影响黄帚橐吾种子生产的因素Ⅰ.生境和花序结构

 通过对黄帚橐吾(Ligularia virgaurea)自然种群在不同生境和种群密度下的种子生产的研究,结果显示：1）黄帚橐吾的种子生产无论是在种群水平,还是在总花序上同一部位头状花序水平,均受到生境条件的影响,其种子数量、种子均重和种子总重量等特征在不同生境间表现出沙地＞滩地＞坡地,在同一生境内则为高密度种群＞低密度种群和植被盖度较低＞植被盖度较高的趋势（滩地例外）;2）种子生产中的种子数量和种子总重与总花序大小、头状花序数量以及无性系株大小多呈显著正相关,与个体密度无关,但种子均重与上述因素（除无性系株大小外）的关系不显著;3）在总花序内不同部位头状花序间表现出的种子生产变化趋势（顶部＞基部）不受生境条件、种群密度等因素的影响; 4）种子生产在总花序上所表现出的这种部位依赖性可能是由于不同部位头状花序间开花时序上的差异引起种子从母体获取资源上的不同所致。     

影响黄帚橐吾种子生产的因素I．生境和花序结构

通过对黄帚橐吾(Ligularia virgaurea)自然种群在不同生境和种群密度下的种子生产的研究,结果显示:1)黄帚橐吾的种子生产无论是在种群水平,还是在总花序上同一部位头状花序水平,均受到生境条件的影响,其种子数量、种子均重和种子总重量等特征在不同生境问表现出沙地>滩地>坡地,在同一生境内则为高密度种群>低密度种群和植被盖度较低>植被盖度较高的趋势(滩地例外);2)种子生产中的种子数量和种子总重与总花序大小、头状花序数量以及无性系株大小多呈显著正相关,与个体密度无关,但种子均重与上述因素(除无性系株大小外)的关系不显著;3)在总花序内不同部位头状花序问表现出的种子生产变化趋势(顶部>基部)不受生境条件、种群密度等因素的影响;4)种子生产在总花序上所表现出的这种部位依赖性可能是由于不同部位头状花序间开花时序上的差异引起种子从母体获取资源上的不同所致。     

黄帚橐吾花序结构的资源配置与环境的关系

 为了系统地了解黄帚橐吾(Ligularia virgaurea) 自然种群的繁殖对策,在其繁殖分配研究的基础上,通过统计不同部位头状花序的生物量投入,进一步分析了存在于总状花序内资源分配上的结构效应及其对不同生境条件的反应。结果表明：1）总状花序、不同部位头状花序在资源投入上受其栖息生境各种生态因子的影响而在不同生境和平均种群密度间存在着差异,并表现出一定的趋势;2）可代表个体水平的总状花序大小、头状花序大小、头状花序数量和头状花序平均重量等特征,都与种群密度呈现出程度不同的负相关关系,而总状花序内不同部位的头状花序大小则与种群密度变化无关;3）总状花序内的资源分配存在着位置依赖性,这种显著差异表现为顶部头状花序比基部和中部头状花序有较大的资源分配;4）总状花序顶部、中部和基部头状花序的资源分配与总状花序大小表现出极显著或显著的负相关关系。     

露蕊乌头（Aconitum gymnandrum Maxim）花序内位置依赖的性分配

植物会采取什么样的繁殖对策来保障它的雌性和雄性繁殖成功,特别是那些生活在高寒地区的植物,已经引起了很多学者的关注.通过野外盆栽试验对青藏高原东部高寒草甸上的常见物种露蕊乌头(Aconitum gymnandrum Maxim)花序内的性分配模式进行了研究,发现同其它顶向式(从花序基部到顶部)开花的植物一样,随着花从基部到顶部的次序,露蕊乌头的心皮数、雌蕊重、种子数和种子重/果实减少;而花药数,花粉数/胚珠数以及雄蕊重/雌蕊重增大,顶部花表现出偏雄的性分配.结籽率在不同的位置间没有显著差异,不受花粉数量的限制;去花实验没有增加剩余部位花的种子数,只是增加了种子大小,这是花序内不可避免的位置效应导致了花序内位置依赖的性分配模式.     

