Seed germination requirements of the rare Helosciadium repens (aka Apium repens) determine persistence of seeds in the soil seed bank.

The rare and threatened Heliosciadium repens grows in moist grasslands and has a distinct life cycle. Plants reproduce both clonally, although ramets tend to be short-lived, and sexually, with seeds that can form a persistent soil seed bank. The germination requirements of H. repens were investigated, yielding important information for its habitat management and conservation. We examined the soil seed bank in three populations and carried out germination experiments and embryo growth measurements with fresh seeds in laboratory, greenhouse and outdoor conditions. We also investigated the effects of storage and burial of seeds. H. repens formed a long-term persistent (>6 years) soil seed bank with very pronounced primary dormancy, but no secondary dormancy or dormancy cycles. Seeds can germinate throughout the growing season when temperatures are sufficiently high. Embryo growth and seed germination are triggered by light and, to a lesser extent, daily temperature fluctuations. Seeds of H. repens seem to have developed a unique germination syndrome with several strategies to remain dormant in the soil until optimal conditions are present for seedling establishment and survival. Both sexual reproduction and seed bank formation are crucial for the long-term survival of the populations.

Invasion patterns of Spartina alterniflora: Response of clones and seedlings to flooding and salinity-A case study in the Yellow River Delta, China.

The invasion of Spartina alterniflora has caused severe damage to the coastal wetland ecosystem of the Yellow River Delta, China. Flooding and salinity are key factors influencing the growth and reproduction of S. alterniflora. However, the differences in response of S. alterniflora seedlings and clonal ramets to these factors remain unclear, and it is not known how these differences affect invasion patterns. In this paper, clonal ramets and seedlings were studied separately. Through literature data integration analysis, field investigation, greenhouse experiments, and situational simulation, we demonstrated significant differences in the responses of clonal ramets and seedlings to flooding and salinity changes. Clonal ramets have no theoretical inundation duration threshold with a salinity threshold of 57 ppt (part per thousand); Seedlings have an inundation duration threshold of about 11 h/day and a salinity threshold of 43 ppt. The sensitivity of belowground indicators of two propagules-types to flooding and salinity changes was stronger than that of aboveground indicators, and it is significant for clones (P < 0.05). Clonal ramets have a larger potentially invadable area than seedlings in the Yellow River Delta. However, the actual invasion area of S. alterniflora is often limited by the responses of seedlings to flooding and salinity. In a future sea-level rise scenario, the difference in responses to flooding and salinity will cause S. alterniflora to further compress native species habitats. Our research findings can improve the efficiency and accuracy of S. alterniflora control. Management of hydrological connectivity and strict restrictions on nitrogen input to wetlands, for example, are potential new initiatives to control S. alterniflora invasion.

High level of somatic mutations detected in a diploid banana wild relative Musa basjoo.

Plants are thought to lack an early segregating germline and often retain both asexual and sexual reproduction, both of which may allow somatic mutations to enter the gametes or clonal progeny, and thereby impact plant evolution. It is yet unclear how often these somatic mutations occur during plant development and what proportion is transmitted to their sexual or cloned offspring. Asexual "seedless" propagation has contributed greatly to the breeding in many fruit crops, such as citrus, grapes and bananas. Whether plants in these lineages experience substantial somatic mutation accumulation is unknown. To estimate the somatic mutation accumulation and inheritance among a clonal population of plant, here we assess somatic mutation accumulation in Musa basjoo, a diploid banana wild relative, using 30 whole-genome resequenced samples collected from five structures, including leaves, sheaths, panicle, roots and underground rhizome connecting three clonal individuals. We observed 18.5 high proportion de novo somatic mutations on average between each two adjacent clonal suckers, equivalent to ~ 2.48 × 10-8 per site per asexual generation, higher than the per site per sexual generation rates (< 1 × 10-8) reported in Arabidopsis and peach. Interestingly, most of these inter-ramet somatic mutations were shared simultaneously in different tissues of the same individual with a high level of variant allele fractions, suggesting that these somatic mutations arise early in ramet development and that each individual may develop only from a few apical stem cells. These results thus suggest substantial mutation accumulation in a wild relative of banana. Our work reveals the significance of somatic mutation in Musa basjoo genetics variations and contribute to the trait improvement breeding of bananas and other asexual clonal crops.

