Growth Of Clonal Plants Research Articles

A PDE model of clonal plant competition with nonlinear diffusion

We present a spatial competition model for clonal plant growth that combines two different mechanisms of competition. The first one is described by the standard underlying Kolmogorov Model for two interacting populations. A second competition mechanism, more specific to clonal plant growth, expresses the motility of each species and their capacity to resist to competitor's space intrusion. This model leads to a degenerated nonlinear reaction–diffusion system in which the diffusion coefficient of each species vanishes wherever the other species is beyond a certain biomass value.Indeed, we show that pattern forming instability cannot occur in general competition systems if the exclusion ability of both species is small even if the diffusions are degenerated. The effect of diffusion degeneracy on patterns formation is carried out. Numerical simulations of this two-level competition model are performed when the reaction terms are given by the competitive Lotka–Volterra equations. We, finally, discuss the potential of such nonlinear reaction–diffusion systems to be a surrogate model for phalanx–guerilla species competition.

Community-level effects of plant traits in a grassland community examined by multispecies model of clonal plant growth

We examine role of natality-related plant traits in a mountain grassland community. We use a spatially explicit, individual-based model of clonal plant population dynamics that includes traits of growth, resource allocation, response to competition, and spatial spread/plant architecture, and parameterize it for four co-occurring grass species. Field measurements of plant growth and architecture were used for parameterization; the subset of parameters that cannot be obtained by field estimation were estimated by fitting model predictions to a fine-scale time series of field data using a formalized gradient-descent procedure. The parameterized model was then validated with a separate set of fine-scale time series of field data.The parameterized model approximated well grassland dynamics over two decades for which empirical data were available for comparison. Over long (>50 years) periods the predictions indicate decrease of spatial correlations and loss of species richness which does not seem to be realistic in terms of our knowledge of the modelled grassland systems. This is likely to be due to structural features of the model, namely equivalence of competition of ramets that was independent of their tussock or species identity.This virtual community was used to test hypotheses on effects of natality-related traits on community dynamics. We changed values of individual traits of generative and vegetative reproduction (including architecture), and examined effects of these changes on (i) performance of the species with the trait changed, and (ii) performance of co-occurring species. The analysis showed that effects of individual traits on its bearer's performance differed across species; the context of other traits thus interacted with the net trait effect. Comparison of trait effects in the simulated monoculture with the effect on the whole community showed that within-community effect of the trait can only be weakly predicted from its monoculture effect. Individual neighbour species also differed in their response to a single trait in the target species. Such modelling approach shows that effects of traits (which typically cannot be easily manipulated) can be examined both in single species and in the community. While there was large variation in trait effects across target and neighbour species, mean effects of individual traits strongly differed, indicating that traits can be sensibly generalized over species and constitute a workable reference level for community studies.

Agent-based modelling of clonal plant propagation across space: Recapturing fairy rings, power laws and other phenomena

Many plants reproduce clonally through vegetative extensions (spacers). This results in a patch of clones connected through a network of spacers. The resulting network has a nontrivial spatial pattern that can be an important determinant of survival and fitness of the clonal plant. Here, we develop general growth rules that dictate how individual clones under local density-dependent conditions add spacers, giving rise to emergent population-level spatial patterns. A population subject to these growth rules is simulated using a stochastic individual-based model. The dependence of network structure on various architectural parameters is explored. The growth rules generate networks similar to those observed in natural populations, and can replicate real-world phenomena such as central die-back with regeneration, ‘fairy rings', and branch entrapment. A shorter spacer length results in higher population density (which may confer resistance to invasion in real populations), while longer spacer length allows the population to spread more quickly. The lateral branching angle, node-by-node angle, and spacer length appear to be the most influential parameters for determining the spatial architecture of the clonal patch. The number of daughter branches per mother branch follows a power law distribution in a diverse set of simulated networks. Continually growing computational power will make such simulation models increasingly useful for understanding the spatial growth of clonal plants, and power law behaviour may be a very common feature of both simulated and real clonal plant populations.

