青檀种子休眠机理及发芽条件的探讨

对青檀 (PteroceltistatarinowiiMaxim .)种子的休眠机理和发芽条件进行了探讨。共设定 5个处理 :剪破种皮、热水处理 (4 0、5 0、6 0和 70℃ )、剪破种皮并变温层积 (0～ 4℃ 16h与 10～ 15℃ 8h)、低温层积 (0～ 4℃ )和变温层积(0～ 4℃ 16h与 10～ 15℃ 8h)。结果表明 ,剪破种皮、剪破种皮并变温层积和热水处理与对照的发芽率均无显著差异 ,说明青檀种子的休眠不是种皮限制所引起的。低温层积和变温层积处理均能打破种子的休眠 ,因而认为青檀种子休眠属于生理休眠。低温层积以 70d为最好 ,发芽率和发芽势分别达 6 7%和 5 5 % ;变温层积以 40d处理效果最好 ,发芽率和发芽势分别达 77%和 5 7%。同时还讨论了 2种层积处理的优缺点     

短梗南蛇藤种子的萌发特性

本文观察了短梗南蛇藤种子的形态和萌发过程,研究了温度、层积方法和时间、假种皮浆液、光照等对短梗南蛇藤种子萌发的影响。结果表明,短梗南蛇藤种子对温度较敏感,较适合萌发的温度为15～20℃。低温层积和变温层积均能显著提高种子发芽率、发芽势和发芽指数,层积20d效果最好。假种皮浆液联合层积处理对种子萌发有显著促进作用,其中联合低温层积20d或联合变温层积10d效果最好。光照在一定程度上抑制种子萌发。     

东北刺人参种子萌发影响因子的研究

东北刺人参(Oplopanax elatus Nakai)种子透水性良好,休眠后萌发不受其影响.种皮和胚乳的水提取物中存在萌发抑制物质,胚乳中提取物对白菜种子萌发的抑制效果比种皮更明显.种子自然脱落时胚尚未分化完全,处于心形胚阶段.种子需要先温暖层积以完成胚的分化与生长,然后转入低温层积完成生理后熟.同批种子胚的发育不完全同步,变温层积处理7个月有极少数种子萌发,连续变温层积处理17个月大部分种子萌发.不同年份受气候条件影响,种子产量和发芽率差异较大.种子耐贮性较强,贮藏2年的种子生活力变化不大,仍具有较高的萌发潜力.     

东北刺人参种子萌发影响因子的研究

东北刺人参(Oplopanax elatus Nakai)种子透水性良好,休眠后萌发不受其影响。种皮和胚乳的水提取物中存在萌发抑制物质,胚乳中提取物对白菜种子萌发的抑制效果比种皮更明显。种子自然脱落时胚尚未分化完全,处于心形胚阶段。种子需要先温暖层积以完成胚的分化与生长,然后转入低温层积完成生理后熟。同批种子胚的发育不完全同步,变温层积处理7个月有极少数种子萌发,连续变温层积处理17个月大部分种子萌发。不同年份受气候条件影响,种子产量和发芽率差异较大。种子耐贮性较强,贮藏2年的种子生活力变化不大,仍具有较高的萌发潜力。     

珍稀植物青檀种子休眠与萌发的研究

为了探讨和研究青檀种子休眠和萌发特性,采用石蜡切片法、生物鉴定(白菜籽发芽实验)法、赤霉素溶液浸种、以及赤霉素与低温层积相结合等方法,寻找引起青檀种子休眠的原因和解除休眠的最佳措施。结果表明:青檀种子本身含有发芽抑制物和存在生理后熟是引起休眠的2个主要原因,用质量浓度为300mg/L的赤霉素溶液浸种24h或低温层积后用赤霉素处理均能在一定程度上解除休眠促进萌发,其中以低温层积25d后用500mg/L的赤霉素浸种36h效果最好。发芽率和发芽势分别达到83.5%和65%。     

