Seedling emergence, growth, and allocation of Oriental bittersweet: effects of seed input, seed bank, and forest floor litter

The establishment of invasive plant populations is controlled by seed input, survival in the soil seed bank, and effects of soil surface disturbance on emergence, growth, and survival. We studied the invasive vine Celastrus orbiculatus Thunb. (Oriental bittersweet) to determine if seedlings in forest understory germinate from the seed bank or from seed rain. We also conducted a greenhouse experiment to investigate the role of leaf litter mass and physical texture on seedling survival, growth, and allocation. In the understory of an invaded mixed hardwood forest, we measured seed input, seedling emergence with seed rain, and seedling emergence without seed rain. Mean seed rain was 168 seeds m⁻²: mean seedling emergence was 107 m⁻², and there was a strong correlation between seed rain and seedling emergence. The ratio of seedlings to seed input (0.61) was close to the seed viability (0.66) leaving very few seeds to enter the seed bank. Seed bank germination under field conditions was low (1 seedling m⁻²). Soil cores were incubated in a greenhouse to determine seed bank viability, and germination from these soil cores did not occur. To determine how litter affects seedling establishment and growth, we measured seedling emergence and biomass allocation in a greenhouse experiment. Seeds were placed below intact and fragmented deciduous leaf litter in amounts ranging from zero to the equivalent of 16 Mg ha⁻¹. Seedling emergence was not affected by fragmented litter, but decreased to <20% as intact litter increased to 16 Mg ha⁻¹. Increasing litter resulted in greater allocation to hypocotyl and less to cotyledon and radicle, and this effect was greater in intact litter. C. orbiculatus seedlings achieve emergence through forest floor litter through plasticity in allocation to hypocotyl growth. The low survival of C. orbiculatus in the seed bank suggests that eradication of seedling advance regeneration and adult plants prior to seed rain may be an effective control strategy. However, the intact forest floor litter of an undisturbed forest will not prevent seedling establishment.     

Effects of calcium on seed germination, seedling growth and photosynthesis of six forest tree species under simulated acid rain

We selected six tree species, Pinus massoniana Lamb., Cryptomeria fortunei Hooibr. ex Otto et Dietr., Cunninghamia lanceolata (Lamb.) Hook., Liquidambar formosana Hance, Pinus armandii Franch. and Castanopsis chinensis Hance, which are widely distributed as dominant species in the forest of southern China where acid deposition is becoming more and more serious in recent years. We investigated the effects and potential interactions between simulated acid rain (SiAR) and three calcium (Ca) levels on seed germination, radicle length, seedling growth, chlorophyll content, photosynthesis and Ca content in leaves of these six species. We found that the six species showed different responses to SiAR and different Ca levels. Pinus armandii and C. chinensis were very tolerant to SiAR, whereas the others were more sensitive. The results of significant SiAR?×?Ca interactions on different physiological parameters of the six species demonstrate that additional Ca had a dramatic rescue effect on the seed germination and seedling growth for the sensitive species under SiAR. Altogether, we conclude that the negative effects of SiAR on seed germination, seedling growth and photosynthesis of the four sensitive species could be ameliorated by Ca addition. In contrast, the physiological processes of the two tolerant species were much less affected by both SiAR and Ca treatments. This conclusion implies that the degree of forest decline caused by long-term acid deposition may be attributed not only to the sensitivity of tree species to acid deposition, but also to the Ca level in the soil.     

Effects of simulated acid rain on seedling emergence and growth of five broad-leaved species

lntroductionAcidrainemergedasanenvironmentalissueofincreasingconcernintheIate197osinChina.TheresuItsofnationwidemonitoringdatagatheredshowedthatwidespreadoccurrenceofacidrainwasconcentratedinsouthernpartoftheYangtZeRiver,especiallyinsouthwesternregion,whereprecipitationintheIate198oswasfoundtohaveaveragepHvaI-uesbetWeen3.5and4.8(Yang1989;Xu199O).ow-ingtotheincreasingseriousnessofacidraininsouthwesternChina,aseriesofresearchprogramshavebeensetupbytheNationaIEnvironmentaIPro-tectionoffice…     

野生欧洲李种子萌发特性

为了掌握野生欧洲李种子萌发特性,探讨野生欧洲李实生繁殖规律,以新疆野生欧洲李为研究对象,观察种子形态,测定种子千粒质量、种皮透水性、种子含水量、种子活力,测定种子浸提液对白菜种子发芽和胚根生长抑制活性的影响。结果表明:新疆野生欧洲李种子的种皮透水性比较差;种子含水量为30.57%;TTC法检测种子活力为81.67%;4℃低温沙藏层积的野生欧洲李种子,在处理后90 d种子出现萌发,持续层积200 d后总萌发率为47%;种子各部分浸提液对白菜种子发芽率作用不明显,但对胚根生长有明显的抑制作用,随着浸提液浓度增长,对白菜种子发芽抑制活性越强,其胚根长度越短;随着野生欧洲李层积天数的增加,浸提液处理的白菜种子胚根长度增加;野生欧洲李种子各部分浸提物对白菜种子发芽抑制活性顺序为:种胚最强,种皮次之,种壳最弱。     

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。     

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...     

