Adventitious rooting in response to long-term cold: a possible mechanism of clonal growth in alpine perennials

Arctic alpine species experience extended periods of cold and unpredictable conditions during flowering. Thus, often, alpine plants use both sexual and asexual means of reproduction to maximize fitness and ensure reproductive success. We used the arctic alpine perennial Arabis alpina to explore the role of prolonged cold exposure on adventitious rooting. We exposed plants to 4°C for different durations and scored the presence of adventitious roots on the main stem and axillary branches. Our physiological studies demonstrated the presence of adventitious roots after 21 weeks at 4°C saturating the effect of cold on this process. Notably, adventitious roots on the main stem developing in specific internodes allowed us to identify the gene regulatory network involved in the formation of adventitious roots in cold using transcriptomics. These data and histological studies indicated that adventitious roots in A. alpina stems initiate during cold exposure and emerge after plants experience growth promoting conditions. While the initiation of adventitious root was not associated with changes of DR5 auxin response and free endogenous auxin level in the stems, the emergence of the adventitious root primordia was. Using the transcriptomic data, we discerned the sequential hormone responses occurring in various stages of adventitious root formation and identified supplementary pathways putatively involved in adventitious root emergence, such as glucosinolate metabolism. Together, our results highlight the role of low temperature during clonal growth in alpine plants and provide insights on the molecular mechanisms involved at distinct stages of adventitious rooting.

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

BACKGROUND

Clonal 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).

RESULTS

Warming 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.

CONCLUSIONS

The 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.

Plant clonality in a soil-impoverished open ecosystem: insights from southwest Australian shrublands

BACKGROUND AND AIMS

Clonality is a key life-history strategy promoting on-spot persistence, space occupancy, resprouting after disturbance, and resource storage, sharing and foraging. These functions provided by clonality can be advantageous under different environmental conditions, including resource-paucity and fire-proneness, which define most mediterranean-type open ecosystems, such as southwest Australian shrublands. Studying clonality-environment links in underexplored mediterranean shrublands could therefore deepen our understanding of the role played by this essential strategy in open ecosystems globally.

METHODS

We created a new dataset including 463 species, six traits related to clonal growth organs (CGOs; lignotubers, herbaceous and woody rhizomes, stolons, tubers, stem fragments), and edaphic predictors of soil water availability, nitrogen (N) and phosphorus (P) from 138 plots. Within two shrubland communities, we explored multivariate clonal patterns and how the diversity of CGOs, and abundance-weighted and unweighted proportions .of clonality in plots changed along with the edaphic gradients.

KEY RESULTS

We found clonality in 65 % of species; the most frequent were those with lignotubers (28 %) and herbaceous rhizomes (26 %). In multivariate space, plots clustered into two groups, one distinguished by sandy plots and plants with CGOs, the other by clayey plots and non-clonal species. CGO diversity did not vary along the edaphic gradients (only marginally with water availability). The abundance-weighted proportion of clonal species increased with N and decreased with P and water availability, yet these results were CGO-specific. We revealed almost no relationships for unweighted clonality.

CONCLUSIONS

Clonality is more widespread in shrublands than previously thought, and distinct plant communities are distinguished by specific suites (or lack) of CGOs. We show that weighting belowground traits by aboveground abundance affects the results, with implications for trait-based ecologists using abundance-weighting. We suggest unweighted approaches for belowground organs in open ecosystems until belowground abundance is quantifiable.

Population Genomics Study and Implications for the Conservation of Zabelia tyaihyonii Based on Genotyping-By-Sequencing

Zabelia tyaihyonii (Nakai) Hisauti and H. Hara is a perennial shrub endemic to Republic of Korea that grows naturally in only a very limited region of the dolomite areas of Gangwon-do and Chungcheongbuk-do Provinces in the Republic of Korea. Given its geographical characteristics, it is more vulnerable than more widely distributed species. Despite the need for comprehensive information to support conservation, population genetic information for this species is very scarce. In this study, we analyzed the genetic diversity and population structure of 94 individuals from six populations of Z. tyaihyonii using a genotyping-by-sequencing (GBS) approach to provide important information for proper conservation and management. Our results, based on 3088 single nucleotide polymorphisms (SNPs), showed a mean expected heterozygosity (He) of 0.233, no sign of within-population inbreeding (G_IS that was close to or even below zero in all populations), and a high level of genetic differentiation (F_ST = 0.170). Analysis of molecular variance (AMOVA) indicated that the principal molecular variance existed within populations (84.5%) rather than among populations (17.0%). We suggested that six management units were proposed for conservation considering Bayesian structure analysis and phylogenetic analysis, and given the various current situations faced by Z. tyaihyonii, it is believed that not only the in situ conservation but also the ex situ conservation should be considered.