曼陀罗种子休眠机理与破眠方法研究

通过对曼陀罗种子生活力测定、发芽试验、吸水率测定及种子萌发抑制物研究,揭示曼陀罗种子休眠机理,并利用物理、化学法处理曼陀罗种子,以探寻打破曼陀罗种子休眠的最佳方法.结果表明:(1)新采收的曼陀罗种子为综合休眠,休眠原因包括:种皮障碍、缺少萌发所需激素以及种皮和种仁中存在萌发抑制物,其中种皮障碍是限制种子萌发的首要因素.(2)室温存储6个月可解除曼陀罗种子种仁的休眠,但种皮障碍始终是其种子萌发的限制因素.(3)机械摩擦、浓H2SO4处理和NaOH处理均可打破除曼陀罗种皮的休眠障碍,促进种子萌发,其中用10% NaOH处理90 min为破除曼陀罗种皮休眠障碍的最佳方法,且发芽率比对照提高了83%.     

不同天然居群小檗种子萌发障碍因子研究

以西天山野果林霍城居群、新源居群和特克斯居群黑果小檗以及特克斯居群红果小檗种子为试验材料,研究了4组野生小檗种子生物学特性、吸水特性以及去种皮、低温层积和不同浓度GA₃处理对小檗种子休眠与萌发特性的影响,结果表明：（1）4组野生小檗种子的吸水率均表现出逐渐增加的趋势,黑果小檗种子与红果小檗种子吸水率差异不明显,其种皮透水透气性相似;（2）霍城居群、新源居群和特克斯居群黑果小檗种子的种皮对萌发存在强烈的抑制作用;而新源居群红果小檗种子的种皮抑制作用不明显;（3）4℃低温层积处理对4组野生小檗种子萌发影响很大,随层积时间的增加小檗种子发芽率均逐渐提高,3组黑果小檗种子层积90 d时,休眠基本被解除;红果小檗种子层积30 d时,休眠基本被解除;（4）浓度为200 mg·L^-1的GA₃溶液处理可显著提高4组小檗种子发芽率,浓度过高或过低均会对小檗种子萌发起到抑制作用。层积60 d时霍城居群、新源居群和特克斯居群黑果小檗去种皮种子用200 mg·L^-1的GA₃溶液处理2 h后,发芽率分别为85.00%、83.33%和86.67%;红果小檗层积15 d时去种皮种子用浓度为200 mg·L^-1的GA₃溶液处理后,发芽率可达86.67%。研究结果将为今后野生小檗的种质资源保护,利用及可持续发展提供技术支持和科学依据。     

影响琼花种子休眠的因素

琼花种皮有吸水性,休眠非因种皮的不透水性造成.种仁中存在导致休眠的抑制物质,胚的抑制物质含量最高.种子须先经4℃低温层积60 d,再经25℃暖温处理90 d,而后在较低温(15℃)条件下才能解除休眠而萌发.当年成熟种胚在翌年10月才能彻底破除休眠.6-BA和GA对种胚破眠均无明显作用.     

不同处理方法对油楠成熟和过熟种子萌发特性的影响

为破除油楠(Sindora glabra Merr.ex de Wit)种子的物理休眠,研究不同处理方法对油楠种子萌发特性的影响。结果表明,所有处理方法对油楠成熟和过熟种子萌发均产生显著影响。40℃热水和50 mgL~(-1)萘乙酸有利于成熟种子的萌发,发芽率超过55%,较对照显著提高约10%,而其他方法处理的成熟种子发芽率为4.0%~46.0%,低于对照。采用98%浓硫酸浸泡25 min最有利于过熟种子的萌发,其发芽率、发芽势和发芽指数分别较对照显著提高90%、76%和7以上,且发芽时间显著缩短了9 d,对过熟种子处理的其他方法均能不同程度地促进萌发。因此,对于成熟种子,推荐采用低温热水浸泡或弱腐蚀性的化学处理;而对于过熟种子,宜采用浓硫酸浸泡25 min的处理。     

