Distribution of clonal growth traits among wetland habitats

Clonality resulting from the growth of specialized organs is common among plants in wetland habitats. We hypothesize that different wetland habitats select for different attributes of clonal traits. This hypothesis is based on studies of individual species but has not been previously tested at the level of habitat. We compared the functional diversity of clonal growth traits of plants in bogs, fens, wet heathlands, floodplains, river beds, open fresh water habitats, salt marshes, and open marine habitats. Clonal traits (including number of offspring, lateral spread, persistence of connections between ramets, and shoot life span) were analysed with multivariate techniques using species frequency data and with permutation tests using presence/absence data. Based on species frequencies, clonal plants in aquatic habitats (open fresh water habitats, open marine habitats, and river beds) were characterized by the abundant production of freely dispersible propagules, annual shoots, and splitting clones. Species of daily flooded salt marshes were characterized by bi-annual connections between ramets and medium dispersability. In contrast, plants in permanently wet bogs were characterized by polycyclic shoots and low offspring production. The specificity of river beds and open freshwater habitats was also confirmed by permutation tests, which gave equal weight to rare and abundant species. However, species in all other wetland habitats were characterized by the entire range of clonal traits, suggesting weak environmental filtering of analyzed traits by habitat at the present scale.     

Stochastic simulation of clonal growth in the tall goldenrod,Solidago altissima

Summary As clonal plants grow they move through space. The movement patterns that result can be complex and difficult to interpret without the aid of models. We developed a stochastic simulation model of clonal growth in the tall goldenrod, Solidago altissima. Our model was calibrated with field data on the clonal expansion of both seedlings and established clones, and model assumptions were verified by statistical analyses.When simulations were based on empirical distributions with long rhizome lengths, there was greater dispersal, less leaf overlap, and less spatial aggregation than when simulations were based on distributions with comparatively short rhizome lengths. For the field data that we utilized, variation in rhizome lengths had a greater effect than variation for either branching angles or rhizome initiation points (see text). We also found that observed patterns of clonal growth in S. altissima did not cause the formation of fairy rings. However, simulations with an artificial distribution of branching angles demonstrate that fairy rings can result solely from a plant's clonal morphology.Stochastic simulation models that incorporated variation in rhizome lengths, branching angles, and rhizome initiation points produced greater dispersal and less leaf overlap than deterministic models. Thus, variation for clonal growth parameters may increase the efficiency of substrate exploration by increasing the area covered and by decreasing the potential for intraclonal competition. We also demonstrated that ramet displacements were slightly, but consistently lower in stochastic simulation models than in random-walk models. This difference was due to the incorporation of details on rhizome bud initiation into stochastic simulation models, but not random-walk models. We discuss the advantages and disadvantages of deterministic, stochastic simulation, and random-walk models of clonal growth.     

Classifying clonal growth forms based on vegetative mobility and ramet longevity: a whole community analysis

We measured rhizome branching, clonal mobility, and ramet longevity of 98 meadow plant species. A cluster analysis applied to this dataset revealed nine clonal growth types that differ mainly by the ramet lifespan and vegetative mobility. Then we compared the abundance of these groups of clonal species between the three following plant communities: (1) open, (2) restored and (3) overgrown wooded meadows in the Laelatu-Nehatu-Puhtu Nature Reserve, Estonia. This is the first study where the quantitative values of belowground clonal traits have been measured for all species of a species-rich community. We show that species with annual ramets and with a low vegetative mobility were most abundant in open grasslands. The relative abundance of perennial species with annual ramets was positively correlated with shoot density and species diversity, indicating that high ramet turnover rates combined with a high genet longevity can positively affect species coexistence in meadow communities. Hence, this study provides evidence for the fact that the average values of clonal life-history parameters differ between these communities. Herb communities under forest canopy consist, in average, of species with ramets that live longer and are clonally more mobile than in the communities of open sites.     

克隆植物蝴蝶花在光梯度环境上的形态适应性研究

对四川缙云山毛竹林和针阔叶混交林具有林窗、林缘和林下3种光照差异明显生境下的克隆草本植物蝴蝶花的形态可塑性进行了研究．统计了分株、根茎和叶生长方向等特征．经方差分析和t检验后表明．蝴蝶花在光梯度环境下,其形态特征表现出适应性变化．从林窗→林绿→林下,随着光强度的减弱,分株的高度、密度相应减小．在林下达到最小;而根茎的长度、节间长则相反,在遮荫大的林下最大．研究发现,叶片数目和根茎直径在不同的样地和生境中无明显变化,但叶片的生长方向和光照方向关系极大,表现出极强的向光性．此外,文章还对蝴蝶花表现出的可塑性进行了分析和讨论．     

