Ecophysiological characteristics of the seed of the tropical forest pioneer Urera caracasana (Urticaceae)

Urera caracasana (Jacq.) Griseb is a small, fast-growing evergreen pioneer tree which colonizes openings in the tropical rain forest of 'Los Tuxtlas', Veracruz, Mèxico. Annual seed production by 10 trees was estimated to range from 0.4 x 10(5) to 1.6 x 10(6) seeds per tree. Fifteen species of resident and migratory birds were observed to visit the plants and disperse the seeds. Most seeds imbibed in petri dishes placed on the forest floor beneath a small opening in the canopy, where the red/far-red ratio of the light was around 1.0, germinated within 2 weeks. Germination beneath the forest canopy, where the red/far-red ratio of the light was approximately 0.2, was much slower and did not exceed 40%. A minimum of 4 h daily exposure to unfiltered natural light was required for rapid germination in the forest. In the laboratory rapid germination at 25 degrees C required a minimum of 4 h white light. However, if temperature during the light period was 35 degrees C, 30 min exposure to white light daily was sufficient to induce germination. Seeds that failed to germinate when imbibed for 60-360 days in petri dishes placed on the forest floor beneath the forest canopy, germinated rapidly in the laboratory when held at 25 degrees C and exposed daily to 12 h white or red light. Seeds imbibed for 120 days or more beneath the forest canopy were also induced to germinate by 12 h daily exposure to far-red light when this was combined with a 35/25 degrees C day/night temperature regime. Seeds buried in vermiculite-filled nylon mesh bags disappeared rapidly with few remaining after 2 months. Seeds that survived remained viable and germinated when incubated in petri dishes at 25 degrees C. Initially, buried seeds required light for germination. However, after 17 months' burial, seeds germinated in darkness when transferred to the laboratory and incubated on agar at 25 degrees C.     

Photosynthesis and biomass allocation of beech (Fagus crenata) and dwarf-bamboo (Sasa kurilensis) in response to contrasting light regimes in a Japan Sea-Type beech forest

Regeneration of beech (Fagus crenata) forests depends on the formation of canopy gaps. However, in Japan Sea-type beech forests, a dwarf bamboo (Sasa kurilensis) conspicuously occupies sunny gaps. Therefore,F. crenata seedlings must escape the severe interference ofS. kurilensis in the gaps and persist beneath a closed canopy of the beech forest. We hypothesized that the growth ofF. crenata seedlings in the understory would be favored by their being more plastic thanS. kurilensis in photosynthetic and morphological traits, which would support the matter production ofF. crenata seedlings in a wide range of light availabilities. To examine this hypothesis, the photosynthetic-light response of individual leaves and the biomass allocation in aboveground parts (i.e., the culm/foliage ratio) were surveyed at sites with contrasting light availabilities in a Japan Sea-type beech forest in central Japan. InF. crenata, photosynthetic light utilization efficiency at relatively low light was greater, and the dark respiration rate was smaller in the leaves of seedlings (10 cm in height) beneath the closed canopy than in the leaves of saplings at the sunny forest edge. The culm/foliage (C/F) ratio of theF. crenata seedlings at the shady site was small, suggesting effective matter-production beneath the beech canopy. On the other hand,S. kurilensis both in the gap and beneath the beech canopy showed low plasticity in photosynthesis and the culm/foliage ratio. Because the shoot density ofS. kurilensis was smaller beneath the beech canopy than in the gap, the light availability at the bottom of theS. kurilensis layer was greater beneath the beech canopy. These results suggest that the photosynthetic productivity of theF. crenata seedlings would be enough for the seedlings to survive in the understory with a low density ofS. kurilensis shoots beneath the closed beech canopy.     

不同条件下紫珠种子萌发特征研究

通过设定L9(34)3因素3水平正交试验,探究了萌发温度条件、光照条件和激素(GA3)条件.结果表明:在紫珠发芽率、发芽指数、发芽势和活性指数指标方面,温度是其影响的最主要因子,光照次之,GA3的影响相对最低,综合分析结果显示,紫珠发芽率、发芽指数、发芽势和活性指数指标最优的萌发条件组合为A3 B3 C2,即1000L...     