绞股蓝种子休眠机理及其破除方法研究

以采自广西金秀县的绞股蓝种子为研究材料,对其休眠原因、休眠类型及其破眠方法进行了研究,为绞股蓝种子繁殖提供理论依据和技术支持。结果表明:(1)绞股蓝新采收成熟种子的生活力达91%,在10℃~35℃恒温和15℃/25℃变温中的发芽率均低于10%,新种子的生活力极显著大于发芽率,具有显著的休眠现象。(2)绞股蓝种皮不限制吸水,胚分化发育完全,离体胚发芽率为(78.0±4.8)%,且能够长成正常幼苗,说明绞股蓝种子的胚在离体条件下无休眠现象。(3)绞股蓝完整种子及其粉碎种子的水提液对白菜种子的萌发率、苗高及根长均有抑制作用,随水提液浓度增加抑制作用均显著增强,且粉碎种子的抑制作用较强;当粉碎种子的水提液浓度为5%时白菜种子萌发率、苗高、根长分别为18.0%、0.1cm、0.1cm,分别显著低于对照77.1%、97.3%、95.8%,说明绞股蓝种子的种皮和胚乳中存在水溶性萌发抑制物质,是绞股蓝种子休眠的主要原因。(4)GA3和6-BA不能促进绞股蓝种子萌发,低温层积对绞股蓝种子休眠的解除具有促进作用;绞股蓝种子的休眠属于生理休眠类型,休眠水平属于中间型。(5)低温干藏能够打破绞股蓝种子休眠,是绞股蓝种子破除休眠及种子保存较为理想的方式。     

Seed size selection by olive baboons

Seed size is an important plant fitness trait that can influence several steps between fruiting and the establishment of a plant’s offspring. Seed size varies considerably within many plant species, yet the relevance of the trait for intra-specific fruit choice by primates has received little attention. Primates may select certain seed sizes within a species for a number of reasons, e.g. to decrease indigestible seed load or increase pulp intake per fruit. Olive baboons (Papio anubis, Cercopithecidae) are known to select seed size in unripe and mature pods of Parkia biglobosa (Mimosaceae) differentially, so that pods with small seeds, and an intermediate seed number, contribute most to dispersal by baboons. We tested whether olive baboons likewise select for smaller ripe seeds within each of nine additional fruit species whose fruit pulp baboons commonly consume, and for larger seeds in one species in which baboons feed on the seeds. Species differed in fruit type and seed number per fruit. For five of these species, baboons dispersed seeds that were significantly smaller than seeds extracted manually from randomly collected fresh fruits. In contrast, for three species, baboons swallowed seeds that were significantly longer and/or wider than seeds from fresh fruits. In two species, sizes of ingested seeds and seeds from fresh fruits did not differ significantly. Baboons frequently spat out seeds of Drypetes floribunda (Euphorbiaceae) but not those of other plant species having seeds of equal size. Oral processing of D. floribunda seeds depended on seed size: seeds that were spat out were significantly larger and swallowed seeds smaller, than seeds from randomly collected fresh fruits. We argue that seed size selection in baboons is influenced, among other traits, by the amount of pulp rewarded per fruit relative to seed load, which is likely to vary with fruit and seed shape.     

