Vegetative Ramets Research Articles

Preferential Carbon Allocation Into Vegetative Ramets and Belowground Organs During the Seed-Filling Stage Limits Seed Set in Leymus chinensis.

Clonal perennial grasses are the dominant species in almost all natural grasslands, however their seed production is typically low. The reasons why seed set is so low remains unclear. We studied a rhizomatous grass (Leymus chinensis) using 13C tracing the different photosynthetic organs to investigate carbon fixation and allocation during the seed-filling stage. We found that the vegetative ramet leaves are the largest (81%) source for total plant fixed carbon, whereas almost all carbon is allocated to vegetative reproduction. The spike is the largest (54%) carbon source for the seeds. However, the spike produced carbon only allocated 37% to the seeds, with the majority allocated to vegetative reproduction. This preferential carbon allocation to vegetative reproduction limits sexual reproduction. Nitrogen application significantly increased assimilated carbon. However, nearly all increased carbon accumulated in the vegetative reproduction rather than in the seeds. Only the carbon produced by the spike increased its allocation to the seeds by 13%. Taken together, we conclude that the predominance of vegetative reproduction, combined with self-incompatibility, results in low ovule fertilization and very weak seed sink strength for carbon competition, suggests that the weak seed sink strength is the key reason causing low seed set in L. chinensis.

Unequal carbon and nitrogen translocation between ramets affects sexual reproductive performance of the clonal grass Leymus chinensis under nitrogen addition

Sexual reproduction is crucial for population continuity in clonal plants. The effect of nutrient translocation between ramets on sexual reproduction of clonal plants under nitrogen addition remains unclear. In this study, we focused on clonal fragments of Leymus chinensis reproductive ramets with different number of vegetative ramets connected to tillering nodes. A series of pot experiments was conducted under nitrogen addition, including 13C and 15N bidirectional labelling of vegetative ramets and reproductive ramets at the milk-ripe stage, determination of the 13C and 15N amount translocated, and assessment of the quantitative characteristics, nitrogen and carbon concentrations of reproductive ramets and vegetative ramets. Nitrogen addition promoted the translocation of 13C while inhibiting 15N between vegetative ramets and reproductive ramets. With an increase in the number of connected vegetative ramets, the 13C translocated by reproductive ramets and the 15N translocated by reproductive and vegetative ramets gradually increased. The translocation of 13C and 15N between vegetative and reproductive ramets was bidirectional and unequal. The translocated amount of 13C and 15N from reproductive ramets to vegetative ramets was always higher than that from vegetative ramets to reproductive ramets. Nitrogen addition did not prominently affect the sexual reproductive performance of L. chinensis, whereas the number of connected vegetative ramets both positively and negatively affected sexual reproductive performance. Ramet biomass is an important driver of nutrient acquisition by L. chinensis ramets. We demonstrate for the first time that unequal nutrient translocation between ramets affects sexual reproductive performance in L. chinensis. The findings contribute to an enhanced understanding of the reproductive strategies of clonal plant populations in future environments.

Warming in combination with increased precipitation mediate the sexual and clonal reproduction in the desert steppe dominant species Stipa breviflora

BackgroundClonal plants can successfully adapt to various ecosystems. A trade-off between sexual and clonal reproduction is generally assumed in clonal plants, which may be influenced both by the characteristics of the plant itself and environmental conditions. Currently, it is unclear how climate change, and specifically warming and increased precipitation, might affect sexual and clonal reproduction in clonal plants. Therefore, this study aimed to investigate both the sexual and clonal reproduction responses of Stipa breviflora to warming and increased precipitation. A controlled experiment was conducted by inducing increases in precipitation (ambient condition, 25% and 50% increases) and warming (ambient temperature, 1.5 °C and 3.0 °C increases).ResultsWarming significantly influenced both the ratio of reproductive ramet shoot biomass to total shoot biomass, and the ratio of reproductive ramet number to total ramet number. Additionally, the ratio of reproductive ramet shoot biomass to total shoot biomass was also significantly affected by increased precipitation. Increased precipitation benefited sexual reproduction, while effects of warming on reproductive and/or vegetative ramets varied from negative to positive depending on precipitation conditions. There was no relationship between the number or shoot biomass of reproductive ramets and vegetative ramets. Reproductive ramets displayed greater sensitivity to climate change than vegetative ramets.ConclusionsThe findings of our study suggest that there was no trade-off between sexual and clonal reproduction in S. breviflora. The combined impact of warming and increased precipitation promoted sexual reproduction but did not inhibit clonal reproduction. Clonal plants with the capacity for both sexual and clonal reproduction, may cope with climate change well via clonal reproduction, ensuring their survival.