种子贮藏和播种方式对红椆发芽及苗木生长的影响

以红椆种子为试验材料,进行贮藏和播种方式对红椆种子发芽和苗木生长的影响试验。结果表明:不同贮藏方式对红椆种子发芽率有极显著影响;不同播种方式对红椆种子发芽率和苗木地径生长无显著影响,但对苗木成活率和苗木高生长影响极显著。     

珍稀濒危植物连香树种子萌发的研究

进行了濒危植物连香树种子萌发特性的研究,探讨不同光照条件(12 h,1 500 lux和黑暗)、不同温度(15℃、20℃、25℃和30℃)、不同浓度的赤霉素(0.5 mg.L-1、1 mg.L-1、2 mg.L-1、4 mg.L-1)浸泡连香树种子不同时间(2 h、4 h6、h、8 h)、50℃温水预处理15 min以及不同储藏条件对连香树种子萌发的影响。结果表明:25℃是连香树种子发芽的最适温度;在光照条件下连香树种子的发芽势高,光照可以促进连香树种子发芽迅速、整齐;经过赤霉素处理的干藏种子的发芽率和发芽势比没经过其处理的干藏种子的发芽率和发芽势高,且在一定浓度范围内随着赤霉素浓度的增大和处理时间的延长,发芽率和发芽势逐渐提高;湿藏有助于连香树种子萌发;50℃温水预处理15 min对种子的萌发有促进作用。     

濒危树种极东锦鸡儿(Caragana fruticosa)种子的萌发特性

以濒危树种极东锦鸡儿成熟种子为材料,研究极东锦鸡儿种子物理性状和温度对其种子萌发及幼苗生长的影响。结果表明:极东锦鸡儿种荚结实率较低,且约有1/4种子受虫害;成熟种子含水量为6.6%,千粒重18.6 g。种子长、宽和厚存在一定变异。种子长度平均为0.42 cm,宽度平均为0.27 cm,厚度平均为0.24 cm,长宽比为0.64。种皮透水性良好。不同温度条件对种子发芽率具有极显著影响。25℃条件下种子发芽率最高,为38.33%。随着温度的升高或降低,种子发芽率降低。发芽试验的第八天是计算种子发芽势的适宜时期。不同温度条件对极东锦鸡儿幼苗高度的影响极显著,对胚根长度影响显著。25℃有利于幼苗高度和胚根长度的增加,较高温度(30℃)有利于幼苗生物量增加。     

Influence of typhoon disturbances on the understory light regime and stand dynamics of a subtropical rain forest in northeastern Taiwan

In 1996 and 1997 we examined the effects of typhoon disturbance on the understory light environment and sapling dynamics of the Fu-shan Experimental Forest, a subtropical rain forest in northeastern Taiwan. Mean understory light levels were approximately 30% of those in the open immediately following the two 1996 typhoons which affected the forest, yet in 1997, following two more typhoons, mean understory light levels were 10%–20% of those in the open. The decline of understory light levels to those present prior to the typhoons was more rapid in 1996 than in 1997, even though the two typhoons in 1996 were more intense than those in 1997. This difference might be the result of the timing of the typhoons. In 1996 the typhoons occurred earlier in the growing season, before August 1 rather than the middle and end of August in 1997. The regular defoliation caused by the frequent typhoons that impact Fu-shan (average of 1.4 per year) and the low stature of the forest (mean canopy height of 10.6m), results in much higher light levels beneath the canopy (9%–30% of levels in the open) than those found in most tropical and temperate forests. As a result, understory light levels are not limiting the distribution of canopy tree saplings within the forest and there is no evidence that canopy gaps play an important role in canopy tree regeneration within the Fu-shan Experiment Forest. This is in contrast with the pattern reported for some tropical forests. With frequent typhoons impacting northeastern Taiwan, the forests of this region are perpetually recovering from wind disturbances.     

