Ramet Population Research Articles

Trade-offs in growth and reproduction of rhizomatous clonal plant Phragmites communis in response to aeolian processes

Abstract Trade-offs in growth and reproduction are essential parts of the adaptive strategies of clonal plants. How rhizomatous psammophytes respond to aeolian processes (sand burial and wind erosion) by means of trade-offs is supposed to be especially important for their colonization on the active sand dune. Despite partial documentation of the responses of rhizomatous species to aeolian processes, how these clonal species respond to aeolian processes by means of potential trade-offs in growth and reproduction still remains unclear. In this study, we employed field investigation and biomass modeling to evaluate the trade-offs between vegetative and reproductive growth as well as between the number and size of ramets of Phragmites communis in response to sand burial and wind erosion. Sand burial enhanced the accumulation of seed biomass and reproductive effort. Wind erosion reduced reproductive effort but had no significant influence on seed biomass. Sand burial increased the biomass of ramets, while wind erosion increased ramet population density and accelerated ramet maturation. Our results demonstrate that rhizomatous psammophytes adjust their growth strategies in response to aeolian processes, i.e. reproductive growth and ramet size increase in response to sand burial, while vegetative growth and ramet numbers increase in response to wind erosion.

Clonal integration affects growth and sediment properties of the first ramet generation, but not later ramet generations under severe light stress

Abstract Clonal integration benefits clonal plants by buffering environmental stress and increasing resource extraction efficiency. However, the number of connected ramet generations that benefit from clonal integration in a clonal system has received relatively little attention. A pot experiment was conducted to evaluate the extent of physiological integration within the clonal system of Vallisneria natans consisting of a mother ramet and three sequentially connected offspring ramets. Mother ramets were grown in full sunlight, and offspring ramets were heavily shaded with limited light availability. Stolons between mother ramets and offspring ramets were severed or connected, but connection among the three offspring ramets remained. The photosynthetic ability of unshaded mother ramets of V. natans was significantly enhanced, but their biomass accumulation was greatly reduced when connected to shaded offspring ramets. Clonal integration significantly increased biomass accumulation, C and N availabilities, extracellular enzyme activities and microbial biomass of the first ramet generation (adjacent ramet), but not later ramet generations. Our results indicate that support from the mother ramet of V. natans may be limited to the adjacent offspring ramet in a clonal system under severe light stress, implying an effect of ramet generation. Our results contribute to a better understanding of the hierarchy and segmentation of clonal plants. These findings suggest that the extent of clonal integration plays a vital role in ecological interactions of the ramet population.

Shade Avoidance and Light Foraging of a Clonal Woody Species, Pachysandra terminalis.

(1) Background: A central subject in clonal plant ecology is to elucidate the mechanism by which clones forage resources in heterogeneous environments. Compared with studies conducted in laboratories or experimental gardens, studies on light foraging of forest woody clonal plants in their natural habitats are limited. (2) Methods: We investigated wild populations of an evergreen clonal understory shrub, Japanese pachysandra (Pachysandra terminalis Siebold & Zucc.), in two cool-temperate forests in Japan. (3) Results: Similar to the results of herbaceous clonal species, this species formed a dense stand in a relatively well-lit place, and a sparse stand in a shaded place. Higher specific rhizome length (i.e., length per unit mass) in shade resulted in lower ramet population density in shade. The individual leaf area, whole-ramet leaf area, or ramet height did not increase with increased light availability. The number of flower buds per flowering ramet increased as the canopy openness or population density increased. (4) Conclusions: Our results provide the first empirical evidence of shade avoidance and light foraging with morphological plasticity for a clonal woody species.