Genetic structure in patchy populations of a candidate foundation plant: a case study of Leymus chinensis using genetic and clonal diversity

PREMISE

The distribution of genetic diversity on the landscape has critical ecological and evolutionary implications. This may be especially the case on a local scale for foundation plant species because they create and define ecological communities, contributing disproportionately to ecosystem function.

METHODS

We examined the distribution of genetic diversity and clones, which we defined first as unique multilocus genotypes (MLG), and then by grouping similar MLGs into multilocus lineages. We used 186 markers from inter-simple sequence repeats (ISSR) across 358 ramets from 13 patches of the foundation grass Leymus chinensis. We examined the relationship between genetic and clonal diversities, their variation with patch size, and the effect of the number of markers used to evaluate genetic diversity and structure in this species.

RESULTS

Every ramet had a unique MLG. Almost all patches consisted of individuals belonging to a single multilocus lineages. We confirmed this with a clustering algorithm to group related genotypes. The predominance of a single lineage within each patch could be the result of the accumulation of somatic mutations, limited dispersal, some sexual reproduction with partners mainly restricted to the same patch, or a combination of all three.

CONCLUSIONS

We found strong genetic structure among patches of L. chinensis. Consistent with previous work on the species, the clustering of similar genotypes within patches suggests that clonal reproduction combined with somatic mutation, limited dispersal, and some degree of sexual reproduction among neighbors causes individuals within a patch to be more closely related than among patches.

Intensity and mode of Lindera melissifolia reproduction are affected by flooding and light availability

We studied the impact of flooding and light availability gradients on sexual and asexual reproduction in Lindera melissifolia (Walt.) Blume, an endangered shrub found in floodplain forests of the Mississippi Alluvial Valley (MAV), USA. A water impoundment facility was used to control the duration of soil flooding (0, 45, or 90 days), and shade houses were used to control light availability (high = 72%, intermediate = 33%, or low = 2% of ambient light) received by L. melissifolia established on native soil of the MAV. Sexual reproductive intensity, as measured by inflorescence bud count, fruit set, and drupe production, was greatest in the absence of soil flooding. Ninety days of soil flooding in the year prior to anthesis decreased inflorescence bud counts, and 45 days of soil flooding in the year of anthesis lessened fruit set and drupe production. Inflorescence bud development was the greatest in environments of intermediate light, decreased in high-light environments, and was absent in low light environments. But low fruit set diminished drupe production in intermediate light environments as compared to high light environments. Asexual reproduction, as measured by development of new ramets, was greatest in the absence of soil flooding and where plants were grown in high or intermediate light. Plants exhibited plasticity in reproductive mode such that soil flooding increased the relative importance of asexual reproduction. The high light environment was most favorable to sexual reproduction, and reproductive mode transitioned to exclusively asexual in the low light environment. Our results raise several implications important to active management for the conservation of this imperiled plant.

Age-dependent plasticity in reproductive investment, regeneration capacity and survival in a partially clonal animal (Hydra oligactis)

Asexual reproduction diversifies life-history priorities and is associated with unusual reproduction and somatic maintenance patterns, such as constant fertility with age, extensive regeneration ability and negligible senescence. While age-dependent plasticity in relative allocation to sexual versus asexual reproductive modes is relatively well studied, the modulation of somatic maintenance traits in parallel with age-dependent reproduction is much less well understood in clonal or partially clonal animals. Here, we asked how age-dependent investment into sexual and asexual reproduction co-varies with somatic maintenance such as regeneration in a partially clonal freshwater cnidarian Hydra oligactis, a species with remarkable regeneration abilities and experimentally inducible sex. We induced gametogenesis by lowering temperature at two ages, 1 or 4 weeks after detachment from an asexual parent, in animals of a male and a female clone. Then we measured phenotypically asexual and sexual reproductive traits (budding rate, start day and number of sexual organs) together with head regeneration rate, survival and the cellular background of these traits (number of reproductive and interstitial stem cells) for 2 or 5 months. Younger animals had higher asexual reproduction while individuals in the older group had more intensive gametogenesis and reproductive cell production. In parallel with these age-dependent reproductive differences, somatic maintenance of older individuals was also impacted: head regeneration, survival and interstitial stem cell numbers were reduced compared to younger polyps. Some of the traits investigated showed an ontogenetic effect, suggesting that age-dependent plasticity and a fixed ontogenetic response might both contribute to differences between age groups. We show that in H. oligactis asexual reproduction coupled with higher somatic maintenance is prioritized earlier in life, while sexual reproduction with higher maintenance costs occurs later if sex is induced. These findings confirm general life-history theory predictions on resource allocation between somatic maintenance and sexual reproduction applying in a partially clonal species. At the same time, our study also highlights the age-dependent integration of these resource allocation decisions with sexual/asexual strategies. Accounting for age-related differences might enhance repeatability of research done with clonal individuals derived from mass cultures.