杉木种子萌发及幼苗生长对光强的响应

设置不同光强梯度(透光率分别为100%、40%、20%、10%和5%,光照强度PPFD分别为201.3、77.0、37.5、19.2、9.8 μmol·m^-2·s^-1),研究光对杉木种子萌发和幼苗早期生长的影响,分析杉木种子萌发、幼苗存活、生长、形态响应、生物量积累及其分配格局对不同光环境的响应策略.结果表明: 杉木种子的萌发率、存活率、建植率和萌发指数在不同光强梯度下均有显著差异,且40%的透光率是种子最适萌发条件,萌发率最高,而全光照下存活率和建植率最高;随光照强度的减弱,杉木幼苗茎长增大,根长、子叶长、子叶厚、真叶数呈降低趋势,而基径在各光照强度间无显著差异;总生物量、根生物量、茎生物量、叶生物量均表现为全光照下最大.随着光照强度的减弱,光合组织与非光合组织生物量比、叶生物量比呈降低趋势,茎生物量比呈增加趋势,根冠比和根生物量比无显著差异.弱光环境促进杉木种子萌发,不利于杉木幼苗存活和生长.在弱光环境下,杉木幼苗通过增大茎生物量来提高对弱光环境的耐受力.     

位置效应对巫山淫羊藿花蜜分泌和结实的影响

位置效应在开花植物中广泛存在。以野生巫山淫羊藿种群为研究对象,运用单因素方差分析法,研究位置效应对结实性和花蜜分泌的影响。结果表明:三个巫山淫羊藿种群不同位置的结实率显著差异,其中基部的结实率明显大于中部和顶部; 位置效应对果实重量及果实长、宽的影响均显著,表现出基部>中部>顶部的趋势; 总状花序上不同开花位置对单个果实种子数的影响显著,且基部大于顶部。但位置效应对单个果实种子败育率的影响不显著,均值呈现顶部>中部>基部变化规律; 巫山淫羊藿不同开花位置的花蜜常备量和含糖量的差异显著。三个种群基部的花蜜常备量较高,而花蜜含糖量在顶部较高。因此,对巫山淫羊藿野生种群进行研究与保护时应注意位置效应对生殖成功的影响,选择基部果实进行试验或育种,应维持种群多样性及稳定性。     

种子特征和播种深度对辽东栎种子萌发和幼苗生长的影响

该文在玻璃温室内的遮阴环境下,采用盆播方法研究了辽东栎种子特征(大小和种皮)和播种深度(0、3、6、10 cm)对种子萌发和幼苗生长的影响。结果表明:(1)辽东栎大种子萌发率、萌发速率、萌发值和萌发指数在所有播种深度均高于小种子。其中非去皮种子萌发率、萌发速率和萌发指数在0 cm播种深度的不同大小种子间差异显著,去皮种子所有萌发参数在6和10 cm播种深度的不同大小种子间均差异显著;去皮可促进大种子萌发,但抑制小种子萌发;不同大小种子所有萌发参数均在0 cm播种深度最大,在10cm播种深度最小。(2)不论有无种皮,大种子萌发幼苗的叶片数、单株叶面积、总干物质质量和根冠比在所有播种深度均大于小种子萌发幼苗;去皮种子萌发幼苗的株高、基径、叶片数、单株叶面积和总干物质质量在所有播种深度均不同程度地小于非去皮种子萌发幼苗,但前者根冠比在0、3、6 cm播种深度大于后者;随着播种深度增大,幼苗株高、叶片数、单株叶面积、总干物质质量和根冠比等生长参数均呈减小趋势,但基径随播种深度增大而增大。     

小五台山森林落叶层对天然青杨种群更新方式的影响

通过野外样方调查和室内种子萌发实验两种方法, 对河北小五台山天然青杨(Populus cathayana)种群的更新方式进行了研究, 以揭示落叶层的化感作用和机械阻挡作用对青杨种子萌发的干扰机理。结果显示: 1)种群样方中的幼苗都为无性繁殖的克隆分株, 种子繁殖的幼苗年自然存活率为0%; 2)落叶层对种子幼苗的存活率有显著影响。50 mg·mL^-1浓度的落叶水浸液可使青杨种子发芽率降低41%, 使主根长度减少95%, 100 mg·mL^-1浓度的落叶水浸液则完全抑制种子萌发; 单层和多层落叶对种子萌发产生的影响差异不显著, 都能完全阻碍种子的根系正常生长, 导致幼苗脱水干枯死亡。结果表明, 在高海拔山区的青杨天然林中, 由于不断积累的落叶层通过化感作用和机械阻挡作用严重影响种子的萌发、定根以及正常生长, 从而导致种子更新的途径受阻, 而只能通过无性繁殖来完成正常的种群更新。     

