The role of fleshy pericarp in seed germination and dispersal under flooded conditions in three wetland forest species

In flooded habitats, inundations affect important forest regeneration processes, such as seed dispersal and germination. The main seed dispersal mechanism used by species in Austral South American temperate swamp and riparian forests is endozoochory, which releases seeds from the fleshy pericarp. Endozoochory could be favorable or unfavorable in wetland habitats, since this mechanism exposes seeds directly to water and can, in some cases, be detrimental to germination. In this study, we studied whether or not the fleshy pericarp favors germination after the flooding period's end. Furthermore, we quantified if the number of days which the fruit was found to be floating related to its germination success. We used the seeds of three common fleshy fruit species of flooded habitats from southern Chile, the trees Luma apiculata and Rhaphithamnus spinosus, and the vine Luzuriaga radicans. We simulated flooding periods of 7, 15, 30 and 45 days submerging seeds, with and without pericarps, in water. We found that the pericarp's presence significantly increased Luma's germination success and significantly decreased that of Luzuriaga. The germination of Rhaphithamnus was low after periods of flooding in both seed treatments, with no significant differences found between them. The fruits could float for an average of one to four weeks, depending on the species, which did not relate to their germination success. These results show that germination was affected by the presence of fleshy pericarps in flooded conditions and furthermore, that flotation allows for hydrochory from one week to one month. We suggest that in swamp forests multiple seed dispersal mechanisms are advantageous, especially for fleshy-fruited species.     

Phloem unloading in developing walnut fruit is symplasmic in the seed pericarp and apoplasmic in the fleshy pericarp

The sieve element-companion cell (SE-CC) complex of the sepal bundles feeding the fleshy pericarp of developing walnut (Juglans regia L.) fruit is structurally symplasmically isolated, but the SE-CC complex of the minor ventral carpellary bundles located in the seed pericarp and feeding the seed is structurally symplasmically connected to its adjacent parenchyma cells. 14C-autoradiography indicated that the phloem of both the sepal and carpellary bundles was functional for unloading. Confocal laser scanning microscopy imaging of carboxyfluorescein unloading showed that the dye is confined to the phloem strands of the sepal bundles in the fleshy pericarp, but released from the phloem strands of the minor ventral carpellary bundles into the surrounding parenchyma cells in the seed pericarp. A 60-kDa acid invertase was immunolocalized to the cell wall of SE-CC complex and parenchyma cells in both the fleshy and seed pericarp. These data provide clear evidence for an apoplasmic phloem unloading pathway in the fleshy pericarp and a predominant symplasmic phloem unloading pathway parallel with a possible apoplasmic path as suggested by the presence of the extracellular invertase in the seed pericarp. A model of complex phloem unloading pathways in developing walnut fruit has been proposed.     

Seed mass and the evolution of fleshy fruits in angiosperms

Fleshy fruits, like drupes and berries, have evolved many times through angiosperm history. Two hypotheses suggest that fleshy fruit evolution is related to changes in the seed mass fitness landscape. The reduced dispersal capability following from an increase in seed mass may be counterbalanced by evolution of traits mediating seed dispersal by animals, such as fleshy fruits. Alternatively, increasing availability and capabilities of frugivores promote evolution of fleshy fruits and allow an increase in seed size. Both these hypotheses predict an association between evolution of fleshy fruits and increasing seed size. We investigated patterns of fruit and seed evolution by contrasting seed mass between fleshy and non‐fleshy fruited sister clades. We found a consistent association between possession of fleshy fruits and heavier seeds. The direction of fruit type change did not alter this pattern; seed mass was higher in clades where fleshy fruits evolved and lower in clades where non‐fleshy fruits evolved, as compared to their sister clades. These patterns are congruent with the predictions from the two hypotheses, but other evidence is needed to distinguish between them. We emphasize the need to integrate studies of seed disperser effectiveness, seed morphology, and plant recruitment success to better understand the frugivores’ role in fleshy fruit evolution.     