Clonal dominant grass Leymus chinensis benefits more from physiological integration in sexual reproduction than its main companions in a meadow.

The bioecological characteristics of plants determine their status and role in the community. The advantages of dominant species in the community compared with companion species in terms of physiological and ecological characteristics remain unclear. When both dominant and companion species in grassland plant communities are clonal, these plants are able to share resources within clones (physiological integration). However, it is unclear how the clonal dominant and companion species differ in the effect of their physiological integration on sexual reproduction. We chose Leymus chinensis, the dominant species of the most widespread meadow plant communities in the semiarid and arid regions of northern China, and its main companion species L. secalinus, Calamagrostis ripidula, C. pseudophragmites, and C. epigeios and conducted a series of in situ field experiments in a homogeneous environment, including the determination of the phenotypic characteristics of reproductive ramets with connected (allowing physiological integration) and disconnected (preventing integration) tillering nodes for each species, as well as 15N leaf labeling of ramet pairs at the milk-ripe stage. In the clonal populations of the five grasses, physiological integration between vegetative ramets and reproductive ramets interconnected by tillering nodes significantly increased the leaf, stem, inflorescence and ramet biomasses of reproductive ramets, and relative changes in ramet biomass were greatest in L. chinensis. 15N labeling showed that vegetative ramets supplied nutrients to reproductive ramets through tillering nodes; the amount of translocated 15N per unit of reproductive ramet biomass was highest in L. chinensis. Overall, our results indicate that in the five clonal grasses, physiological integration between functionally different ramets under tillering node connections had a significant positive effect on sexual reproduction, indicating interspecific consistency in the contribution of physiological integration to sexual reproduction between the dominant and companion species, but this positive effect was greater in the dominant species L. chinensis than in the four main companion species. Therefore, differences in the physiological integration ability between the dominant and main companion species, identified for the first time in this study, may explain, at least partly, the dominance of L. chinensis in the community.

The spatial arrangement of sexes is related to reproductive allocation in mosses: a comparative study of reproductive allocation in three different monoicous sexual systems.

We examined the relationship between reproductive allocation and vegetative growth in three monoicous sexual systems of bryophytes. The sexual systems show a gradient of increasing distance between the sexes, from gonioautoicous to cladautoicous to rhizautoicous. Here, we investigated the following two hypotheses: (1) reproductive allocation differs between sexes and sexual systems, and male reproductive allocation increases with increasing distance between male and female gametangia; and (2) reproductive allocation is negatively related to vegetative growth. We sampled the three sexual systems, represented by three moss species of the genus Fissidens in the Atlantic Forest of Southeastern Brazil. Ramets were washed in the laboratory; the reproductive structures were detached from the vegetative ramets and sorted regarding sex and individual, dried at 70 °C for 72 h, and weighed in an ultramicrobalance. We calculated the mean reproductive and vegetative mass and reproductive allocation and used generalized linear models to test our predictions. Reproductive allocation differed between species and sexes. It was higher in the rhizautoicous than in the cladautoicous and gonioautoicous species. Mean reproductive allocation was greater in males than in females of the rhizautoicous species, greater in females than males of the cladautoicous species, and did not differ between the sexes in the gonioautoicous species. Estimates of reproductive and vegetative mass were positively related in females of the rhizautoicous species. Vegetative mass was not related to reproductive allocation in the gonioautoicous species, but negatively related to reproductive allocation in the male and female branchlets of the cladautoicous species and in the female ramets of the rhizautoicous species. The reproductive allocation patterns differ between the rhizautoicous species and the 'truly' monoicous species, with shorter intersexual distances, which implies that our hypotheses were supported only in part. We suggest that the hypotheses should be reformulated and tested further by comparing 'truly' monoicous species with dioicous species and by including other genera.

Physiological Integration Increases Sexual Reproductive Performance of the Rhizomatous Grass Hierochloe glabra.