毛翠雀花花序内的性分配和繁殖成功

两性花植物花序内不同位置的性分配和繁殖成功一般存在差异,通常认为资源竞争、结构效应和交配环境是形成这种差异的主要原因。为了研究雄性和雌性繁殖资源在花序内不同位置间的最优分配问题,该文以青藏高原高寒草甸典型高山植物毛翠雀花为材料,通过比较花序内不同位置的花部特征和种子性状,对其花序内的性分配模式和雌性繁殖成功进行研究,并通过观察传粉者运动特点以及人工去花和补授花粉实验,探讨花序内资源竞争和交配环境对繁殖资源分配的影响。结果表明:(1)不同位置间的雄蕊数、雄蕊鲜重/雌蕊鲜重、花粉数及花粉胚珠比从花序基部到上部显著增加,而雌蕊鲜重和胚珠数逐渐减少,表现出上部花偏雄的性分配;上部花的结籽率显著低于基部花和中部花,不同位置间的发育种子数/果实和发育种子重/果实随着花位置的升高而显著降低,说明基部花具有更佳的雌性繁殖成效。(2)去花处理后,剩余果实的单个种子重/果实显著增加,但发育种子数/果实没有显著增加;而给上部花人工补授异花花粉后,位置间结籽率的差异消失,说明传粉限制而非资源竞争导致了花序内位置依赖的种子生产模式。(3)毛翠雀花雄性先熟的开花特征,以及传粉者苏氏熊蜂从花序基部到上部的定向访花行为,导致了花序内交配环境的变化。综上结果表明,毛翠雀花花序内的性分配和繁殖成功差异是对交配环境适应的结果,对其在高山环境中实现雌雄适合度最优化具有重要意义。     

红松和蒙古栎种子萌发及幼苗生长对升温与降水综合作用的响应

研究气候变暖导致的温度升高和降水格局的变化对典型植被类型建群种植物种子萌发和幼苗存活的影响,对于预测森林群落的发展趋势、种质资源保育及森林抚育更新具有重要意义.以寒温带针阔混交林的建群种和优势种红松Pinus koraiensis、蒙古栎Quercus mongolica种子和幼苗为研究对象,采用空间替代法模拟温度升高和降水变化,观察其种子萌发和幼苗生长情况.结果表明:与种源地相比,蒙古栎种子在温度升高与降水增加(年均温+4.9℃,+330 mm)或降水减少(年均温+2.8℃,-249 mm)的条件下萌发率分别下降了13％和18％,但差异不显著.红松种子在温度升高与降水增加的情况下萌发率比种源地提高了2.29倍,而降水减少时则下降了64％,不同的地点对红松的萌发率差异极显著;不同的温度、降水组合对红松和蒙古栎幼苗的生长均产生不同影响,在温度升高与降水增加与降水减少的情况下,1年生蒙古栎幼苗的株高、基径和主根长度均有明显下降,与种源地差异显著,而对红松幼苗生长的影响差异不显著;温度升高和降水增加或降水减少的交互作用使蒙古栎幼苗和红松幼苗总生物量下降,尤其是在温度升高与降水增加的条件下两种幼苗的生物量最小,分别比种源地下降了62％和20％.但统计分析表明,红松幼苗生物量在3个样地间没有显著差异.温度升高和降水变化均降低了两种幼苗的根冠比,而比叶面积没有显著差异.     