Effect of disturbance on population structure, regeneration and conservation of Moghania chappar in sal forests of Gorakhpur, India

Non-seed regeneration is essentially a vagrant strategy of woody plants causing assemblage of homozygous populations in disturbed forests. We tried to understand how such hardy species like Moghania chappar produce close groups of individuals at different level of disturbance. The hypothesis of trade-off between ramet proliferation and disturbance level, and between growth pattern and resource conservation was tested. The three 1-ha sample plots of sal forest, facing low, moderate or high level of disturbance were observed within Sohagibarwa Wildlife Sanctuary. A total of 40 quadrats per 1-ha plot were sampled to record the age structure of genet and ramet populations of M. chappar. The architecture and foraging of the root-stock was mapped, the biomass of root and shoot was measured and the soil conserved by the root-complex was estimated at each disturbance level. The growth characteristics suggest that M. chappar conforms to Stone’s model of tree architecture. At moderate disturbance, the root-shoot junction sent many more sprouts, garnered much biomass and became flat and curved. The insurrection of ramets caused fragmentation of the root-complex. This clonal growth strategy, however, was neither clearly ‘phalanx’ nor ‘guerrilla’ type. It resulted in intermittent shallow cavities within fragmented root-stock that got filled with soil rich in organic matter. The growth strategy of the species showed potential to restore the soil system and to conserve the diversity of minor biota. In moderately disturbed sal forest, the understorey paved way to prolific non-seed regeneration of this fugitive mid-successional species. At moderate heat stress, the number of individuals as well as the proportion of seedlings per population was highest. The species rapidly increased the understorey foliage by producing a metapopulation of usable sprouts/ramets that facilitated retention of soil and nutrients within their root traps. The total extractible shoot biomass per plant was quite large as a ~ 6 year old individual weighed 473.5 ± 27.4 g. This study of clonal plant ecology may provide new impetus to the conservation of degraded forest ecosystems.

Responses to Sedimentation in Ramet Populations of the Clonal Plant Carex brevicuspis.

In aquatic ecosystems, sedimentation is an important factor that affects plant growth, mainly due to sediment depth. Clonal morphological plasticity is an effective strategy in clonal plants for acclimatization to sediment burial. To date, few studies have examined growth responses to sedimentation on the clonal plants at the ramet population level. This study aimed to explore the interactive effects of population size and burial depth on growth and clonal morphology of Carex brevicuspis. Three population sizes (2, 8, and 32 ramets) and 3 burial depths (0 cm, 5 cm, and 10 cm) were used in this experiment. Under shallow (5 cm) and deep (10 cm) burial conditions, biomass accumulation and relative growth rate (RGR) were lower than in the no burial treatment (P < 0.05). RGR of the small and medium populations was especially high compared to the large populations (P < 0.05). Biomass allocation was higher to belowground parts than aboveground parts, except for the small populations in the 5 cm burial treatments. Both shallow burial and smaller populations led to more biomass being allocated to aboveground parts. Deep burial elongated the first order spacer more than shallow burial, and sedimentation had negative effects on the second order spacer length. The number of new ramets did not decrease in the 5 or 10 cm burial treatments compared to the unburial treatment, and larger populations usually had more ramets than smaller ones; the proportion of clumping ramets was higher than the proportion of spreading ramets, and deeper burial and smaller populations led to higher proportions of spreading ramets. These results indicated that the growth of C. brevicuspis was limited by sediment burial at the ramet population level. Smaller populations enable C. brevicuspis to adjust its escape response to burial stress, may allow this species to effectively survive and widely distribute in Dongting Lake wetland.

Population Structure and Site Characteristics of the Rare Shasta Snow-Wreath (Neviusia cliftonii)

The Shasta snow-wreath (Neviusia cliftonii Shevock, Ertter & D.W. Taylor; Rosaceae) is a rare shrub, endemic to areas near Shasta Lake in the eastern Klamath Range of northern California, USA. Since discovery in 1992, the number of known populations has increased from 3 to 33. Shasta snow-wreath is a thicket-forming shrub, thought to reproduce primarily vegetatively, where individual stems (ramets) arise from the root system. We provide the first descriptions of demography and site characteristics using data collected in eight populations of Shasta snow-wreath. We established permanently-marked transects and recorded the number of ramets, individual stem heights, and the number of inflorescences in 2011, 2012, and 2013. We also characterized sites by tree canopy, shrub components, fuels, vegetation, and ground cover. Using the number of ramets recorded and the total population area, we estimated the number of ramets in each population (‘ramet population size'). Ramet population size ranged from 716 to 18,641 (mean = 5467), and the average maximum stem height ranged from 50 to 159 cm (mean = 104 cm). Larger ramet population size and taller stems were both associated with less tree cover. The two largest ramet population sizes were found at the two highest elevations and most west-facing sites. The average number of inflorescences per stem over three years ranged from 0.08 to 4.91 (mean = 2.76) and showed an increase with elevation. How Shasta snow-wreath will respond to succession or disturbances is unknown, but the negative relationship of ramet population size and canopy cover indicates that fire may have been important for influencing the population size historically. Continued monitoring of the studied populations, and the addition of more populations to the monitoring program, would be useful for detecting demographic changes and for better understanding the factors that govern Shasta snow-wreath.

