高寒草甸矮嵩草种群繁殖对策的研究

繁殖对策是指生物对环境的生殖适应趋势,是资源或能量向生存、生长和生殖等活动中最适分配的结果,在不同的环境中具有其独特的表现形式.研究植物在不同环境中的繁殖对策可以反映出植物对环境的适应能力和在该生境中的生殖潜能.国内外学者对植物繁殖对策的研究已有不少报道 [2,4,5,6]. 但对高寒草甸矮嵩草(Kobresia humilis)种群繁殖对策的研究报道甚少.     

高寒草甸矮蒿草种群繁殖对策的研究

繁殖对策是指生物对环境的生殖适应趋势 ,是资源或能量向生存、生长和生殖等活动中最适分配的结果 ,在不同的环境中具有其独特的表现形式。研究植物在不同环境中的繁殖对策可以反映出植物对环境的适应能力和在该生境中的生殖潜能。国内外学者对植物繁殖对策的研究已有不少报道[2 ,4 ,5,6] 。但对高寒草甸矮嵩草 (Ｋｏｂｒｅｓｉａｈｕｍｉｌｉｓ)种群繁殖对策的研究报道甚少。矮嵩草是青藏高原矮嵩草草甸的建群种 ,它具有草质柔软、营养丰富、热值含量较高等特点 ,是青藏高原重要的可更新草地资源。本研究对矮嵩草的繁殖对策进行了较全面、…     

不同放牧强度对人工草地牧草生殖分配及种子重量的影响

不同放牧强度对白三叶,红三叶,鸭茅的生殖分配及种子千粒重影响极显著,一定强度的放牧干扰有利于提高休牧后三叶草的花序密度,但鸭茅花序密度却随放牧强度却随放牧强度的提高而出现明显下降,放牧草地三种牧草种群的生殖分配均低于对照草地,在放牧草地,随放牧强度的提高,白三叶生殖分配逐渐增加,红三叶及鸭茅生殖分配逐渐减少,提高放牧强度后,三叶草千粒重出现递减趋势,而鸭茅却出现递增趋势,在无放牧干扰草地,三叶草种群趋于生产数量较少的大粒种子,在放牧干扰下,趋于生产数量较多的小粒种子;鸭茅种群则出现相反的变化。     

不同刈牧强度对冷蒿生长与资源分配的影响

利用野外实验与盆栽实验,对不同刈牧强度下冷蒿生长与资源分配影响的研究结果表明,按比例刈割冷篙的再生生长大于留茬高度刈割,在生长季前期,不刈割冷蒿净生长高于刈割处理,而进入生长季中后期(8月中旬以后),轻度刈割净生长高于不刈割处理,冷篙种群生物量分配的总体格局是根>叶>茎,刈牧明显影响冷蒿生物量分配格局,尤其是叶和花的分配,3／4刈割或留茬4cm刈割叶生物量分配显著高于其它各处理,而花的生物量及其分配显著低于其它处理,根、茎生物量分配各处理间差异不显著．冷蒿有性生殖分配随刈牧强度的增加而降低,繁殖方式发生了改变,优先将光合产物分配给再生茎以及繁殖方式转向营养繁殖,通过克隆生长维持和扩大种群是冷蒿对强度放牧的生态适应对策。     