Polyploidization-enhanced effective clonal reproduction endows the successful invasion of Solidago canadensis.

Clonality and ploidy levels are positively associated with plant invasiveness. However, there is still no consensus on whether polyploidization can promote the invasion of alien plants by enhancing clonality. Our recent long-term community succession study found that the more vigorous clone of introduced polyploid Solidago canadensis succeeded into mono-dominant community, which seems to be a positive correlationship between polyploidization and clonal reproduction. However, the formation process of clonal ramet and how polyploidization improves the clonal reproduction of S. canadensis remains unknown. Here, we compared clonal growth ability among diploids and polyploids of S. canadensis from native and introduced ranges in a common garden. Results showed that the rhizomes of S. canadensis originated from axillary buds of dense nodes at the basal stem of seedling and then produced into clonal ramets from the rhizomes. Diploids had denser nodes and more buds, developed more rhizomes per unit mass and produced more clonal propagules at the early growth stage compared with polyploids. However, the number of juvenile and secondary rhizomes, as well as the diameter and length of rhizomes in polyploid populations was significantly higher or greater than those of diploids, and those clonal traits in introduced polyploids were significantly higher than in native polyploids. Moreover, a phalanx growth form was observed in native and introduced diploid populations, which allocated about 3% and 5% of the total biomass to rhizomes, respectively, resulting in short and weak rhizomes. However, native and introduced polyploids allocated about 35% and 40%, respectively, of the total biomass to rhizomes, resulting in long and strong rhizomes, which were guerrilla growth forms. This study firstly shows that polyploidization enhanced the effective clonal reproduction of S. canadensis through pre-adaptation and rapid post-adaptation evolution, and consequently contributed to its successful invasion.

Effects of high ammonium enrichment in water column on the clonal growth of submerged macrophyte Vallisneria natans.

As we know, the survival of young ramets and stolons is essential for the clonal growth of many aquatic plants. However, few NH4+ enrichment experiments on clonal growth of submerged macrophytes have been conducted to provide possible evidences for their declines in eutrophic lakes. Here, the growth and physiological responses of V. natans to the enrichment of NH4+-N were examined under six inorganic nitrogen (IN, i.e., the sum of nitrate nitrogen (NO3--N) and ammonium nitrogen (NH4+-N)) concentrations (control, 2.5, 4.5, 6.5, 8.5, and 10.5 mg L-1). When NH4+-N concentration increased over 0.5 mg L-1, free amino acid (FAA) contents in leaves and stolons increased while soluble carbohydrate (SC) and starch contents decreased, and major growth indices (total biomass of plants, number of ramets, and stolon dry weight (DW)) also showed a degressive tendency. Remarkably, the stolon DW significantly declined with increasing FAA, but significantly positively related to SC and starch. These results indicated that clonal growth of V. natans was inhibited by high NH4+-N concentration, and imbalance of C-N metabolism of stolons partly explained the decline of submerged clonal macrophytes. In this study, the leaves of new and small (NS) ramets contained significantly more FAA and less SC than that of mature and mother (MM) plants, indicating that the C-N metabolism of young ramets was easier to be disrupted, consequently inhibiting the clonal growth of aquatic plants. Furthermore, under the condition of high NH4+-N concentration, FAA may be a useful indicator of both macrophyte growth and physiological stress of plants.

Effects of clonal integration on the proximal and distal ramets of Cynodon dactylon under shade stress

ABSTRACT In a pot experiment, clonal ramets of Cynodon dactylon, a stolon herbaceous plant, were treated with heterogeneous lighting. Proximal ramets (elder ramets) were subjected to shade stress at three different degrees, and stolons between proximal and distal ramets of each pair were treated in a connected or severed manner. Results showed that in moderate shade stress, the number of ramets and leaves, biomass, net photosynthetic rate (Pn), maximum quantum yield (Fv/Fm), effective quantum yield of PSII (ФPSII), and soil and plant analysis development values (SPAD) of proximal ramets were significantly reduced, regardless of whether stolons were kept intact or severed. However, the growth of distal ramets was not significantly influenced, and keeping the stolons intact also did not bring apparent benefits for the whole clonal fragments. These results show that clonal integration does not help alleviate the shade stress suffered by proximal ramets and the costs of distal ramets and does not significantly influence the whole clonal fragments. The possible reasons are that distal ramets may be at the cost of metabolism for resource transportation when the proximal ramets suffer from shade stress; thus, clonal integration is not favorable.