How does the longevity of Sasa kurilensis ramets respond to a light gradient? An analysis of ontogenetic changes to hydraulic resistance and carbon budget within a ramet

AbstractWe investigated how Sasa kurilensis ramet longevity differs under three light conditions. Ramet longevity is an important factor affecting the abundance of ramet populations and their biomass. The objectives of this study were to clarify: (1) whether ramet longevity varies spatially along a gradient of light conditions; (2) whether physiological functions, including water transport in culms, change with ontogenesis; (3) whether ramet longevity is associated with the most effective turnover for gaining a carbon profit within a ramet following a cost‐benefit model or is affected by other factors such as death caused by a decline in physiological function. We analyzed S. kurilensis ramet longevity, hydraulic resistance, photosynthetic rate, and carbon content. We then estimated the ramet carbon budget. The longevity of S. kurilensis ramets was 2.8–4.5 years in Beneath‐patch plots, 5.8–8.7 years in Edge‐patch plots, and 1.6–2.2 years in Open‐patch plots. Although leaf photosynthetic activity was stable, the instantaneous photosynthetic rate decreased during clear days in the open area. This may have been due to increased ramet hydraulic resistance. The rotation period of the most efficient carbon budget quantified by ecophysiological measurements was consistent with ramet longevity in Open‐patch (2 years) and Edge‐patch (5 years) sites. Meanwhile, the longevity of ramets grown under canopies was inconsistent with the cost‐benefit model rules for a carbon budget because the carbon gain was low throughout the ramet life span.

Responses of native plant populations on an unprotected beach to disturbance by storm-induced overwash events

Extreme climatic events disturb plant communities, altering species composition, and abundance. For herbaceous populations on coastal beaches, responses to disturbance are often spatially heterogeneous and depend on species’ life history. This study documents the effects of two overwash events, caused by Hurricane Irene in August 2011 and Superstorm Sandy in October 2012, on the abundance of native species on a low-lying, unprotected beach on Staten Island, New York, USA. Temporary plots (33 cm diameter) spaced at 3-m intervals along 30-m transects perpendicular to shoreline, were used in September 2007, 2011, 2012, and 2013 to survey lower (0–9 m), middle (12–21 m), and upper (24–30 m) regions of the same beach. The same procedure was used to quantify seedling recruitment in spring (May) after each overwash. Complex changes in density the year after each overwash were specific for distinct beach regions and depended on species’ life history. Rhizomatous perennial grasses (Ammophila breviligulata and Panicum amarum) maintained or increased ramet populations, possibly stimulated by sand deposition on the middle and upper beach. The first overwash was early enough in the growing season to permit subsequent seed production during autumn, and seedling recruitment occurred for three native annuals (Cenchrus tribuloides, Heterotheca subaxillaris, and Triplasis purpurea), and the tall perennial Solidago sempervirens the next spring. The second overwash was later in autumn and probably removed seeds from the site and/or deeply buried the seeds of two annuals (Cenchrus and Heterotheca) which did not recruit seedlings the next spring. Triplasis seedlings were abundant in a blowout on the lower beach. Given more frequent storms and sea-level rise in the future, it becomes imperative to maintain an assemblage of native plant species with diverse life histories when restoring coastal beaches.

