Growth Of Clonal Plants Research Articles

Can "Risk-Sharing" Mechanisms Help Clonal Aquatic Plants Mitigate the Stress of Nanoplastics?

Most aquatic plants applied to ecological restoration have demonstrated a clonal growth pattern. The risk-spreading strategy plays a crucial role in facilitating clonal plant growth under external environmental stresses via clonal integration. However, the effects of different concentrations of nanoplastics (NPs) on the growth traits of clonal aquatic plants are not well understood. Therefore, this study aimed to investigate the impact of NPs exposure on seedlings of parent plants and connected offspring ramets. A dose response experiment (0.1, 1, and 10 mg L-1) showed that the growth of Eichhornia crassipes (water hyacinth) was affected by 100 nm polystyrene nanoplastics after 28 days of exposure. Tracer analysis revealed that NPs are accumulated by parent plants and transferred to offspring ramets through stolon. Quantification analysis showed that when the parent plant was exposed to 10 mg L-1 NPs alone for 28 days, the offspring ramets contained approximately 13 ± 2 μg/g NPs. In the case of connected offspring ramets, leaf and root biomass decreased by 24%-51% and 32%-51%, respectively, when exposed to NP concentrations ranging from 0.1 to 10 mg L-1. Excessive enrichment of NPs had a detrimental effect on the photosynthetic system, decreasing the chlorophyll content and nonphotochemical quenching. An imbalance in the antioxidant defense systems, which were unable to cope with the oxidative stress caused by NP concentrations, further damaged various organs. The root system can take up NPs and then transfer them to the offspring through the stolon. Interference effects of NPs were observed in terms of root activity, metabolism, biofilm composition, and the plant's ability to purify water. However, the risk-spreading strategy employed by parent plants (interconnected offspring ramets) offered some relief from NP-induced stress, as it increased their relative growth rate by 1 to 1.38 times compared to individual plants. These findings provide substantial evidence of the high NP enrichment capacity of E. crassipes for ecological remediation. Nevertheless, we must also remain aware of the environmental risk associated with the spread of NPs within the clonal system of E. crassipes, and contaminated cloned individuals need to be precisely removed in a timely manner to maintain normal functions.

Root hemiparasites suppress invasive alien clonal plants: evidence from a cultivation experiment

Alien invasive plants threaten biodiversity by rapid spread and competitive exclusion of native plant species. Especially, tall clonal invasives can rapidly attain strong dominance in vegetation. Root-hemiparasitic plants are known to suppress the growth of clonal plants by the uptake of resources from their below-ground organs and reduce their abundance. However, root-hemiparasites’ ability to interact with alien clonal plants has not yet been tested. We explored the interactions between native root-hemiparasitic species, Melampyrum arvense and Rhinanthus alectorolophus and invasive aliens, Solidago gigantea and Symphyotrichum lanceolatum. We investigated the haustorial connections and conducted a pot experiment. We used seeds from wild hemiparasite populations and those cultivated in monostands of the invasive plants to identify a possible selection of lineages with increased compatibility with these alien hosts. The hemiparasitic species significantly suppressed the growth of the invasive plants. Melampyrum inflicted the most substantial growth reduction on Solidago (78%), followed by Rhinanthus (49%). Both hemiparasitic species reduced Symphyotrichum biomass by one-third. Additionally, Melampyrum reduced the shoot density of both host species. We also observed some transgenerational effects possibly facilitating the growth of hemiparasites sourced from subpopulations experienced with the host. Native root hemiparasites can effectively decrease alien clonal plants’ biomass production and shoot density. The outcomes of these interactions are species-specific and may be associated with the level of clonal integration of the hosts. The putative selection of lineages with higher performance when attached to the invasive novel hosts may increase hemiparasites’ efficiency in future biocontrol applications.