Clonal diversity and spatial genetic structure in the long-lived herb, Prairie trillium

Combining population genetic studies with demographic surveys in long-lived clonal herbs can yield insight into the population dynamics of clonal plant populations. In this study, we assayed clonal diversity and spatial genetic structure in a population of a long-lived understory herb, Trillium recurvatum, that has been the focus of a demographic study spanning 26 years at the Meeman Biological Station in Memphis, Tennessee, USA. Using a set of five newly developed simple sequence repeat markers first reported here, we assessed 1) the extent of clonal diversity within the Meeman site, 2) the degree to which genetic diversity varies with stage class (juvenile, non-flowering, and flowering adults) at this site, 3) whether there is spatial genetic structure at the Meeman site, and 4) how measures of genetic diversity and inbreeding at the Meeman site compare to two additional nearby populations. Along with these analyses, we calculated and compared traditional population genetic metrics with information theory-based diversity indices. Although clonal propagation was present, the focal population displayed moderate levels of clonal diversity comprising 81 genets from the 174 individuals sampled. In the focal site, we also found that genetic diversity was highest in the flowering stage class when compared to the non-flowering and juvenile classes. We report that genets exhibited spatial genetic structure in the focal site exhibiting values for the Sp statistic of 0.00199 for linear distance and 0.0271 for log distance. Measures of unbiased gene diversity and the inbreeding coefficient were comparable across the sampled populations. Our results provide complementary genetic data to previous demographic studies in T. recurvatum, and these findings provide data for future studies aimed at integrating the degree of clonality, genetic variation, and population dynamics in this species. Our findings suggest that T. recurvatum at the focal Meeman site displays higher levels of sexual reproduction than were previously suggested, and spatial genetic structure estimates were comparable to other plant species with mixed and outcrossing mating strategies.

The plant body as a network of semi-autonomous agents: a review

Plants can solve amazingly difficult tasks while adjusting their growth and development to the environment. They can explore and exploit several resources simultaneously, even when the distributions of these vary in space and time. The systematic study of plant behaviour goes back to Darwin's book The power of movement in plants. Current research has highlighted that modularity is a key to understanding plant behaviour, as the production, functional specialization and death of modules enable the plant to adjust its movement to the environment. The adjustment is assisted by a flow of information and resources among the modules. Experiments have yielded many results about these processes in various plant species. Theoretical research, however, has lagged behind the empirical studies, possibly owing to the lack of a proper modelling framework that could encompass the high number of components and interactions. In this paper, I propose such a framework on the basis of network theory, viewing the plant as a group of connected, semi-autonomous agents. I review some characteristic plant responses to the environment through changing the states of agents and/or links. I also point out some unexplored areas, in which a dialogue between plant science and network theory could be mutually inspiring. This article is part of the theme issue 'Liquid brains, solid brains: How distributed cognitive architectures process information'.

Factors influencing distribution and local coexistence of diploids and tetraploids of Vicia cracca: inferences from a common garden experiment

Vicia cracca diploids and autotetraploids are highly parapatric in Europe; tetraploids reside in western and northern part, whereas diploids occupy much drier south-eastern part. They meet together in a Central European contact zone. This distribution pattern raised questions about a transformative effect of polyploidization on plant performance and environmental tolerances. We investigated plant survival, growth, and seed production in two water regimes in a common garden experiment using seeds collected from five localities in the Central European contact zone where diploids and tetraploids occur in sympatry. Obtained data imply that tetraploids of V. cracca are not generally superior in performance to diploids. Significantly larger seeds from tetraploid mother plants collected in the field were not correlated with greater stature of the seedlings. Nonetheless, tetraploids might have a potential to out-compete diploids in the long run due to the tetraploids' ability of greater growth which manifested in the second year of cultivation. Considering the response of diploids and tetraploids to water supply, drought stressed tetraploids but not diploids produced a higher proportion of aborted seeds than watered ones, which implies that tetraploids are more drought susceptible than diploids. On the other hand, decreased plant height in drought stresses tetraploids, which simultaneously increased total seed production, may suggest that tetraploids have a greater ability to avoid local extinction under unfavourable conditions by enhancing biomass allocation into production of seeds at the cost of lower growth. The significant interaction between ploidy level and locality in several traits suggests possible polyfyletic origin of tetraploids and the necessity to clarify the history of the tetraploids in Europe.