Seed dormancy and germination of Ficus lundellii and tropical forest restoration

We investigated seed dormancy and germination in Ficus lundellii Standl. (Moraceae), a native species of Mexico's Los Tuxtlas tropical rain forest. In an 8-h photoperiod at an alternating diurnal (16/8 h) temperature of 20/30 degrees C, germination was essentially complete (96%) within 28 days, whereas in darkness, all seeds remained dormant. Neither potassium nitrate (0.05-0.2%) applied continuously nor gibberellic acid applied either continuously (10-200 ppm) or as a 24 hour pretreatment (2000 ppm) induced germination in the dark. Germination in the light was not reduced by a 24-h hydrochloric acid (0.1-1%) pretreatment, but it was reduced both by a 24-h pretreatment with either H(2)O(2) (0.1-5 M) or 5% HCl, or by more than 5 days of storage at 40 degrees C (4.5% seed water content). In a study with a 2-dimensional temperature gradient plate, seeds germinated fully and rapidly in the light at a constant temperature of 30 degrees C, and fully but less rapidly in the light at alternating temperatures with low amplitudes (< 12 degrees C) about the optimal constant temperature. The base, optimal and ceiling temperatures for rate of germination were estimated as 13.8, 30.1 and 41.1 degrees C, respectively. In all temperature regimes, light was essential for the germination of F. lundellii seeds.     

老挝过度采伐热带混合落叶林区的人工补植(英文)

人工补植通常用于增加低商业价值树种盛行的次生林中期望树种的密度。本研究评估了均格种植法(vis-à-vis gap)和行植法(line planting)2种人工补植方法,以及老挝过度采伐的热带混合落叶林中的青皮木(Vatica cinerea) 和龙脑香木(Dipterocarpus alatus)和3种豆科植物(缅茄 Afzeliax ylocarpa,大果紫檀Pterocarpus macrocarpus,酸枝木Dalbergia cochinchinensis)的表现。人工补植实验安捧在了一个随机完整的大块场地,做了7个重复。栽植7年后测定了存活率、高度和直径生长,并进行方差分析。用2种人工补植方法栽植的幼苗的存活率没有发生变化(p0.05)。然而,就直径和高度生长而言,均格种植法要比行植法效果更好。这与林冠在格间和行间块速封闭有关,这种情况在行间更加明显。在存活率,高度和直径生长方面,存在着明显的种间变异。耐阴的龙脑香科树种存活率和生长表现优于喜光树种(p0.0001)。个体的大小分布不规则,说明林下光照条件不均衡。考虑到行植法很难维持恒定线条宽度和均匀光线条件,及其每年用于清理的成本和僵硬的几何模式,我们推荐采用均格种植法。龙脑香木(Diperocarpus alatus)和青皮木(V.cinerea)可用于混合阔叶林人工补植的树种。缅茄、酸枝木和大果紫檀可作为人工林的混合树种,在较宽林隙地、直线区域和开放地种植或在火耕林幼林冠下种植。     

Conspecific negative density dependence in a long-lived conifer,yew <Emphasis Type="Italic">Taxus baccata</Emphasis> L.

Conspecific negative density dependence in tree species can have major consequences for structuring of communities, yet in temperate forests this phenomenon remains largely unexplored. We investigated density-dependent recruitment in the long-lived conifer yew (Taxus baccata L.), for which low levels of regeneration have been linked with reduced light availability beneath conspecific canopies and speculative autotoxic effects. We combined in situ assessment of yew regeneration in a temperate forest in southwest Ireland with ex situ pot experiments to assess whether light and/or beneath conspecific canopy conditions inhibit the germination and early growth of yew. In field experiments, recruitment was related to distance from adult conspecifics, with higher levels of regeneration found in areas not beneath yew canopies. However, reduced light availability beneath the dense yew canopy was not responsible for this pattern, with abundant seedlings found in areas of equivalent or even lower light availability. Pot experiments showed that seedling survival was highest in deep shade treatments. Experiments also demonstrated that the addition of yew needles negatively affected seedling growth, but not seed germination. Together, our results suggest that under natural forest conditions, the absence of regeneration beneath mature yew canopies, often attributed to low light availability, may at least be partly related to substances in yew canopy or leaf leachates.     

Tree regeneration in gap-understory mosaics in a subtropical Shorea robusta(Sal) forest