Effects of Clonal Integration on Foraging Behavior of Three Clonal Plants in Heterogeneous Soil Environments

Environments are ubiquitously heterogeneous in nature, and clonal plants commonly benefit from both clonal integration and foraging responses in heterogeneous environments. While many studies have examined clonal integration and foraging responses separately, few have tested the effect of clonal integration on the foraging response of clonal plants to environmental heterogeneity. We grew offspring ramets of each of three clonal plants (Hydrocotyle vulgaris, Duchesnea indica, and Glechoma longituba) in both homogeneous and heterogenous soil environments and severed their stem connection to a mother ramet (to prevent clonal integration from the mother ramet) or kept it intact (to allow clonal integration). Without clonal integration from the mother ramet, soil heterogeneity had no effect on biomass or number of ramets for any of the three species. With clonal integration, soil heterogeneity also had no effect on biomass or number of ramets of D. indica and G. longituba, but significantly decreased biomass and marginally significantly decreased number of ramets of H. vulgaris. Without clonal integration, offspring ramets did not demonstrate either shoot or root foraging responses in terms of total, shoot and root biomass and ramet number in the heterogeneous soil environment in any of the three species. With integration, offspring ramets of H. vulgaris also did not demonstrate either root or shoot foraging responses, but offspring ramets of G. longituba demonstrated both root and shoot foraging responses, and those of D. indica demonstrated a root foraging response when they grew in the heterogeneous soil environment. We conclude that clonal integration can alter the foraging response of clonal plants, but this effect is species-specific. Our results also suggest that foraging responses of clonal plants in heterogeneous soil environments may not necessarily benefit the growth of clonal plants.

Effects of resource sharing directionality on physiologically integrated clones of the invasive Carpobrotus edulis

Abstract Aims One of the key traits associated with clonal growth in plants is the capacity for physiological integration, which allows resource sharing between connected ramets within a clonal system. Resource transport is expected to occur following a source–sink relationship: from ramets established in rich patches to ramets growing in poor patches. However, some experiments have shown that acropetal transport (from basal to apical modules) usually exceeds basipetal transport (from apical to basal ramets). In this study, we aimed to determine the resource transport directionality in physiologically integrated modules of the invader Carpobrotus edulis. Methods We conducted two manipulative experiments under common garden conditions that studied the effect of different nutrient levels located at different positions (basal, medial and apical) on connected and disconnected clonal systems of C. edulis. We compared the biomass partitioning patterns and final biomass of ramets to elucidate whether the effect of physiological integration is affected by the directionality of the resource transport. Important Findings Results indicate a prevalent acropetal transport of resources in C. edulis, with a developmentally programmed division of labor where basal ramets were specialized in obtaining soil-based resources and apical ramets specialized in aboveground growth. This biomass partitioning pattern was not affected by the nutrient conditions in which basal or apical ramets were growing, although the highest benefit was achieved by apical ramets growing under the most stressed conditions. This developmentally programmed division of labor is expected to increase the lateral growth of C. edulis, and therefore could have meaningful implications for the expansion of this invasive species.

Patterns, localized structures and fronts in a reduced model of clonal plant growth

A simplified model of clonal plant growth is formulated, motivated by observations of spatial structures in Posidonia oceanica meadows in the Mediterranean Sea. Two levels of approximation are considered for the scale-dependent feedback terms. Both take into account mortality and clonal, or vegetative, growth as well as competition and facilitation, but the first version is nonlocal in space while the second is local. Study of the two versions of the model in the one-dimensional case reveals that both cases exhibit qualitatively similar behavior (but quantitative differences) and describe the competition between three spatially extended states, the bare soil state, the populated state, and a pattern state, and the associated spatially localized structures. The latter are of two types, holes in the populated state and vegetation patches on bare ground, and are organized within distinct snaking bifurcations diagrams. Fronts between the three extended states are studied and a transition between pushed and pulled fronts identified. Numerical simulations in one spatial dimension are used to determine front speeds and confront the predictions from the marginal stability condition for pulled fronts.