Clonal plants usually reproduce asexually through vegetative propagation and sexually by producing seeds. Physiological integration, the translocation of essential resources between ramets, usually improves vegetative reproduction. However, how physiological integration affects sexual reproduction has been less studied in clonal grasses. Here, we chose Hierochloe glabra, a major early spring forage of the eastern Eurasian steppe, and conducted a series of field experiments, including sampling reproductive ramets connected by tillering nodes to different numbers of vegetative ramets and 15N leaf labeling of ramet pairs at the seed-filling stage. In the natural populations of H. glabra, vegetative ramets were taller, had more and larger leaves, and greater biomass than reproductive ramets. Except for reproductive ramet biomass, sexual reproductive characteristics significantly increased with an increase in the number and biomass of vegetative ramets connected to tillering nodes. 15N labeling showed that vegetative ramets supplied nutrients to reproductive ramets through tillering nodes. Overall, our results indicate that significant differences in morphological characteristics and biomass allocation underlie resources translocation from vegetative ramets towards reproductive ramets. Physiological integration between different functional ramets can increase sexual reproductive performance, which will be beneficial to population persistence in H. glabra.

Effects of Flag Leaf and Number of Vegetative Ramets on Sexual Reproductive Performance in the Clonal Grass Leymus chinensis

Sexual reproduction is vital for population adaptation in clonal plants. The flag leaf is considered to be the primary contributor to sexual reproduction in cereal crops, and there is no unified conclusion on the effect of the number of vegetative ramets on grain yield. However, what effects of the flag leaf and the number of vegetative ramets on sexual reproductive performance of clonal grasses are largely unknown. To test this, under field natural conditions, we grew the rhizomatous grass Leymus chinensis in a homogeneous environment and conducted studies concerning the growth, reproduction and physiology of reproductive ramets in clonal populations. We measured the growth characteristics of different aged leaves, dynamically measured the net photosynthetic rate of different aged leaves and organ biomass, measured the sexual reproductive characteristics of reproductive ramets that had different numbers of connecting vegetative ramets, and performed isotope (15N) labeling of ramet pairs at the seed-filling stage. In L. chinensis clonal populations, from the heading stage, the photosynthetic contribution of the functional leaves to seed production was much greater than that of the flag leaf; the photosynthetic capacity of both the functional leaves and the flag leaf all gradually declined. Vegetative ramets translocated their own resources to the connected reproductive ramets, and a large proportion of translocated resources were allocated to the leaf and stem to sustain life activities; increase in the number of connecting vegetative ramets increased floret number, seed number, seed-setting rate, inflorescence biomass, seed biomass, and reproductive allocation of reproductive ramets, and these parameters significantly and positively correlated with the biomass of connecting vegetative ramets. We conclude that the functional leaf rather than the flag leaf of L. chinensis is the primary contributor to seed production. Reproductive ramets adopt a strategy of growth first and reproduction later to allocate the translocated resources between the organs, but vegetative ramets are very advantageous for sexual reproduction under the tillering node connection form in L. chinensis. Overall, our study implies that vegetative ramets not only play an important role in the spatial expansion but also in the sexual reproduction of clonal plant populations.

Population and community‐level compositional patterns shape the realized niche of the rare arctic‐alpine species Carex lachenalii Schkuhr

The ability for vegetative growth and development of generative organs often reflects an adaptation to the environment and may be a suitable proxy for understanding population dynamics of rare relict species. An example of such a plant is Carex lachenalii Schkuhr, an arctic‐alpine species, in the temperate zone of Europe only occurring in isolated localities of high‐elevation mountain ranges. We aimed to assess whether there were relationships between flower production and clonal growth of C. lachenalii, both at the tuft and plot level, and how co‐occurring vegetation could modify this relationship. In the study we focused on population‐level traits of C. lachenalii, vegetation traits and components of functional diversity. At the tuft level we found that the proportion of flowering ramets of C. lachenalii decreased with increasing diameter of the tuft. At the plot level, in snowbed vegetation C. lachenalii produced more flowering ramets. We suggest this is due to higher environmental stress, expressed by high importance of habitat filtering (low functional dispersion) in shaping species composition of co‐occurring vegetation. In granite grasslands and milder environment (expressed by higher functional dispersion), C. lachenalii produced more vegetative ramets, which we suggest is a result of a more competitive environment. While in snowbeds investment in flowering ramets could promote successful persistence of C. lachenalii, survival of subpopulations occurring in the highly competitive conditions of granite grasslands may be uncertain due to potentially weak adaptation to competition with graminoids and dwarf shrubs.