Removal of seeds from frugivore defecations by ants in a Costa Rican rain forest

At our Costa Rican field site, seeds defecated by frugivorous birds usually do not remain where they have been deposited. Many species of ants are attracted to frugivore defecations and remove seeds and/or pulp. Pheidole species selectively remove seeds, fungus-growing species (tribe Attini) remove both pulp and seeds. Seeds of many Melastomataceae have an appendage, which we hypothesized is an elaiosome. Indeed, preference trials demonstrated that two species of Pheidole selected seeds with the appendage over seeds of the same species in which the appendage had been removed. However, we found that these ants did not take the appendage when it was offered by itself. We conclude that the appendage is not an elaiosome. In further trials, different ant species preferentially selected different seed species. These ants consumed some seeds and deposited others unharmed in refuse piles. We conclude that because the composition of leaf-litter ant communities is highly variable between neighboring square meter plots, and the probability of seed predation depends upon the species of ant, the over-all effect of ants on seed shadows and seed banks is spatially unpredictable. Addendum: The names of the two Pheidole emphasized in this study. P. nebulosa and P. nigricula, are unpublished names from a generic revision being prepared by E. O. Wilson and W. L. Brown. Their use here is not intended to constitute taxonomic publication but is solely for more precise indentification in future ecological research of similar nature     

Structural aspects of ovule and seed development and nonrandom abortion inMelilotus officinalis (Fabaceae)

Summary Only one ovule matures into a seed inMelilotus officinalis. Although eight ovules form within an ovary, only the basal ovule develops into a mature seed, whereas the other ovules degenerate. The investigation of ovule and seed structure at different developmental stages and a comparison of quantitative characters of differently fated ovules within an ovary were undertaken by light, phase contrast, and fluorescence microscopy. In this species, campylotropous ovules develop simultaneously on marginal placentae in an apocarpous unilocular gynoecium. Megasporo- and megagametogenesis proceed normally and are completed in bud. The maturation of the Polygonum type embryo sac takes place after the flower opens. Shortly before fertilization, synergids show signs of degeneration in all ovules. At this stage, neither the structure nor the sizes of ovules within one ovary differ significantly. In spite of this, only the basal ovule develops into a seed. Rarely, one of the upper-situated ovules or the basal and another ovule mature into seeds. Seed enlargement is insignificant until the stage when globular embryo and nuclear endosperm are formed. At the seed-filling stage, other ovules have collapsed and the seed gradually comes to occupy the total volume of the pod. The fruit-to-seed length ratio decreases considerably during seed ripening. At fertilization, ovary length is four times greater than ovule length. In the mature state, the fruit and seed lengths are approximately equal. Seed size and weight diminish with an increase in seed number within a pod, although pod size remains constant. It is assumed that nonrandom abortion of young seeds inM. officinalis is under maternal control and is not related to structural abnormalities in ovule development or with limitation in pollen. We suppose that evolution of this species may have proceeded in the direction of a decrease in seed number and an increase in its sizes, which may play an important role in seed dispersal and seedling establishment.     

Seed germination and dormancy in the medicinal woodland herbs Collinsonia canadensis L. (Lamiaceae) and Dioscorea villosa L. (Dioscoreaceae)

We used a double germination phenology or “move-along” experiment (sensu Baskin and Baskin, 2003) to characterize seed dormancy in two medicinal woodland herbs, Collinsonia canadensis L. (Lamiaceae) and Dioscorea villosa L. (Dioscoreaceae). Imbibed seeds of both species were moved through the following two sequences of simulated thermoperiods: (a) 30/15 °C→20/10 °C→15/6 °C→5 °C→15/6 °C→20/10 °C→30/15 °C, and (b) 5 °C→15/6 °C→20/10 °C→30/15 °C→20/10 °C→15/6 °C→5 °C. In each sequence, seeds of both species germinated to high rates (>85%) at cool temperatures (15/6 and 20/10 °C) only if seeds were previously exposed to cold temperatures (5 °C). Seeds kept at four control thermoperiods (5, 15/6, 20/10, 30/15 °C) for 30 d showed little or no germination. Seeds of both species, therefore, have physiological dormancy that is broken by 12 weeks of cold (5 °C) stratification. Morphological studies indicated that embryos of C. canadensis have “investing” embryos at maturity (morphological dormancy absent), whereas embryos of D. villosa are undeveloped at maturity (morphological dormancy present). Because warm temperatures are required for embryo growth and cold stratification breaks physiological dormancy, D. villosa seeds have non-deep simple morphophysiological dormancy (MPD). Neither species afterripened in a 6-month dry storage treatment. Cold stratification treatments of 4 and 8 weeks alleviated dormancy in both species but C. canadensis seeds germinated at slower speeds and lower rates compared to seeds given 12 weeks of cold stratification. In their natural habitat, both species disperse seeds in mid- to late autumn and germinate in the spring after cold winter temperatures alleviate endogenous dormancy.     