Clonal plants in disturbed mountain forests: Heterogeneity enhances ramet integration

Clonal plants confer a range of ecologically important traits related to local heterogeneity (e.g., foraging and integration). Disturbances generally impact heterogeneity at a variety of scales, but there is a paucity of research linking disturbance, heterogeneity, and clonal plant response. Further, there is a growing need to understand how different plants respond to changing disturbance regimes if stewards want to predict ecosystem response and successfully manage public lands. Thus, we examined clonal plant response to disturbance in the Tatra Mountains (Western Carpathians, Slovakia and Poland) at both the community and population levels. We collected 30 plots (10 m × 10 m) of data from four disturbance site types (DR = windthrow and not salvaged; DS = windthrow salvaged; NF = Forest without gap; NG = forest with canopy gap) in the Western Carpathians. Collected data included cover of all species, heterogeneity metrics, soil temperature 10 cm beneath the surface and clonal connectedness data (through dye experiments on selected species). Windthrow (DR) sites that were not salvaged had the greatest heterogeneity while forest sites with full canopy cover (NF) had the least. We found distinct differences in community composition and structure among the four treatments; however, floristic clonal dominance and the type of clonal growth organ did not change but made up over 90% of cover throughout. Clonal integration was related to disturbance and heterogeneity for Calamagrostis villosa and Rubus idaeus; R. idaeus had greater distances among ramets in the more heterogenous windthrown sites. Clonal plant growth was also related to compositional richness for C. villosa, having greater numbers of ramets under higher diversity pressure. These data suggest the dominance of clonal plants in the understory of mountain spruce forests in the Tatras are responding to changes in heterogeneity through growth and integration but in a species-specific manner.

Physical space interacts with clonal fragmentation and nutrient availability to affect the growth of Salvinia natans.

Physical space, clonal fragmentation and nutrient availability can each affect the growth of clonal plants, but their interactive effect has been little studied. We grew un-fragmented (connected) and fragmented (disconnected) ramet pairs of the floating, clonal plant Salvinia natans in cylindrical containers with different diameters and heights (volumes) filled with solutions of two nutrient levels (high vs. low). To simulate competition environments that are commonly confronted by S. natans, we also added two ramets of another floating plants Spirodela polyrrhiza in each container. Biomass (total biomass, floating biomass and submerged biomass) and number of ramets of S. salvinia were higher in the containers with a larger diameter. Compared to the low nutrient level, the high nutrient level increased number of ramets, and altered submerged to floating mass ratio of S. salvinia. The impacts of physical space on floating mass and number of ramets were stronger under the high than under the low nutrient level. Clonal fragmentation positively affected biomass in the containers with a smaller volume (a smaller height and diameter), but had little impact in the containers with a larger volume (a larger height or diameter). Our results suggest that physical space can interact with nutrients and clonal fragmentation to affect the performance of S. salvinia under competition.

The effect of ramet mortality on clonal plant growth

Clonal plants grow horizontally by producing multiple physiological individuals (ramets). We studied clonal growth in a homogeneous environment using a dynamic spatial model based on a stochastic cellular automaton. We investigated different growth forms from the aspect of ramet mortality. Non-steady-state and quasi-steady-state cases were defined, and we determined the number of steps suitable for making a reliable difference between these two types of cases. This given number of steps was used when testing for the proportion of quasi-steady-state cases in 1000 repetitions. We also tested the efficiency of occupation in these cases. Our expectation was that higher occupation would be associated with lower ramet mortality. The results only partially verified this hypothesis. Though with increasing ramet mortality, the average number of ramets tended to decrease, it was not the lowest ramet mortality that resulted in the highest occupation. Our results showed that very low ramet mortality was unfavourable for the plant, as the spreading front and the area behind this front were so packed that the plant was not able to return and recolonize the vacated sites in the central area. This resulted in a lower proportion of quasi-steady-state cases and lower occupation in these cases. Our results may contribute to a deeper understanding of clonal plant growth and its limiting factors.

Effects of Temporal Heterogeneity of Water Supply and Spatial Heterogeneity of Soil Nutrients on the Growth and Intraspecific Competition of Bolboschoenus yagara Depend on Plant Density.