Testing Broadcast Seeding Methods to Restore Urban Forests in the Presence of Seed Predators

Forest restoration in urban areas often occurs in isolation from remnant forest, limiting the chances for recolonization by native species. Plants with bird‐dispersed seeds can be particularly vulnerable to dispersal limitation and regeneration can be further impeded by non‐native seed predators. We used a factorial experiment to investigate broadcast seeding as a method to reintroduce trees with large seeds and fleshy fruits into early successional forests. We assessed rates of seed and fruit loss, germination and seedling establishment in three seed treatments: (1) caging to exclude introduced mammalian seed predators; (2) removal of fleshy fruit pericarp; and (3) placing seeds in nutritionally enriched clay balls. Across all species (Beilschmiedia tawa, Elaeocarpus dentatus, and Litsea calicaris) seeds and fruits accessible to mammalian predators suffered significantly greater loss (58%) than those protected by cages (4%). However, seed and fruit loss in the presence of predators was reduced to only 35% across all species by the treatment combining the removal of fruit flesh and clay ball application to seeds. Establishment of B. tawa seedlings after 1 year was significantly enhanced by the clay ball treatment (12% of seeds sown vs. 6% without clay balls). Very low establishment rates were recorded for E. dentatus and L. calicaris. Broadcast seeding was found to be a viable method of improving regeneration of large‐seeded late successional trees and may be a cost‐effective alternative to planting saplings. Seedling establishment can be improved with fruit flesh removal and clay ball treatments, especially in the presence of mammalian seed predators.     

苦槠传播体的萌发特性与种子休眠类型

种子的萌发特性是植物在长期进化过程中形成的一种适应环境变化的固有属性。对种子萌发特性的研究有助于我们理解物种的种群更新和种子育苗。本文旨在阐明我国重要资源植物苦槠（Castanopsis sclerophylla）的种子休眠类型和萌发特性。研究结果发现：①苦槠种子在其果实中占比非常高;②苦槠的果皮限制了种子对水分的吸收;③苦槠果皮阻碍了种子的萌发,除去果皮以后种子能够在较大温度范围内萌发;④除去果皮以后,苦槠种子在低温（15/5 ℃、20/10 ℃）下萌发困难,在25/15 ℃、30/20 ℃和35/25 ℃这3个温度梯度下均能迅速萌发。结果表明,苦槠的传播体（果实）具有物理休眠的特性。因此,壳斗科（Fagaceae）是具有物理休眠和脱水敏感性的一个新纪录科。结合壳斗科的系统发育位置,本研究支持物理休眠是一种较为进化的性状这一假说。     

The grapevine fleshless berry mutation. A unique genotype to investigate differences between fleshy and nonfleshy fruit

In flowering plants, fruit morphogenesis is a distinct process following fertilization resulting in the formation of a specialized organ associated with seeds. Despite large variations in types and shapes among species, fleshy fruits share common characteristics to promote seed dispersal by animals such as organ growth and metabolite accumulation to attract animal feeding. The molecular biology of fruit ripening has received considerable attention, but little is known about the determinism of early fruit morphogenesis and why some fruits are fleshy while others lack flesh. We have identified in grapevine (Vitis vinifera) a mutation we have named fleshless berry (flb) that reduces by 20 times the weight of the pericarp at ripening without any effect on fertility or seed size and number. The flb mutation strongly impaired division and differentiation of the most vacuolated cells in the inner mesocarp. The timing of ripening was not altered by the mutation although the accumulation of malic acid in the green stage was noticeably reduced while sucrose content (instead of hexoses) increased during ripening. The mutation segregates as a single dominant locus. These results indicate that the Flb- mutant is suitable material to advance our understanding of the genetic and developmental processes involved in the differentiation of an ovary into a fruit.     