Phenotypic Plasticity in Sexual Reproduction Based on Nutrients Supplied From Vegetative Ramets in a Leymus chinensis Population.

Phenotypic plasticity is considered a major mechanism that allows plants to adapt to heterogeneous environments. The physiological integration between the interconnected rhizomes or stolons of clonal plants influences the plasticity of such plants in heterogeneous environments. However, the determinants of plasticity of reproductive ramets in clonal plants in homogeneous environments are unclear. Here, we chose Leymus chinensis, a perennial rhizomatous grass, and conducted a series of field experiments in situ, including grading sampling of reproductive ramets and different connection forms of vegetative ramets labeled with 15N at four reproductive stages. Reproductive ramet biomass, inflorescence biomass, seed number, seed-setting percentage, reproductive allocation, and reallocation significantly increased with an increase in the number of vegetative ramets connected to tillering nodes, and the plasticity indexes of these six phenotypic characteristics showed similar increasing trends. The amount of nutrients supplied from the connected vegetative ramets to the reproductive ramets was significantly affected by the transfer direction, reproductive stage, and position order of the vegetative ramets. Throughout the sexual reproduction stage, nutrients were preferentially transferred to the acropetal reproductive ramet in L. chinensis populations. The amount of nutrients supplied from the connected vegetative ramets to the reproductive ramets at the milk-ripe stage, when sexual reproduction was most vigorous, was significantly larger than that at other reproductive stages. The amount of nutrients supplied from the spacer vegetative ramet to the acropetal reproductive ramet was significantly larger than that to the basipetal reproductive ramet. The closer the vegetative ramet was to the reproductive ramet, the more nutrients were supplied; the amount of nutrients supplied was significantly negatively related to the position order of the vegetative ramet. We identified the determinant of plasticity in sexual reproduction in clonal plants in a homogeneous environment: physiological integration between ramets within clones. Our results are vital for better understanding the adaptation of populations and even the evolution of species of clonal plants.

Ramet demography of Aechmea distichantha (Bromeliaceae) in two contrasting years in the understory and open areas of a South American xerophytic forest

Abstract The Schinopsis balansae forests of the Wet Chaco are characterized by convex areas with woody vegetation and plain areas with herbaceous vegetation. In the Wet Chaco, Aechmea distichantha is a terrestrial bromeliad that forms dense colonies in the understory and open areas of these forests. The aim of this study was to analyze the spatial and temporal variations in population dynamics of this bromeliad species. We monitored ramets growing in sun and shade conditions during two contrasting years. We analyzed the spatial and temporal variations in survival, flowering, and ramet production. Variations in survival, flowering, and ramet production were more marked between years than between habitats. During the year with wetter and milder temperature conditions, survival and ramet production were higher than during the drier year with more extreme temperatures. Survival of vegetative ramets was less variable than survival of young and reproductive ramets. In the colder year, lower winter temperatures reduced the populations in all stages, being more important in the open areas. Our results highlight the importance of low temperatures on A. distichantha demography at this xerophytic forest located at the southernmost distribution range of this bromeliad species.

Near infrared spectroscopy as a tool for predicting growth habit and gender of Araucaria angustifolia

ABSTRACTAraucaria angustifolia is the only native conifer of economic importance in Brazil for wood and nut production. There are several constraints to the genetic improvement of the species. Vegetative ramets display strong and lasting plagiotropism, which is difficult to pre-select for, and it is a dioecious species. Trees reach reproductive maturity at 12–15 years old and there is currently no method to distinguish the sex of the plant before this time. Early detection of plagiotropism or early identification of plant sex would improve efficiencies in breeding programs and seed orchard establishment. Therefore, we investigate the potential of near infrared (NIR) spectroscopy analysis as a tool for predicting growth habit and gender of A. angustifolia. Spectra from needles at the stem apex were taken from 12-month-old plants for growth habit calibration using the presence or absence of a lateral shoot to distinguish between future growth habits. Model validation was done on needles from the apical shoots of orthotropic trunks and from clones displaying plagiotropic growing habit. For plant sex, spectra were collected on wood from bark windows and from multiple needles located midway up the main stem. Needle spectra from individual plants were averaged to produce a single spectrum per plant. Multivariate analysis was performed on spectra and associated reference data. Results indicate that NIR has the potential to predict sex and growth habit and may be a useful screening tool in improvement of Araucaria.