Clonal plants may face various types of resource heterogeneity in their natural habitats; as such, spatial or temporal resource heterogeneity can affect the growth of clonal plants. Clonal plants can concentrate their organs in a smaller area where resources are high would cause heterogeneity to increase competition between plants. Most studies on resource heterogeneity have investigated the response of plants under a single density or by manipulating a single resource. Few studies have tested the effects of the heterogeneous distribution of two covariable resources on plant growth and intraspecific competition. A greenhouse experiment was therefore conducted to study plant responses to the spatial and temporal heterogeneity of the soil and water supply under a variety of plant densities (one, two, four, or six plants per container). The perennial clonal herb Bolboschoenus yagara was grown under different combinations of water supply patterns, soil nutrient distribution types and plant densities while maintaining the total water and soil nutrient availability per container constant. Compared with that at a relatively high plant density, soil nutrient heterogeneity resulted in significantly less total plant biomass and less-modified morphological traits when the plant density is relative low. At the highest plant density, compared with the homogeneous soil treatments, the heterogeneous soil treatments significantly increased the total biomass and R/S ratio. Water supply patterns also clearly affected plant morphological traits at the highest plant density. Furthermore, soil heterogeneity significantly increased intraspecific competition intensity at low plant densities, but did not significantly affect intraspecific competition intensity at higher plant densities. Water heterogeneity had little impact on intraspecific competition. These results suggest that the growth performance and intraspecific competition of B. yagara are more strongly affected by soil nutrient distribution rather than by water supply patterns and that competition for soil nutrients may increase plant sensitivity to soil heterogeneity.

Interactive effects of fragment size, nutrients, and interspecific competition on growth of the floating, clonal plant Salvinia natans

Groups of connected ramets produced by clonal growth in plants are particularly susceptible to fragmentation in aquatic ecosystems. Both clonal fragment size and nutrient availability are likely to affect the competitive ability of clonal aquatic plants, but the effects of fragment size, nutrients, and competition on plant performance have rarely been studied in combination. We hypothesized that larger fragments have greater competitive ability and that this effect is greater when nutrients are lower. To test this and other interactive effects, we grew fragments of the widespread, floating, clonal pteridophyte Salvinia natans initially containing 1, 2, 3, or 6 ramets at two levels of nutrients with and without a co-occurring, floating pteridophyte, Azolla pinnata, for 7 weeks. Floating mass of S. natans was mostly higher and submerged mass lower at high than at low nutrients, summing to a 0–30 % increase in total mass with higher nutrients at different initial fragment sizes. The presence of A. pinnata reduced total mass of S. natans by 30–60%. In partial agreement with the hypotheses, response of S. natans to competition was less negative in larger fragments in the low nutrient treatment but did not vary consistently with initial fragment size in the high nutrient treatment. Results show that growth of aquatic clonal plants can be determined by complex interactions and suggest that eutrophication may increase the competitive ability of very small clonal fragments.

Clonal plant Duchesnea indica Focke forms an effective survival strategy in different degrees of Pb-contaminated environments

Clonal plants in heterogeneous environments can benefit from habitat selection, giving them the ability to utilize patchily distributed resources efficiently. However, most research is conducted in a resource heterogeneous environment, and the study of heterogeneous environment of non-resource material (copper, cadmium, lead, and so on) is limited. Research into clonal plant growth under heterogeneous toxic conditions could contribute to our understanding of the strategy of the selective establishment pattern. Thus, we examined clonal growth in a heterogeneous lead environment to enhance understanding of habitat selection strategies. The growth indices (stolon-length, ramet number, biomass, and lead-concentrations) of Duchesnea indica were examined under three levels (low, moderate, and high were represented by 0, 50 and 100%) of lead contamination and two degrees of heterogeneity (low and high heterogeneity under moderate contamination) environments in a glasshouse study. Habitat selection strategy was analyzed by clone growth pattern, labor division, and risk-spreading. The clones under the moderate contamination level, especially with high heterogeneity, demonstrated the optimal growth. They expanded their growth-pattern to escape the toxic environment, and rooted more ramets in the unpolluted patches, allocating more aboveground biomass to these areas. Moreover, parent ramets transported their lead in the soil to the offspring. The offspring spread the toxic risk by accumulating lead in their roots and producing more ramets. Optimal growth of clonal plants occurred in environments moderately contaminated with lead, especially under higher heterogeneity, which performed effective survival strategy by expensive growth architecture, aboveground biomass increase and risk-spreading.