Phenotypic plasticity and population differentiation in seeds and seedlings of the grass Anthoxanthum odoratum

Summary Seeds of Anthoxanthum odoratum were transplanted reciprocally between a xeric and a mesic field population that were genetically differentiated in adult traits. In one experiment seeds were reciprocally buried in bags in the soil, in a second experiment seeds were reciprocally sown in small plots. For most traits, site effects were much larger than seed-source effects. Germination, emergence, mortality of buried seed and recruitment were significantly higher at the xeric site than at the mesic site, irrespective of population of origin. Seed dormancy, was significantly higher for seed originating from the mesic than from the xeric population. Seedling recruits originating from the xeric population tended to be larger at both sites. Fecundity of seedling recruits depended on the environment; fecundities of plants growing in the xeric site had more than double the fecundity of plants growing in the mesic site. Phenotypic plasticity rather than population differences determined variation in performance in the seed and seedling stages.     

Alternative seed-handling strategies in primates: seed-spitting by long-tailed macaques (Macaca fascicularis)

Summary The seeds in fruits consumed by primates may be chewed and digested, swallowed and defecated intact, or separated from the flesh and spat out. We show by a combination of close field observations and experiments with caged animals, that long-tailed macaques (Macaca fascicularis) have a remarkably low threshold of 3–4 mm for swallowing seeds and also that wild macaques rarely break them. The seeds of 69% of the ripe fruit species eaten are spat out intact or cleaned outside the mouth and dropped. Seed-spitting significantly reduces the swallowed food bulk and may lessen the risk of releasing seed toxins during mastication. However, it requires that even small fruits are processed in the mouth one or a few at a time. We suggest that fruit storage in the cheek pouches of cercopithecine monkeys allows them to spit seeds individually without excessively slowing fruit intake while feeding on patchily distributed fruit. In contrast, Apes and New World monkeys apparently swallow and defecate most ripe seeds in their diet and colobine monkeys break and digest them, detoxifying seed defenses by bacterial fermentation.     

Seed coat anatomy ofCrossostylis (Rhizophoraceae): its evolutionary and systematic implications

The seed coat structure of all 13 species ofCrossostylis was studied to contribute to an understanding of species delimitation and relationships within the genus. The mature seed coat is relatively uniform and consistently constructed mainly by a well-developed exotesta and a well-developed fibrous exotegmen. The species differ in the thickness of the exotesta and exotegmen, the anatomy of exotestal cells, the presence and absence of persistent mesotesta, and so forth. On the basis of comparisons of these characters, close relationships are suggested in the species groups such as:Crossostylis banksiana andC. cominsii; C. biflora, C. raiateensis andC. multiflora; C. gandiflora, C. sebertii andC. imera; and five species in the Fiji Islands. These relationships except for those of Fijian five species are also supported by cladistics as their common characters are evaluated as synapomorphy. Species-level separation ofC. banksiana, C. pedunculata andC. raiateensis each from the closest species is doubted based on the results of seed coat structure.     