Spatial variation in tree-regeneration density is attributed to the specialization of tree species to light availability for germination and growth. Light availability,in turn, varies across the gap-understorey mosaic. Canopy gaps provide an important habitat for the regeneration of tree species that would otherwise be suppressed in the understory. In subtropical forests, there is still a knowledge-gap relating to how canopy disturbances influence tree-regeneration patterns at local scale, and if they disproportionately favor regeneration of certain species. We aim to analyze whether canopy gaps promote tree regeneration, and tree species are specialized to gaps or understory for germination and growth. We sampled vegetation in 128 plots(0.01 ha), equally distributed in gaps and below canopy, in two subtropical Shorea robusta Gaertn.(Sal) forests in Nepal, recording the number of tree seedlings and saplings in each plot. We compared the regeneration density of seedlings and saplings separately between gaps and the understorey. The mean densities of seedlings and saplings were higher in the gaps at both sites;although there was no difference in the seedling density of the majority of the species between the habitats. No species were confined to either gap or understorey at the seedling stage. We conclude that gaps are not critical for the germination of tree species in Sal forests but these are an important habitat for enabling seedlings to survive into saplings. The classification of trees into regeneration guilds mainly based on germination does not apply to the majority of tree species in subtropical Sal forests. Our results reaffirm that gap creation promotes tree regeneration by favouring seedling survival and growth and can influence forest management for conservation, as well as for plantations.     

Seasonal photosynthetic responses to light and temperature in white spruce (Picea glauca) seedlings planted under an aspen (Populus tremuloides) canopy and in the open

Photosynthetic light and temperature response curves were measured seasonally in seedlings of white spruce (Picea glauca (Moench.) Voss) grown for two years in the understory of aspen (Populus tremuloides Michx.) or in the open in central Alberta. Light-saturated rate of net photosynthesis, the optimum temperature for net photosynthesis, transpiration rate, photochemical efficiency, and stomatal and mesophyll conductances increased from spring to summer and declined thereafter, whereas dark respiration rate and compensation and saturation points were highest in spring. Depression of photosynthetic parameters was greater in open-grown seedlings than in understory seedlings during the periods in spring and autumn when night frosts were common. Net photosynthetic rates were similar in understory and open-grown seedlings in summer, but they were significantly lower in open-grown seedlings in spring and autumn. Significantly lower transpiration rates and stomatal conductances in open-grown seedlings than in understory seedlings were also observed at 15 and 25 degrees C in the autumn. Shoot and needle growth were less in open-grown seedlings than in understory seedlings. In summer, when irradiances were low in the aspen understory, understory white spruce seedlings maintained a positive carbon balance by decreasing their compensation and saturation points and increasing their photochemical efficiency compared to spring and autumn.     

Germination and seedling growth of Quercus (section Erythrobalanus) across openings in a mixed-deciduous forest of southern New England, USA

In this study three species of the genus Quercus section Erythrobalanus (Quercus coccinea, Quercus rubra, Quercus velutina) were investigated. All occur together as canopy trees in forests of southern New England. Acorns of each Quercus species were planted in plots located in five zones that represent a range of forest gap/canopy conditions that can occur within a southern New England forest. These five zones were demarcated adjacent to and across large openings of two physiographic sites—valley and ridgetop. Experiments were designed to monitor germination and initial growth of seedlings for the first three growing seasons. During the start of the first growing season germination was monitored. At the end of the first growing season measurements of height and number of flushes were taken and destructive samples of seedlings made for dry mass of root, stem and leaves. At the end of the third growing season height was recorded for surviving seedlings. Comparisons were made of germination and growth of seedlings located in the different gap/canopy conditions.

Results demonstrated clear differences in patterns of germination and early growth among species and among gap/canopy conditions of the sites. All species showed an increased lag in germination with reduced amounts of light. Highest growth and flushing rate were in the center conditions of the openings for all species during the first growing season. Quercus rubra had the greatest height growth the first growing season but a lower number of flushes than Q. velutina and Q. coccinea. In comparison with the other species, Q. rubra had the greatest total dry mass in most gap/canopy conditions after the first growing season. However, Q. velutina had the greatest total dry mass in the center of the ridgetop opening. In almost all gap/canopy conditions Q. velutina had greater proportions of dry mass allocated to roots compared with the other species.

After 3 years, greatest height growth in any of the gap/canopy conditions was recorded for all three species in the center of the valley site. Under this condition Q. rubra had significantly greater growth than Q. velutina and Q. coccinea. Quercus rubra also had significantly greater height growth and survival beneath the canopy conditions of the valley site than the other species. On the ridgetop site regeneration failed to establish beneath canopy conditions that provided low amounts of light. Quercus velutina showed greatest height growth after three years in the center and edge conditions of the ridgetop opening compared with the other species. Environmental influences that determine species germination and growth performance are suggested.     