Clonal plant allocation to daughter ramets is a simple function of parent size across species and nutrient levels

The evolution of clonal growth is a widespread phenomenon among plant species, characterized by the production of genetically identical clonal fragments (ramets) via rhizomes or stolons that form an interconnected clonal organism (genet). Clonal plant species are known to differ in their investment into ramet production, and exhibit considerable variation in ramet morphology both within and among species. While patterns of resource allocation are thought to be linked to a number of plant characteristics, many analyses are limited by uncertainty in how clonal plants determine the morphology and resources allocated to new ramets. In this study, we attempted to discern what aspects of parent ramets best predicted resource allocation to new daughter ramets, and the relationship between resource allocation and daughter ramet rhizome morphology. We grew two sedge species, Schoenoplectus tabernaemontani and Eleocharis elliptica, in a greenhouse under two levels of fertilizer addition. By harvesting daughter ramets that had initiated stem production, yet remained aphotosynthetic, we were able to isolate parental investment into non-independent daughter ramets at a point where daughter ramet spacer length became fixed. Our results indicate that parent ramets allocated a non-linear proportion of parent rhizome biomass to the production of daughter ramets. Moreover, this relationship was unaffected by environmental nutrient availability. Daughter ramet biomass, in turn, was strongly correlated with daughter ramet spacer length. These observations shed light on key processes governing clonal growth in plants, and their potential application in unifying allocational and morphological perspectives to explore the fitness implications of variability in clonal growth.

Clonal integration affects allocation in the perennial herb Alternanthera philoxeroides in N-limited homogeneous environments

Most work on clonal growth in plants has focused on the advantages of clonality in heterogeneous habitats. We hypothesized (1) that physiological integration of connected ramets within a clone can also increase plant performance in homogeneous environments, (2) that this effect depends on whether ramets differ in ability to take up resources, and (3) that only ramets with relatively low uptake ability benefit. We tested these hypotheses using the perennial amphibious herb Alternanthera philoxeroides. We grew clonal fragments and varied numbers of rooted versus unrooted ramets, connection between the apical and basal parts of fragments, and availability of nitrogen. Patterns of final size and mass of fragments did not support these hypotheses. By some measures, severance did reduce the growth of more apical ramets and increase the growth of less apical ones, consistent with net apical transfer of resources. Rooting of individual ramets strongly influenced their growth: second and third most apical ramets each grew most when they were the most apical rooted ramet, and this pattern was more pronounced under higher nitrogen levels. This adds to the evidence that signalling between ramets is an important aspect of clonal integration. Overall, the results indicate that physiological integration between ramets within clones in homogeneous environments can alter the allocation of resources between connected ramets even when it does not affect the total growth of clonal fragments.

Effects of Spatial Patch Arrangement and Scale of Covarying Resources on Growth and Intraspecific Competition of a Clonal Plant.

Spatial heterogeneity in two co-variable resources such as light and water availability is common and can affect the growth of clonal plants. Several studies have tested effects of spatial heterogeneity in the supply of a single resource on competitive interactions of plants, but none has examined those of heterogeneous distribution of two co-variable resources. In a greenhouse experiment, we grew one (without intraspecific competition) or nine isolated ramets (with competition) of a rhizomatous herb Iris japonica under a homogeneous environment and four heterogeneous environments differing in patch arrangement (reciprocal and parallel patchiness of light and soil water) and patch scale (large and small patches of light and water). Intraspecific competition significantly decreased the growth of I. japonica, but at the whole container level there were no significant interaction effects of competition by spatial heterogeneity or significant effect of heterogeneity on competitive intensity. Irrespective of competition, the growth of I. japonica in the high and the low water patches did not differ significantly in the homogeneous treatments, but it was significantly larger in the high than in the low water patches in the heterogeneous treatments with large patches. For the heterogeneous treatments with small patches, the growth of I. japonica was significantly larger in the high than in the low water patches in the presence of competition, but such an effect was not significant in the absence of competition. Furthermore, patch arrangement and patch scale significantly affected competitive intensity at the patch level. Therefore, spatial heterogeneity in light and water supply can alter intraspecific competition at the patch level and such effects depend on patch arrangement and patch scale.

