Distribution of clonal growth forms in wetlands

Clonal multiplication is a predominant type of reproduction in wetland species. However, both wetlands and plant organs of clonal growth are diverse, thus due to different stress factors operating in various wetlands preponderance of plants with specific clonal growth organs (CGOs) can be expected. To test this hypothesis the CGO spectra of wetland communities of the Netherlands were analysed, including a bog, a fen, heathland, a floodplain, river beds, fresh water pools, open salt water and a salt marsh. Moreover, it was evaluated whether different CGOs are characterised by different functional traits (shoot cyclicity, persistence of connections between ramets, number of offspring produced per year and lateral spread per year) in wetland species. Data on types of CGO, i.e., epigeogenous and hypogeogenous rhizomes, fragments and budding plants, stolons, tubers and bulbs, root-splitters, root-sprouters and special adaptations (turions) as well as their functional traits, were taken from the CLO-PLA 3 database. CGO spectra of wetland communities were analysed using two methods: comparison of observed vs. expected CGO spectra based on the presence/absence data and multivariate analysis (CCA) for inter-community differences considering species frequency. Moreover, relationships between CGOs and their functional traits were tested using multidimensional contingency tables. Apart from 26% of non-clonal species, the majority of wetland species was rhizomatous (51%). Other types of CGO were represented in less than 10% of species and root-derived CGOs were underrepresented (<2%) in comparison with terrestrial habitats. Among communities, fresh water pools and open salt water hosted higher proportion of species with fragments (∼10%) and turions (∼30%). Multivariate analysis divided wetland communities along the disturbance and hydric (water) gradients. Highly disturbed communities (salt marshes) were characterised by non-clonal species and species with root-derived CGOs. Aquatic communities (fresh water pools and open salt water) hosted species with the ability to spread by fragmentation and turions, contrary to permanently wet communities (bog and wet heathland) with the prevalence of species with epigeogenous rhizomes. It was also confirmed that the CGOs of wetland species differed in their traits. The most important functional trait characterising individual CGOs in the wetland flora was the degree of lateral spread (explained variability: 53%) followed by duration of persistence of connections between ramets (explained variability: 74%), which is in accordance with earlier distinguished strategies of clonal growth: integrator/splitter and spreading/non-spreading clones.     

资源异质性环境中的植物克隆生长 :觅食行为

植物行为(plantbehaviour)[1,2]和植物克隆生长(clonalgrowthinplants)[3～5]是欧美近年来新兴的两个生态学研究领域。他们的交叉部——克隆植物的觅食行为(foragingbehaviour)[6～8]研究的成果不断地发表在各种重要国际学术刊物上[5,6,8,9]。它主要探讨克隆植物在资源异质性分布的环境中获取需资源的生态对策[8,10]。它突破了传统的植物个体“固定着生”的观念,与其它克隆植物生态学研究结果一道丰富了主要在研究非克隆植物基础上建立的(尤其是关于个体及个体以上组织水平)生物学和生态学的理论。并且具有潜在的应用价值。1　植物克隆生长…     

Clonal Growth in Plants in Relation to Resource Heterogeneity:Foraging Behavior

In nature, essential resources for organisms, such as food for animals and light, water and nutrients for plants, are usually heterogeneously distributed, even at very small scale. As a result, all organisms, particularly plants mostly sessile, have a difficulty in acquiring essential resources from their environments. Animals express various types of foraging behavior to capture heterogeneously distributed essential foods. Clonal growth ( a vegetative reproductive process where by more than one individual of identical genetic composition is formed ) provides clonal plant not only with many \"mouths\" at different spatial positions, but also with a large spacial movability. As a clonal plant grows in environments characterized by a small-scale resource heterogeneity, its inter ramet connection permits a resource-sharing among the connected tamers. In addition, it may also allow certain ramets to respond locally and non-locally to resousce heterogeneity. This may lead to a division of labor among the connected ramets and a selective placement of ramets in favorable micro-habitats. Together these may enhance exploitation of resource heterogeneity by clonal plants, and in turn greatly contribute to maintenance or improvement of fitness. Such a behavior of clonal plants, expressed in heterogeneous environments, is to a large extent comparable to that of animals. Therefore, it has been considered as foraging behavior in clonal plants. More recently, it has been observed that phenotypic plasticity of clonal plants, which is relevant to foraging behavior, varies among species, types of genet architecture as well as among types of plants habitats. Foraging in clonal plants and its diversity have been receiving increasingly intensive investigations.     

