Sexual reproduction and clonal growth in Reinhardtia gracilis (Palmae), an understory tropical palm

Patterns of sexual reproduction and clonal growth were investigated in the understory palm Reinhardtia gracilis var. gracilior over a 3-yr period. R. gracilis is a very abundant clonal palm in the tropical rain forest of Los Tuxtlas, Veracruz, México. Because ramets form clumps, genets are easily identified in the field. Genets were monitored in a 0.5-ha area, and classified by size according to the number of ramets they possessed. In contrast to clonal growth, sexual reproduction was highly dependent on genet size. The probability of reproduction, the number of inflorescences, and the number of fruits produced were positively correlated with genet size. However, neither the probability of producing a ramet, nor the number of ramets produced per genet were correlated with genet size. Over the 3 yr of study, 55% of the genet population had at least one ramet with reproductive structures, while <1% (a single genet in one year) had six ramets with flowers. Thirty-two percent of the mature genets reproduced during each of three consecutive years. In contrast, 58% of the genets produced no new ramets during these 3 yr. No evidence was found of a trade-off between clonal growth and sexual reproduction. Ramet production increases genet size and this in turn increases genet reproductive performance. Clonal growth in this species may be viewed as a growth strategy that tends to maximize genet fitness.     

Dynamics of distribution and performance of ramets constructing genets: a demographic�Cgenetic study in a clonal plant, Convallaria keiskei

Background and Aims

In clonal plants producing vegetative offspring, performance at the genet level as well as at the ramet level should be investigated in order to understand the entire picture of the population dynamics and the life history characteristics. In this study, demography, including reproduction and survival, the growth patterns and the spatial distributions of ramets within genets of the clonal herb Convallaria keiskei were explored.

Methods

Vegetative growth, flowering and survival of shoots whose genets were identified using microsatellite markers were monitored in four study plots for 3 years (2003–2005). The size structures of ramets in genets and their temporal shifts were then analysed. Their spatial distributions were also examined.

Key Results

During the census, 274 and 149 ramets were mapped in two 1 × 2 m plots, and 83 and 94 ramets in two 2 × 2 m quadrats. Thirty-eight genotypes were identified from 580 samples. Each plot included 5–18 genets, and most ramets belonged to the predominant genet(s) in each plot. Shoots foliated yearly for several years, but flowering ramets did not have an inflorescence the next year. A considerable number of new clonal offspring persistently appeared, forming a bell-shaped curve of the size structure of ramets in each genet. Comparing the structures modelled by the normal distributions suggested variation among ramets belonging to a single genet and variation among genets. Furthermore, spatial analyses revealed clumped and distant distributions of ramet pairs in a genet, in which the distant patterns corresponded to the linearly elongating clonal growth pattern of this species.

Conclusion

Characteristics of ramet performances such as flowering and recruitment of clonal offspring, in addition to growth, played a large part in the regulation of genet dynamics and distribution, which were different among the studied genets. These might be characteristics particularly relevant to clonal life histories.Key words: Clonal plant, Convallaria keiskei, demography, genet, genetic identification, growth pattern, life history, ramet, spatial distribution     

Stochastic population dynamics of clonal plants: Numerical experiments with ramet and genet models

Dynamics of ramer and genet populations were analyzed by use of stochastic matrix models. Based on field data, population development and extinction rates during 50 simulated years were estimated for ramet populations of three speciesPotentilla anserina, Rubus saxatilis andLinnaea borealis. Only small initial populations (below 125–250 ramets), experienced a detectable risk of extinction within this time interval. ForP. anserina andR. saxatilis, population increase occurred in some simulations despite negative average growth rates. A model for stochastic genet dynamics was constructed by combining field data and hypothesized parameter values. Growth rate and population structure were insensitive to variation in disturbance intensity and frequency, whereas variation in recruitment affected population structure but only to a minor extent growth rate. Decreasing recruitment causes extinction of genet populations, but the time-scale for the decline is in the magnitude of centuries for initial genet populations of about 1000 individuals. Dynamics of genets in clonal plants thus incorporate processes occurring on widely different scales. Some implications of the results for models of population dynamics in long-lived clonal plants are discussed.     

Clonal Diversity in Differently-Aged Populations of the Pseudo-Annual Clonal Plant Circaea lutetiana L.

