g., quantitative genetics and phenotypic plasticity) under controlled conditions in order to assess the extent of differentiation within this species complex.     

The seed dimorphism of Spergularia marina in relation to dispersal by wind and water

Summary The seeds of the halophyte Spergularia marina differ both within and between individuals in that they either possess or lack a membranaceous border. This paper presents a morphological study of the length, weight and area of the seed types, and their dispersal characteristics under experimental conditions of wind and water dispersal. The winged seeds are shown to be larger both by length and by weight. Their rate of descent increases with wing loading. If the wing is lacking, however, the rate of descent increases with weight only. The distance of dispersal is equal for both seed types except at low wind speeds, when the winged seeds disperse farther. If the seed wing is removed, the excised seeds have shorter dispersal distances. When dispersed by water, a difference in the distance seeds are dispersed can only be detected in the presence of vegetation. The winged seeds are more frequently trapped in the vegetation as compared to the unwinged seeds. The hypothesis that the seed dimorphism is an adaptation for differential dispersal distances is discussed.     

The role of pre- and post-dispersal seed predation in determining total seed loss

Most seed predation studies focus on either pre- or post-dispersal predation and may therefore underestimate the role of predation in regulating plant populations. We therefore estimated total seed predation of an invasive tree, mesquite (Leguminoseae: Prosopis spp.), by examining the entire seed pool from tree to seed bank. The spatio-temporal dynamics of total seed predation was examined by sampling across its Australian distribution and through time. The main predator was a host-specialist multivoltine beetle, Algarobius prosopis L. (Bruchidae), previously introduced as a biocontrol agent. Seed predation exceeded 20% in all seed stages (in pods on and off the tree, and seeds within woody endocarps (capsules) and free seeds on and in the ground) but was consistently highest in capsules on the ground (up to 90%). Pre-dispersal predation contributed little. Total seed predation rates were primarily determined by predation rates on the most persistent seed stage, in this case fallen pods if only pods are considered and seeds in capsules for the total seed pool. This pattern was consistent across the surveyed taxa, regions, years and seasonally. Predation rate was relatively unaffected by seed density, potentially because densities were always low (<150 seeds m⁻²). Average total seed predation within a region reached 55%, but we conclude that any population regulation of mesquite by seed predation will principally be through reduced seed bank persistence. Our results highlight the need to consider the entire seed pool, especially the often cryptic and overlooked long-lived stages, when determining seed loss to predation and its likely population consequences.     

Reproductive indicators in natural populations of Douglas-fir in Mexico

The reproductive capacity in nine Mexican Douglas-fir populations was determined by analyzing seed production traits from 144 trees collected in 2001. Significant variation was found for all traits among populations; they contributed between 21% and 43% of total phenotypic variation found in these traits, indicating broad differences in reproductive capacity for that particular year. Seed efficiency (filled seed/seed potential) varied from 14% to 42% among populations; all populations from Central Mexico had a seed efficiency below 25%. The proportion of developed that were empty seeds varied from 0.40 to 0.81 among populations, whereas seed size varied also from 0.88 to 1.21 g per 100 seeds among them. Average ratio of filled seed weight to cone weight (reproductive efficiency) was 29.6 mg g⁻¹, but it varied three-fold between populations with extreme values. Populations with larger cones had greater seed potential and heavier seed but not necessarily higher reproductive or seed efficiency. Most reproductive indicators were significantly correlated with latitude, with lower values in the marginal populations from Central Mexico, in the southern extreme of the species range. Given these results, the need for conservation of Douglas-fir populations in Central Mexico is discussed.     

Seed dispersal by ants in the semi-arid Caatinga of North-East Brazil

BACKGROUND AND AIMS: Myrmecochory is a conspicuous feature of several sclerophyll ecosystems around the world but it has received little attention in the semi-arid areas of South America. This study addresses the importance of seed dispersal by ants in a 2500-km(2) area of the Caatinga ecosystem (north-east Brazil) and investigates ant-derived benefits to the plant through myrmecochory. METHODS: Seed manipulation and dispersal by ants was investigated during a 3-year period in the Xingó region. Both plant and ant assemblages involved in seed dispersal were described and ant behaviour was characterized. True myrmecochorous seeds of seven Euphorbiaceae species (i.e. elaiosome-bearing seeds) were used in experiments designed to: (1) quantify the rates of seed cleaning/removal and the influence of both seed size and elaiosome presence on seed removal; (2) identify the fate of seeds dispersed by ants; and (3) document the benefits of seed dispersal by ants in terms of seed germination and seedling growth. KEY RESULTS: Seed dispersal by ants involved one-quarter of the woody flora inhabiting the Xingó region, but true myrmecochory was restricted to 12.8 % of the woody plant species. Myrmecochorous seeds manipulated by ants faced high levels of seed removal (38-84 %) and 83 % of removed seeds were discarded on ant nests. Moreover, seed removal positively correlated with the presence of elaiosome, and elaiosome removal increased germination success by at least 30 %. Finally, some Euphorbiaceae species presented both increased germination and seedling growth on ant-nest soils. CONCLUSIONS: Myrmecochory is a relevant seed dispersal mode in the Caatinga ecosystem, and is particularly frequent among Euphorbiaceae trees and shrubs. The fact that seeds reach micro-sites suitable for establishment (ant nests) supports the directed dispersal hypothesis as a possible force favouring myrmecochory in this ecosystem. Ecosystems with a high frequency of myrmecochorous plants appear not to be restricted to regions of nutrient-impoverished soil or to fire-prone regions.     