Seed Removal Rates Under Isolated Trees and Continuous Vegetation in Semiarid Thornscrub

Clearing native vegetation to increase the amount of land available for agriculture in northeastern Mexico has left remnants ranging in size from fragments of continuous vegetation to isolated individual trees. These provide valuable opportunities for restoring larger areas of native vegetation. We explored whether fragmentation of Tamaulipan thornscrub affects the removal of seeds from 12 woody species that encompass a range of sizes and dispersal mechanisms. We tested whether (1) seed removal rates under isolated trees were higher than under continuous vegetation; (2) dispersal structures, such as fleshy pericarps, made some seeds more attractive to seed removers; and (3) microenvironmental variation affected seed removal rates. Seeds were placed under canopies of Texas ebony (Ebenopsis ebano) and Mesquite trees (Prosopis laevigata). Seed removal trials were conducted three times, each trial lasting 30 days. Most seeds were removed in all trials by the end of one month. Seed removal rate was slower under isolated trees. In general, fleshy fruits were removed faster than other fruits; whole fruits and fleshy tissue were removed faster than depulped seeds. In species with fleshy pericarps, acid washing of seeds, to simulate seeds processed in the digestive tract of dispersers, reduced the seed removal rates, suggesting that it would be a good pre‐treatment for restoration efforts.     

Biogeography of seed-dispersal syndromes, life-forms and seed sizes among woody rain-forest plants in Australia's subtropics

Aim To enhance our understanding of the evolutionary interactions between seed‐dispersal syndromes, life‐forms, seed size, and habitat characteristics by studying their association with the regional‐scale distributions of subtropical rain‐forest plants in the context of climatic gradients. Location South‐east Queensland, subtropical eastern Australia (152° E, 26° S). Methods We classified 250 rain‐forest sites into six floristic site‐groups based on their woody plant composition. The resulting classification was strongly associated with variation in rainfall. The distribution of species across the floristic site‐groups was used to assign 568 species to seven habitat classes (one class for ‘widespread’ species, with all other species classified according to the site‐group within which they were most frequent). Species were also classified for three other categorical life‐history factors: three dispersal syndromes based on diaspore morphology (fleshy, wind‐assisted, and unadorned); four life‐forms (trees, shrubs and small trees, tall climbers, and short and shrubby climbers); and four seed‐diameter classes (< 3 mm, ≥ 3 and < 4.5 mm, ≥ 4.5 and < 7 mm, and ≥ 7 mm). We used a basic comparative approach augmented by simple phylogenetically constrained comparisons to assess association between dispersal syndrome, seed size, life‐form, and habitat class. Results Across the rain forests of south‐east Queensland, the proportion of species with fleshy diaspores or of large stature increases with rainfall. High‐rainfall sites also have larger average seed sizes, but the difference in average seed size between high‐ and low‐rainfall sites is small compared with variation within sites. Among species, those with fleshy fruit tend to have larger seeds and to favour high‐rainfall sites. Very few small trees produce diaspores adapted for wind‐assisted dispersal. On average, species with unadorned diaspores have smaller seeds than those with fleshy diaspores. However, within sites, species with unadorned and fleshy diaspores have similar average seed sizes, and some species with unadorned diaspores from high‐rainfall habitats have extremely large seeds. Main conclusions Commonly observed associations between fleshy fruit, larger plants, larger seeds, and productive habitats are apparent within the rain‐forest flora of south‐east Queensland. However, these associations are generally weak and involve complex interactions. For example, the strong tendency for species with fleshy fruit to have larger seeds than those with unadorned diaspores concealed a significant group of species from wetter forests that produce extremely large seeds and unadorned diaspores. The most widespread species in this study tend to be large plants (particularly robust lianes) and to produce fleshy fruit, but they tend not to have relatively large seeds. The association between large seeds, large plants, fleshy fruit and productive habitats is discussed as part of an evolutionary strategy favouring fitness in populations close to carrying capacity. We review some problems with focusing on establishment chances per seed as the driver towards association between large seeds, large plants and productive rain‐forest habitats (the difficult‐establishment hypothesis). Instead we suggest that production of large, short‐lived seeds by long‐lived plants in temporally stable, closed habitats may reflect the limited evolutionary potential for strategies enhancing colonization (e.g. producing large numbers of dormant seeds), thus allowing the establishment benefits of large seeds greater selective influence (the slow‐replacement hypothesis). The association of fleshy fruit with large seeds probably reflects the difficulty of dispersing large seeds by other means (the difficult‐dispersal hypothesis).     