Abstract: In many clonal plant species seedling recruitment is restricted to short colonization episodes early in the development of the population, and clonal diversity (i.e., genet diversity) in the population is expected to decrease with increasing population age. In established populations of the pseudo-annual Circaea lutetiana seedling recruitment has previously not been observed. Therefore, we expected established populations to have low clonal diversities. We analysed number and frequency of genets and spatial distribution of genets in six differently-aged C. lutetiana populations with the use of four informative RAPD primers. We found relatively low clonal diversities in young populations but very high clonal diversities in established populations. Therefore, the hypothesis was rejected that seedling recruitment does not occur in established populations. Moreover, we did not find large genet size asymmetries in established populations. Genet size differences can be caused by stochastic processes or by fitness related traits, such as differences in vegetative reproduction. Because vegetative propagation of ramets is dependent on ramet size, and the number of ramets and the size of each ramet determine genet size, we expected that large genets produced, on average, large ramets. However, this was not the case, suggesting that stochastic processes caused genet size differences. Genet size may also be bounded if spatial distribution of genets is affected by micro-habitat differences. For this we expected to find a clumped spatial distribution of ramets of the same genet. However, ramets of large genets were always found intermingled with ramets belonging to other genets.     

The oldest known clones of Salix herbacea growing in the Northern Apennines,Italy are at least 2000 years old

Premise

Dominant in many ecosystems around the world, clonal plants can reach considerable ages and sizes. Due to their modular growth patterns, individual clonal plants (genets) can consist of many subunits (ramets). Since single ramets do not reflect the actual age of genets, the ratio between genet size (radius) and longitudinal annual growth rate (LAGR) of living ramets is often used to approximate the age of clonal plants. However, information on how the LAGR changes along ramets and how LAGR variability may affect age estimates of genets is still limited.

Methods

We assessed the variability of LAGR based on wood-section position along the ramets and on the duration of the growing season on three genetically distinct genets of Salix herbacea growing in the Northern Apennines (Italy). We compared genet ages estimated by dividing genet radius by the LAGRs of its ramets.

Results

LAGR increased significantly from the stem apex to the root collar; indicating that ramet growth rate decreased with time. Furthermore, a difference of ca. 2 weeks in the onset of the growing period did not impact LAGR. Considering the high LAGR variability, we estimated that the three genets started to grow between ~2100 and ~7000 years ago, which makes them the oldest known clones of S. herbacea even considering the most conservative age estimate.

Conclusions

Our findings indicate that analyzing ramets at the root collar provides an integrative measurement of their overall LAGR, which is crucial for estimating the age of genets.     

Light-induced variation in the growth and dynamics of transplanted ramets of the understory herb,Aster acuminatus

Summary Ramets of the understory herb, Aster acuminatus, were transplanted from two source populations into eight understory garden sites that varied in light and soil moisture levels. Ramet growth, clonal growth, flowering and survivorship were monitored for three growing seasons. Large differences among gardens in ramet growth, clonal growth and flowering developed in the first growing season and increased in the next two years. This variation was positively correlated with garden light level but not at all with soil moisture. Mortality rates were low in all gardens and showed that genets from any particular source could survive over a broad range of environmental conditions. There was no conclusive evidence for any source population differences in the capacity to survive or grow in different environments. The rapid, light-induced responses of transplanted ramets resulted in garden populations very similar in appearance to natural populations experiencing similar light regimes. These results combined with those from other studies of A. acuminatus provide strong evidence for the importance of light in explaining population patterns and dynamics in this species.     

Species-specific sprouting pattern in two dioecious Lindera shrubs: The role of physiological integration

Sprouting is recognized as an important genet persistence strategy for clonal woody plants, but the role of sprouting may differ between species and between sexes, depending on physiological integration. We tested the effect of physiological integration on the mortality, recruitment and growth of the sprouting male and female ramets of two closely related dioecious shrubs of Lindera, in a field experiment using girdling manipulation. Although between-sex differences observed were obscure, we found between-species differences in the sprouting patterns. The rates of ramet mortality and recruitment were significantly lower for L. praecox than L. triloba. In L. praecox genets, the ramet production was low, and the main ramets might actively translocate assimilates towards the small sprouted ramets, which then facilitates high ramet growth and survival (sprout-nursing strategy). Meanwhile, in L. triloba genets, although many ramets were recruited, assimilate translocation from the main ramets to the sprouted ramets might be less abundant, which causes high ramet mortality (sprout-turnover strategy). For a more general knowledge of the various sprouting strategies in clonal plants, our study demonstrated that inter-specific comparisons using girdling experiments at the whole-plant level could reveal the role of physiological integration on the link between the sprouting pattern and above-ground structures of clonal plants.     