Clonal trait diversity in relation to invasiveness of alien macrophytes in twoHimalayanRamsar sites

AbstractQuestionsIn view of the predominance of clonality in aquatic plants and its likely role in plant fitness, we specifically asked whether or not clonality contributes to invasiveness of macrophytes. We also aimed to explore clonal trait diversity in alien aquatic plants and evaluate its implications in the context of species invasiveness.LocationTwoRamsar sites:HokersarWetland andLakeWular,KashmirHimalaya,India.MethodsExtensive field surveys were carried out in the two targetRamsar sites. The clonal growth form categorization was done using theCLO‐PLA3 (clonal plant) database of clonal growth in plants, and the relationship between clonality and invasiveness was examined. We used a stage‐based hierarchical model to categorize the investigated species into different stages of invasion (StagesII,III,IVa,IVb,V) and examine proportion of clonality at various stages of invasion.ResultsA total of 62 wetland plant species were recorded, most of which (58) were alien invasives. We characterized the clonal growth organ (CGO) spectra in the target plant species and categorized them into four space occupancy strategies (i.e. spreading, non‐spreading, splitters and integrators). More than 90% of the studied plants were clonal with a tendency of increasing clonality in plants belonging to higher stages of invasion (StageV).ConclusionsThe present study revealed a significant positive correlation between clonality and species invasiveness, thereby indicating the likely contribution of clonality to invasion success. Given the paucity of studies on the contribution of clonality in invasiveness of alien species, our results have significant implications for invasion management in wetland systems.

Patchy Distributions of Competitors Affect the Growth of a Clonal Plant When the Competitor Density Is High

Environments are patchy in not only abiotic factors but also biotic ones. Many studies have examined effects of spatial heterogeneity in abiotic factors such as light, water and nutrients on the growth of clonal plants, but few have tested those in biotic factors. We conducted a greenhouse experiment to examine how patchy distributions of competitors affect the growth of a rhizomatous wetland plant Bolboschoenus planiculmis and whether such effects depend on the density of the competitors. We grew one ramet of B. planiculmis in the center of each of the experimental boxes without competitors (Schoenoplectus triqueter), with a homogeneous distribution of the competitors of low or high density, and with a patchy distribution of the competitors of low or high density. The presence of competitors markedly decreased the growth (biomass, number of ramets, number of tubers and rhizome length) of the B. planiculmis clones. When the density of the competitors was low, the growth of B. planiculmis did not differ significantly between the competitor patches and competitor-free patches. However, when the density of the competitors was high, the growth of B. planiculmis was significantly higher in the competitor-free patches than in the competitor patches. Therefore, B. planiculmis can respond to patchy distributions of competitors by placing more ramets in competition-free patches when the density of competitors is high, but cannot do so when the density of competitors is low.

Effects of Spatial Scale of Soil Heterogeneity on the Growth of a Clonal Plant Producing Both Spreading and Clumping Ramets

Soil nutrients are commonly heterogeneously distributed at different spatial scales. Although numerous studies have tested the effects of soil nutrient heterogeneity on growth of clonal plants producing either spreading ramets or clumping ramets, no study has examined the effects on the growth of clonal plants producing both spreading and clumping ramets and how spatial scale affects such effects. To test these effects, clones of Buchloe dactyloides, a stoloniferous clonal plant that produces both clumping and spreading ramets, were grown in six heterogeneous environments with different patch sizes and one homogeneous environment containing the same quantity of nutrients. Total biomass, total number of ramets, number of clumping ramets, number of spreading ramets, spacer length, or root:shoot ratio of the whole plants did not differ significantly among the seven treatments. However, at the patch level there were significant effects of patch size by nutrient level on biomass, number of ramets, number of spreading ramets, and number of clumping ramets, and these four variables were significantly larger in the nutrient-rich patches than in the nutrient-poor patches in the heterogeneous treatment with the largest patch size, but not in the other five heterogeneous treatments with smaller patch sizes. Neither nutrient level nor patch size significantly affected spacer length or root:shoot ratio. Based on our results, we propose that B. dactyloides can efficiently exploit nutrient-rich patches by a plastic response of clumping ramets and spreading ramets at larger spatial scales of soil heterogeneity but not at smaller ones.