Brief communication: a preliminary study on the influence of physical fruit traits on fruit handling and seed fate by white-handed Titi monkeys (Callicebus lugens)

Callicebus and the pitheciins are closely related; however, differences in their diets and dental morphology suggest that they differ in the use of mechanically protected food. We describe physical traits of fruits consumed by white-handed titi monkeys (Callicebus lugens) and determine their influence on fruit part selection and immediate seed fate after fruit handling. We tested two hypotheses about the effects of mechanical fruit traits on fruit part selection and seed fate: (1) fruits selected for seed consumption are harder than fruits selected for their fleshy parts and (2) consumed seeds are softer than seeds with other fates. In addition, we analyzed the influence of other physical fruit traits on fruit part selection and seed fate. C. lugens included 69 species in its diet, from which it mainly consumed their fleshy parts. It also consumed seeds, alone or with fleshy fruit parts, but most of them ended up close to parent trees after being dropped or spat out. The first hypothesis was supported while the second was rejected, indicating that C. lugens tends to rely on hard fruits for obtaining seeds, while seed hardness had no influence on fruit part selection and seed fate, contrasting with the pattern reported for Pithecia and Chiropotes in other studies. Ripeness was the most influential factor for fruit part and seed fate discrimination. Results suggest a tendency to sclerocarpic foraging in C. lugens when feeding on seeds.     

Effects of the pericarp on imbibition,seed germination,and seedling establishment in seeds of <Emphasis Type="Italic">Hedysarum scoparium</Emphasis> Fisch. et Mey

Four independent experiments were designed to investigate the effects of the pericarp on seed imbibition, dehydration, germination, seedling establishment, and seed longevity in the field in seeds of Hedysarum scoparium Fisch. et Mey. The results showed that the presence of the pericarp decreased seed imbibition rates in the first 6 h, but the seeds attained significantly higher final water content after 24 h of soaking. The pericarp caused seed dormancy, and removal of the pericarp improved the germination percentage to 90 from 44%. In the pot experiment, where the level of moisture was maintained at field capacity (control), seeds with the pericarp removed had significantly improved seedling establishment. However, no statistical differences were observed in seedling establishment when the experiment was repeated under dry conditions at 40% of the field water capacity. The seedling biomass derived from seeds without the pericarp was much higher in the control but the trend was reversed under dry conditions. For seed longevity, 2 months burial in the field killed almost all seeds without the pericarp, while more than 70% of the seeds with the pericarp intact remained viable. These results indicated that the pericarp was beneficial for seedling establishment and seed longevity in arid environments. The results of this study may have practical application in grassland restoration in dry areas, especially for aerial seeding, which has been extensively used in the northern part of China.     

A mechanism for promoting the germination of Zinnia elegans seeds by hydrogen peroxide

H(2)O(2) promotes seed germination of cereal plants such as barley, wheat and rice, and several mechanisms have been proposed for its action [Naredo et al. (1998) Seed Sci. Technol. 26: 675-689]. We investigated the role of H(2)O(2) in the germination of Zinnia elegans seeds. H(2)O(2) promoted seed germination in a dose-dependent manner as did respiratory inhibitors, indicating that H(2)O(2) itself possibly promotes seed germination rather than O(2). Seed germination was promoted by removal of pericarp from seeds or by removal of ethanol-soluble compounds from the seeds with pericarp. The ethanol-soluble compounds suppressed the germination of seeds having no pericarp, and this effect was reversed by H(2)O(2). These findings indicate that oxidation of the germination inhibitor(s) present in the pericarp by H(2)O(2) promotes seed germination. Antioxidants which are derivatives of well-known germination inhibitors suppressed seed germination in a dose-dependent manner, suggesting that, to initiate seed germination, a germination inhibitor(s) should be decomposed by an oxidant such as H(2)O(2).     