Effects of soil heterogeneity and clonal integration on Alternanthera philoxeroides populations with a radial ramet aggregation

Some clonal plants can spread their ramet populations radially, and soil heterogeneity and clonal integration may greatly affect the establishment of these types of populations. We constructed Alternanthera philoxeroides populations with a radial ramet aggregation, allowing old ramets of clonal fragments to concentrate in central pots and younger ramets to root in peripheral pots. The peripheral pots were supplemented either with three different levels (high, medium and low) of soil nutrients to simulate a heterogeneous soil environment, or only one medium level of soil nutrients to simulate a homogeneous environment. Stolon connections between the central older ramets and the peripheral younger ramets were left intact or severed to test the effect of clonal integration. The maintenance of stolon connection could induce the division of labor between different‐aged ramets, by increasing the root investment in central ramets and the above‐ground growth in peripheral ramets. The maintenance of stolon connection could improve the growth of the central and peripheral ramets, clonal fragments and even the whole population. However, the positive consequence in peripheral ramets and whole fragments was only detected in the high‐nutrient patch of heterogeneous treatment. In sum, in the population with the radial ramet aggregation, clonal integration can play a key role in the rapid recruitment of young ramets of A. philoxeroides fragments, as well as the expansion of the whole population. The magnitude of clonal integration also became more obvious in the peripheral young ramets and whole fragments that experienced high‐nutrient patches.

Pre- and post-vernalization ramet removal reduces flowering of red sorrel (Rumex acetosellaL.) in wild blueberry (Vaccinium angustifoliumAit.)

White, S. N., Boyd, N. S., Van Acker, R. C. and Swanton, C. J. 2015. Pre- and post-vernalization ramet removal reduces flowering of red sorrel (Rumex acetosella L.) in wild blueberry (Vaccinium angustifolium Ait.). Can. J. Plant Sci. 95: 549–556. Red sorrel is a common, ramet-producing herbaceous creeping perennial species in wild blueberry fields. Flowering and seed production occur primarily in overwintering ramets in Nova Scotia, Canada, and growers may therefore be able to adopt fairly simple management strategies to reduce or prevent flowering and seed production in this species. The objective of this research was to determine the effect of pre- and post-vernalization ramet removal on red sorrel flowering ramet density under both controlled and field conditions. Under controlled conditions in a growth facility, ramet populations were subject to pre- and post-vernalization clipping treatments to simulate late autumn and early spring ramet removal. Under field conditions, pre- and post-vernalization ra...

Studies on the flowering biology of red sorrel (Rumex acetosella) ramets from lowbush blueberry (Vaccinium angustifolium) fields in Nova Scotia, Canada

Red sorrel (Rumex acetosella L.) is a ramet-producing herbaceous creeping perennial species commonly found as a weed in commercially managed lowbush blueberry (Vaccinium angustifolium Aiton) fields in Nova Scotia, Canada. Flowering and seed production occur primarily in overwintering ramets of this species, indicating a potential vernalization requirement for flowering. This study was therefore initiated to examine the role of vernalization, photoperiod, and pre-vernalization stimulus on ramet flowering. Red sorrel ramets propagated from creeping roots and seeds collected from established red sorrel populations in lowbush blueberry had an obligate requirement for vernalization to flower. Ramet populations maintained under pre- and post-vernalization photoperiods of 16 h flowered following 12 weeks of vernalization at 4 ± 0.1 °C, whereas those maintained under constant 16, 14, or 8 h photoperiods without vernalization did not flower. Vernalization for 10 weeks maximized, but did not saturate, the flowering response. Pre-vernalization photoperiod affected flowering response, with increased flowering frequency observed in ramet populations exposed to decreasing, rather than constant, photoperiod prior to vernalization. This study represents the first attempt to determine the combined effects of vernalization and photoperiod on red sorrel flowering, and the results provide a benchmark for the future study of flowering and sexual reproduction in this economically important perennial weed species.