Differential effects of water depth and sediment type on clonal growth of the submersed macrophyte <Emphasis Type="Italic">Vallisneria natans</Emphasis>

The response of clonal growth and ramet morphology to water depth (from 60 to 260 cm) and sediment type (sand versus organic clay) was investigated for the stoloniferous submersed macrophyte Vallisneria natans in an outdoor pond experiment. Results showed that water depth significantly affected clonal growth of V. natans in terms of clone weight, number of ramets, number of generations, clonal radius and stolon length. V. natans showed an optimal clonal growth at water depths of 110–160 cm, but at greater depths clonal growth was severely retarded. A high allometric effect was exhibited in ramet morphology. Along the sequentially produced ramet generations, ramet weight and plant height decreased while stolon length and the root:leaf weight ratio increased. When using ramet generations as covariate, sediment type rather than water depth more strongly affected the ramet characteristics. For plants grown in clay, ramet weight, ramet height and stolon length were greater, and plants exhibited lower root:leaf weight ratio. These data suggest that water depth and sediment type have differential effects on clonal growth of V. natans: Water depth appears primarily to affect numerical increase in ramets and spatial spread, whereas sediment type mainly affects biomass accumulation and biomass allocation. Handling editor: S. M. Thomaz     

Effects of moisture availability on clonal growth in bamboo Pleioblastus maculata

The effects of moisture availability on clonal growth and biomass investment in the bamboo Pleioblastus maculata were investigated over a four-year period by transplanting Pleioblastus maculata clones into soils with different levels of moisture availability in the field. The results showed that: (1) The higher the moisture availability, the greater the total biomass of P. maculata clones. Although fewer culms are produced at the higher moisture levels, mean tiller biomass is greater. (2) Under different levels of moisture availability, obvious differences in the total rhizome length (p < 0.01), spacer length (p < 0.05) and the sizes of bamboo culms (height, p < 0.01; diameter, p < 0.01) were observed. Thus, the higher the moisture availability, the shorter the rhizomes and the larger ramets. (3) In microhabitats with low moisture availability, bamboo allocated more biomass to underground organs, which promotes elongation of rhizomes and increases root production, thereby helping to capture underground resources essential to growth. In microhabitats of high moisture availability, the biomass is primarily allocated to the aboveground growth of ramets. (4) We suggest that soil moisture availability effects the foraging strategies of bamboo, that bamboo plants growing with low moisture availability produce longer rhizomes (that is, more, although shorter, spacers) with more biomass allocation than plants in high moisture and have a better ability to forage to increase the probability of locating adequate moisture patches. Also, longer length distance between shoots (that is, longer spacers) in high soil moisture than in low is adapted to avoid intense competition from faster growing aboveground growth in high moisture patches.     

Field evidence of plastic growth responses to habitat heterogeneity in the clonal herbRanunculus repens

Stolon internode lengths were measured on plants of the clonal herbRanunculus repens growing in a hay meadow which was subject to disturbance by mole (Talpa europaea) activity. Within the site three habitat types were recognized: closed grassland, the open ground of fresh molehills and the grass-molehill boundary. The lengths of stolon internodes ofR. repens differed significantly in each of the three habitats. The shortest internodes occurred on stolons on the open molchills. The longest occurred in the closed grassland habitat. The type of habitat in which parent ramets were rooted did not significantly influence the length of internodes on their daughter stolons. The length of a stolon internode was determined by its immediate surrounding habitat type. Consecutive internode lengths on a given stolon showed considerable plasticity, shortening significantly as stolons spread onto molehills from surrounding habitats, and increasing significantly as stolons advanced from a molehill into the surrounding closed grassland habitat. These results are consistent with the proposition that under favorable conditions (on the molehills, where resources are expected to be more abundant, and competition absent) internode lengths shorten and the plant forages intensively, whereas under conditions of low resource availability (in the closed grassland, where competition occurs) internode lengths increase, allowingR. repens to forage extensively. Such morphological plasticity may promote more efficient exploitation of resource-rich sites and more rapid vacation of resource-poor sites.     