Effects of temperature and storage length on seed germination and the effects of light conditions on seedling establishment with respect to seed size in Ligularia virgaurea

Ligularia virgaurea is widely distributed in the alpine meadows of the eastern Qinghai-Tibet plateau. We studied the effects of temperature and seed storage length on seed germination in a laboratory experiment, the effects of seed mass and light intensity on seed emergence in a pot experiment, and the effect of meadow disturbance intensity on seed emergence in a field experiment. Our results showed that seeds of L. virgaurea germinated well under a wide range of temperatures. Germination percentage decreased with increased seed storage length. When seeds were stored for either 6 or 12 months the germination percentage increased with decreasing temperature. The emergence percentage of large seeds was higher than that of small seeds. Seedling survival of large seeds was greater than that of small seeds in 75% and 50% of natural irradiance. Large seeds of L. virgaurea were more successful colonizers in the alpine meadows. Seeds of L. virgaurea germinated in both disturbed meadows and non-disturbed meadows, but seed emergence and seedling establishment were higher in the disturbed meadows, that is, disturbance could facilitate the recruitment and establishment of L. virgaurea .     

Seed size as an indicator of seed quality: a case study of Primula veris

Seed size is a widely accepted measure of seed quality, because many earlier studies have shown that large seeds have high seedling survival, growth and establishment. We tested whether ovule loss increases size of the remaining seeds and whether such size increase affects seedling establishment. We removed all except one flower from inflorescences of Primula veris L. (Primulaceae), a perennial hemicryptophyte herb, at a late stage of flowering. Flower removal (FR) increased seed size by 33% compared to the control plants. We then divided the seeds within each treatment to small, middle-sized and large seeds and carried out a sowing experiment in the field. Within each experimental group, seedling establishment was positively associated with seed size. However, despite size differences, seeds from the FR and control groups had the same seedling establishment probability. Seeds from FR plants had a higher seedling emergence in May than those from control plants, but the number of seedlings alive per sowing plot in the late summer was the same in both experimental groups. Increase in seed mass after partial FR thus did not enhance seedling performance, although seed size variation due to other causes was positively correlated with seedling establishment. Further studies are needed to show whether plastic changes of seed size are usually adaptive or not.     

Seed size as an indicator of seed quality: a case study of Primula veris

Seed size is a widely accepted measure of seed quality, because many earlier studies have shown that large seeds have high seedling survival, growth and establishment. We tested whether ovule loss increases size of the remaining seeds and whether such size increase affects seedling establishment. We removed all except one flower from inflorescences of Primula veris L. (Primulaceae), a perennial hemicryptophyte herb, at a late stage of flowering. Flower removal (FR) increased seed size by 33% compared to the control plants. We then divided the seeds within each treatment to small, middle-sized and large seeds and carried out a sowing experiment in the field. Within each experimental group, seedling establishment was positively associated with seed size. However, despite size differences, seeds from the FR and control groups had the same seedling establishment probability. Seeds from FR plants had a higher seedling emergence in May than those from control plants, but the number of seedlings alive per sowing plot in the late summer was the same in both experimental groups. Increase in seed mass after partial FR thus did not enhance seedling performance, although seed size variation due to other causes was positively correlated with seedling establishment. Further studies are needed to show whether plastic changes of seed size are usually adaptive or not.     

生物土壤结皮对种子萌发和幼苗建植的影响研究进展

生物土壤结皮（BSC）在陆地生态系统中具有重要的生态地位,尤其是旱地生态系统中,BSC占据了种子植物之间的广阔地面。因此,BSC的发展必然影响种子植物更新过程与植被空间格局;但其作用方式、影响程度等因相关研究涉及多气候要素、土壤类型、BSC组成物种和种子植物物种的差异及其不同组合,导致目前的研究结论存在广泛争议。研究综合论述了BSC改变地表微形态对种子传播过程的影响;BSC改变土壤特性（物理、化学、生物学）对种子萌发和幼苗存活与建植等关键环节的影响;并结合种子形态特征及种子萌发、幼苗建植的性状等,综合分析了BSC对种子传播、种子萌发与幼苗建植等更新过程的潜在影响机理;探讨了目前研究矛盾性结论产生的原因。总体来说,深入研究并全面揭示BSC对种子植物更新过程的影响,应加强学科交叉,将分子生物学、植物生理学、生物化学等微观研究,与遥感、野外生态因子过程监测、控制实验等宏观、中观研究结合,从机理到过程方面动态研究BSC对种子植物更新过程的影响,并引入水文模型、气候模型、种群动态模型等模型预测方法,研究气候变化、各类干扰频发的情景下,BSC对种子传播、萌发及幼苗建植过程的潜在影响,以期促进对BSC与种子植物间相互关系的研究,加深对干旱脆弱生态系统植被发展规律的认识。     