Variations in Seed Size Within Populations of Silene dioica (L.) Clairv. in Relation to Habitat

The sizes of seeds in populations of Silene dioica were comparedincluding observations on variation within and between plantsin a population growing wild in south-east England. The meanseed weights of different populations from Europe displayedvariations, which contrasted with rather stable means foundin a population sampled in 4 different years, or compared whengrowing under natural conditions or in cultivation. Variationsfrom plant to plant within a population, between populationswithin a particular area, and between different capsules fromthe same plant were similar in range and distribution to thedifferences found between populations. Seed size did not appearto be correlated with season of maturity, level of dormancy,or position on the flower truss, but significant differenceswere found in mean seed weights from different individual plants. The results are discussed in relation to the natural distributionof the species, and its role as an opportunist species inhabitingthe edges of deciduous woodlands. Silene dioica (L.) Clairv., red campion, seed size     

Variation and Allometry of Seed Weight inAeschynomene americana

One hundred and fifty seeds from each of 72Aeschynomene americanapopulationswith world-wide origin were weighed individually and the meanand distribution of seed weight were calculated and comparedbetween populations. Mean seed weight varied less than five-foldbetween populations with about 80% having a mean seed weightbetween 2–3 mg. However, differences between the largestand smallest seeds (2–8 mg) ranged two-17-fold withinpopulations. Populations that had larger mean seed weights alsohad larger maximum and minimum seed weights but not larger standarddeviations than those with smaller mean seed weights. Seed distributionsfor populations with a mean seed weight2 mg were positivelyskewed while those for all populations with a mean seed weight4mg were negatively skewed. Populations that flowered later producedsmaller seeds than those that flowered earlier.Copyright 1998Annals of Botany Company. Seed weight, weight distribution, inter-population variation, correlation among traits,Aeschynomene americana.     

Spatial Variation in the Strength of a Trophic Cascade Involving Ruellia nudiflora (Acanthaceae), an Insect Seed Predator and Associated Parasitoid Fauna in Mexico

Spatial variation in the strength of herbivore top-down control represents an important source of variation in plant fitness measures and community structure and function. By measuring seed predator (larvae of a Noctuid moth) and parasitoid impacts on Ruellia nudiflora across a broad spatial scale in Yucatan (Mexico), this study addressed the following: (1) to what extent does seed predator and parasitoid attack intensity associated with R. nudiflora vary spatially? (2) Does parasitoid attack result in a positive indirect effect on the plant, and does the intensity of this effect vary spatially? During the peak of fruit production (late June–early July) of 2005, we collected fruits from 21 R. nudiflora populations and grouped them into four regions: center, east, north and south. For each fruit we recorded: observed seed number, number of seeds eaten, seed predator presence, parasitoid presence and number of seeds ‘saved’ by parasitoids. Seed predators attacked ca 30 percent of fruits/plant on average, while parasitoids were found in 24 percent of seed predator-attacked fruits. Results indicated spatial variation in seed predator and parasitoid attack levels; interestingly, a contrasting spatial gradient of attack intensity was observed: populations/regions with greatest parasitoid attack levels usually had the lowest seed predator attack levels and vice versa, suggesting top-down control of parasitoids on seed predators. We observed a weak overall indirect impact of parasitoids on R. nudiflora (4% seeds ‘saved’ on average), which nonetheless varied strongly across populations (e.g., close to 14% seeds saved at one population). Findings indicate a geographical structuring of interaction strengths across populations, as well as spatial variation in the strength of parasitoid cascading effects on plant reproduction.     

金线兰种子萌发及其原球茎的增殖培养

研究了影响金线兰种子非共生萌发的因素,并应用正交试验研究基本培养基、6-BA、ZT、NAA四种因素对原球茎增殖的作用。结果表明:授粉类型对金线兰种子非共生萌发影响较大,异株异花、同株异花以及同株同花授粉所得的种子的萌发率分别为78.53%、69.62%、39.87%;蒴果成熟度以生长150d为宜,采收后萌发率可达78.59%;冷藏影响种子的活力,种子的萌发率随冷藏时间的延长而降低;使用次氯酸钠浸泡后的种子与对照相比,其萌发率无明显差异;NAA对原球茎增殖作用显著,适宜于原球茎增殖的培养基为1/2MS+ZT0.5mg/L+NAA1.0mg/L。