Demographic consequences of greater clonal than sexual reproduction in Dicentra canadensis

Clonality is a widespread life history trait in flowering plants that may be essential for population persistence, especially in environments where sexual reproduction is unpredictable. Frequent clonal reproduction, however, could hinder sexual reproduction by spatially aggregating ramets that compete with seedlings and reduce inter-genet pollination. Nevertheless, the role of clonality in relation to variable sexual reproduction in population dynamics is often overlooked. We combined population matrix models and pollination experiments to compare the demographic contributions of clonal and sexual reproduction in three Dicentra canadensis populations, one in a well-forested landscape and two in isolated forest remnants. We constructed stage-based transition matrices from 3 years of census data to evaluate annual population growth rates, λ. We used loop analysis to evaluate the relative contribution of different reproductive pathways to λ. Despite strong temporal and spatial variation in seed set, populations generally showed stable growth rates. Although we detected some pollen limitation of seed set, manipulative pollination treatments did not affect population growth rates. Clonal reproduction contributed significantly more than sexual reproduction to population growth in the forest remnants. Only at the well-forested site did sexual reproduction contribute as much as clonal reproduction to population growth. Flowering plants were more likely to transition to a smaller size class with reduced reproductive potential in the following year than similarly sized nonflowering plants, suggesting energy trade-offs between sexual and clonal reproduction at the individual level. Seed production had negligible effects on growth and tuber production of individual plants. Our results demonstrate that clonal reproduction is vital for population persistence in a system where sexual reproduction is unpredictable. The bias toward clonality may be driven by low fitness returns for resource investment in sexual reproduction at the individual level. However, chronic failure in sexual reproduction may exacerbate the imbalance between sexual and clonal reproduction and eventually lead to irreversible loss of sex in the population.

Biomass allocation and nutrients balance related to the concentration of Nitrogen and Phosphorus in Salvinia auriculata (Salviniaceae)

Abstract Aquatic plants can use differential allocation (trade-off) of carbon among their structures depending on the nutrition concentration. Given that N and P are limiting in the growth of plants, our questions were: Are the N and P concentrations in S. auriculata related to the biomass allocation to its structures? Is a differential allocation of N and P between floating and submerged leaves? We evaluated the relation between the nutrients and the biomass allocation, and the trade-off among the leaves using the Spearman correlation. Our results showed that N and P concentrations in S. auriculata are related to the biomass allocation to its structures, and that there is no trade-off of these nutrients between “shoot and root”. Thus, we can see the importance of N and P concentration in the biomass of S. auriculata, and why this plant is capable to development in different environments as a weedy.

Trade-off between allocation to reproductive ramets and rhizome buds in Carex brevicuspis populations along a small-scale elevational gradient

The trade-off between allocation to sexual and clonal reproduction in clonal plants is influenced by a variety of environmental factors; however, it has rarely been examined under field conditions. In this study, we investigated the trade-off between two modes of reproduction in Carex brevicuspis C. B. Clarke across a small-scale elevational gradient (21–27 m a.s.l.) at the Dongting Lake wetlands, China. The proportion of biomass allocated to and the density of reproductive ramets were higher at low than at intermediate and high elevations. In contrast, the proportion of biomass allocated to and the density of rhizome buds were lower at low than at intermediate and high elevations. Redundancy analysis showed that sexual reproduction was positively correlated with soil moisture content, soil organic matter, total phosphorus, and pH, and negatively correlated with elevation and ramet density. Our findings suggested that allocation to sexual reproduction is favored in disturbed habitats with fertile soils, whereas allocation to vegetative propagation is favored in stable and competitive habitats. Trade-off between allocation to sexual reproduction and vegetative propagation along an elevational gradient might be a reproductive strategy of C. brevicuspis to adapt to the water level fluctuations in wetland habitats.