Senescence in growth and reproductive allocation in a bunchgrass.

Senescence is a puzzling phenomenon. Few convincing studies of senescence in perennial herbaceous plants exist. While ramets are known to senesce, whether senescence of bunchgrasses actually occurs is not clear. In this study, we grew a set of plants of Elymus excelsus, a bunchgrass, to examine plant size, sexual reproduction and bud formation in individual plants in relation to their gradual ageing, in order to determine whether E.excelsus experiences senescence. We collected data in two consecutive years (2009 and 2010) from field samples of plants from 1 to 5years old. Using regression models, we performed age-related analyses of growth and reproduction parameters. Our results showed that individual plant size (diameter, individual biomass), total biomass of ramets, number and biomass of reproductive ramets, percentage of ramets that were reproductive, reproductive allocation, over-wintering buds and juvenile ramets all declined with age. However, vegetative growth (number and biomass of vegetative ramets) did not decrease with age. Those plants that survived, dwindled in size as they aged. However, no plants shifted their resource allocation between growth and reproduction as they aged, so the shift in allocation did not account for the fall in size.

Resolving the naturalization strategy of Solidago\xa0\xd7\xa0niederederi (Asteraceae) by the production of sexual ramets and seedlings

In this study, the authors aimed to revise the ability of Solidago × niederederi, a hybrid between S. canadensis and S. virgaurea, to produce sexual ramets and seedlings as a part of its naturalization strategy. Based on a two-season garden cultivation experiment, we showed that the hybrid produces more generative ramets than vegetative ones and the number of generative ramets increases from one season to another with an increasing number of stem buds located on the caudices. We also revealed a spontaneous seedling recruitment by the hybrid during cultivation in the garden. Based on the seed germination test under laboratory conditions, we evidenced that the hybrid can reach a higher final germination percentage than S. canadensis but a lower one than S. virgaurea. Based on field studies conducted in 35 populations in Poland, the hybrid formed the largest populations in tree plantations and on abandoned fields, reaching 16.5 and 15.7 ramet clusters on average, respectively. The most abundant populations were found on abandoned fields; however, the mean number of ramets per cluster did not differ remarkably among habitats (H = 6.5, p = 0.163). In all populations, the mean number of vegetative ramets per cluster reached 0.85, while the generative ones achieved 6.43 on average. The statistical analysis proved that the aforementioned differences are significant (t = −12.6, p = 0.0002). Our results suggest that S. × niederederi is able to generate its own offspring by sexual reproduction and that abandoned fields seem to be the most suitable habitats for its establishment.

The role of seedling recruitment from juvenile populations of Carex brevicuspis (Cyperaceae) at the Dongting Lake wetlands, China.

Seedlings and vegetative ramets may contribute differentially to the recruitment of clonal populations in different growth phases, but this has rarely been investigated. In this study, we quantified the number and survivorship of seedlings and vegetative ramets monthly in juvenile and mature populations of Carex brevicuspis. During the first growing season after flooding (from October to January), 9 seedlings m−2 (13% of all established shoots) were found in juvenile populations, while no seedlings were found in mature populations. During the second growing season before flooding (from February to May), no new seedling recruits were found either in juvenile or in mature populations. All shoots of seedlings were withered during the dormant season (January and February), but 62.5% seedlings could produce vegetative ramets in the following growing season. During the dormant season, all the early emerging ramets (sprouted in October) withered, but the later emerging ones (sprouted in November and December) survived in both mature and juvenile populations. These results indicated that seedling recruitment was only apparent in juvenile populations of C. brevicuspis. The genetic diversity in mature C. brevicuspis populations may be established in juvenile populations by seedling recruitment, and sustained in mature populations by vegetative reproduction.