The plant in the labyrinth: Adaptive growth and branching in heterogeneous environments.

The "ant in the labyrinth" problem describes spatial constraints upon a moving agent in a disordered medium. In contrast with an animal-like agent (an "ant"), a clonal plant can stay in a place and move at the same time: some parts develop roots, while others continue moving by horizontal growth and branching. Hereby we present a spatially explicit, dynamic model for the study of percolation by plant growth rules in lattices that consist of open and closed sites. Growth always starts from a single seed in an open percolation cluster (patch). By increasing the proportion of open sites (p), we describe a new kind of threshold (the "tracking threshold", approximately pt=0.73), which is higher than the site percolation threshold (pc=0.5 in this lattice). At pc

Epigenetic Memory as a Basis for Intelligent Behavior in Clonal Plants.

Environmentally induced epigenetic change enables plants to remember past environmental interactions. If this memory capability is exploited to prepare plants for future challenges, it can provide a basis for highly sophisticated behavior, considered intelligent by some. Against the backdrop of an overview of plant intelligence, we hypothesize: (1) that the capability of plants to engage in such intelligent behavior increases with the additional level of complexity afforded by clonality, and; (2) that more faithful inheritance of epigenetic information in clonal plants, in conjunction with information exchange and coordination between connected ramets, is likely to enable especially advanced intelligent behavior in this group. We therefore further hypothesize that this behavior provides ecological and evolutionary advantages to clonal plants, possibly explaining, at least in part, their widespread success. Finally, we suggest avenues of inquiry to enable assessing intelligent behavior and the role of epigenetic memory in clonal species.

Posible influencia de los rametes en la estructura poblacional y distribución del árbol gigante Warszewiczia uxpanapensis, Cordillera de Tilarán, Costa Rica / Possible influence of ramets on the population structure and distribution of the giant tree Warszewiczia uxpanapensis, Tilarán Mountain Range, Costa Rica

The distribution and population structure of Warszewiczia (=Elaeagia) uxpanapensis, a tree that reaches a height of 45 m, a DBH of 1.40 m and 8 m tall buttresses, was studied on two 1-ha plots of premontane pluvial forest. It had a frequency of 49 % and a mean dominance of 6.5 %. The adult distribution was random (mean distance to the nearest neighboring tree in plot 1, it was 14.26 m, n = 15; Clark-Evans Index (IC-E) = 1.07; in plot 2, it was 15.33 m, n = 18, IC-E = 1.34,). The seedlings represented 60.3 % of the sampled population (plot 1, n = 94; plot 2, n = 85). This species has a very high capability of propagating itself vegetatively through clones ("ramets"), which influence its distribution and population structure. With a ramet density in plot 1 of 0.8 and in plot 2 of 0.3/100 m2, its propagation could be from fallen trees or branches (which also create clearings in the forest) or from standing trees and even live branches that produce adventitious roots.

Se estudió los rametes, la distribución y estructura de la población de Warszewiczia uxpanapensis, en 2 ha de bosque pluvial premontano. Este árbol alcanza hasta 45 m de altura, DAPs hasta de 1.40 m y gambas de 8 m de altura. Su frecuencia fue de 49 % y su cobertura promediode 6.5 %. La distribución de los adultos fue aleatoria (distancia promedio al vecino más cercano en la parcela 1 de 14.26 m, IC-E= 1.07, n= 15 en la parcela 2 de 15.33 m, n= 18, IC-E= 1.34). Sus plántulas representaron el 60.3 % de la población estudiada (parcela 1, n= 94; parcela 2, n= 85). Se descubrió que esta especie tiene una alta capacidad de propagarse vegetativamente por rametes, los cuales influyen en la estructura de población y distribución de la especie (con una densidad de rametes parcela 1, 0.8 y parcela 2, 0.3 rametes/100 m2). Su propagación vegetativa puede ser a partir de troncos caídos o ramas desprendidas (las cuales abren claros en el bosque), rebrotes de árboles, o ramas todavía adheridas a los árboles que son capaces de producir raíces adventicias aéreas.