Variation in floral sex allocation, female success, and seed predation within racemiform synflorescence in the gynomonoecious Ligularia virgaurea (Asteraceae)

Studies of diclinous species have showed that floral sex allocation and female reproductive success were quite variable within inflorescences. However, little attention has been paid to gynomonoecious species, in which individuals produce both female and bisexual flowers. The purpose of this study was to investigate the variations in reproductive patterns at different capitulum positions within racemiform synflorescence in Ligularia virgaurea, and to determine selective mechanisms of variations in reproductive patterns. We conducted observational and experimental studies in natural populations of the gynomonoecious composite L. virgaurea. Floral sex allocation, seed production and pre-dispersal seed predation were quantified in the field. The results showed several patterns of variation from top to bottom capitula, including an increase in bisexual flowers and flower number per capitulum, but a decrease in seed set and size. Removing earlier capitula during bud stage did not change floral sex allocation in later capitula. And no effect was found on seed set under supplemental pollination. Thus, although it has been reported many times in previous studies, the variation of floral sex allocation in L. virgaurea may not result from architectural effect or mating environment, and the variation of seed production could not be fully explained by pollination success. Additionally, our results showed that L. virgaurea was susceptible to high levels of bisexual biased predation, which was greater for top capitula. We therefore suggest that these variations may help to enhance reproductive success of L. virgaurea in the face of bisexual-biased seed predation.     

Irrigation and fertilization effects on seed number,size, germination and seedling growth: implications for desert shrub establishment

Plants with limited resources adjust partitioning among growth, survival, and reproduction. We tested the effects of water and nutrient amendments on seed production, size, and quality in Sarcobatus vermiculatus (greasewood) to assess the magnitude and importance of changes in reproductive partitioning. In addition, we assessed interactions among the environment of seed-producing plants (adult plant scale), seed size, and seedling microenvironment (seedling scale) on successful seedling establishment. Interactions of these factors determine the scale of resource heterogeneity that affects seedling establishment in deserts. Both total number of seeds produced per plant and seed quality (weight and germination) increased significantly in the enriched treatment in a 3-year field experiment. Seedling length 3 days after germination and seed N concentration, other measures of seed quality, were higher for seed from both irrigated and enriched plants than for seed from control plants. Field S. vermiculatus seed production and quality can be substantially increased with irrigation and nutrient enrichment at the adult plant scale and this allows management of seed availability for restoration. However, based on a greenhouse study, seedling environment, not the environment of the seed-producing plant or seed size, was the most important factor affecting seedling germination, survival, and growth. Thus it appears that production of more seed may be more important than improved seed quality, because higher quality seed did not compensate for a low-resource seedling environment. For both natural establishment and restoration this suggests that heterogeneity at the scale of seedling microsites, perhaps combined with fertilization of adult shrubs (or multi-plant patches), would produce the greatest benefit for establishing seedlings in the field.     

Seed Priming with Polyethylene Glycol Induces Physiological Changes in Sorghum (Sorghum bicolor L. Moench) Seedlings under Suboptimal Soil Moisture Environments

Osmopriming with PEG has potential to improve seed germination, seedling emergence, and establishment, especially under stress conditions. This research investigated germination performance, seedling establishment, and effects of osmopriming with PEG on physiology in sorghum seedlings and their association with post-priming stress tolerance under various soil moisture stress conditions. Results showed that seed priming increased the environmental range suitable for sorghum germination and has potential to provide more uniform and synchronous emergence. Physiologically, seed priming strengthened the antioxidant activities of APX, CAT, POD, and SOD, as well as compatible solutes including free amino acid, reducing sugar, proline, soluble sugar, and soluble protein contents. As a result, seed priming reduced lipid peroxidation and stabilized the cell membrane, resulting in increased stress tolerance under drought or excessive soil moisture environments. Overall, results suggested that seed priming with PEG was effective in improving seed germination and seedling establishment of sorghum under adverse soil moisture conditions. Osmopriming effectively strengthened the antioxidant system and increased osmotic adjustment, likely resulting in increased stress tolerance.     