Deer herbivory and habitat type influence long-term population dynamics of a rare wetland plant

Pinpointing the factors that alter the population viability of long-lived organisms, such as perennial plants, is especially useful for informing conservation management policies for threatened and endangered species. In this study, I used 4 years of demographic data on rare plant Polemonium vanbruntiae (Eastern Jacob’s ladder, Polemoniaceae) to determine how white-tailed deer herbivory and habitat type (wet meadow and forest seep) affect long-term population viability. I incorporated these factors into matrix population models to estimate the deterministic and stochastic growth rates (λ and λs, respectively), stable stage distribution (SSD), the reproductive value for each stage class, the cumulative probability of extinction, and the elasticity values for all vital rates under each browsing and habitat scenario. Population growth rates of P. vanbruntiae in wet meadow sites are expected to increase at a slightly faster rate than at forest seep sites. Herbivory significantly decreased the predicted population growth rate under stochastic conditions. However, P. vanbruntiae ramets are expected to increase in the future as the population growth rate (λ) > 1 under both “browse” and “no browse” scenarios, but deer herbivory increased the extinction risk to a detectable level. Deer preferentially browsed vegetative and reproductive adult ramets over yearlings and seedlings, and browsing significantly reduced fertility of reproductive ramets and increased the probability of stasis for small and large vegetative ramets. Browsing shifted the elasticity values of vital rates and changed the potential for younger life histories stages, such as seedlings, to change future population growth. Under herbivore pressure, survival and stasis of large vegetative ramets have the largest potential impact on future population growth. This study provides empirical evidence that white-tailed deer are an important ecological factor affecting long-term population dynamics of rare plant populations and offers management suggestions for remaining populations of P. vanbruntiae.

Stage-dependent patterns of drought tolerance and gas exchange vary between sexes in the alpine willow, Salix glauca

Females and males of sexually dimorphic species have distinct resource demands due to differential allocation to reproduction. Sexual allocation theory predicts that functional traits will diverge between sexes to support these demands. However, such dimorphism may be masked by the impact of current reproduction on source-sink interactions between vegetative and reproductive organs. We ask whether natural selection has led to genetic dimorphism in homologous physiological traits between sexes of the dioecious willow shrub, Salix glauca. In a common garden experiment we compared physiological responses to drought stress by male and female ramets in the absence of confounding demands from reproductive structures. Ramets experienced similar pre-dawn leaf water status (Psi(l)) as parental genets in flower within the natural population, indicating that experimental dry-down mirrored environmental conditions in nature. Male and female ramets achieved similar instantaneous water use efficiency, based on the ratio of carbon gain to water loss, under wet and dry conditions. However, female ramets experienced greater water stress (i.e., more negative Psi(l)) than males under dry conditions. Lower Psi(l) for female ramets may partly reflect the maintenance of conductance under drought; males, in contrast, maintain Psi(l) under drought by reducing conductance. Differences between sexes in terms of conductance and leaf water status of the vegetative ramets were absent in a concomitant comparison of parental flowering plants. Our results show (1) genetic divergence in physiology between sexes of S. glauca occurs in the absence of gender-specific reproductive sinks, (2) males are the more physiologically plastic sex with respect to water use, and (3) paradoxically, divergence in water relations between sexes is not detectable at sexual maturity under natural conditions.

Biomass and nutrient responses of a clonal tundra sedge to climate warming

We explored how climate change affects biomass, nutrient status, and late-season resource-allocation patterns in a rhizomatous tundra sedge, and how differentiation and development of ramets may constrain plant responses. We simulated climate warming for 5 years at a subarctic–alpine tundra site by using open-top chambers before destructively sampling clonal fragments of the dominant and widespread sedge, Carex bigelowii Torr. ex Schwein. We found differential growth response among ramets to experimental warming, but reduced aboveground tissue nutrient concentrations across entire clonal systems. Warming did not affect biomass allocation within ramets, but it did change biomass allocation among developmental stages and ramet types (i.e., long- and short-rhizome ramets, termed guerrilla and phalanx). A positive warming effect on biomass was mostly confined to mature vegetative ramets and the response of individual plant parts was significantly greater for guerrilla ramets than for phalanx ramets. Despite the differential biomass response, warming significantly reduced nitrogen and phosphorus concentrations in aboveground tissues across all developmental stages within the integrated clonal system (10% decrease in green leaf nitrogen concentration, 18%–25% decrease in phosphorus concentration). However, late-season nutrient concentrations in storage organs (rhizomes) were not affected. Nutrient pools significantly increased in mature vegetative ramets, especially those of the guerrilla type, apparently as a result of both redistribution of nutrients among ramets and increased nutrient uptake. At the community level, estimated aboveground biomass per unit area was similar in warmed and control plots. Rhizome and dead-leaf mass and all nutrient pools per unit area were 10%–20% less in warmed plots than in controls. The ecosystem implications of the responses of C. bigelowii, a forage species favoured by a range of herbivores, to warming are a reduction in forage quality without compensation in terms of quantity and, eventually, a reduction in litter quality.