Long-term population dynamics of two Carex curvula species in the Central Alps on native and alien soils.

The demography of two closely related alpine sedges, Carex curvula subsp. curvula and Carex curvula subsp. rosae (=C. curvula and C. rosae) has been investigated on their typical sites in the Central Alps. Both species proliferate vegetatively and develop dense tussocks but they show different dominance behaviours in their respective grasslands. It was hypothesized that this may be caused by different growth abilities. The main aim of the study was to compare the vegetative growth of the species under field conditions, under competition-free conditions and under changed soil conditions. An attempt was also made to clarify whether vegetative growth is density dependent. Permanent plots were established in the respective grasslands of the two species and the ramet density was counted over 3 years. Groups of 10 and of 30 ramets of each species were grown in pots with typical and with alien substrate and their growth was observed for 5 years at the field site. The grassland populations of both species were very stable and the overall ramet growth rate (λ) was close to 1.0. Within the pots, both species reached a high ramet number. Only the group of 30 ramets of C. curvula on alien soil could not recover from the transplantation shock. Within the pots, C. rosae showed a greater ramet turnover and a higher increase in ramets than C. curvula. On their native substrate, both species had a significantly higher ramet increase than on the alien substrate. Ramet growth was found to be density dependent for both species, the increases recorded for the groups of 10 being significantly greater than for the groups of 30. Although C. curvula produced fewer ramets than C. rosae, the aboveground dry weight of the former was significantly higher. This may be decisive for its greater competitive success in closed grasslands.

Divergent dispersal strategies in the freshwater bryozoan Plumatella repens: ramet size effects on statoblast numbers.

Evaluation of size-dependent variation in statoblast numbers in Plumatella repens indicates that this freshwater bryozoan employs divergent strategies in dispersing its asexual offspring in space and time. While the numbers of sessoblasts which were cemented to local substrates did not vary per unit ramet size, numbers of floatoblasts which disperse away from the parent to colonize substrates elsewhere varied in a size-dependent manner. Large ramets produced disproportionately more floatoblasts than did small ramets. In general, this result is consistent with the optimal dispersal predictions of three alternative theoretical models. However, the fact that the total number of sessoblasts in a ramet increased with ramet size appears to violate the "constant disperser principle" of one alternative model, and the occurrence of fusion in P. repens may violate the assumption of local competition for sites in another. In order to determine which model represents an appropriate description of dispersal in P. repens, future studies should evaluate the relative importance of local competition, cooperative phenomena like fusion, and mortality among dispersed and nondispersed offspring.

Mineral nutritional inter-relations amongst stolons and tiller ramets in Agrostis stolonifera L.

The functional organization of the clonal plant Agrostis stolonifera L. was investigated in terms of the mineral nutrient inter-relations between individual well-established stolons and between adjacent tiller ramets on a single stolon. Tillers on developing stolons were rooted individually and treatments established in which different patterns of mineral nutrient supply were given to various parts of the clone. In the first experiment with plants consisting of 2 main stolons and where the ramets of each stolon were supplied with either nutrient solution or water, the stolons displayed distinctly independent nutrient economies irrespective of the pattern of nutrient supply. In a second experiment, where the effect of uniform or local nutrient supply to a single stolon of rooted ramets was followed, the growth of ramets was very closely related to their local nutrient supply. In a further experiment the performance of rooted and unrooted ramets was compared in contrasting nutrient regimes. When situated between ramets supplied with nutrients, the growth and development of an unrooted ramet closely matched one that was rooted and supplied with nutrient solution but greatly exceeded that of one that was rooted and given only water. The independent mineral nutrient economies displayed by individual rooted stolons and by rooted tiller ramets is discussed in relation to the underlying physiological integration of the stolon axis that allows unrooted ramets and the unrooted extending apical region of a stolon to be provided with adequate mineral resources for their growth and development.