Inter-simple sequence repeat data reveals high genetic diversity in wild populations of the narrowly distributed endemic Lilium regale in the Minjiang River Valley of China

Lilium regale E.H. Wilson is endemic to a narrow geographic area in the Minjiang River valley in southwestern China, and is considered an important germplasm for breeding commercially valuable lily varieties, due to its vigorous growth, resistance to diseases and tolerance for low moisture. We analyzed the genetic diversity of eight populations of L. regale sampled across the entire natural distribution range of the species using Inter-Simple Sequence Repeat markers. The genetic diversity (expected heterozygosity= 0.3356) was higher than those reported for other narrowly distributed endemic plants. The levels of inbreeding (Fst = 0.1897) were low, and most of the genetic variability was found to be within (80.91%) than amongpopulations (19.09%). An indirect estimate of historical levels of gene flow (Nm =1.0678) indicated high levels of gene flow among populations. The eight analyzed populations clustered into three genetically distinct groups. Based on these results, we recommend conservation of large populations representing these three genetically distinct groups.

Intraspecific competition and light effect on reproduction of Ligularia virgaurea, an invasive native alpine grassland clonal herb

The relationship between sexual reproduction and clonal growth in clonal plants often shows up at the ramet level. However, only a few studies focus on the relationship at the genet level, which could finally account for evolution. The sexual reproduction and clonal growth of Ligularia virgaurea, a perennial herb widely distributed in the alpine grasslands of the Qinghai-Tibetan Plateau of China, were studied under different competition intensities and light conditions at the genet level through a potted experiment. The results showed that: (1) sexual reproduction did not depend on density or light, and increasing clonal growth with decreasing density and increasing light intensity indicated that intraspecific competition and light intensity may affect the clonal life history of L. virgaurea; (2) both sexual reproduction and clonal growth show a positive linear relationship with genet size under different densities and light conditions; (3) a threshold size is required for sexual reproduction and no evidence of a threshold size for clonal growth under different densities and light conditions; (4) light level affected the allocation of total biomass to clonal and sexual structures, with less allocation to clonal structures and more allocation to sexual structures in full sunlight than in shade; (5) light determined the onset of sexual reproduction, and the genets in the shade required a smaller threshold size for sexual reproduction to occur than the plants in full sunlight; and (6) no evidence was found of trade-offs between clonal growth and sexual reproduction under different densities and light conditions at the genet level, and the positive correlation between two reproductive modes indicated that these are two integrated processes. Clonal growth in this species may be viewed as a growth strategy that tends to maximize genet fitness.

Herbivory affects salt marsh succession dynamics by suppressing the recovery of dominant species

Disturbance can generate heterogeneous environments and profoundly influence plant diversity by creating patches at different successional stages. Herbivores, in turn, can govern plant succession dynamics by determining the rate of species replacement, ultimately affecting plant community structure. In a south-western Atlantic salt marsh, we experimentally evaluated the role of herbivory in the recovery following disturbance of the plant community and assessed whether herbivory affects the relative importance of sexual and clonal reproduction on these dynamics. Our results show that herbivory strongly affects salt marsh secondary succession by suppressing seedlings and limiting clonal colonization of the dominant marsh grass, allowing subordinate species to dominate disturbed patches. These results demonstrate that herbivores can have an important role in salt marsh community structure and function, and can be a key force during succession dynamics.

Trade-offs between clonal and sexual reproduction in Sagittaria latifolia (Alismataceae) scale up to affect the fitness of entire clones

Many plants combine sexual reproduction with vegetative propagation, but how trade-offs between these reproductive modes affect fitness is poorly understood. Although such trade-offs have been demonstrated at the level of individual shoots (ramets), there is little evidence that they scale up to affect genet fitness. For hermaphrodites, reproductive investment is further divided between female and male sexual functions. Female function should generally incur greater carbon costs than male function, which might involve greater nitrogen (N) costs. Using a common garden experiment with diclinous, clonal Sagittaria latifolia we manipulated investment in reproduction through female and male sex functions of 412 plants from monoecious and dioecious populations. We detected a 1:1 trade-off between biomass investment in female function and clonal reproduction. For male function, there was no apparent trade-off between clonal and sexual reproduction in terms of biomass investment. Instead, male function incurred a substantially higher N cost. Our results indicate that: trade-offs between investment in clonal propagation and sexual reproduction occur at the genet level in S. latifolia; and sexual reproduction interferes with clonal expansion, with investment in female function limiting the quantity of clonal propagules produced, and investment in male function limiting the nutrient content of clonal propagules.

How past and present influence the foraging of clonal plants?