Ramet dynamics in a centrifugally expanding clonal sedge: a matrix analysis

Carex humilis is a clonal sedge that can form distinct rings of densely aggregated ramets. We hypothesize that rings form because both production of new ramets and ramet dispersal are positively correlated to ramet size. This would lead to an overrepresentation of fast-moving and large ramets with high ramet production at the periphery, whereas slow-moving and small ramets with low ramet production would mainly be found in the interior of rings. We use matrix models to analyse how ramet populations both at the periphery and in the interior develop in the absence of ramet dispersal. We found that the stable size class distributions of ramets predicted by the models were not different from the distributions found in the field. Also, the asymptotic ramet population growth rates (λ₁) were the same. Hence, we conclude that rings would form even in the absence of a link between ramet dispersal and ramet production. Further analysis of the matrix models showed that the ramet population increases at the periphery but decreases in the interior of rings because medium and large ramets produce fewer large ramets in the interior than at the periphery. We also found that the temporal variance in λ₁ and transitions rates during the four study years was much higher at the periphery than in the interior. Our results suggest that rings may form because C. humilis ramets use below-ground resources from a much larger area than the one covered by the shoots. As the clone grows larger, the soil volume available to the ramets in the interior decreases because their access to soil outside the ring is cut-off by the ramets at the periphery. Ramet density in the interior is therefore decreasing.     

Simulations of clonal species genotypic diversity – trembling aspen (Populus tremuloïdes) as a case study

We built two models to follow clonal species genotypic diversity (G/N) over long periods of time at the stand and landscape levels. The models were then validated with empirical data from trembling aspen (Populus tremuloides) populations in Quebec’s boreal forest. Data was collected using a chronosequence approach in seven sites that burned in 1717, 1760, 1797, 1823, 1847, 1944, and 1916. Genetic identification was done by using four microsatellite loci. At the stand scale, simulations were repeated for a genet size of 5, 25, 50 and 100 ramets each. At the landscape level, we simulated the cumulative genet survival rate under different fire cycles (5–500 years) for 500 years after fire. Stand simulations indicated that ramet mortality within genets rather than genet mortality accounts for the increase in G/N with time since fire. Both the initial genet size and the recurrent suckering of some genets (or ramet recruitment) play an important role in maintaining high G/N levels for long periods of time. In general, the larger the number of ramets per genet, the longer the genet survives under a gap disturbance regime and a minimum of 100 ramets per genet is required to maintain aspen genet survival for 500 years. At the landscape level, genet loss increases as the fire cycle gets longer. In Quebec’s boreal forest, short rotation even-aged management practices seem to maintain a genet survival rate similar to that produced by the natural succession regime.     

Reproductive demography of ramets and genets in a rhizomatous clonal plant <Emphasis Type="Italic">Convallaria keiskei</Emphasis>

Clonal growth occurring below the ground makes it difficult to identify individuals and demonstrate the demographic features of a focal plant species. In this study, genotypically identified ramets of a rhizomatous clonal herb, Convallaria keiskei Miq., were monitored for their growth, survival, and reproduction from 2003 to 2006. After the monitoring period, their subterranean organs were excavated to explore the underground connections of established ramets and the direction of clonal growth. We then combined data on the fate of the monitored ramets with the information of rhizome connections, clarifying reproductive demography at both the ramet and genet levels. Although each ramet initiated both sexual reproduction (via flowering) and clonal growth, clonal growth tended to precede sexual reproduction. In a surveyed genet, 51.0% of ramets produced flowers and 29.6% generated clonal offspring during the study period. Consequently, we clarified the reproductive demography of C. keiskei: clonal growth tended to precede flowering in a ramet, and a genet can keep reproducing every season at the genet level, despite a ramet not having inflorescence every year.     

Morphological and Physiological Acclimation Responses to Contrasting Light and Water Regimes in <Emphasis Type="Italic">Primula sieboldii</Emphasis>