内源脱落酸和赤霉素对番茄发育果实和种子水分关系的影响

利用热偶湿度计（ｔｈｅｒｍｏｃｏｕｐｌｅｐｓｙｃｈｒｏｍｅｔｅｒ）研究了野生型、ＧＡ－缺陷型和ＡＢＡ－缺陷型番茄发育过程中果实种子的水分关系,发现除ＡＢＡ－缺陷型种子胶囊和果肉水势变化特殊外,３种类型果实水分状况变化基本一致;在整个发育时期内．前期种子胶囊和果肉水分流向种子,中期种子水分流向种子胶囊和果肉,后期种子和果实间的水势达到平衡。鉴于种胚脱水是一种主动过程,种胚水势一直低于整个种子、种子胶囊和果肉。内源赤霉素可明显增加果实和种子的重量,但对增加种胚溶质的作用不大。由于内源脱落酸可以促使果实成熟和衰老,促进果实细胞解体,大大降低种子胶囊和果肉水势,因而抑制成熟种子在果实内萌发。     

Reproductive ecology of Thymelaea velutina (Thymelaeaceae)- Factors contributing to the maintenance of heterocarpy

Thymelaea velutina (Thymelaeaceae) is a dioecious shrub that presents a unique type of heterocarpy which consists of the simultaneous production of dry and fleshy fruits. It is endemic to the Balearic Islands (Western Mediterranean) and is found both in dunes and mountain areas. The goal of this study was to identify which factors influence the production of both fruit types, examining the variation of their effects at a spatio-temporal scale (comparing two localities in different years). Specifically, we investigated (1) whether pollen limitation influences the type of fruit produced, and (2) the possible differences in seed size, mass, dispersal capacity, seed predation, germination patterns and seedling survival between fruit types. We also examined if the production of fleshy fruits was modified with the application of gibberellins to reproductive branches. Although fleshy fruits were consistently more abundant than dry ones at both populations, their proportion was significantly higher at the site with greater precipitation. The addition of either pollen or gibberellins did not affect the proportion of each fruit type. Seeds in fleshy fruits are consistently larger, heavier and more likely to be dispersed than seeds in dry fruits, but germinability, germination rate and seedling survival was similar among fruit types. Heterocarpy in this species is currently maintained as there is no apparent factor that exerts any strong selective pressure on either fruit type. The two fruit types might even have different `functions', one serving especially for dispersal and population expansion and the other for producing a seed bank that ensures an eventual germination.     

Correlated evolution of diaspore traits and potential frugivore-mediated selection in a fleshy-fruited tropical lineage (Artabotrys,Annonaceae)

Dispersal syndromes are often defined by reference to fruit traits that are associated with distinct frugivore guilds. Studies rarely examine the relationship between seed traits and frugivores or test the alternative hypothesis that traits are shaped by climatic variables. We assess whether the evolution of seed size and physical defense are correlated with dispersal-related traits and climatic variables in Artabotrys, a fleshy-fruited tropical lineage. Diaspore traits and WorldClim bioclimatic variables were compiled for 43 species. Correlated evolution was evaluated using phylogenetic regression and model-fitting approaches. The best-fitting multioptima Ornstein-Uhlenbeck model suggests that lineages with smooth testa and thin pericarp (SP) have evolved toward smaller seeds with a thinner testa, whereas lineages with rough testa and/or thick pericarp have evolved toward larger seeds with a thicker testa. A smooth testa facilitates spitting and/or swallowing of intact seeds while fruits with thin pericarp may be preferentially consumed by frugivores with less destructive oral processing, enabling lower investment in seed physical defense in SP lineages. Moreover, small seeds are more likely to be swallowed intact with a food bolus. The effect of climate on seed size and physical defense is equivocal and warrants further investigation.     

Seed and 4-chloroindole-3-acetic acid regulation of gibberellin metabolism in pea pericarp.

In this study, we investigated seed and auxin regulation of gibberellin (GA) biosynthesis in pea (Pisum sativum L.) pericarp tissue in situ, specifically the conversion of [14C]GA19 to [14C]GA20. [14C]GA19 metabolism was monitored in pericarp with seeds, deseeded pericarp, and deseeded pericarp treated with 4-chloroindole-3-acetic acid (4-CI-IAA). Pericarp with seeds and deseeded pericarp treated with 4-CI-IAA continued to convert [14C]GA19 to [14C]GA20 throughout the incubation period (2-24 h). However, seed removal resulted in minimal or no accumulation of [14C]GA20 in pericarp tissue. [14C]GA29 was also identified as a product of [14C]GA19 metabolism in pea pericarp. The ratio of [14C]GA29 to [14C]GA20 was significantly higher in deseeded pericarp (with or without exogenous 4-CI-IAA) than in pericarp with seeds. Therefore, conversion of [14C]GA20 to [14C]GA29 may also be seed regulated in pea fruit. These data support the hypothesis that the conversion of GA19 to GA20 in pea pericarp is seed regulated and that the auxin 4-CI-IAA can substitute for the seeds in the stimulation of pericarp growth and the conversion of GA19 to GA20.     