Soil Particle Heterogeneity Affects the Growth of a Rhizomatous Wetland Plant

Soil is commonly composed of particles of different sizes, and soil particle size may greatly affect the growth of plants because it affects soil physical and chemical properties. However, no study has tested the effects of soil particle heterogeneity on the growth of clonal plants. We conducted a greenhouse experiment in which individual ramets of the wetland plant Bolboschoenus planiculmis were grown in three homogeneous soil treatments with uniformly sized quartz particles (small: 0.75 mm, medium: 1.5 mm, or large: 3 mm), one homogeneous treatment with an even mixture of large and medium particles, and two heterogeneous treatments consisting of 16 or 4 patches of large and medium particles. Biomass, ramet number, rhizome length and spacer length were significantly greater in the treatment with only medium particles than in the one with only large particles. Biomass, ramet number, rhizome length and tuber number in the patchy treatments were greater in patches of medium than of large particles; this difference was more pronounced when patches were small than when they were large. Soil particle size and soil particle heterogeneity can greatly affect the growth of clonal plants. Thus, studies to test the effects of soil heterogeneity on clonal plants should distinguish the effects of nutrient heterogeneity from those of particle heterogeneity.

Growth responses of a rhizomatous herb <I>Bolboschoenus planiculmis</I> to scale and con-trast of soil nutrient heterogeneity

Aims Spatial heterogeneity in soil nutrients is common in nature, and clonal plants are supposed to be able to better use spatially heterogeneously distributed soil nutrients. Although scale and contrast are two of the most important elements of spatial heterogeneity, few studies have tested effects of scale and contrast of soil nutrient het- erogeneity on the growth of clonal plants. Methods We conducted a greenhouse experiment in which we grew individual ramets of a rhizomatous clonal plant, Bolboschoenus planiculmis (synonym Scirpus planiculumis), in heterogeneous conditions consisting of nu- trient-rich and nutrient-poor patches. The experiment had two levels of patch scale (large vs. small patch) crossed with two levels of patch contrast (high vs. low contrast), thereby consisting of four treatments. In each treatment, the total area of the nutrient-rich patches and that of the nutrient-poor patches were the same, and the total amount of soil nutrients was also the same in all the four treatments. Important findings At both clone (whole plant) level and patch level, patch scale, contrast or their interaction did not significantly affect biomass, number of ramets, total rhizome length or number of tubers of B. planiculmis. At the patch level, however, biomass, number of ramets, total rhizome length and number of tubers of B. planiculmis were significantly greater in the nutrient-rich patches than in the nutrient-poor ones, whereas spacer length (i.e., distance between adjacent ramets) was smaller. Such effects depended on neither patch scale nor patch contrast. Therefore, when growing in environments with heterogeneous soil nutrients, B. planiculmis was able to shorten its spacer length and likely also increased branching intensity of the rhizomes, such that more ramets and tubers (i.e., potential ramets) were placed in nutrient-rich patches. These responses are generally considered one aspect of the foraging behavior of clonal plants and are thought to be adaptive. However, the patch scale or contrast designed in the present experiment could not affect the placement of the ramets in the heterogeneous environments. We presume that the responses of B. planiculmis are likely different if a wider range of scale and contrast is used and thus future studies to test effects of scale and contrast of resource heterogeneity should consider a wider range of scale and/or contrast.

Water integration in the clonal emergent hydrophyte, Justicia americana: benefits of acropetal water transfer from mother to daughter ramets

Clonal plant growth is common in aquatic freshwater plants and their success is largely attributed to the sharing of resources (e.g., photosynthates, minerals, and water) within the greater genet. The flow of materials within the clone is largely driven by source-sink dynamics, and in established genets may involve acropetal and/or basipetal flow. During the production of new ramets, however, the mother often provides needed resources to the daughter through acropetal flow. In this study, we consider the role of water sharing in a clonal hydrophyte, Justicia americana, when soil moisture levels around the daughter plant declined. The results of this study indicate that acropetal water sharing is an important function between mother and daughter ramets in this species, as indicated by sustained growth and higher survival in connected daughters residing in water-deprived soils. Interestingly, mother plants, when connected to a drought daughter, began to develop similar xeromorphic features (e.g., greater leaf succulence) even though the parent remained in flooded conditions. We suspect that some physical or chemical signal was conveyed from the daughter to the mother that “forecast” water scarcities, which could prepare the entire genet for potential drought conditions.