Demography of Rumex acetosella in lowbush blueberry (Vaccinium angustifolium)

SummaryThe demography of Rumex acetosella ramets and seedlings was monitored within and between blueberry clones over the two‐year lowbush blueberry production cycle in Nova Scotia, Canada. Overwintering ramets constituted the majority (&gt;70%) of the flowering ramet population. A small proportion of ramets emerging in May and June flowered, but no ramets emerging between July and November flowered in the year of emergence. Emergence of new ramets was season‐long and ramet populations were regulated by a cycle of birth and death in each production year. Ramet populations in blueberry patches had higher growth rates and lower mortality than ramet populations in bare soil patches in the non‐bearing year, resulting in large net gains to ramet populations in blueberry patches during this production year. Ramet population growth rates and mortality were similar in blueberry and bare soil patches in the bearing year and net ramet populations declined during this production year. Survival rates of overwintering and new ramets varied, but ramets from both the overwintering and monthly cohorts contributed to a distinct ramet age structure at the end of each season. Seedling survival ranged from 6 ± 6 to 51 ± 12% across sites, and no seedlings flowered in the year of emergence. Transition probabilities of ramets and seedlings were used to develop a life‐cycle model of R. acetosella for the 2‐year lowbush blueberry production cycle. This model has utility in developing new management strategies for R. acetosella in lowbush blueberry.

Effect of clonal integration on ramet population regeneration of two Fargesia (bamboo) species under simulated ingesting interference

Aims Herbaceous species can have compensatory growth after grazing.Clonal integration contributes greatly to the re-growth of clonal plants.To date,however,very few studies have addressed how clonal integration affects bamboos' regeneration at a ramet level.Our objectives were to test the following hypotheses:(1) clonal integration benefits bamboo's compensatory growth greatly after grazing and(2) differences in branching pattern of rhizomes lead to different contributions of clonal integration to the compensatory effects.Methods In Tangjiahe National Nature Reserve,we subjected Fargesia scabrida and F.denudata ramets within 1.2 m × 1.2 m plots to four clipping treatments,i.e.,no clipping and 25%,50% and 75% shoot removal,and kept rhizomes at the plot edges either connected or disconnected.Important findings In plots with no clipping,rhizome severing stimulated new shoot generation and population recruitment of F.scabrida,but reduced the height and biomass of new shoots.The shooting rate and recruitment of F.denudata were significantly decreased in plots where rhizomes remained connected.When rhizomes were kept connected,25% clipping reduced the biomass of F.scabrida,and 25% and 50% clipping reduced recruitment of F.denudata.However,rhizome severing increased the recruitment of F.denudata.Under 75% clipping,the recruitments of both bamboos did not decrease significantly,but the quality of new shoots declined.Such negative effects were negated or greatly ameliorated in F.scabrida when rhizomes were connected.In general,clonal integration contributes greatly to the growth of new ramets,but contributes little to compensatory growth of both bamboos after grazing.

The responses of the quantitative characteristics of a ramet population of the ephemeroid rhizomatous sedge Carex physodes to the moisture content of the soil in various locations on sand dunes.

In this study, the soil moisture content was measured, and the quantitative characteristics of this sedge species were compared. The phenotypic plasticity of each parameter and the linear regression relationships were analyzed. The results showed that the soil moisture content was significantly affected by location, soil depth, and sampling date. The aboveground biomass, underground biomass, biomass density, and population density at the peak were significantly higher than elsewhere on the dune. However, the morphological plasticity index of the quantitative characteristics was higher at the base and middle of the dune. When the soil moisture content decreased, the underground biomass and ramet biomass density increased. The aboveground and underground biomasses were strongly negatively correlated, but the ramet height and aboveground biomass were strongly positively correlated. These results indicated that the soil water content significantly affected the clonal growth of C. physodes. The responsiveness of C. physodes may be adaptive when the soil resource supply is low. The strong morphological plasticity of the species appears to be ecologically important for the maintenance and dominance of this species in the dune habitat.