Spatio-temporal variation of environmental signals inducing seed germination in temperate conifer plantations and natural hardwood forests in northern Japan

To document the spatial and temporal variation of environmental signals inducing seed germination in temperate forests, we measured temporal patterns of environmental signals and seed germination of six pioneer tree species in unthinned and thinned stands of conifer forests (Cryptomeria japonica plantations) and in the understory and gaps of hardwood forests in Japan. We also conducted germination experiment in laboratory for the six pioneer species to test the effects of red:far-red (R:FR) light ratio and temperature fluctuations on the seed germination. In conifer forests, the photosynthetic photon flux density (PPFD), the R:FR ratio, and the amplitude of temperature fluctuations in thinned stands were 2, 1.5, and 3 times higher, respectively, than those of unthinned stands. The PPFD and R:FR ratios just above forest floor also increased after the removal of thick litter accumulation. As a result, higher seed germination was observed in thinned compared to unthinned stands for three photoblastic species, whereas little differences were observed for three non-photoblastic species. These findings suggest that thinning, which frequently reduces litter accumulation, can substantially affect the regeneration of pioneer species and the resultant species diversity in conifer plantations. None of the measured environmental signals changed seasonally in unthinned stands of conifer forests, but they all changed remarkably in the understory of the hardwood forests. In this system, all signals were high and nearly identical to those in the gaps in early spring prior to canopy closure. Thus, the percent germination of the three photoblastic species was enhanced by high R:FR ratios and/or large temperature fluctuations even beneath the canopy and was nearly equal to that in the thinned conifer stands where the environmental conditions were nearly identical to those in the gaps. However, all of the environmental signals decreased with the expansion of canopy leaves and reached minimums at canopy closure. Even in the thinned stands and the gaps, the PPFD and magnitude of temperature fluctuations decreased over time due to shading by growing herbs and/or emerging canopy leaves. In these temporally changing environments, the germination of all photoblastic species ceased simultaneously. This study clearly demonstrated that the environmental signals inducing seed germination of photoblastic pioneer species spatially and temporally change in temperate forests, particularly in deciduous hardwood forests. Furthermore, these signals, PPFD, R:FR ratio, and the amplitude of temperature fluctuations, appear to play a very important role in tree regeneration and subsequent species diversity.     

Comparison of light-regulated seed germination in Ficus spp. and Cecropia obtusifolia: ecological implications

The major components of annual seed deposition in the rain forest at Los Tuxtlas, Veracruz, México are seeds of the pioneer tree species Cecropia obtusifolia and those of some species of Ficus. Cecropia obtusifolia Bertol. forms a relatively persistent viable soil seed bank, whereas seeds of Ficus are seldom found in the soil. Both genera require light for seed germination; however, the species differ in their germination responses to far red (FR) light under laboratory and field conditions. Seeds of C. obtusifolia did not germinate in low red/far red (R/FR) or pure FR, whereas seeds of the Ficus species did. This suggests that Ficus seeds do not become dormant under the light conditions (low R/FR ratio) beneath the leaf canopy of the rain forest. This difference may explain why the species differ in their presence in the soil seed bank.     

Effects of osmopriming and hydropriming on vigour and germination of China aster (Callistephus chinensis (L.) Nees.) seeds

The aim of this research was to evaluate the effects of osmopriming and different hydropriming treatments on the vigour and germination of China aster (Callistephus chinensis) seeds. Seed vigour and germination tests were conducted at 10, 20 and 30°C in darkness for untreated, osmoprimed and hydroprimed seeds. The following parameters and categories of seeds and seedlings were evaluated: the mean germination time (MGT), T10, T50, U75–25, U90–10, the percentage of germinating seeds (Gmax), germination capacity, percentage of abnormal seedlings and dead seeds. The results showed that osmopriming accelerated seed germination to the largest extent and improved the uniformity of germination at 10 and 30°C. Among the hydropriming treatments the highest speed of germination was observed for seeds hydrated in 500 μL of water per 1 g of seeds for 48 h at 15°C. This treatment accelerated seed germination at 10°C compared with the control. Osmopriming increased seed germination capacity at 30°C. None of the applied hydropriming treatments improved this parameter.     