Clonal plants spreading horizontally and forming a network structure of ramets exhibit complex growth patterns to maximize resource uptake from the environment. They respond to spatial heterogeneity by changing their internode length or branching frequency. Ramets definitively root in the soil but stay interconnected for a varying period of time thus allowing an exchange of spatial and temporal information. We quantified the foraging response of clonal plants depending on the local soil quality sampled by the rooting ramet (i.e. the present information) and the resource variability sampled by the older ramets (i.e. the past information). We demonstrated that two related species, Potentilla reptans and P. anserina, responded similarly to the local quality of their environment by decreasing their internode length in response to nutrient-rich soil. Only P. reptans responded to resource variability by decreasing its internode length. In both species, the experience acquired by older ramets influenced the plastic response of new rooted ramets: the internode length between ramets depended not only on the soil quality locally sampled but also on the soil quality previously sampled by older ramets. We quantified the effect of the information perceived at different time and space on the foraging behavior of clonal plants by showing a non-linear response of the ramet rooting in the soil of a given quality. These data suggest that the decision to grow a stolon or to root a ramet at a given distance from the older ramet results from the integration of the past and present information about the richness and the variability of the environment.

FREQUENT CLONALITY IN FUCOIDS (FUCUS RADICANS AND FUCUS VESICULOSUS; FUCALES, PHAEOPHYCEAE) IN THE BALTIC SEA(1)

Asexual reproduction by cloning may affect the genetic structure of populations, their potential to evolve, and, among foundation species, contributions to ecosystem functions. Macroalgae of the genus Fucus are known to produce attached plants only by sexual recruitment. Recently, however, clones of attached plants recruited by asexual reproduction were observed in a few populations of Fucus radicans Bergström et L. Kautsky and F. vesiculosus L. inside the Baltic Sea. Herein we assess the distribution and prevalence of clonality in Baltic fucoids using nine polymorphic microsatellite loci and samples of F. radicans and F. vesiculosus from 13 Baltic sites. Clonality was more common in F. radicans than in F. vesiculosus, and in both species it tended to be most common in northern Baltic sites, although variation among close populations was sometimes extensive. Individual clonal lineages were mostly restricted to single or nearby locations, but one clonal lineage of F. radicans dominated five of 10 populations and was widely distributed over 550 × 100 km of coast. Populations dominated by a few clonal lineages were common in F. radicans, and these were less genetically variable than in other populations. As thalli recruited by cloning produced gametes, a possible explanation for this reduced genetic variation is that dominance of one or a few clonal lineages biases the gamete pool resulting in a decreased effective population size and thereby loss of genetic variation by genetic drift. Baltic fucoids are important habitat-forming species, and genetic structure and presence of clonality have implications for conservation strategies.

An experimental demonstration of the cost of sex and a potential resource limitation on reproduction in the moss Pterygoneurum (Pottiaceae)

The cost of sexual reproduction is incurred when the current reproductive episode contributes to a a decline in future plant performance. To test the hypotheses that a trade-off exists between current sexual reproduction and subsequent clonal regeneration and that resources limit reproduction and regeneration, plants of the widespread moss Pterygoneurum ovatum were subjected to induced sporophytic abortion, upper leaf removal, and nutrient amendment treatments. Sexually reproducing plants were slower or less likely to produce regenerative structures (protonemata or shoots) and produced fewer regenerative tissue areas or structures. The ability and the timeline to reproduce sexually and regenerate clonally were unaffected by an inorganic nutrient amendment. However, when leaves subtending the sporophyte were removed, the sporophytes were less likely to mature, tended to take a longer time to mature, and were smaller compared to sporophytes from shoots with a full complement of upper leaves. Our findings indicate that plants investing in sexual reproduction suffer a cost of decreased clonal regeneration and indicate that sporophyte maturation is resource-limited, with upper leaves contributing to the nutrition of the sporophyte. This study represents only the second explicit experimental demonstration of a trade-off between sexual and asexual reproduction in bryophytes.

On the vegetative biomass partitioning of seed plant leaves, stems, and roots

A central goal of comparative life-history theory is to derive the general rules governing growth, metabolic allocation, and biomass partitioning. Here, we use allometric theory to predict the relationships among annual leaf, stem, and root growth rates (GL, GS, and GR, respectively) across a broad spectrum of seed plant species. Our model predicts isometric scaling relationships among all three organ growth rates: GL is proportional to GS is proportional to GR. It also provides a conceptual basis for understanding the differences in the absolute amounts of biomass allocated to construct the three organ types. Analyses of a large compendium of biomass production rates across diverse seed plant species provide strong statistical support for the predictions of the theory and indicate that reproductive investments may scale isometrically with respect to vegetative organ growth rates. The general rules governing biomass allocation as indexed by the scaling exponents for organ growth rates are remarkably indifferent to plant size and taxonomic affiliation. However, the allometric "constants" for these relationships differ numerically as a function of phenotypic features and local environmental conditions. Nonetheless, at the level of both inter- and intraspecific comparisons, the same proportional biomass allocation pattern holds across extant seed plant species.