放牧格局和生境资源对矮嵩草（Kobresia humilis）分株生物量分配和补偿性生长的影响

为研究密集型克隆植物对放牧扰动和生境资源变化的生物量分配和补偿生长响应特性,验证克隆植物的觅食模型和3个有关植物个体补偿反应的假说(①放牧优化假说,grazing optimization hypothesis,GOH;②反应连续谱假说,continuum of responses hypothesis,CRH;③增长率模型,growth rate model,GRM),在具有不同放牧利用格局和土壤养分水平的高寒矮嵩草草甸(Ⅰ.畜圈草地:重度放牧、资源丰富;Ⅱ.牧道草地:中度放牧、资源贫乏;Ⅲ.封育草地:不放牧、资源贫乏)中通过设置扣笼/无扣笼样方对其建群种矮嵩草(Kobresia humilis)进行了研究.结果表明不论当年解除家畜放牧与否,春季采摘率越高(畜圈草地),分株生物量向生长的投入越少,向贮藏器官的投入越多.繁殖分配在中度采摘下最高(牧道草地),扣笼内外分株各部分的生物量分配无差异.矮嵩草分株在中度采摘×资源贫乏条件下产生了超补偿响应,在重度采摘×资源丰富条件下为等量补偿,重度采摘导致分株密度显著减少.生物量分配格局与觅食模型的预测不符.补偿生长响应特性证实了GOH和GRM的预测,但与CRH的预测不符.这说明在研究地区放牧扰动格局对克隆植物矮嵩草分株的生物量分配和补偿生长具有重要影响,适度放牧利用更利于引起超补偿,而重度利用可能会对该种群的长期保持产生不利影响.     

放牧退化群落中冷蒿种群生物量资源分配的变化

对放牧退化群落中冷蒿种群生物量及生物量资源分配的变化进行了研究.结果表明,在放牧干扰下,随着放牧退化程度的增加,冷蒿种群叶、茎、根的生物量及总生物量增加.其中根的重量增加幅度较大,但生殖构件(花序、果实)的生物量在轻度退化群落中增加,中度退化群落中迅速减少,重度退化群落中未发现生殖构件.随着放牧退化程度增加,冷蒿种群生物量的资源分配发生变化,对根的分配增加,对茎、叶的分配减少,根冠比增加;对无性繁殖的分配增加,对有性生殖的分配减少.在重度退化群落,冷蒿有性生殖严重受阻,繁殖格局发生变化.从资源分配的动态来看,随着放牧退化程度的增加,生长初期至盛期,冷蒿种群资源优先分配给地上部分,尤其是光合器官叶;而生长盛期至末期,资源优先分配给有性生殖或贮藏器官.繁殖格局的转变是冷蒿种群耐牧,在重度退化下成为建群种的关键.资源分配格局的时空变化,使生长、维持和繁殖等方面的分配达到和谐,是冷蒿种群在重度退化下成为建群种的物质基础.     

放牧对草原植物功能性状影响研究进展

植物功能性状的表达和植被环境适应性相关,植物功能性状之间的权衡变化体现了植物在放牧胁迫下资源的重新整合和获取。本文总结了放牧干扰下植物功能性状表达的差异性,着重将放牧干扰与植物功能性状相结合,介绍了植物功能性状的变异来源是植物遗传特征与环境过滤相互协调的结果,归纳了放牧对植物营养性状、繁殖性状的影响,以及植物可以通过调整生存和繁殖策略以适应放牧干扰。本文集中于放牧对植物种群、群落和生态系统的影响。不同放牧干扰下植物功能性状的表达具有差异性,因此植物功能性状可作为解释种群生长和繁殖、群落构建过程和生态系统功能的指标。为使植物功能性状的研究更好地服务于草地生态环境,可依据植物功能性状筛选合理的草地抗牧物种;依据草地植物种群的生活史特征,制定科学的放牧机制;以植株为整体综合考虑植物功能性状变化,提出放牧研究中植物功能性状的发展方向。     