Functional specialization of ramets in Scirpus maritimus – Splitting the tasks of sexual reproduction, vegetative growth, and resource storage

Clonal plant species can be considered as populations of interconnected ramets which are basically identical in form and function, and potentially independent from each other. Experimental studies and field observations suggest that an intra-clonal specialization of ramets with different roles (division of labour) can increase the performance of clonal systems under heterogeneous conditions. This paper explores structural and functional variation in the emergent macrophyte Scirpus maritimus, which forms ramets that specialize in three main activities: sexual reproduction, photosynthetic assimilation and vegetative growth, and reserve storage. The main question asked in this study is whether such specialization is a developmentally programmed syndrome in this species, and whether environmental conditions can alter the pattern of ramet differentiation along rhizome systems.We analyzed clonal fragments collected from a population in the field, and grew clones individually in pots of two sizes to simulate different degrees of crowding and shoot density. Specialization of ramets was largely predictable from their position along the rhizome system, indicating that specialization is an inherent feature (developmentally programmed) of clone ontogeny in S. maritimus. In the field, sexual ramets were always situated at the base of rhizome systems, vegetative ramets were in first and intermediate positions, and shoot-less storage ramets were almost always formed distally on rhizomes (terminal ramets). In the pot experiment flowering ramets were observed in all positions along rhizome systems, suggesting that specialization for sexual reproduction shows a plastic response to environmental conditions.S. maritimus can adjust the relative numbers of ramets with and without above-ground shoots when grown in different shoot densities, i.e. the frequency of individual ramets responsible for a certain functional or developmental process can be adjusted to environmental conditions and internal needs. In S. maritimus, the density-dependant regulation of storage versus vegetative growth and sexual reproduction may represent a mechanism to limit shoot competition in crowded populations.     

Differential effects of light quantity and spectral light quality on growth, morphology and development of two stoloniferous Potentilla species

Plant species from open habitats often show pronounced responses to shading. Apart from a reduction in growth, shading can lead to marked changes in morphology and architecture, and it may affect the rate of plant development. Natural shade comprises two basically different features, a reduction in light quantity (amount of radiation) and changes in the spectral light quality. The first aspect represents changes in resource availability, while the latter acts as a source of information for plants and can prompt morphogenetic responses. A greenhouse experiment was carried out to study the effects of changes in light quality and quantity on the growth, morphology and development of two stoloniferous Potentilla species. Individual plants were subjected to three light treatments: (1) full daylight (control); and two shade treatments, in which (2) light quantity (photon flux density) and (3) light spectral quality (red/far-red ratio) were changed independently. Plant development was followed throughout the study. Morphological parameters, biomass and clonal offspring production were measured at the end of the experiment. Morphological traits such as petiole length, leaf blade characteristics and investment patterns into spacers showed high degrees of shade-induced plasticity in both species. With a few exceptions, light quality mainly affected morphological variables, while production parameters were most responsive to changes in light quantity. Potentilla anserina allocated resources preferentially to established rosettes at the cost of stolon growth and branching, while in P. reptans, all parameters related to development and allocation were slowed down to the same extent by light limitation. Light quality changes also positively affected biomass production via changes in leaf allocation. Changes in the spectral light quality had major effects on the size of modular structures (leaves, ramets), whereas changes in light quantity mainly affected their numbers. Received: 12 December 1997 / Accepted: 8 July 1998     

Restoration of genetic diversity from soil seed banks in a threatened aquatic plant, <Emphasis Type="Italic">Nymphoides peltata</Emphasis>