Local forest environment largely affects below-ground growth, clonal diversity and fine-scale spatial genetic structure in the temperate deciduous forest herb Paris quadrifolia

Paris quadrifolia (herb Paris) is a long-lived, clonal woodland herb that shows strong differences in local population size and shoot density along an environmental gradient of soil and light conditions. This environmentally based structuring may be mediated by differences in clonal growth and seedling recruitment through sexual reproduction. To study the interrelationship between environmental conditions and spatial patterns of clonal growth, the spatial genetic structure of four P. quadrifolia populations growing in strongly contrasting sites was determined. In the first place, plant excavations were performed in order to (i) determine differences in below-ground growth of genets, (ii) investigate connectedness of ramets and (iii) determine total genet size. Although no differences in internode length were found among sites, clones in moist sites were much smaller (genets usually consisted of 1-3 interconnected shoots, most of them flowering) than genets in dry sites, which consisted of up to 15 interconnected shoots, the majority of which were vegetative. Further, amplified fragment length polymorphism (AFLP) markers were used. Clonal diversity was higher in populations located in moist and productive ash-poplar forests compared to those found in drier and less productive mixed forest sites (G/N: 0.27 and 0.14 and Simpson's D: 0.84 and 0.75, respectively). Patterns of spatial population genetic structure under dry conditions revealed several large clones dominating the entire population, whereas in moist sites many small genets were observed. Nevertheless, strong spatial genetic structure of the genet population was observed. Our results clearly demonstrate that patterns of clonal diversity and growth form of P. quadrifolia differ among environments. Limited seedling recruitment and large clone sizes due to higher connectedness of ramets explain the low clonal diversity in dry sites. In moist sites, higher levels of clonal diversity and small clone sizes indicate repeated seedling recruitment, whereas strong spatial genetic structure suggests limited seed dispersal within populations.

The interplay between shifts in biomass allocation and costs of reproduction in four grassland perennials under simulated successional change

When perennial herbs face the risk of being outcompeted in the course of succession, they are hypothesized to either increase their biomass allocation to flowers and seeds or to invest more in vegetative growth. We tested these hypotheses in a 3-year garden experiment with four perennials (Hypochaeris radicata, Cirsium dissectum, Succisa pratensis and Centaurea jacea) by growing them in the midst of a tall tussock-forming grass (Molinia caerulea) that may successionally replace them in their natural habitat. In all species except for the short-lived H. radicata, costs of sexual reproduction were significant over the 3 years, since continuous bud removal enhanced total biomass or rosette number. To mimic succession we added nutrients, which resulted in a tripled grass biomass and higher death rates in the shorter-lived species. The simulated succession resulted also in a number of coupled growth responses in the survivors: enhanced plant size as well as elevated seed production. The latter was partly due to larger plant sizes, but mostly due to higher reproductive allocation, which in turn could be partly explained by lower relative somatic costs and by lower root-shoot ratios in the high-nutrient plots. Our results suggest that perennial plants can increase both their persistence and their colonization ability by simultaneously increasing their vegetative size and reproductive allocation in response to enhanced competition and nutrient influxes. These responses can be very important for the survival of a species in a metapopulation context.

Sexual reproduction, clonal diversity and genetic differentiation in patchily distributed populations of the temperate forest herb Paris quadrifolia (Trilliaceae)