Deviation of Mass-Density Allometry in Ramet Populations of Switchgrass

We studied a ramet population of switchgrass, caespitose in appearance, and proved the absence of density-dependent mortality. We present a deviation of mass-density allometry based on spatially explicit densities along the vertical space of the population. The number of ramets in the mean-ramet-height space explains the variation in the average weight of whole ramets (M) more accurately, with an asymptote towards critical self-thinning trajectory for such a mass-density relationship. With the development of size heterogeneity, a ‘vertical packing’ process appears in the population. We define the process as a similar ‘self-thinning’ trajectory, through the initial crowding of ramets in the mean-ramet-height space and continued transferring into the upper space and the lower space. The process presents a possibly competitive mechanism of self-thinning, local-competition-driving size deviation and vertical space packing. Here, log10 (M) = 2.91 - 1.25 log10 (NL). Local crowding degree (NL) is the number of ramets per unit area (m2) in the mean-ramet-height space class. Similar ‘self-thinning’ occurs in the ramet population, but it just indicates how those ramets escape out of the mean-ramet-height space class, and therefore how the mean weight of whole ramets increases. Self-thinning should be the result of local competition among effective number of individuals in a population, rather than apparent crowding degree presented by whole individuals. The critical mass-density allometry based on whole individuals should be only a special case.

Demography of the Clonal PalmPrestoea Acuminatain the Colombian Andes: Sustainable Household Extraction of Palm Hearts

Prestoea acuminata is a highland clonal palm traditionally used as a source of palm hearts by the Awá Indians of Colombia and Ecuador; its commercial use thrived in the 1980's. Extraction pressure on the resource is particularly strong during Holy Week, as campesinos use it as a substitute for meat. We studied P. acuminata demography at La Planada Reserve, southwestern Colombia, and elaborated a ramet-based matrix model to assess the impact of different palm heart harvest regimes. The 1.5 ha study area had 1182 genets, composed of 5389 ramets. Harvestable stems were 23-40 years old and accounted for 0.32% of the stable stage distribution (SSD). Ramet population asymptotic growth rate λ was 1.0485, and was more sensitive to changes in the survival of stemless ramets. Observed stage distribution (OSD) differed from predicted SSD, which suggests the population was exhibiting transient dynamics. As our census was conducted four years after a severe ENSO, we argue that the OSD could be reflecting this environmental disturbance. Thus, harvest simulations must be interpreted with caution. Although P. acuminata ramets are abundant at La Planada, the typical genet architecture, with many stemless ramets (≈20) and only 1-2 stems appropriate for palm heart extraction, accounts for a very low resource yield (127 palm hearts ha−1in our survey). This, and its slow growth rate, make P. acuminata suitable only for household extraction. As harvest has a strong effect on sexual recruitment, we recommend a maximum annual extraction of 10% of harvestable ramets.

Rhus glabra response to season and intensity of fire in tallgrass prairie

Altered fire regimes play a key role in shrub expansion in grasslands worldwide. We assessed how season and type or intensity of fire affected the growth and demography of Rhus glabra, a common woody invader in North American mesic grasslands. Fire during any season killed 99% of ramets but stimulated new ramet recruitment from belowground buds, resulting in a near-complete turnover of ramet populations. During the first 2 years following fire, populations on spring-burned sites had the greatest post-fire ramet densities and population growth rates, and winter- and spring-burned populations showed the highest resprouting rates. However, after 10 years, R. glabra cover on summer-burned sites was 3.5 times greater than on autumn- or winter-burned treatments. Thus, short-term post-fire responses may not be good predictors of long-term changes in abundance. Low-intensity spring backfires resulted in the highest ramet population growth rates, whereas high-intensity headfires in any season resulted in slower growth, and populations burned with low-intensity winter fires declined. In addition, season of fire influenced browsing pressure, suggesting that plant responses may be partially a result of indirect effects of fire on rates of herbivory. Overall, our results demonstrate that the application of frequent autumn or winter backfires is an effective management tool for limiting R. glabra expansion in grasslands, and that long-term data are critical for management decision-making, particularly in systems characterised by high interannual climate variability.