热水处理对山皂荚种子萌发的影响

分别用30、60、75和95℃的热水及用浓硫酸处理山皂荚种子的结果表明,30℃热水处理2min与5min的种子差异不显著,处理10min的种子与前两组差异显著。60℃热水处理的3组时间间的差异显著,75℃的热水处理的3组时间间的差异显著,95℃处理2min与5min的种子差异显著,处理2min与10min的种子差异显著,处理5rnin与10min的种子差异不显著。用75℃热水处理种子10min对山皂荚的种子萌发最为有利,浓硫酸处理60rain的山皂荚种子较热水处理山皂荚种子吸水性能大。     

不同基质对三种樟科植物种子萌发及幼苗生长的影响

以河沙、草木灰、锯末配成的三种栽培基质为试验材料,以黑壳楠、楠木、闽楠为供试品种,采用露天播种育苗的方式,研究不同基质对三种樟科植物种子的萌发、幼苗生长情况的影响.结果表明:黑壳楠在河沙中的发芽率、发芽指数最高,幼苗生长情况最好;楠木和闽楠在河沙+草木灰的基质中萌发情况和幼苗生长情况最好.     

贵州茂兰喀斯特山地顶部森林群落种子库研究

在茂兰喀斯特森林山顶地段设置固定样地,定期观察植物的开花结实、种子雨、种子库的结构、组成及其萌发。结果表明:900m2样地内共有种子植物36种,其中21种已进入繁殖阶段,每年产生成熟种子520.9粒·m-2。种子雨量大,每年达910.3粒·m-2,其中对群落有用的成熟有效种子314.7粒·m-2。在天然萌发开始时的种子库中,有大量现存植物的活力种子,群落更新潜力很好。在天然情况下,1月上旬到5月中旬种子库中活力种子萌发。在天然萌发季节,900m2样地内每年共萌发出18种苗(7245株),当年存活幼苗2970株,群落更新良好。裸子植物华南五针松、短叶黄杉和翠柏在喀斯特山顶地段有良好的适应性,能长期稳定存在。     

秋水仙素对洋紫荆种子萌发及幼苗生长的影响

以洋紫荆(Bauhinia variegata)成熟种子为试验材料,采用质量浓度为0.5、1.0、1.5、2.0 mg/mL的秋水仙素溶液分别处理12、24、36和48 h,并以蒸馏水浸泡种子作为对照,观察测定其种子萌发特性及幼苗生长指标.结果表明,随着秋水仙素质量浓度的增加,种子发芽率逐渐降低,2.0 mg/mL溶液使大部分种子致死,0.5、1.0 mg/mL质量浓度秋水仙素处理24 h有利于种子萌发;种子胚根的伸长随着秋水仙素质量浓度的增加也受到不同程度地抑制;秋水仙素对发芽种子胚芽的发育有一定的抑制作用;不同质量浓度秋水仙素处理后第7个月,各处理间苗高与地径差异均极显著(P<0.01),质量浓度为1.0 mg/mL,处理36 h时,苗高和地径都最大;当秋水仙素质量浓度为2.0 mg/mL时,对叶片平均分裂角度有一定促进作用.     

山苍子种子育苗试验

针对山苍子种子休眠期长,苗木繁育困难的现状,采用7月采的种子和9月采的种子进行种子育苗试验。结果表明:7月采的种子的出苗数和苗高生长量只有9月采的种子的20%和63.3%,两者达到极显著差异。7月采种,由于种子尚未完全成熟,种子发芽率低,苗木生长较差;9月采种,种子已完全成熟,种子发芽率高,苗木生长较好。     

Effect of sowing date on seedling emergence of species with seeds enclosed in a stony endocarp

The aim of the present study was to investigate the effect of the natural sequence of temperature conditions between the time of seed sowing and their germination on dormancy release of Prunus avium, P. mahaleb, P. divaricata, P. laurocerasus, P. spinosa, Cornus mas, C. sanguinea, and Celtis australis seeds which are enclosed in a hard stony endocarp. According to their collection date, the seeds (with the endocarp) of the above species were sown outdoor in summer, autumn, and winter and the number of emerged seedlings was counted during the following two springs. For all species, the first sowing date was immediately after seed collection and cleaning. In all species, seedling emergence occurred in early spring and dormancy was released only after the exposure of seeds to specific season conditions. The exposure of seeds of all studied species, except C. australis, to a period of warm temperatures prior to winter was necessary for dormancy breaking and germination. Autumn sowing of P. laurocerasus and C. sanguinea seeds, which were collected in summer, and the sowing immediately after seed collection of the rest species, resulted in a maximum percentage of seedling emergence in the following spring.     