空心莲子草地下茎克隆繁殖特征

空心莲子草是一种原产于南美洲的苋科多年生草本植物,目前在许多地方已经成为一种危害十分严重的外来入侵植物。通过地下茎等营养器官进行无性繁殖是其主要繁殖方式。本文以空心莲子草的地下茎为实验材料,对其克隆繁殖特征进行了研究。研究结果表明:(1)地下茎的节是克隆繁殖的必要条件,节的有无决定克隆繁殖是否发生;(2)地下茎可以通过控制单位节上的出芽率来调节其克隆生长过程,从而使克隆繁殖结果更有利于整个种群的生长;(3)地下茎的粗细程度对其克隆繁殖也有显著影响。空心莲子草地下茎的单位节数与其单位节出芽率、无性系小株的高度和地上部分的节数之间存在密切联系。     

Sexual dimorphism in clonal growth forms and ramet distribution patterns in <Emphasis Type="Italic">Rumex acetosella</Emphasis> (Polygonaceae)

We investigated clonal traits in the dioecious herb Rumex acetosella to characterize sexual dimorphism in clonal forms and to correlate below-ground clonal patterns and above-ground ramet distributions. We recorded creeping root length, branching patterns, ramet and clump (caespitose ramets from the same position on the root) sprouting patterns, and biomass allocations in three females and males. We also estimated the patch size of flowering ramets within a quadrat. No sexual dimorphism was detected in the frequencies of branches and flowering ramets per root length. Male plants allocated proportionally more biomass to below-ground organs. Total root length did not differ between the sexes. Females sprouted more clumps with fewer flowering ramets per root length than males, which sprouted fewer clumps with more flowering ramets, which meant that clump sprouting patterns were phalanx-like in females and guerrilla-like in males. Flowering ramets were aggregately distributed in both females and males and patch sizes were similar between sexes, indicating that the spreader propagations were not found in the guerrilla-like males. We assumed that sexual dimorphism occurred in response to physiological integration for higher reproductive effort in females.     

The importance of clonal growth to the recovery of Gaultheria procumbens L. (Ericaceae) after forest disturbance

We investigated the importance of clonal growth to the recovery of a common eastern North American sub-shrub, Gaultheria procumbens L. (Ericacea), after clearcut logging. Changes in vegetative growth and development of G. procumbens clones and clonal populations were examined in a chronosequence of logged stands representing different stages of successional development after clearcutting (open habitat, young regenerating forest, closed regenerating forest) and in neighboring undisturbed late-successional forests representative of presettlement conditions. We specifically quantified seedling presence and above-ground ramet production, demographic condition (e.g., sexual vs. vegetative stems), belowground rhizome growth and spread, and assessed the degree of intraspecific variation in clonal morphology and biomass allocation in stands differing in their disturbance history and degree of successional development. Recovery in G. procumbens was largely driven by the “release growth” of pre-existing clonal bud-banks in response to canopy removal. Release growth was expressed as greater ramet initiation, rhizome branching and clonal spread. Conversely, we found no evidence of sexual establishment in the species, although production of reproductive biomass (e.g., inflorescence mass, number of flowering shoots) was significant. These findings support a deterministic model of vascular resistance and resilience to catastrophic disturbance, in which recovery of forest plant communities derives from the life-history characteristics of constituent species.     

毛乌素沙地中国沙棘无性系生长调节

根据无性系跟踪挖掘资料。分析了毛乌素沙地中国沙棘无性系生长调节规律,结果表明,无性系分株群（同一无性系所有分株的集合）结构由增长型发展到稳定型,最后演变成衰退型,在衰退过程中或其后的一段时间内,无性系能够通过分株出生调节使分株群结构（年龄和高度级）恢复到稳定型,在分株群结构变化的同时,种群通过分株的死亡调节不断改变着分株的克隆生长型,提高了无性系 种群的持久性以及对空间和资源的利用率。     

Differences in allocation patterns in clonal and sexual offspring in a woodland pseudo-annual

We compared the patterns of allocation to reproduction among seed-derived and clonal offspring of a woodland pseudo-annual. Pseudo-annuals are clonal plants which survive the winter only as seeds and hibernacles produced by the rhizome system. Previous studies indicate that flowering is related to the size of these hibernacles. Since seedlings do not have a hibernacle, we did not expect that these plants would reproduce sexually. Assuming a trade-off between sexual and asexual reproduction, and assuming a linear relationship between vegetative plant weight and weight of all reproductive structures (i.e., rhizomes, hibernacles, inflorescences, and seeds), we expected that seed-derived plants would have a stronger biomass allocation to rhizomes and hibernacles. Since resource supply affects plant size, and thus hibernacle and seed production, we also subjected the plants to different levels of shade. At the start of the experiment seed-derived and clonal offspring hardly differed in total fresh weight. At the final harvest in September seed-derived and clonal offspring did not differ in vegetative plant weight (i.e., leaves, stems, and roots). Only light availability significantly affected these plant structures. As predicted, seed-derived plants did not flower in either of the light treatments. Seed-derived plants allocated more biomass to rhizomes and hibernacles, but this was only significant in the highest-light treatment. This result was due only to an increase in the number of hibernacles. Dry weight of single hibernacles was not affected by plant type. The ecological implications of this allocation pattern are discussed. Received: 2 October 1997 / Accepted: 8 March 1998     