Age structures of modules of clonal peatland sedge Carex middendorffii

Age structure of a plant population carries important information on population dynamics. The traditional age classification of individuals by development phases could not explain the generation relationship neither between individuals nor between modules, and it could not accurately predict the future of population or the tendency of peatland evolution. In a peatland of the Xiao Hinggan Mountains, China, at the middle of the growth season, the age structures of 3 modules, ramets, active buds and rhizomes of a Carex middendorffii clonal population were investigated, with the method of classifying age classes of ramets and active buds by counting generation quantity of tiller nodes, and classifying age classes of rhizomes by their real survival time. The quantity of vegetative ramets was dominant. Tiller nodes of ramets can propagate vegetatively for a maximum of 3 generations. The population of ramets consisted of 3 age classes of ramets at the middle of the growth season, and showed a stable age structure. In the two sampling events, there was no significant difference between quantities and age structure of the population. The maximum age of an excavated rhizome was 12 years old. Rhizomes were classified in 8 age classes, and age classes 4–6 contributed most to the total biomass. There was no significant difference in total length and total biomass per unit area, or in biomass per unit length in rhizomes between the two samplings. Four age classes of active buds were recognized, and their number increased from July to August. The Carex middendorffii clonal population achieved regeneration by budding from the tiller nodes of ramets. The age structures of the 3 modules suggested that the Carex middendorffii clonal population could persist in the early development phase of the oligotrophic peatland in the Xiao Hinggan Mountains, but it could not be dominant. It also faces the risk to disappear from the community as the peatland develops further.

Is two company or a crowd: How does conspecific density affect the small-scale dispersal of a weed biocontrol agent?

To predict the growth and spread of an insect population introduced for the biological control of weeds, one must first understand the factors affecting the movement of individuals in the population. The purpose of this study was to determine how the dispersal rate of Aphthona lacertosa (Rosenhauer) (Chrysomelidae) was affected by conspecific density and by the characteristics of leafy spurge (Euphorbia esula L.: Euphorbiaceae) in patches where these beetles feed. In 2002 in Manitoba and in 2003 in Alberta, Canada, between 200 and 2500 insects were released in small patches (<10 m2) of spurge. The number and location of beetles within patches was monitored over subsequent days. In 1 m2 plots within patches, spurge ramet density, the proportions of vegetative and reproductive ramets, and ramet height were measured. In both years, beetle movement within patches and emigration from patches, was not affected by conspecific density. In Manitoba in 2002, beetles aggregated non-randomly on either vegetative or reproductive ramets within plots, but plot characteristics were not related to the formation of aggregations. In Alberta in 2003, plots in which beetles aggregated had significantly higher spurge density but did not differ in either the proportion of vegetative ramets or in the amount of non-spurge vegetation. These results suggest that density-dependent dispersal does not limit the population's ability to reach densities up to 2500 beetles/m2.

Intraclonal variation in defence substances and palatability: a study on Carex and lemmings

Clonal sedges consist of integrated ramets at different development stages. Many of these sedges are important food for herbivores, yet differences in herbivore preferences and defence allocation between ramet development stages have not previously been evaluated. In this study we investigated intraclonal ramet variation in level of plant defence and nutrient compounds and intraclonal ramet preferences by lemmings (Lemmus trimucronatus) in field samples of a rhizomatous sedge (Carex stans). Plant defence was measured as the level of proteinase inhibitor activity (PIA) and the ratio of PIA to soluble plant proteins (SPP), whereas plant nutrients were measured as the level of soluble plant sugars (SPS) and SPP. Flowering ramets generally had a higher content of defence compared to vegetative ramets, which is consistent with the optimal defence theory predicting that defence compounds are allocated to the ramet stage of the highest fitness value. Compared to vegetative ramets, the flowering ramets had a lower content of SPP and a higher content of SPS. The lemmings showed preference differences between the ramet development stages, and to a large extent the ramet content of defence compounds and nutrient compounds covaried with these preferences in the predicted way. This study shows that defence allocation between ramet development stages of the clonal sedge Carex conforms to predictions of the optimal defence theory.