国外产竹种子形态特征及其育苗技术

测定分析了10种国外产竹种子的形态特征,并对他们进行育苗试验。结果表明：种子形状多为卵形、长锥形、椭球形,颜色以黄褐色、褐色、褐黑色为主,长度和直径分别为4~60 mm和0.9~5.5 mm;果实一般为圆锥形、锥形、卵形,颜色以灰褐色、灰色为主,长度和直径分别为5~64 mm和1.2~7.5 mm;大藤竹种子播种品质指标最好,具有最高的纯净度（97.4%）、千粒质量（201.0 g）、发芽率（95.4%）、发芽势（51.5%）、含水量（9.3%）、生活力（98.8%）及较低的病虫害感染度（6.5%）;有机质是有效提高各竹种出苗率的首选基质;宜采用先撒播种子,待胚苗有1~3片叶时再移入营养袋培育的育苗方式;育苗时施用氮磷钾复合肥,并在苗木离地50 cm处进行封顶处理,能有效促进苗木生长。     

预处理对巴西盾柱木种子吸涨、活力测试及其加速老化的影响

对巴西盾柱木(Peltophorum dubium)种子进行了4种处理的吸胀实验,即将种子分别置于10℃和27℃下0.2% Captan溶液中和-1.0MPa的PEG6000溶液中,每个处理有四个重复,40粒种子,置于培养皿中浸满实验溶液的双层过滤纸上,覆以透气良好的薄膜.种子在实验前均用98%的浓硫酸处理15分钟以打破机械休眠.吸胀曲线显示,种子在吸胀过程中最终重量的增加值为70%-150%,以后进入一个停滞期.在5种处理下(对照组,PEG6000溶液中10℃和27℃下预处理,Captan溶液中10℃和27℃下预处理),对种子萌发所受到的影响进行了实验.每一个处理分别进行3个次级处理,即在实验前,将种子用蒸馏水分别浸泡12、24和36小时.萌发率最高的是经过蒸馏水浸泡12小时对照组种子和PEG 27℃组的种子,萌发率达到100%;萌发率最低的是蒸馏水中浸泡36小时的PEG 27℃组的种子,萌发率为52%;经过蒸馏水浸泡24小时的PEG 10℃组种子的平均萌发时间为1.08天.蒸馏水中浸泡12小时的PEG 27℃组种子平均萌发时间为2.42天,其它处理的萌发时间值介于两者之间.对预处理和未经预处理种子通过加速老化实验,对其活力和生存力进行了测试.经72小时加速老化,种子萌发率低或没有萌发力.对照组种子在培养皿(27℃)和室温条件下蛭石中的萌发率都比处理组高,表现了对老化更强的抗性.     

Storage of non-dormant seeds of Fraxinus angustifolia Vahl

The effects of drying and storage on the quality of Fraxinus angustifolia non-dormant seeds have been investigated. Mature seeds subjected to a 2-week warm stratification (20 °C) followed by a 2-week cold stratification (3 °C), were exposed to a gentle air stream at room temperature to dry them to 9.5% moisture content. After 4, 8 and 12 months of storage at –3 °C, in hermetically sealed containers, germination tests were conducted in darkness at 30/20 °C and 25/5 °C to evaluate possible changes in seed quality. The results obtained suggest the feasibility of drying non-dormant seeds. In fact, though causing a slight decrease in seed quality, such a process enables storage of ready to sow seeds for at least 12 months without any further loss. The temperature regime of 30/20 °C, prescribed by the International Seed Testing Association (ISTA), was found to be suboptimal for the particular conditions tested in this trial, the 25/5 °C cycle being more stimulating for germination.     

高盆樱桃种子萌发特性初探

高盆樱桃 Cerasus cerasoides 原生于西藏和云南地带,为我国唯一冬季开花的樱属树种。其树形优美,花色艳丽,造景效果好,目前多应用于云南地区的绿化及造林。为探索高盆樱桃种子的萌发特性,测定其长、宽、厚、百粒重、吸水特性、发芽特性以及芽苗质量指标,并初步探索种子大小对种子萌发的影响。结果表明：高盆樱桃种子浅褐色,呈卵圆状;平均长 10.56 mm,平均宽 7.89 mm,平均长宽比为 1.34,平均厚 6.06 mm,平均百粒重为 25.48 g;在培养皿铺纱布保湿的环境下种子发芽率为 42.67%;大种子发芽势、发芽率等数值均高于中、小种子,种子大小与发芽率呈正相关。