Effects of light quality and quantity on growth of the clonal plant Eichhornia crassipes

Summary Plant canopy shade reduces photosynthetic photon flux density (PPFD) and ratio of red to far-red light (z). Both effects can cause plants to increase potential for light acquisition through vertical growth and leaf area expansion. Clonal plants such as Eichhornia crassipes might alternatively increase light interception via horizontal growth of stolons or rhizomes and placement of new ramets in less shaded microsites. Effect of simulated canopy shade and component effects of PPFD and z were tested by filtering or adding light uniformly, to a whole group of connected ramets, or locally, to individual ramets within a group. In uniform treatments, low PPFD reduced total growth but low z did not. Low PPFD and low z independently reduced stolon and ramet production and caused etiolation of petioles; effect of low PPFD plus low z on ramet production was greater than that of either factor alone. Lateral clonal growth thus did not seem to be a response to uniform shading; instead, uniformly low PPFD or low z increased partitioning to established ramets. Low z changed partitioning without changing total growth. In local treatments, reduction of growth of individual ramets due to low PPFD and inhibition of new ramet production attributable to spectral composition of light were mitigated when connected ramets were unshaded; plants may respond differently to patchy than to uniform shade.     

Regeneration capacity and carbohydrate reserves in a clonal plant Rumex alpinus: effect of burial

The morphological and anatomical responses to different depths of burial were examined in Rumex alpinus (Polygonaceae), a perennial plant with monopodial, horizontally growing rhizome. Its segments, which consist of 12–20 internodes, 1 to 2 mm in length each, are products of single growing seasons. The rhizomes regenerated from 5, 10 and 20 cm, but failed to emerge from 30 cm. Number of internodes produced during a growing season was not affected by burial but the length of internodes increased up to about 30-fold. The rhizomes growing up to the surface were subsidized by older rhizome segments. In the case of deeply buried rhizomes the carbohydrate reserves of the last-year-segment were nearly completely depleted. Evolutionary significance of the regeneration capacity is discussed.     

Demography and modelling of clonal fragments in the pseudoannual plant shape Trientalis europaea L.

The clonal growth pattern and demography of clonal fragments (aggregation of ramets derived from a common parent ramet) in the pseudoannual plant Trientalis europaea were studied in field conditions from 1991 to 1993. During this period the population of clonal fragments declined, with a half-life of 7.4 years. Number and size of the clonal progeny and stolon length were positively related to the size of the mother ramet. Survival rates of ramets and tubers increased with size. The rate of clonal growth was low: after three years, about 70% of the clonal fragments had only one ramet. This suggests that the pseudoannual growth habit in T. europaea is more important as mechanism of perennation than of ramet multiplication.Field data were used in a simulation model of architecture and population dynamics of clonal fragments. About 10% of the clonal fragments survived to the end of the simulation (15 years) and the mean survival was 4.7 years. The model predicted a positive correlation between persistence of the clonal fragment and number of ramets produced. Sensitivity analysis showed that the production of a daughter ramet of at least the same size as the parent ramet was the most important pathway for the survival and the number of ramets of the clonal fragment, whereas the production of secondary ramets had a very small effect. This confirms the interpretation of the pseudoannual life-cycle as a mechanism of ramet replacement in this species. Sensitivity analysis also revealed that changes in survival probabilities of the smallest ramets had the largest impact on clonal fragment dynamics. This reflects the important role of the smallest size class of ramets as a source of new vegetative propagules, maintaining a hierarchy in the size structure of the population.     

The choice between desiccation of wetlands or the spread of Rhine water over The Netherlands

The dry summer of 1976 triggered a wholesale installation of sprinkler systems for agriculture. This dry summer also revealed areas in The Netherlands most susceptible to drought, namely sandy regions and the coastal fringe. This resulted in distribution of Rhine water to new areas, and in quantities hitherto unknown. The Second National Water Management Plan (1982) consequently focussed on enlarging the capacity of water distribution works. This distribution has led to a multitude of ecological effects, such as changes in salinity and nutrient concentration, as well as the spreading of contaminants. Consequently, the Third National Water Management Plan (1990) includes fewer distribution works because of the adverse environmental effects and the reduced feasibility due to increasing costs and decreasing agricultural benefits.A climatic change as predicted may result in climatic conditions in The Netherlands resembling those of France or the Mediterranean, implying drier summers and more precipitation in winter. An increased frequency of dry summers will no doubt revive water distribution plans now shelved and may even bring new ones to the drawing board. An increase in Rhine water distribution will have serious consequences for many aquatic and terrestrial ecosystems, as will a lowering of the groundwater table. In this paper we will discuss the dilemma of choosing between allowing increased desiccation of wetlands as the climate becomes drier or increasing the distribution of Rhinewater and the potential ecological effects of these choices. Alternative strategies to water management also are discussed.This article is largely based on Duel et al. 1989.     