The effects of the availability of light (high, medium and low) and soil water (wet and dry) on morphological and physiological traits responsible for whole plant carbon gain and ramet biomass accumulation were examined in a splitter-type clonal herbaceous species Primula sieboldii, a spring plant inhabiting broad range of light environments including open grassland and oak forest understory. Growth experiments were conducted for three genets originated from natural microhabitats differing in light and soil water availability. Ramets of a genet from high light and wet microhabitat, which were grown in low light (relative photon flux density: R-PPFD of 5%) showed 41% less light-saturated photosynthetic rate, 50% less dark respiration rate and earlier defoliation than the ramets in high light (R-PPFD of 61%). The estimation of daily photosynthesis revealed that the light acclimation response in leaf gas exchange contributes to efficient carbon gain of whole plants, irrespective of experimental light conditions. Water stress increased root weight ratio, decreased ramet leaf area, petiole length and photosynthetic capacity. These morphological effects of water stress were larger in high and medium light regimes than in low light regime. The consequence of the above responses was recognized in the relative growth rate of the ramets. The relative growth rate of the ramets in high light with wet regime was four-fold of that in low light plus wet regime, and was 1.5-fold of that in high light plus dry regime. However, even in low light and/or dry regimes, ramets kept positive relative growth rates and produced gemma successfully. We could not detect significant variation in growth responses among genets. The high photosynthetic plasticity revealed in the present study should enable Primula sieboldii to inhabit in a broad range of light and soil water availability.     

Effects of mycorrhizae on growth and demography of tallgrass prairie forbs

The effects of arbuscular mycorrhizal (AM) symbiosis on ramet and genet densities, vegetative growth rates, and flowering of three forb species were studied in native tallgrass prairie in northeastern Kansas. Mycorrhizal activity was experimentally suppressed for six growing seasons on replicate plots in an annually burned and an infrequently burned watershed with the fungicide benomyl. Benomyl reduced mycorrhizal root colonization to an average of 4.2%, approximately a two-thirds reduction relative to controls (13.7% colonization). Mycorrhizae influenced the population structure of these forbs. Although mycorrhizal suppression had no long-term effect on genet densities and no effect on ramet survivorship throughout the growing season, the number of ramets per individual was significantly increased such that ramet densities of all three species were approximately doubled in response to long-term mycorrhizal suppression. Effects of mycorrhizae on ramet growth and reproduction varied among species. Ramet growth rates, biomass, and flowering of Salvia azurea were greater in plots with active mycorrhizal symbiosis, whereas mycorrhizae reduced ramet growth rates and biomass of Artemesia ludoviciana. Aster sericeus ramet growth rates and biomass were unaffected by the fungicide applications, but its flowering was reduced.The pattern of responses of these three species to mycorrhizae differed considerably between the two sites of contrasting fire regime, indicating that the interaction of fire-induced shifts in resource availability and mycorrhizal symbiosis together modulates plant responses and the intensity and patterns of interspecific competition between and among tallgrass prairie grass and forb species. Further, the results indicate that effects of mycorrhizae on community structure are a result of interspecific differences in the balance between direct positive effects of the symbiosis on host plant performance and indirect negative effects mediated through altered competitive interactions.     

Genet structure and determinants of clonal structure in a temperate deciduous woodland herb, Uvularia perfoliata

1 We used isozyme variation to examine the genet structure of Uvularia perfoliata patches in gap and closed canopy habitats in a temperate deciduous forest in Maryland, USA.
2 A large patch in a gap habitat was composed of a small number of widely spread genets with many ramets, and a large number of genets with more restricted distribution and few ramets. Genets with many ramets were patchily distributed at a metre scale. Analysis of genet structure on a scale of square centimetres, however, revealed that the genets were highly intermingled with no clear boundaries between them. The presence at both scales of sampling of many genets with unique multilocus genotypes indicated continuing genet recruitment within the population.
3 In the closed canopy habitat, the patches examined were each composed of a single unique multilocus genotype, suggesting that each had developed by asexual propagation following the establishment of a single genet.
4 The clonal structure of U. perfoliata patches in both gap and closed canopy habitats therefore appears to depend on recruitment patterns of genets. Populations in closed canopy habitats are characterized by a 'waiting' strategy, in which asexual ramet production maintains populations until genet recruitment by seed production can occur under the more optimal conditions associated with canopy gaps. Extended sampling suggests that the genetic diversity of U. perfoliata populations is primarily controlled by the disturbance regime of the forest canopy.     