不同载畜率下瓣蕊唐松草的生长和繁殖对策

放牧是内蒙古草原最主要的利用方式, 而草原植物在不同放牧压力下的生长和繁殖策略是它们与有蹄类动物长期协同进化的结果。为了了解瓣蕊唐松草(Thalictrum petaloideum)的生长和繁殖策略如何响应载畜率的变化, 作者依托中国科学院内蒙古草原站的大型放牧实验平台, 从种群、个体和器官三个组织水平上研究了该物种对放牧强度的响应。结果表明: 1)在种群水平上, 随着载畜率的增加, 瓣蕊唐松草减少了生殖株丛数或不进行有性生殖生长。该实验条件下, 载畜率每hm ² 7.5只羊(夏季)是瓣蕊唐松草不再进行生殖生长的阈值; 2)在个体水平上, 随着载畜率的增加, 瓣蕊唐松草降低了株高和个体生物量, 减少了生殖枝、花朵和种子等生殖器官的数量。随着载畜率的增加, 瓣蕊唐松草生殖分配的调节从依赖于植株个体大小向不依赖于植株个体大小转变。3)在器官水平上, 随着载畜率的增加, 瓣蕊唐松草减少了生殖枝的花朵负荷, 提高了单粒质量。籽粒数量和籽粒质量之间的权衡是瓣蕊唐松草应对放牧干扰的重要机制。     

Growth and reproductive strategies of Thalictrum petaloideum under different stocking rates

放牧是内蒙古草原最主要的利用方式, 而草原植物在不同放牧压力下的生长和繁殖策略是它们与有蹄类动物长期协同进化的结果。为了了解瓣蕊唐松草(Thalictrum petaloideum)的生长和繁殖策略如何响应载畜率的变化, 作者依托中国科学院内蒙古草原站的大型放牧实验平台, 从种群、个体和器官三个组织水平上研究了该物种对放牧强度的响应。结果表明: 1)在种群水平上, 随着载畜率的增加, 瓣蕊唐松草减少了生殖株丛数或不进行有性生殖生长。该实验条件下, 载畜率每hm ² 7.5只羊(夏季)是瓣蕊唐松草不再进行生殖生长的阈值; 2)在个体水平上, 随着载畜率的增加, 瓣蕊唐松草降低了株高和个体生物量, 减少了生殖枝、花朵和种子等生殖器官的数量。随着载畜率的增加, 瓣蕊唐松草生殖分配的调节从依赖于植株个体大小向不依赖于植株个体大小转变。3)在器官水平上, 随着载畜率的增加, 瓣蕊唐松草减少了生殖枝的花朵负荷, 提高了单粒质量。籽粒数量和籽粒质量之间的权衡是瓣蕊唐松草应对放牧干扰的重要机制。     

克隆植物种子繁殖和营养繁殖的适合度分析和度量

植物种群繁殖的适合度指繁殖行为适应环境变化的能力及其对各群更新发展的贡献,不仅表现在个体水平也表现在基因水平。提出度量种子繁殖和营养繁殖在个体和基因水平的适合度的计算公式,并计算了白三叶草繁殖的适合度,较好地解释了种子繁殖和营养繁殖对克隆植物种群更新发展朱同作用。     

Trade-offs between sexual and asexual reproduction in a monoecious species Sagittaria pygmaea (Alismataceae): the effect of different nutrient levels

Available resources could influence the trade-offs among different reproductive components in plants. Here, we created three nutrient levels to test the nutrient effects on trade-offs among sexual reproduction, clonal propagation and vegetative growth in a monoecious clonal herb Sagittaria pygmaea. The results of this study showed that the plant exhibited different trade-off patterns among different nutrient levels. When the nutrient level was low, there were weak trade-offs between sexual reproduction and vegetative growth and between clonal propagation and vegetative growth; when the nutrient level was moderate, we found a strong trade-off between sexual reproduction and clonal propagation; but when the nutrient level was high, we found no trade-offs among these three different reproductive components. These results indicated that the plant could adjust its trade-off patterns to fit the nutrient variation and suggested that trade-offs are unlikely to constrain the evolution of reproductive strategy in this species.     