Aggregated seed dispersal by wreathed hornbills at a roost site in a moist evergreen forest of Thailand

Hornbills (Bucerotidae) are widely regarded as important seed dispersers in tropical forests in Africa and Asia. We investigated how the roosting behavior of wreathed hornbills (Aceros undulatus) influences seed deposition and seedling survival at a roost site in a moist evergreen forest of Khao Yai National Park, Thailand. Fallen fruits and seeds were collected in traps that were placed around a roosting site for 14 months, and seedlings were monitored in adjacent quadrats for 3 years. Seedfall and seedlings of species represented in the hornbill diet occurred at significantly higher densities in the traps and quadrats located beneath the crown of the roosting tree than in those located beyond the crown. With the exception of Cinnamomum subavenium, the seeds and seedlings of most diet species rarely survived beyond the first year. The quality of hornbill dispersal to this roosting site may be poor due to the highly concentrated seedfall, which results in high seed and seedling mortality. However, the number of seeds deposited by each hornbill each day at roosting sites is relatively low. Wreathed hornbills are primarily scatter dispersers during the day and probably serve as agents of seed dispersal in the moist evergreen forest of Khao Yai.     

Allometric allocation in fruit and seed packaging conditions the conflict among selective pressures on seed size

Selective pressures on seed size could vary among the different stages of plant life cycles, so no simple relation could explain a priori its evolution. Here, we determined the relationships between seed size and two fitness components—seed dispersal and survival from predation—in a bird-dispersed tree, Crataegus monogyna. We interpret these relationships in relation to the patterns of mass allocation to fruit and seed components. Selection patterns were assessed at two levels (1) selection pressures on the parent tree; comparing seed dispersal efficiency among individual plants and (2) selection pressures at the individual seed level; comparing seed size variation (i) before and after dispersal, and (ii) before and after postdispersal seed predation. Dispersal efficiency (percentage of seed crop dispersed) was positively correlated with fruit mass and fruit width. Differences in crop size did not offset this effect, and larger seeds were overrepresented in the seed rain relative to the seed pool before dispersal. However, the advantage of larger seeds during the dispersal stage was cancelled later by an opposite selection pressure exerted by seed predators. As a result, smaller seeds had a higher probability of surviving postdispersal seed predation, establishing an evolutionary conflict imposed by the need for dispersal and the danger of being predated. Birds and rodents preferentially selected highly profitable fruits and seeds in terms of the relative proportion of their components. Larger fruits had a higher pulp to seed proportion than smaller ones, and all seeds had the same proportion of coat relative to the embryo-plus-endosperm fraction. Hence, although predator pressures were stronger than disperser ones, larger seeds invested proportionally less in structural defense than in dispersal.     

The effects of seed abundance on seed predation and dispersal by rodents in <Emphasis Type="Italic">Castanopsis fargesii</Emphasis> (Fagaceae)

Based on the animal dispersal hypothesis and the predator satiation hypothesis, we examined the effects of seed abundance at both population (i.e., mast seeding) and community levels on seed predation and dispersal of Castanopsis fargesii (Fagaceae), a rodent-dispersed mast species in Eastern Asia. In a subtropical evergreen broadleaved forest in the Dujiangyan region of Sichuan Province, China, individual seeds with coded tin tags were tracked in two contrasting stands (seed-poor and seed-rich) over two years (2000, a low-seed year; 2001, a high-seed year). Our results showed that: (1) small rodents did not harvest the tagged seeds of C. fargesii more rapid in the high-seed year than in the low-seed year in either stand. But, seed harvest was significantly faster in the seed-rich stand than in the seed-poor stand. (2) The removal proportion was significantly lower in the high-seed year than in the low-seed year for either stand, but the removal proportion was slightly higher in the seed-poor stand than in the seed-poor stand. This indicates that high seed abundance decreases seed removal (predator satiation hypothesis). (3) There were only small differences about seed caching, seed survival and seedling establishment of C. fargesii between years and stands. During the survey, no cached seeds survived to geminate in the spring for both stands and years. (4) Mean dispersal distances of the cached seeds are much shorter in the high-seed year (3.1 m) than in the low-seed year (8.1 m) in the seed-rich stand, though similar trend is not examined in the seed-poor stand. Our results indicate that seed predation and dispersal of C. fargesii are influenced by both mast seeding and community-level seed abundance, which is not completely consistent with either the animal dispersal hypothesis or the predator satiation hypothesis, but seems more related to the predator satiation hypothesis.