Effects of altitude and livestock on the regeneration of two tree line forming <Emphasis Type="Italic">Polylepis</Emphasis> species in Ecuador

Regeneration is known to be limited at many temperate tree lines, but very little data is available on the impacts of altitude and anthropogenic disturbance on regeneration patterns along tropical tree lines. The study focused on the reproductive traits of two Polylepis species in the Páramo de Papallacta in Ecuador along an altitudinal gradient, and involved different intensities of cattle trampling within subsequent altitudinal ranges. We analyzed flowering, fruit set, seed viability, germination, and seedling establishment as well as stand structure of Polylepis incana and P. pauta. The numbers of P. incana inflorescences and seedlings per m2 showed a marginally significant decrease with increasing altitude. Mean tree height was significantly lower at higher altitudes, while stem number increased. The number of P. pauta inflorescences also decreased significantly upslope. In both forest types, trampling was found to have a positive impact on seedling abundance, presumably due to the removal of the litter layer. Thus, there was no evidence of negative effects of moderate cattle grazing on both tree line species. However, sapling establishment was minimal inside the forest stands at all altitudes and grazing levels, and we consequently observed a low proportion of narrow stems within all investigated forests. Our results show that, along with vegetative growth limitations of adult trees, important regeneration traits such as seedling and inflorescence numbers are also influenced by altitude, which might contribute to the formation of the upper tree line. Nevertheless, recruitment in the forest interior was low overall indicating that further factors, such as light conditions, affect regeneration of the studied species.     

Priming effects on seed germination in Tecoma stans (Bignoniaceae) and Cordia megalantha (Boraginaceae), two tropical deciduous tree species

Successful revegetation necessarily requires the establishment of a vegetation cover and one of the challenges for this is the scarce knowledge about germination and seedling establishment of wild tree species. Priming treatments (seed hydration during a specific time followed by seed dehydration) could be an alternative germination pre-treatment to improve plant establishment. Natural priming (via seed burial) promotes rapid and synchronous germination as well as the mobilisation of storage reserves; consequently, it increases seedling vigour. These metabolic and physiological responses are similar to those occurring as a result of the laboratory seed priming treatments (osmopriming and matrix priming) applied successfully to agricultural species. In order to know if natural priming had a positive effect on germination of tropical species we tested the effects of natural priming on imbibition kinetics, germination parameters (mean germination time, lag time and germination rate and percentage) and reserve mobilisation in the seeds of two tree species from a tropical deciduous forest in south-eastern México: Tecoma stans (L Juss. Ex Kunth) and Cordia megalantha (S.F Blake). The wood of both trees are useful for furniture and T. stans is a pioneer tree that promotes soil retention in disturbed areas. We also compared the effect of natural priming with that of laboratory matrix priming (both in soil). Matrix priming improved germination of both studied species. Natural priming promoted the mobilisation of proteins and increased the amount of free amino acids and of lipid degradation in T. stans but not in C. megalantha. Our results suggest that the application of priming via the burial of seeds is an easy and inexpensive technique that can improve seed germination and seedling establishment of tropical trees with potential use in reforestation and restoration practices.     

浇水频率和凋落物覆盖量对黧蒴锥种子萌发及幼苗存活的影响

黧蒴锥是华南用于人工造林和生态恢复的优良乡土树种.选取浇水频率和凋落物覆盖量两个控制因子,研究在不同的土壤湿度和凋落物覆盖量条件下,黧蒴锥种子萌发及幼苗存活和生长特征.结果表明: 凋落物对黧蒴锥种子萌发和幼苗生长的影响与环境的潮湿程度相关.当浇水频率为每天1次时,凋落物覆盖会抑制黧蒴锥种子萌发和幼苗早期生长,导致种子萌发率降低、幼苗死亡率提高; 在浇水频率为2 d 1次和3 d 1次时,凋落物覆盖可以改善土壤的水分状况,有助于种子萌发和幼苗存活.凋落物覆盖还可以显著地提高幼苗的生物量.在通过播种来实现亚热带灌木林地更新时,可利用凋落物覆盖促进黧蒴锥的种子萌发和幼苗存活.