Effects of clonality on the genetic variability of rare,insular species: the case of Ruta microcarpa from the Canary Islands

Many plant species combine sexual and clonal reproduction. Clonal propagation has ecological costs mainly related to inbreeding depression and pollen discounting; at the same time, species able to reproduce clonally have ecological and evolutionary advantages being able to persist when conditions are not favorable for sexual reproduction. The presence of clonality has profound consequences on the genetic structure of populations, especially when it represents the predominant reproductive strategy in a population. Theoretical studies suggest that high rate of clonal propagation should increase the effective number of alleles and heterozygosity in a population, while an opposite effect is expected on genetic differentiation among populations and on genotypic diversity. In this study, we ask how clonal propagation affects the genetic diversity of rare insular species, which are often characterized by low levels of genetic diversity, hence at risk of extinction. We used eight polymorphic microsatellite markers to study the genetic structure of the critically endangered insular endemic Ruta microcarpa. We found that clonality appears to positively affect the genetic diversity of R. microcarpa by increasing allelic diversity, polymorphism, and heterozygosity. Moreover, clonal propagation seems to be a more successful reproductive strategy in small, isolated population subjected to environmental stress. Our results suggest that clonal propagation may benefit rare species. However, the advantage of clonal growth may be only short‐lived for prolonged clonal growth could ultimately lead to monoclonal populations. Some degree of sexual reproduction may be needed in a predominantly clonal species to ensure long‐term viability.     

Flowering does not decrease vegetative competitiveness of Lolium perenne

The theory of life-history evolution commonly assumes a trade-off between sexual and vegetative reproduction. Hence, production of flowers and fruits should have measurable costs in terms of reduced vegetative growth. This trade-off may be meaningful for breeding of forage and turf grasses as reduced flowering could free resources and increase productivity. But if so, less-flowering cultivars might be more competitive and invade natural swards. We tested for costs of sexual reproduction on vegetative propagation and competitiveness of the perennial grass Lolium perenne, one of the most important forage and turf grasses worldwide. We used the differences in vernalisation requirement between northern and southern European provenances to manipulate the degree of flowering. Over three growing seasons, we counted the number of flower stems and measured the clone diameter. The vernalisation treatments were successful in producing clones with largely differing degrees of flowering. However, we found no negative correlation between flowering and vegetative propagation and competitiveness. Early and strongly flowering southern provenances showed less clonal growth and higher mortality, but within provenances the response of clone diameter to flowering was positive or neutral. We conclude that investment of resources into flowering has no measurable costs on vegetative propagation and competitiveness of L. perenne. The apparent lack of costs of sexual reproduction could be explained by bet-hedging strategy that is focused on survival and growth rather than reproductive effort in order to maximise the life-time fitness.     

After grazing exclusion,is there any modification of strategy for two guerrilla species: <Emphasis Type="Italic">Elymus repens</Emphasis> (L.) Gould and <Emphasis Type="Italic">Agrostis stolonifera</Emphasis> (L.)?

Elymus repens (L.) Gould and Agrostis stolonifera (L.), are competitive grasses with guerrilla strategy that invade grasslands with a low stocking rate. In this work, we tested the hypotheses that grazing exclusion facilitates vegetative development of rhizomes and stolons of these clonal grasses and that such change is a key mechanism for their abundance in set-aside grasslands. The competitive capacities of these two guerrilla species were characterised by samples in plant community (species richness and biomass) and on the level of individual species (morphometric measurements on stolons and rhizomes) during a growing season. Compared to grasslands where grazing was excluded for three years, species richness was higher in grazed site and the plant community structure differed. Indeed, with grazing exclusion, a shift from annual species with a diversified growth-form to perennial species with a tall tussock and graminoid growth-form was monitored. In ungrazed situation, Elymus repens and Agrostis stolonifera were the dominant grasses, and the standing biomass for the lowland community showed a significant increase compared to the grazed site. Vegetative development increased competitive capacities of these two guerrilla species and led by phenomenon of competitive exclusion to the disappearance of annuals species. With grazing cessation, Elymus repens was found to increase the size of aerial traits (shoot length and the number of leaves per shoot) and this may both be propitious for achieving dominance within plant communities and also maintaining its competitive local advantage. By contrast, Agrostis stolonifera showed an increase in a root trait, i.e. rhizome length, in the fenced site, which provide good ability for spatial propagation and then to explore adjacent patches. We concluded that Elymus repens presented a morphological capacity to change its colonising strategy from a guerrilla strategy to a phalanx strategy, by morphological variability of aerial organs, when it was submitted to competitive stress and environment modifications. Agrostis stolonifera showed a capacity to escape aerial competition resulting from grazing cessation, than to increase underground propagation capacity. The present study highlighted the capacities of Elymus repens to respond in an adaptative way to competitive pressure.     