Large scale parameter study of an individual-based model of clonal plant with volunteer computing

Understanding clonal strategies (i.e. the ability of plants to reproduce vegetatively) is particularly important to explain species persistence. A clonal individual may be considered as a network of interconnected ramets that colonizes space. Resources in this network can be shared and/or stored. We developed an individual-based model (IBM) to simulate the growth of an individual clonal plant. Typically a realistic IBM requires a large set of parameters to adequately represent the complexity of the clonal plant growth. Simulations in the literature are often limited to small subsets of the parameter space and are guided by the a priori knowledge and with heuristic aims of the researcher. The aim of this paper was to demonstrate the benefit of volunteer computing in computational ecology to systematically browse the parameter space and analyze the simulation results in order to draw rigorous conclusions. To be specific, we simulated clonal plant growth using nine growth rules related to the metabolic process, plant architecture, resource sharing and storage and nineteen input parameters. We chose 2–4 values per input parameter which corresponded to 20 millions of combinations tested through volunteer computing. We used three criteria to evaluate plant performance: plant total resource, ramet production and maximum length of one branch. The 1% top-performing plants were sorted according to these criteria. Plant total resource and ramet production were correlated while considering the top-performing plants. The maximum length of one branch was independent from the other two performance traits. We detected two processes promoting at least one of the plant performance traits: (i) a relatively high metabolic gain (high photosynthetic activity and low production cost for new growth units), a low resource storage and long integration distance for resource sharing; (ii) short spacer lengths and the predominance of elongation of existing branches over branching. Interactive effects between parameter values were demonstrated for more than half of the input parameters. Best performance was reached for plants with slightly different combinations of values for these parameters (i.e. different strategies) rather than a single one (i.e. unique strategy). This modeling approach with volunteer computing enabled us to proceed to large-scale virtual experiments which provided a new quality of insight into ecological processes linked with clonal plant growth.

Effects of Orientation on Survival and Growth of Small Fragments of the Invasive, Clonal Plant Alternanthera philoxeroides

BackgroundThe ability of small clonal fragments to establish and grow after disturbance is an important ecological advantage of clonal growth in plants and a major factor in the invasiveness of some introduced, clonal species. We hypothesized that orientation in the horizontal position (typical for stoloniferous plants) can increase the survival and growth of dispersed clonal fragments, and that this effect of orientation can be stronger when fragments are smaller and thus have fewer reserves to support initial growth.Methodology/Principal FindingsTo test these hypotheses, we compared performance of single-node pieces of stolon fragments of Alternanthera philoxeroides planted at angles of 0, 45 or 90° away from the horizontal position, with either the distal or the proximal end of the fragment up and with either 1 or 3 cm of stolon left attached both distal and proximal to the ramet. As expected, survival and growth were greatest when fragments were positioned horizontally. Contrary to expectations, some of these effects of orientation were stronger when attached stolons were longer. Orientation had smaller effects than stolon length on the performance of fragments; survival of fragments was about 60% with shorter stolons and 90% with longer stolons.Conclusions/SignificanceResults supported the hypothesis that orientation can affect establishment of small clonal fragments, suggested that effects of orientation can be stronger in larger rather than smaller fragments, and indicated that orientation may have less effect on establishment than amount of stored resources.

A meta-analysis of the relation between mating system, growth form and genotypic diversity in clonal plant species

Next to its well-described ecological advantages, clonal growth in plants may incur fitness costs, which are associated with the effects of typically large clonal individuals on the patterns of pollen dispersal. These fitness costs include increased selfing and inbreeding depression in self-compatible species, and reduced mate availability in self-incompatible species. Although fitness costs may affect mating system evolution, there is currently no strong evidence available that either self-compatibility or self-incompatibility is associated with clonality. One reason for this may be the variety in growth forms (from guerrilla to phalanx habits) within clonal species, and the fact that growth form may strongly affect mating patterns. We present the results of a formal meta-analysis of 72 published studies, aiming at reporting genotypic diversities across studies and at relating mating system with clonal growth form and genotypic diversity. We found lower genotypic diversities in clonal self-incompatible species compared to self-compatible species, suggesting that mate availability may indeed be reduced in clonal self- incompatible species. We also cannot confirm that mating system is associated with clonal growth form.

A functional-structural model for growth of clonal bunchgrasses

Interactions between structural architecture and resource allocation affect the ability of plants to utilise environmental resources. Architecture defines the structural layout and relationships of organs and other structural units at different hierarchical levels in plants. Resource allocation determines how competing structural units are awarded resources at different levels of hierarchy. Functional-structural plant models combine architecture and resource allocation as interacting components of plant growth and functioning. Existing functional-structural plant models concentrate on growth of unitary trees and therefore, lack sufficient structural definition to simulate growth of clonal plants. On the other hand, simulation models designed to consider clonal growth rarely attempt to simulate clonal architecture at a more detailed level than individual ramets. This paper introduces a functional-structural type model, TILLERTREE, which integrates the architectural growth of bunchgrasses with resource capture and allocation of nitrogen and carbohydrate. Resource allocation is implemented using a procedural algorithm based on object hierarchy and priority, and not mechanistically. The model is used to illustrate that growth of bunchgrass clones is regulated by patterns of resource allocation between competing units at low levels of hierarchy, by considering the effect of resource rules controlling secondary tiller recruitment on clonal growth. Simulations are conducted using a chosen model C 4 bunchgrass species Themeda triandra.