Influences of the genetic neighborhood on ramet reproductive success in a clonal desert cactus

Clonal structure in clonal plants can affect sexual reproduction. Individual ramets can decrease reproduction if their neighbors are ramets of the same genet due to inbreeding depression or self-incompatibility. We assessed ramet reproductive success in the partial self-incompatible Ferocactus robustus (Cactaceae) as a function of floral display size in focal ramets and floral display size and clonal structure of their reproductive neighborhoods. Ramets were labeled, sized in number of stems, mapped and genetically identified through RAPD markers in one population. A pollen dispersal area of 15-m radius was established for each ramet to determine the clonal diversity in the neighborhoods. Flower production and fruit set were counted on a monthly basis during one reproductive season as a surrogate of ramet fitness. We expected a decrease in individual ramet reproductive success as a function of the number of reproductive ramets of the same genet in the neighborhood. A total of 272 sampled ramets revealed 116 multilocus genotypes, showing high clonal diversity in the population (G/N = 0.43, D = 0.98). Clonal diversity of neighborhoods ranged from 0.06 to 1 and fruit set varied from 0 to 76.9%. Individual ramet reproductive success was influenced by (1) mate availability, (2) floral display size of a genet within the reproductive neighborhood, and (3) the proportion of distinguishable genotypes. Floral display size of genets and ramets coupled with the genetic diversity within the reproductive neighborhood determines the low sexual reproduction in F. robustus.     

Dynamic process,spatial pattern and species coexistence in plants

The significance of dynamic processes of individual genets/ramets for the spatial pattern of plant species and community structure is discussed. It is suggested that under a different mode of competition (symmetric vs. asymmetric), spatial distribution of individuals, initial size distribution at the establishment stage and boundary conditions as recruitment influence differently the species coexistence pattern. It is therefore important to consider the mode of competition for the study of community structure. To know the mode and degree of intra- and interspecific competition, the dynamic processes of individual genets/ramets must be studied by following the growth, mortality and recruitment of each genet/ramet of each component species in a plant community. The models and methods of plant population ecology are therefore useful also for plant community ecology.     

A predictive relationship between population and genetic sex ratios in clonal species

Sexual reproduction depends on mate availability that is reflected by local sex ratios. In species where both sexes can clonally expand, the population sex ratio describes the proportion of males, including clonally derived individuals (ramets) in addition to sexually produced individuals (genets). In contrast to population sex ratio that accounts for the overall abundance of the sexes, the genetic sex ratio reflects the relative abundance of genetically unique mates, which is critical in predicting effective population size but is difficult to estimate in the field. While an intuitive positive relationship between population (ramet) sex ratio and genetic (genet) sex ratio is expected, an explicit relationship is unknown. In this study, we determined a mathematical expression in the form of a hyperbola that encompasses a linear to a nonlinear positive relationship between ramet and genet sex ratios. As expected when both sexes clonally have equal number of ramets per genet both sex ratios are identical, and thus ramet sex ratio becomes a linear function of genet sex ratio. Conversely, if sex differences in ramet number occur, this mathematical relationship becomes nonlinear and a discrepancy between the sex ratios amplifies from extreme sex ratios values towards intermediate values. We evaluated our predictions with empirical data that simultaneously quantified ramet and genet sex ratios in populations of several species. We found that the data support the predicted positive nonlinear relationship, indicating sex differences in ramet number across populations. However, some data may also fit the null model, which suggests that sex differences in ramet number were not extensive, or the number of populations was too small to capture the curvature of the nonlinear relationship. Data with lack of fit suggest the presence of factors capable of weakening the positive relationship between the sex ratios. Advantages of this model include predicting genet sex ratio using population sex ratios given known sex differences in ramet number, and detecting sex differences in ramet number among populations.     

贺兰山丁香自然居群克隆生长格局及遗传多样性的ISSR分析

运用ISSR分子标记技术,通过制定挖掘采样、"+"形采样及"垂直"采样3种采样方案,对贺兰山丁香(Syringa pinnatifolia var.alanshanica)不同居群的克隆多样性、克隆生长格局及其遗传多样性进行了分析.克隆多样性分析表明:挖掘采样方式采到的3个克隆系内,各自所包含的单株间具有完全相同的基因型;"垂直"采样及"+"形采样的7个居群、 239个样品表现出136个不同的基因型或克隆,显示贺兰山丁香具有较高的克隆多样性(D=0.994)及基因型分布均匀性(E=0.985).克隆生长空间格局分析表明,贺兰山丁香为密集型克隆植物.每个居群都由多克隆组成,克隆生长只发生在同一丛内,多数基株只含有1个分株,最多可达8个.物种水平上的平均克隆大小(N_C)和平均基因型比例(PD)分别为1.757和0.569.对贺兰山丁香遗传多样性分析的结果显示,在居群水平和物种水平上都保持着较高的遗传多样性,其遗传变异主要存在于居群内;但居群间分化程度较低(G_ST=0.320),表明自然居群间基因交流有限.     