内蒙古典型草原退化机理的研究

在内蒙古冷蒿小禾草退化草原上,经过６年围栏定量的放牧,分别对９种主要植物种群的形态学特征对放牧的响应进行了研究．结果表明,不同生活型和营养繁殖方式的牧草对放牧率的响应策略是不同的,从而构成了不同放牧率下群落演替的基础．匍匐以不定根行营养繁殖生长或分蘖性强的种群是较适应于重牧的,如冷蒿（Ａｒｔｅｍｉｓｉａｆｒｉｇｉｄａ）和星毛委陵菜（Ｐｏｔｅｎｔｉｌａａｕｃｕｌｉｓ）;以根茎和分蘖行营养繁殖的羊草（Ｌｅｙｍｕｓｃｈｉｎｅｎｓｅ）和冰草（Ａｇｒｏｐｙｒｏｎｃｒｉｓｔａｔｕｍ）及丛生禾草克氏针茅（Ｓｔｉｐａｋｒｙｌｏｖｉ）属宜轻牧植物;以根茎和分蘖行营养繁殖的寸草苔（Ｃａｒｅｘｄｕｒｉｕｓｃｕｌａ）和小丛生禾草糙隐子草（Ｃｌｅｉｓｔｏｇｅｎｅｓｓｑｕａｒｒｏｓａ）属宜中牧植物;而以分枝行营养繁殖的扁蓿豆（Ｍｅｌｉｓｉｔｕｓｒｕｔｈｅｎｉｃａ）和木地肤（Ｋｏｃｈｉａｐｒｏｓｔａｔａ）则宜轻牧．随着放牧率的增大,群落发生明显的变化,小禾草的比例逐渐减少,冷蒿小禾草退化草原最终进一步趋同于星毛委陵菜退化草原;而轻牧可以维持草原现状或使其发生恢复演替,禾草比例增加,即可达到利用式改良的目的     

Density-dependent reproductive and vegetative allocation in the aquatic plant Pistia stratiotes (Araceae)

Pistia stratiotes is an aquatic macrophyte that grows in temporary-ponds in the southern Pantanal, Brazil. It reproduces both sexually and asexually and is usually observed forming dense mats on the water surface, a condition favored by the plant's vegetative reproduction coupled with an ability for rapid growth. In this study we examined the effect of densely crowded conditions on the production of reproductive and vegetative structures. In addition, we verified whether there is a trade-off between clonal growth and investment in sexual reproductive structures, and whether there is an allocation pattern with plant size. Individual plant biomass and the number of the rosettes producing sexual reproductive structures and vegetative growth structures both increased with density. Increase in plant size resulted in increased proportional allocation to sexual reproductive structures and vegetative growth structures. Allocation of biomass to reproduction did not occur at the expense of clonal growth. Thus, the density response appears as a increase of rosettes producing sexual reproductive structures and vegetative growth structures. Therefore, long leaves and stolons may be adaptive under densely crowded conditions where competition for light is intense. An important aspect in the study of trade-offs is the size-dependency of the allocation patterns .Usually, larger plants produce more biomass. Therefore, larger plants can allocate more biomass to both vegetative and sexual reproduction than smaller plants and thus show a positive correlation between both traits rather than the expected negative one.     