Clonal plant species have been shown to adopt different strategies to persist in heterogeneous environments by changing relative investments in sexual reproduction and clonal propagation. As a result, clonal diversity and genetic variation may be different along environmental gradients. We examined the regional and local population structure of the clonal rhizomatous forest herb Paris quadrifolia in a complex of forest fragments in Voeren (Belgium). Relationships between population size (the number of shoots), shoot density (the number of shoots per m2) and local growth conditions were investigated for 47 populations. Clonal diversity and genetic variation within and among 19 populations were investigated using amplified fragment length polymorphism markers. To assess the importance of sexual reproduction, seed set, seed weight and germination success were determined in 18 populations. As predicted, local growth conditions largely affected population distribution, size and density of P. quadrifolia. Populations occurring in moist and relatively productive sites contained significantly more shoots. Here, shoots were also much more sparsely distributed compared to populations occurring in dry and relatively unproductive sites, where shoots showed a strongly aggregated distribution pattern. Clonal diversity was relatively high, compared with other clonal species (G/N ratio=0.43 and Simpson's D=0.81). Clonal diversity significantly (P<0.01) decreased with increasing shoot density while molecular genetic variation was significantly (P<0.01) affected by population size and local environmental conditions. Lack of recruitment and out-competition of less-adapted genotypes may explain the decreased genetic variation in dry sites. Analysis of molecular variance revealed significant genetic variation among populations (PhiST=0.42, P<0.001), whereas pairwise genetic distances were not correlated to geographic distances, suggesting that gene flow among populations is limited. Finally, the number of generative shoots, the number of seeds per fruit and seed weight were significantly and positively related to population size and local growth conditions. We conclude that under stressful conditions populations of clonal forest plant species can slowly evolve into remnant populations characterized by low levels of genetic variation and limited sexual reproduction. Conservation of suitable habitat conditions is therefore a prerequisite for effective long-term conservation of clonal forest plant species.

Trade-offs between sexual and clonal reproduction in an aquatic plant: experimental manipulations vs. phenotypic correlations

That trade-offs result from the allocation of limited resources is a central concept of life history evolution. We quantified trade-offs between sexual and clonal reproduction in the aquatic plant, Butomus umbellatus, by experimentally manipulating sexual investment in two distinct nutrient environments. Increasing seed production caused a significant but nonlinear trade-off. Pollinating half of all flowers strongly reduced clonal bulbil production, but pollinating the remaining flowers did not cause any further trade-off. Trade-offs were not stronger under low nutrient conditions that clearly limited plant growth. Experimentally induced trade-offs were not reflected in negative phenotypic correlations between sexual and clonal allocation among plants within eight populations grown in a uniform greenhouse environment. Diminishing effects of increased sexual allocation plus a lack of accord between experimental manipulations and phenotypic correlations suggest that trade-offs between sexual and clonal reproduction are unlikely to constrain the evolution of reproductive strategy in this species.

Experimental life-history evolution: selection on growth form and its plasticity in a clonal plant

The growth form along the continuum from compact phalanx plants to more loosely packed guerilla plants is an important life-history trait in clonal plants. Prerequisite for its evolution is heritable genetic variation. Starting with 102 genotypes of the stoloniferous herb Ranunculus reptans, we performed one selection experiment on spatial spread per rosette as measure of guerillaness (broad-sense heritability 0.198) and another on plasticity in this trait in response to competition (broad-sense heritability 0.067). After two generations, spatial spread was 36.9% higher in the high line than in the low line (realized heritability +/- SE 0.149 +/- 0.039). Moreover, compared with the low line genotypes of the high line had fewer rosettes, a lower proportion of flowering rosettes, a higher proportion of rooted rosettes, more branches per rosette, longer internodes and longer leaves. In the second experiment, we found no significant direct response to selection for high and low plasticity in spatial spread (realized heritability +/- SE -0.029 +/- 0.063), despite a significant correlated response in plasticity in the length of the first three stolon internodes. Our study indicates a high potential for further evolution of the clonal growth form in R. reptans, but not for its plasticity, and it demonstrates that the clonal growth form does not evolve independently of other clonal life-history characteristics.

Effects of four generations of density‐dependent selection on life history traits and their plasticity in a clonally propagated plant

Life history evolution of many clonal plants takes place with long periods of exclusively clonal reproduction and under largely varying ramet densities resulting from clonal reproduction. We asked whether life history traits of the clonal herb Ranunculus reptans respond to density-dependent selection, and whether plasticity in these traits is adaptive. After four generations of exclusively clonal propagation of 16 low and 16 high ramet-density lines, we studied life history traits and their plasticities at two test ramet-densities. Plastic responses to higher test-density consisted of a shift from sexual to vegetative reproduction, and reduced flower production, plant size, branching frequency, and lengths of leaves and internodes. Plants of high-density lines tended to have longer leaves, and under high test-density branched less frequently than those of low-density lines. Directions of these selection responses indicate that the observed plastic branching response is adaptive, whereas the plastic leaf length response is not. The reverse branching frequency pattern at low test-density, where plants of high-density lines branched more frequently than those of low-density lines, indicates evolution of plasticity in branching. Moreover, when grown under less stressful low test-density, plants of high-density lines tended to grow larger than the ones of low-density lines. We conclude that ramet density affects clonal life-history evolution and that under exclusively clonal propagation clonal life-history traits and their plasticities evolve differently at different ramet densities.