Intersimple Sequence Repeats Distinguish Genetic Differences in Easter Lily ‘Nellie White’ Clonal Ramets within and among Bulb Growers over Years

The large genome size of easter lily [Lilium longiflorum (77.1 pg/2C nucleus)], coupled with repetitive DNA sequences, makes it difficult to use molecular techniques to identify or fingerprint lily (Lilium) species, hybrids, and clones. Previous research demonstrated that amplified fragment length polymorphisms could not be optimized for consistency and repeatability to obtain reliable genetic variation assessments of lily species and clones. The objective of this research was to analyze the effectiveness and stringency of intersimple sequence repeats (ISSRs) to determine genetic differences between L. longiflorum ‘Nellie White’ clonal ramet populations from bulb growers over years. DNA from closely related clones of L. longiflorum ‘Nellie White’ included 2002 (n = 11 bulb lots) and 2003 (n = 12 bulb lots). Comparison cultivars and species were also included. Five University of British Columbia (UBC) primers (P808, P810, P811, P814, and P818) that were used produced 56 polymorphic loci. ISSR banding patterns were consistent among three replications within ‘Nellie White’ clonal genotypes. ‘Nellie White’ clones differed significantly within (82%) and among (18%) growers in 2002 and 2003. ‘Nellie White’ clones are not uniform or part of a single ramet population. Principal clades within years separated at Nei's genetic distances (GDs) of GD = 0.6 (growers 2, 4, and 12) to GD = 0.82 (grower 6) in 2002 and GD = 0.51 (grower 4) to GD = 0.78 (grower 14). The most closely related ‘Nellie White’ clones within growers ranged from GD = 0.8 to 0.95 in 2002 and GD = 0.7 to 0.91 for 2003. Five top-performing growers (1, and 3–6) from previous morphological studies and, particularly growers 3 and 5, were in similar clades, cosegregating with phenotypic traits of stem emergence and flowering dates. The lack of a meiotic sieve (Muller's ratchet) may be responsible for the high level of mutational differences present in the ‘Nellie White’ clones and significantly affects the ability of commercial greenhouse growers to produce a uniform easter lily crop, particularly in years when the Easter holiday is early.

Can clone size serve as a proxy for clone age?An exploration using microsatellite divergence in Populus tremuloides

In long-lived clonal plants, the overall size of a clone is often used to estimate clone age. The size of a clone, however, might be largely determined by physical or biotic interactions, obscuring the relationship between clone size and age. Here, we use the accumulation of mutations at 14 microsatellite loci to estimate clone age in trembling aspen (Populus tremuloides) from southwestern Canada. We show that the observed patterns of genetic divergence are consistent with a model of increasing ramet population size, allowing us to use pairwise genetic divergence as an estimator of clone age. In the populations studied, clone size did not exhibit a significant relationship with microsatellite divergence, indicating that clone size is not a good proxy for clone age. In P. tremuloides, the per-locus per-year neutral somatic mutation rate across 14 microsatellite loci was estimated to lie between 6 x 10(-7) (lower bound) and 4 x 10(-5) (upper bound).

Clonal integration improves compensatory growth in heavily grazed ramet populations of two inland-dune grasses

Herbaceous species possess several mechanisms to compensate for tissue loss. For clonal herbaceous species, clonal integration may be an additional mechanism. This may especially hold true when tissue loss is very high, because other compensatory mechanisms may be insufficient. On inland dunes in northern China, we subjected Bromus ircutensis and Psammochloa villosa ramets within 0.5 m×0.5 m plots to three clipping treatments, i.e., no clipping, moderate (50% shoot removal) and heavy clipping (90% shoot removal), and kept rhizomes at the plot edges connected or disconnected. Moderate clipping did not reduce ramet, leaf or biomass density of either species. Under moderate clipping, rhizome connection significantly improved the performance of Psammochloa, but not that of Bromus. Heavy clipping reduced ramet, leaf and biomass density in the disconnected plots of both species, but such negative effects were negated or greatly ameliorated when the rhizomes were connected. Therefore, clonal integration contributed greatly to the compensatory growth of both species. The results suggest that clonal integration is an additional compensatory mechanism for clonal plants and may be important for their long-term persistence in the heavily grazed regions in northern China.