高寒草甸放牧扰动与两种植物的反应研究

对不同放牧强度下矮嵩草草甸植物垂穗披碱草和鹅绒委陵菜的生长和繁殖特性进行了5年研究。结果表明,垂穗披碱草株高、分蘖数、地上物量、地下生物量、有性繁殖效力在不放牧或轻度放牧下最大,营养生长效力在重度放牧中最大,而贮藏效力在重度放牧中最小。鹅绒委陵菜叶数、匍匐茎长度、地上生物量、匍匐茎生物量、开花数、生殖生物量、有性繁殖效力及营养繁殖效力在放牧区显著高于不放牧的对照区。说明适当的放牧干扰有利于垂穗披碱草营养生长,但放牧过重会抑制其有性繁殖;由于放牧采食减少了种间竞争影响,从而提高了鹅绒委陵菜营养,生长效力和有性繁殖效力。两物种地下贮藏物的比例随着放牧强度增加显著减少。放牧强度对高寒草甸的群落演替方向有显著影响。     

甘南亚高山草甸群落的物候谱研究──兼论群落种多样性维持的机制

本文研究了亚高山草甸群落中常见的４２种植物的物候期。研究结果表明,此４２种植物在返青时间顺序、进入生殖生长的个体数量比例和进入生殖生长阶段的起始时间、历期上各不相同。根据返青顺序可将４２种植物分为三类。以单子叶禾莎草的返青时间为最早,多年生双子叶植物的返育时间较晚。根据进入生殖生长的个体占种群总个体数量的比例可分为：（１）生殖生长的个体比例在２０％以下,主要靠营养繁殖的种类;（２）具有双重繁殖特性的种类;（３）生殖个体占５０％以上的种类和（４）完全依靠有性繁殖的种类共四类。根据进入生殖生长的起始时间可分为三类。以上结果在一定程度上说明了植物种间由于在生长发育时间上的错位,减缓了种间对资源（如土壤矿物质营养）的竞争,使得群落中有多个种共存。     

The biology of Butomus umbellatus in shallow waters with fluctuating water level

Butomus umbellatus L. is a plant species typical of littoral communities of river and stream shores. It can form continuous stands in shallow reservoirs with fluctuating water level. Their expansion is promoted by: (a) intensive vegetative reproduction of plants, (b) crowded sprouting from rhizome fragments on emerged pond bottom, (c) shallow water layer in the year following summer drainage. Expansion of B. umbellatus depends on ploidy level: two cytotypes were found in the Czech and Slovak Republics, differing in their reproductive ability. Seed production of triploids is strongly limited (they are self-incompatible within clones), while diploids can be fully fertile. Nevertheless, even in diploids, the efficiency of seed reproduction under natural conditions is low. Triploids spread by intensive vegetative reproduction, which is decisive for clonal growth of populations and their regeneration after scraping of bottom surface. During seasonal development, maximum of aboveground biomass is produced in early summer, while underground biomass increases till autumn. Growth of the plants is limited by cutting before maximum underground biomass is attained, or by duck grazing.     

Strategies in Mediterranean grassland annuals in relation to stress and disturbance

Abstract. Morphological (size and shape) and functional (growth, reproduction and phenology) attributes are used to characterize 42 annual species of Mediterranean grasslands according to their strategy. Principal component analysis of the matrix of 42 species x 9 attributes shows that the main trend of variation is related to plant size. Larger species have larger seeds, lower relative growth rates and lower reproductive output. The second and third trends of variation are related to plant shape. Ordination of species shows differences in shape between taxa and growth forms (grasses, legumes, forbs). The relative abundance of species with different attributes vary with the level of stress (water and nutrient availability) and disturbance (grazing and ploughing). Size is related to stress, with larger plants dominating in productive habitats and smaller ones in the most unproductive. Disturbance is related to shape and phenology, since grazing favours species with low canopies and ploughing favours species with shorter life cycles, that are usually small in size. Relations between plant attributes and habitat characteristics are examined within the more general framework of plant strategy theory.