An analysis of the costs and benefits of physiological integration between ramets in the clonal perennial herb Glechoma hederacea

Summary The costs and benefits, measured in terms of dry weight, of physiological integration between clonal ramets, were analysed in two experiments conducted on the clonal herb Glechoma hederacea. Firstly, integration between consecutively-produced ramets was examined in an experiment in which stolons grew from one set of growing conditions (either unshaded or shaded and either nutrient-rich or nutrient-poor) into conditions in which light or nutrient level was altered. Comparisons were made between the dry weight of the parts of the clones produced before and after growing conditions were changed, and the dry weights of the corresponding part of control clones subjected to constant growing conditions. In a second experiment, integration between two distinct parts of G. hederacea clones was investigated. In this experiment clones were grown from two connected parent ramets and the parts of the clone produced by each parent ramet were subjected independently to either nutrient-rich or nutrient-poor conditions. Ramets in resource-rich conditions provided considerable physiological support to those in resource-poor conditions. This was measured as a dry weight gain compared with the weight of the corresponding part of the control clones growing in resource-poor conditions. However, when stolons grew from resource-poor conditions into resource-rich conditions, there was no similar evidence of the resourcepoor ramtes receiving support from resource-rich ramets. Physiological integration did not result in dry weight gains when this would have necessitated basipetal translocation of resources.Because of the predominantly acropedal direction of movement of translocates in G. hederacea, the structure of the clone was important in determining the effectiveness of integration between ramets. Where physiological integration was effective, the cost to the supporting ramets in terms of dry weight was insignificant. Physiological integration allows clones to maintain a presence in less favourable sites with insignificant cost to ramets in favourable sites, thereby reducing the probability of invasion by other plants, and providing the potential for rapid clonal growth if conditions improve. Integrated support of ramets in unfavourable conditions also enables the clone to grow through unfavourable sites, thus increasing the probability of encountering more favourable conditions by wider foraging.     

The plant remains from Gouda-Oostpolder, a twelfth century farm in the peatlands of Holland

An excavation in the near surroundings of the town of Gouda revealed the remains of a wooden farmhouse. Radiocarbon dates and pottery indicate that the farm was built around A.D. 1120–1135. It belongs to the initial phase of land reclamation in the wetlands of the part of the Netherlands called Holland. Pollen and wood analysis show that the original vegetation consisted of ash and alder woodland on a subsoil of eutrophic peat. People used local wood very economically for the construction of the house. A triangular figure of splitPinus sp. andAbies alba branches near the entrance provides an exotic and probably ritual element. The farmers practised mixed farming based on the raising of cattle, pigs and crops comprisingTriticum dicoccum (emmer wheat),Hordeum sp. (barley).Avena sativa (oats),Linum usitatissimum (flax) andCannabis sativa (hemp). Conspicuously absent isSecale cereale (rye). There are no indications of an orchard.     

Potential role of seed banks and understory species in restoring quaking fens from floating forests

Quaking fens and floating forests in the Westbroek Polder, the Netherlands, have seed banks with an estimated mean total seed density of 920 and 690 seeds m^-2, respectively. Fifty nine species were found in two or more quaking fens of which 39 were also found in their seed banks. Fifty species were found in two or more floating-forests and 31 of these were also found in their seed banks. The seed banks of fens and forests had 36 species in common. The seed banks of fens and forests were more similar (Spearman rank order correlation coefficients of 0.64 on the basis of percent presence and 0.61 on the basis of mean seed density in the seed bank and mean species cover in the vegetation) than were the seed banks and vegetation of either fens or forests (0.46 and 0.46 for fens; 0.26 and 0.23 for forests).When the tree canopy is removed from a floating forest to try to restore it to a quaking fen, it is predicted that a total of 47 species from the floating-forest understory will persist. Eleven of these species are not present in fens. Fifteen additional species can become established potentially from the forest seed banks. Sixteen species found in fens, however, are predicted to be missing from cleared sites. Of these 16 species, 7 are uncommon aquatic-and fen species.