Sexual differences in physiological integration in the dioecious shrub Lindera triloba: a field experiment using girdling manipulation

Background and Aims

It is important to consider the modular level when verifying sexual dimorphism in dioecious plants. Nevertheless, between-sex differences in resource translocation among modules (i.e. physiological integration) have not been tested at the whole-plant level. In this study, sexual differences in physiological integration were examined among ramets, within a genet in the dioecious sprouting shrub Lindera triloba, by a field experiment with girdling manipulation.

Methods

Female and male genets were randomly assigned to girdled or intact groups. Girdling of the main ramets was conducted in May 2009 by removing a ring of bark and cambium approx. 1 cm wide at a height of 80–100 cm. The effects of treatment and sex on ramet dynamics (mortality, recruitment and diameter growth) and inflorescence production during 1 year after girdling were examined.

Key Results

The diameter growth rate of main ramets of both sexes was lower at ground level (D₀) but higher at breast height (dbh) in girdled than in intact groups. In sprouted ramets with a dbh of 0–2 cm, males in girdled groups had lower growth rates at D₀ than those of intact groups, whereas no girdling effect was found for females. The main ramets in girdled groups produced more inflorescences than intact groups, irrespective of sex, but male ramets showed a greater response to the treatment than females.

Conclusions

In L. triloba, physiological integration exists at the whole-plant level, and sprouted ramets are dependent on assimilates translocated from main ramets, but this dependence weakens as sprouted ramets get larger. Female sprouted ramets can grow in a physiologically independent manner from the main ramet earlier than those of males. This study highlights the importance of considering modular structures and physiological integration when evaluating sexual differences in demographic patterns of clonal plants.     

Fine-scale spatial structure of genets and sexes in the dioecious plant <Emphasis Type="Italic">Dioscorea japonica</Emphasis>, which disperses by both bulbils and seeds

To understand the evolution of clonal reproduction and the diversity of clonal plants, it is necessary to clarify the characteristics of each clonal habit. There has been little research on whether bulbils alter spatial genetic structure (SGS) because of the lack of connection to maternal ramets. We used simple-sequence-repeat (SSR) markers to determine the fine-scale SGS of the dioecious plant Dioscorea japonica, which disperses both as bulbils and as seeds. We also evaluated the contributions of sexual and clonal reproduction and tested for spatial sex segregation (SSS). We discovered 111 genets from 394 ramets in a 2.8-ha plot. Genotypic richness (R = 0.28) and clonal diversity (Simpson’s D = 0.94, Fager’s E = 0.90) were high. We did not find SSS, suggesting that the population does not suffer from a shortage of mating pairs due to clonal reproduction. The Sp values revealed moderate SGS at the genet level (Sp = 0.013–0.014), and the genets intermingled at a local scale. Significant SGS at the ramet level showed that ramets within the same genet tended to aggregate. We also found a skewed clonal spatial distribution. The spatial extent of genets was positively correlated with the number of ramets within a genet. The contribution of bulbil production to the variance of parent–offspring gene dispersal was about one–fifth the contribution from sexual reproduction. These results suggest that the dispersal via bulbils affects the SGS in D. japonica, although its contribution to gene dispersal is small compared to the contribution of sexual reproduction.     

Responses of two bunchgrasses to nitrogen addition in tallgrass prairie: the role of bud bank demography

Growth of tallgrass prairie plants, many of which maintain substantial bud banks, can be limited by nitrogen (N), water, and/or light. We hypothesized that tallgrass prairie plants respond to increases in N through demographic effects on the bud bank. We tested the effects of a pulse of N on (1) bud bank demography, (2) plant reproductive allocation, and (3) ramet size. We parameterized matrix models, considering each genet as a population of plant parts. Nitrogen addition significantly impacted bud bank demography in two subdominant species of bunchgrass: Sporobolus heterolepis (a C(4) grass) and Koeleria macrantha (a C(3) grass), but had no effect on the size of individual ramets. Emergence from the bud bank and ramet population growth rates (λ) were significantly higher in S. heterolepis genets that received supplemental N. Nitrogen addition also affected the bud demography of K. macrantha, but N addition decreased rather than increased λ. Prospective and retrospective demographic analyses indicated that bud bank dynamics were the most important demographic processes driving plant responses to nutrient availability. Thus, the variation in productivity in these tallgrass prairie species is driven principally by the demography of the bud bank rather than by the physiology and growth of aboveground tillers. Improved understanding of bud bank dynamics may lead to improved predictive models of grassland responses to environmental changes such as altered N deposition and precipitation.