Effects of drought stresses induced by polyethylene glycol on germination of Pinus sylvestris var. mongolica seeds from natural and plantation forests on sandy land

Effects of drought stresses induced by polyethylene glycol (PEG) (0.0%, 10%, 15%, 20%, 25%, and 30%, with four replicates) on germination of Mongolian pine (Pinus sylvestris var. mongolica) seeds produced in plantations (southern Keerqin sandy land) and natural forests (Hulunbeier sandy plain) were observed. The results indicated that the seeds from both provenances did not germinate when PEG concentration was more than 25%. The time of initial germination and that of its completion of stressed seeds from both provenances were delayed when compared with the unstressed seeds. The germination capacity and germination rate of natural seeds were significantly higher than those of plantation seeds for all treatment levels (P < 0.05). The mean growth rates of radicle and hypocotyl from natural seeds were significantly higher than those from plantation seeds at all treatment levels below 20% PEG treatment (P < 0.05). The ratios of radicle to hypocotyl of 20% PEG treatment were significant higher than those of the corresponding controls for both provenances (P < 0.05). These results suggested that Mongolian pine seeds/seedlings had stronger resistance to PEG drought stresses; 10% PGE stress did not significantly influence germination. Natural seeds exhibited more resistance to PEG stress than plantation seeds. It was concluded that drought stress on seed germination might be one cause of obstructed natural regeneration of Mongolian pine plantations on sandy land. It is recommended that natural seeds be used for afforestation, and light drought stress (e.g., 10% PEG stress) may be useful in improving seed germination and the growth of radicles and hypocotyls.     

女贞种子和幼苗对模拟酸雨的反应

将女贞种子和１年生幼苗置于不同ｐＨ值的模拟酸雨条件下观测和分析其形态和生理变化。结果表明,不同处理间女贞种子发芽率无统计上的显著差异,但ｐＨ２．０和ｐＨ３．５的模拟酸雨对种子发芽显示了一定的抑制作用。在ｐＨ２．０的模拟酸雨条件下,女贞幼苗叶片表现明显的受害症状,叶绿素含量下降,细胞透性增加,叶汁液酸化,从而使幼苗生长严重受阻。在ｐＨ３．５的处理下幼苗没有表现明显的形态和生理变化,但生长量呈现下降趋     

Scots pine (Pinus sylvestris L.) plantations contribute to the regeneration of holly (Ilex aquifolium L.) in mediterranean central Spain

The aim of this study is to evaluate the recruitment possibilities of holly (Ilex aquifolium L.) populations under Pinus sylvestris plantations in the mountains of Central Spain. Population recruitment of holly under P. sylvestris L. plantations was studied at two localities. We sampled holly seed rain, seed bank, and seedling emergence and survival (of both emerged and planted seedlings) in both localities. Seed germination was analysed by randomly sowing Ilex seeds and their subsequent recollection and analysis over the following 3 years (only in one locality). Seed rain, seed bank and emerged seedling densities did not differ between localities. Seed bank density was between 10 and 20 seeds m⁻², considerably higher than the observed seed rain (0.4–1.2 seeds m⁻²), and also higher than the emerged seedling density (0–4 seedlings m⁻²). But Ilex is not very efficient in germinating under pine forests (29.1% germination after 3 years). This may indicate a seed accumulation process of at least 5 years. Seedling survival for the first year differed among the studied sites (50–60 vs. 17%). Nevertheless these survival rates are higher than those found for the same seedling populations in different forest habitats (not Scots pine forests) from near locations. Differences in summer water stress between the study sites are proposed as the main cause of the observed differences in seedling survival. It is concluded that P. sylvestris forests may provide one of the best regeneration habitats for holly in the Mediterranean area, where this species is close to the Southern limit of its distribution.     