甜荞果皮开裂类型及其对籽粒早期萌发性状的影响

甜荞是我国传统的药食同源植物,籽粒是甜荞的重要贮藏器官,籽粒果皮的开裂类型及其开裂行为影响种子的萌发性状。该研究以5份甜荞为材料,进行果皮裂口的建模与分型,并通过纸床发芽法,检测种子的发芽率、胚根及下胚轴长度。结果表明:(1)甜荞籽粒果皮开裂主要包括纵向完全开裂型、种孔端部半开裂型、种脊中部半开裂型、种脐端部半开裂型和横裂型等5种类型;(2)开裂型籽粒比完整型萌发时间提早约12 h;(3)开裂型籽粒早期萌发率均高于相应的果皮完整型,但48 h后,完整型籽粒的萌发率超过果皮开裂型;(4)开裂型籽粒胚根及下胚轴的早期增长速度比完整型快,但果皮开裂型籽粒胚根与下胚轴增长比值显著小于果皮完整型;(5)不同开裂类型的萌发率从大到小依次为种孔端部半开裂型、纵向完全开裂型、种脐端部半开裂型、种脊中部半开裂型、横裂型,而种子霉烂率从大到小依次为种脐端部半开裂型、纵向完全开裂型、种脊中部半开裂型、种孔端部半开裂型、横裂型。果皮开裂虽然可以提高甜荞种子早期的萌发率,促进胚根及下胚轴早期的伸长速度,但会降低甜荞整体的萌发率以及胚根/下胚轴增长比值,种子霉烂率显著增加,不利于田间壮苗与全苗的形成。     

水稻红米的遗传分析与组织学研究

用来源于倍加单倍体的红米水稻（rdh）与无色米水稻做正反交,结果表明：杂种F1种子颜色由其所着生的母体植株基因型决定.当rdh作母本时,所结下的F1种子全是红色,当蜀恢527,蜀恢168,蜀恢368三个具有无色颖果皮（简称无色米）水稻作母本时,所结下的F1种子全是无色的.而且不管母本有没有颜色,所产生的F2种子都是红色,F3代产生红色种子与无色种子的单株分离,而且红色种子的单株对无色种子的单株是3：1（1%水平达极显著）,根据杂种F1、F2和F3代种子颜色和植株分离比例,rdh种子红色表现型是由单显性基因控制的,并受母性影响.组织学研究发现rdh颖果皮有3个基本的结构层：果皮、种皮和糊粉层.果皮是类黄酮色素累积的部位,红色色素就在果皮层累积.在未成熟的种子中,种皮是累积叶绿素的部位,在成熟种子中叶绿素消失.在未成熟的种子中,糊粉层白色.显微镜分析灌浆期的rdh种子不显红色,而显绿色,绿色来自于种皮,果皮无色透明.风干期的rdh种子显示：红色色素在果皮层累积,同期种皮的绿色清晰可见.rdh成熟种子红色色素急剧增加,同期绿色渐渐消失,最后肉眼观测不到.组织切片显示种子外皮中,果皮是最厚的一层,糊粉层次之,种皮最薄.果皮外层由4列较小的长方形细胞构成,里层由5～8列不规则的细胞构成.种皮由3列薄壁细胞构成.糊粉层由5～8列椭圆形细胞构成.色素累积的发育时间实验显示红色的沉积是从种子风干期开始到完全成熟期为止.在蜀恢527无色种子中,绿色色素从受精后开始积累,到风干期达到最深;然后绿色开始变浅,成熟种子中没有绿色.比较而言,rdh种子在发育早期,从灌浆到风干期呈现的颜色与蜀恢527相同,均是绿色;但从风干期开始,较多的红色色素开始累积,到种子接近成熟,红色仍在加深,这时种皮的绿色还隐约可见;直到种子完全成熟,红色达到最深,同时绿色渐渐消失.     