Populations of a threatened aquatic plant, Nymphoides peltata, have rapidly degenerated under the influence of recent artificial changes in Lake Kasumigaura of Japan. To estimate the potential of soil seed banks for genetic restoration of the species, we used 10 microsatellite markers to analyze the genetic variation in adults and in seedlings that emerged from soil seed banks. About 187 leaf samples from the cultured stocks that were collected in 17 adult subpopulations in 1995 and 2000 and from three subpopulations that were newly discovered in 2002 were analyzed. As a result, only 18 genets could be identified, suggesting that clonal diversity of the adult population had already become extremely low. Genetic tests were performed on 430 seedlings from seed banks at six locations of natural lakeshores and three of the restoration sites that were artificially constructed in an attempt to assign them to the remnant adult population; many of the seedlings showed genetic variation different from the adults. Furthermore, the seedlings preserved seven alleles that had been lost from remnant adults. However, they had lower average numbers of alleles and heterozygosity levels (NA = 1.5–3.1, H _E = 0.146–0.487) than the remnant adults (NA = 3.5, H _E = 0.539) and showed high inbreeding coefficients, suggesting that the seed banks were produced by inbreeding. Thus, although the seed banks had a certain potential to restore genetic diversity, the fitness reduction in seed banks caused by inbreeding could affect the success of restoration based on seed banks.     

Plant population growth and competition in a light gradient: a mathematical model of canopy partitioning

Can a difference in the heights at which plants place their leaves, a pattern we call canopy partitioning, make it possible for two competing plant species to coexist? To find out, we examine a model of clonal plants living in a nonseasonal environment that relates the dynamical behavior and competitive abilities of plant populations to the structural and functional features of the plants that form them. This examination emphasizes whole plant performance in the vertical light gradient caused by self-shading. This first of three related papers formulates a prototype single species Canopy Structure Model from biological first principles and shows how all plant properties work together to determine population persistence and equilibrium abundance. Population persistence is favored, and equilibrium abundance is increased, by high irradiance, high maximum photosynthesis rate, rapid saturation of the photosynthetic response to increased irradiance, low tissue respiration rate, small amounts of stem and root tissue necessary to support the needs of leaves, and low density of leaf, stem, and root tissues. In particular, equilibrium abundance decreases as mean leaf height increases because of the increased cost of manufacturing and maintaining stem tissue. All conclusions arise from this formulation by straightforward analysis. The argument concludes by stating this formulation's straightforward extension, called a Canopy Partitioning Model, to two competing species.     

Seaweed micropropagation techniques and their potentials: an overview

The seaweed industry worldwide uses 7.5–8.0 million tonnes of wet seaweeds annually with a majority of it derived from cultivated farms, as the demand for seaweed based-products exceeds the supply of seaweed raw material from natural stocks. The main advantage of cultivation is that it not only obviates overexploitation of natural populations but also facilitates the selection of germplasm with desired traits. To enhance the economic prospects of seaweed cultivation, varied practices, such as simple and cost effective cultivation methods, use of select germplasm as seed stock coupled with good farm management practices, etc., are adopted. Nevertheless, in vitro cell culture techniques have also been employed as they facilitate development and propagation of genotypes of commercial importance. There are more than 85 species of seaweeds for which tissue culture aspects have been reported. Although the initial aim of these techniques focuses mostly on genetic improvement and clonal propagation of seaweeds for mariculture, recently the scope of these techniques has been extended for use in bioprocess technology for production of high value chemicals of immense importance in the pharmaceutical and nutraceutical sectors. Recently, there has been a phenomenal interest in intensifying seaweed tissue and cell culture research to maximize the add-on value of seaweed resources. This paper deals with the status of seaweed micropropagation techniques and their applications in the context of the marine biotech industry. Further, it also provides an analysis of the problems to be resolved for removing the barriers that are impeding the true realization of potentials offered by these techniques for sustainable development and utilization of seaweed resources.     

Invertebrate grazing during the regenerative phase affects the ultimate structure of macrophyte communities

1. Although the biomass of freshwater macrophytes consumed by invertebrate herbivores (excluding crayfish) is usually low, there is growing evidence that invertebrates do exert a structuring effect on macrophyte communities. To explain this, we postulated that the effect of invertebrates may be concentrated on macrophytes during their regenerative phase.
2. We tested this hypothesis by means of a mesocosm-based experiment, in which we investigated the effects of different densities of pond snails [ Lymnaea stagnalis (L.)] on macrophytes regenerating from the natural sediment propagule bank.
3. After 2 months, a diverse macrophyte community had established in the absence of snails, mainly from sexual propagules. Under moderate snail grazing (4 individuals m⁻²), the ultimate biomass of macrophytes was similar, but its species composition differed dramatically. Only a few unpalatable taxa, such as Ceratophyllum demersum and Nymphaeaceae, persisted. Moreover, the relative success of macrophytes regenerating from vegetative rather than sexual propagules improved. Under higher snail grazing (20 m⁻²), all macrophytes disappeared before the end of the experiment.
4. These results confirm that snails at natural densities can have a strong effect on the ultimate structure of macrophyte communities by selectively consuming some species at a juvenile stage. Therefore, the regenerative phase can be seen as a window of opportunity for invertebrate grazers, which can have a qualitative effect on communities that is disproportionate to the biomass consumed.     