三峡地区柏木林种子雨和种子库的研究

柏木种子雨在8月底开始降落,10月达到顶峰,翌年5月结束,历经9个月左右。整个过程呈单峰曲线,10~11月的种子雨量占全年的67.5%。种子雨时间变化格局差异极显著,而水平空间分布格局没有显著差异。种子雨中柏木种子的年均密度为5 982.2粒.m-2。63.4%的柏木种子直径大于2.5 mm,构成了柏木种子雨的主体。由于这一级别柏木种子的萌发能力较强,因此三峡地区柏木林的更新能力强。柏木林中非柏木种子的种子雨每年主要发生在1月和5月,形成2个高峰,年均种子雨密度为1 842.8粒.m-2。土壤种子库中柏木种子的平均密度为608.8粒.m-2。柏木种子在土壤种子库中垂直分布格局差异极显著。0~2 cm土壤层所分布的柏木种子占种子库中柏木种子的80.49%。其它土壤层次所含有的种子比例很低,且萌发能力较低,因此,柏木林的更新主要依赖于表层土壤种子库的种子。柏木种子在种子库中的水平分布格局虽然随坡位的不同而有所变化,但是差异不显著,表明整个柏木林的更新能力在水平格局上无显著差异。     

Seed supply and the regeneration potential for plantations and shrubland in southern China

Assessing the characteristics of seed supply will be vital to better understand the dynamics of forest regeneration. In this study, we surveyed the aboveground vegetation, the seed rain, the seed bank, and natural seedling emergence in four typical 24-year-old plantations (eucalyptus, mixed-native, mixed-legume, and mixed-conifer) and a naturally successioned shrubland in southern China. The dominant species in the understory were similar among the five plant communities. The seed rain and the seed bank were dominated by shrubs and herbs but indigenous tree species were rare. Species that were common to all five-plant communities represented a great proportion of the seeds in the seed rain and seed bank. The seed rain consisted mostly of seeds derived from the local plant community. Seed abundance was greater in the seed bank than in the seed rain, and species richness was greater in the seed bank and in the corresponding plant community than in the seed rain. Species composition similarity between the seed rain, the seed bank, and the aboveground vegetation was low, because the seed rain contained much fewer species, and the seed bank and aboveground vegetation contained many different species, respectively. These findings indicate that both the seed rain and the seed bank play important roles in providing seeds for plant recruitment in the understory, but the seed bank contributes more than the current seed rain to the diversity of recruited plants. The current plant community has little impact on the qualitative composition of the seed rain and seed bank. Based on these data, it appears that succession to the desired zonal, mature forest community is unlikely to result from seeds in the seed rain or seed bank. Lack of seed availability of desired zonal mature forest species is the main bottleneck currently limiting succession in the plantations. Reintroduction of late-successional species could facilitate the desired succession.     

模拟酸雨对广西4个树种苗木生长的影响研究

采用盆栽试验,设置4个水平(pH3.0、pH4.0、pH5.0、pH5.6)、一个对照(pH6.0),共5种处理,测定4个树种在不同pH值酸雨处理下其苗高、地径和生物量变化情况,分析不同pH值及处理方式的酸雨对广西地区速生及珍贵树种幼苗生长的影响。研究结果表明,随酸雨pH值的降低,4个树种的苗高相对生长量和地径相对生长量总体均呈下降趋势;巨尾桉9号在模拟酸雨pH3.0时,其地上生物量显著大于对照,在pH5.0时,其地下生物量、总生物量略大于对照,在pH5.6时,其根冠比最大;格木在模拟酸雨pH5.6时,其苗高相对生长量显著大于对照,根冠较对照大;降香黄檀在模拟酸雨pH5.0时,其苗高相对生长量显著高于对照,根冠比最大;在不同浓度酸雨处理下,土沉香各生长指标均显著小于对照。     

Adaptations to intermittent drying in germinating Eucalyptus sieberi L. Johnson seeds and young seedlings

Before Eucalyptus sieberi L. Johnson seeds germinate, the protein reserves in a small group of cells in the collet are mobilized and the cells swell sufficiently to break the seed coat allowing further water uptake. If the seedling is desiccated at this stage, the embryo remains viable and when the seed is rewetted reserves are mobilized in the cells immediately behind those which expanded initially. Mobilization of reserves and subsequent cell elongation occur sequentially along the hypocotyl after successive dry periods until the reserves are exhausted. Early in the sequence, the distal end of the hypocotyl extends and is positively geotropic, whereas at the end of the sequence the proximal end of the hypocotyl extends and is negatively geotropic, raising the cotyledons rapidly. If the radicle is destroyed or unable to elongate, it is replaced by two adventitious roots, one below the petiole of each cotyledon. Indole acetic acid and sucrose can substitute for the cotyledons in the production of adventitious roots.     

楠属种子萌发过程中过氧化物酶活力研究

种子的发芽力是判断种子质量的重要指标。本文通过对楠木属中桢楠、细叶楠及浙江楠等3树种的种子萌发过程中过氧化物酶活力所作的研究表明：过氧化物酶活力与种子发芽力存在着紧密的相关关系．它可作为确定种子活力的重要依据。