异子蓬二型种子的萌发与休眠特性及其生态适应

异子蓬为中亚荒漠的特有种,其果实为胞果,花被片在结果时宿存包被果实形成浆果状的散布单位.对异子蓬的散布单位、果实形态进行比较观察,并在5/15℃、5/25℃、15/25 ℃(暗/光=12h/12h)3个温变周期下进行种子萌发实验,结果表明:(1)异子蓬的散布单位绿色、浆果状,有大小两种形态;大小两种散布单位内包被的果实在形状、大小、颜色上存在着明显差异.(2)大的散布单位内包被的果实圆形,扁平,褐色,无光泽,直径(2.64±0.03) mm,重量(3.68±0.04) mg;小的散布单位内包被的果实双凸镜形,黑色,有光泽,直径(2.40±0.04) mm,重量(2.86±0.06) mg.(3)褐色种子在3个温变周期下的萌发率都在81%以上,萌发速度快,而黑色种子萌发率低,萌发慢,具有休眠现象.(4)划破种皮及低温层积处理可显著提高黑色种子在3个温变周期下的萌发率,延长储存时间也可有效地促进黑色种子的萌发,表明黑色种子处于非深度生理休眠状态.异子蓬产生的两种不同类型的种子及其在时间和空间上的萌发差异对荒漠异质环境具有重要的适应意义.     

Hardness as a basis of fruit choice in two sympatric primates

Fruit color and size are significant determinants of food choice in mammals and birds, but hardness, an important physical property of fruit and seeds, has generally been overlooked as a determinant of food choice in studies of mammalian foraging behavior. Two methods were used to determine fruit hardness during a field study of two sympatric primates, the black spider monkey (Ateles paniscus) and the bearded saki monkey (Chiropotes satanas) in Surinam. We measured both puncture resistance of fruit pericarp and crushing resistance of seeds. Puncture resistance of the pericarp of some fruit opened by Chiropotes was as much as 15 times greater than that of all fruit successfully opened by Ateles. In contrast, crushing resistance of species of seeds masticated by Chiropotes was significantly lower than that of seeds swallowed by Ateles. These data demonstrate that hardness of both fruit pericarp and seed may play a significant role in food choice among sympatric vertebrates. Measurements of both puncture resistance of the pericarp and crushing resistance of the seed are necessary for understanding the significance of fruit hardness in these primates.     

Seed arrival under different genera of trees in a neotropical pasture

Trees in pastures attract seed dispersers, leading to increased seed arrival under their canopies and more rapid regrowth around them. The characteristics that make some trees better `recruitment foci' than others, however, are poorly understood. In a neotropical pasture, we examined the arrival of seeds to open areas and underneath four genera of trees that varied in canopy architecture and type of fruit produced: Ficus trees had dense canopies and fleshy fruits, Pentaclethra trees had dense canopies and dry fruits, Cecropia trees had sparse canopies and fleshy fruits, and Cordia trees had sparse canopies and dry fruits. We found that all trees received more seeds than open pasture, probably because trees provided seed dispersers with better perches, protection from predators, nesting sites, etc. Among the tree genera, more seeds arrived under trees that produced fleshy fruits than trees that did not. This occured even during periods when trees were not fruiting (i.e., non-fruiting Ficus and Cecropia trees received more seeds than Cordia or Pentaclethra trees). Seed dispersers may periodically check Ficus and Cecropia trees for fruits, or they may become familiar with these trees while feeding and thereafter use them for other reasons. Height of trees had a slight positive effect on seed arrival, possibly because taller trees offered more protection from predators. Canopy architecture and distance to forest edge did not significantly affect seed arrival. This study demonstrates that trees in general are potentially important recruitment foci, but that different types of trees vary in the kind of recruitment that they foster in pastures.