科尔沁沙地69种植物种子重量比较研究

 研究了科尔沁沙地69种植物的繁殖体（30种为种子,39种为果实）重量。结果表明：1）传播体为果实的植物可分为4个组别（即果实单粒重<0.1 mg、0.1～0.999 9 mg、1～9.999 9 mg、10～99.999 9 mg）;黄蒿（Artemisia scoparia）果实(0.051 7 mg)和小香蒲（Typha minima）果实(0.068 2 mg)最轻,苍耳（Xanthium sibiricum）单个果实（77.894 3 mg）最重;2）传播体为种子的植物可分为3个组别（即种子单粒重0.1～0.999 9 mg、1～9.999 9 mg、10～99.999 9 mg）;马齿苋（Portulaca oleracea）种子（0.151 4 mg）最轻,苦参（Sophora flavescens）种子(46.781 6 mg)最重;3）黄蒿、马齿苋、轮叶沙参（Adenophora tetraphylla）、碱地肤（Kochia sieversiana）、狼尾花（Lysimachia barystachys）、灰绿藜（Chenopodium glaucum）、刺沙蓬（Salsola ruthenica）、菟丝子（Cuscuta chinensis）、大籽蒿（Artemisia sieversiana）、狗尾草（Setaria viridis）、野古草（Arundinella hirta）等植物所以广泛分布可能是因为它们繁殖体轻（<1 mg）且具有持久土壤种子库;4）流沙上的先锋植物或沙生演替系列前期植物沙蓬（Agriphyllum squarrosum）、差巴嘎蒿（Artemisia halodendron）、乌丹蒿（Artemisia wudanica）、狗尾草、雾冰藜（Bassia dasyphylla）的繁殖体要么重量居中或偏大,要么有降低位移的其它机制。     

植食性哺乳动物觅食的功能反应及其模型

章主要介绍植食性哺乳动物觅食功能反应与模型的研究进展。植食性哺乳动物觅食的摄入率与其食物可利用性的功能反应是动物觅食生态学过程的基础。可利用植物的生物量密度、植物密度、植物大小、以及动物觅食的口量是影响动物觅食功能反应的潜在变量集。这些变量的差异导致动物功能反应格局的复杂化。生物量密度和植物密度对动物摄入率无明显影响,而植物大小对动物摄入率则有显影响。有食物密集的斑块条件下,以植物大小代替动物     

Spatial structure of stoloniferous herbs: an interplay between structural blue-print, ontogeny and phenotypic plasticity

Plant form and spatial structure reflect the basic architectural blue-print of a plant. In most plant species, the expression of the structural blue-print is systematically altered during ontogeny resulting in predictable changes in the allometry of plant structures and in the types of structures that are produced. The expression of the structural blue-print or the timing of ontogenetic changes is also frequently altered by environmental conditions. This latter source of variability, referred to as phenotypic plasticity, is manifested through changes in the timing and rates of meristem initiation and development, the likelihood that meristems will remain dormant or commit to different demographic fates (i.e., vegetative vs. reproductive structures), or the size and structure of the organs formed. Complex interactions among these components can result in considerable differences in form and spatial structure among individuals of the same species. This paper focuses on the importance of these different components in determining the architecture of clonal plants with long internode connections between ramets.A case study is presented that attempts to separate ontogenetic variation and phenotypic plasticity in two stoloniferous species with different structural blue-prints, in their responses to shading. In both species the rate of ontogenetic development responded to intermediate shading levels, but only at very low levels of light availability did plastic changes in branch formation occur. Under shaded conditions the two species achieved similar changes in their architecture in conspicuously different ways. We discuss how different mechanisms leading to a given architecture can be distinguished and what the ecological implications of this are.