The consequences of clone size for paternal and maternal success in domestic apple (Malus × domestica)

Clonal growth in plants can increase pollen and ovule production per genet. However, paternal and maternal reproductive success may not increase because within-clone pollination (geitonogamy) can reduce pollen export to adjacent clones (pollen discounting) and pollen import to the central ramets (pollen limitation). The relationship between clone size and mating success was investigated using clones of Malus × domestica at four orchards (blocks of 1-5 rows of trees). For each block, maternal function was measured as fruit and seed set in all rows and paternal function as siring rate estimated from isozyme profiles in the first row of the adjacent block. Expected relations between reproductive success and clone size were generated from simulations and data on pollen dispersal in this species. Siring rate per clone averaged 70% and did not increase significantly with block size, consistent with simulations of pollen dispersal under pollen discounting. Simulations also indicated that the ratio of compatible to incompatible pollen received by a tree should decline with increased block size and from the periphery to the center of blocks. However, female function was not significantly reduced among block sizes or within blocks. The results suggest that paternal function may be more sensitive to the effects of clonality than female function.

Physiological integration affects growth form and competitive ability in clonal plants

Clonal plants translocate resources through spacers between ramets. Translocation can be advantageous if a plant occurs in heterogeneous environments (‘division of labour’); however, because plants interact locally, any spatial arrangement of ramets generates some heterogeneity in light and nutrients even if there is no external heterogeneity. Thus the capacity of a clonal plant to exploit heterogeneous environment must operate in an environment where heterogeneity is partly shaped by the plant growth itself. Since most experiments use only simple systems of two connected ramets, plant-level effects of translocation are unknown. A spatially explicit simulation model of clonal plant growth, competition and translocation is used to identify whether different patterns of translocation have the potential to affect the growth form of the plant and its competitive ability. The results show that different arrangements of translocation sinks over the spacer system can completely alter clonal morphology. Both runners and clumpers can be generated using the same architectural rules by changing translocation only. The effect of translocation strongly interacts with the architectural rules of the plant growth: plants with ramets staying alive when a spacer is formed are much less sensitive to change in translocation than plants with ramets only at the tip. If translocation cost is low, translocating plants are in most cases better competitors than plants that do not translocate; the difference becomes stronger in more productive environments. Key traits that confer competitive ability are total number of ramet, and their fine-scale aggregation.

A simulation study of the effects of architectural constraints and resource translocation on population structure and competition in clonal plants

(1) Spatially explicit simulation of clonal plant growth is used to determine how rametlevel traits affect ramet density, spatial pattern of ramets and competitive ability of a clonal plant. The simulation model used combines elements of (i) an individual-based model of plant interactions, (ii) an architectural model of clonal plant growth, and (iii) a model of resource translocation within a set of physiologically integrated plant individuals. (2) The effects of two groups of parameters were studied: growth and resource acquisition parameters (resource accumulation, density-dependence of resource accumulation, resource translocation between ramets) and architectural rules (branching angle and probability of branching, internode length). The model was parameterised by values approximating those of clonally growing grasses as closely as possible. The basic parameter values were chosen from a short-turf grassland. Sensitivity analysis was carried out on relevant parameters around three basic points in the parameter space. Both single-species and two-species systems were studied. (3) It is shown that increasing resource acquisition and growth parameters increase ramet density, genet number and competitive ability. Translocation parameters and architectural parameters modify the effects of resource acquisition and growth, but their effect in single-species stands was smaller. (4) The simulations of species with fixed ramet sizes showed that ramet density in single-species stands cannot be used for predicting competitive ability. Increase in resource acquisition and growth parameters was correlated with an increase in equilibrium ramet density and competitive ability. Increasing branching angle, branching probability or internode length lead to an increased competitive ability, but did not affect equilibrium ramet density. Change of architectural parameters could therefore affect competitive ability independently of their effect on the final ramet density. (5) Spatial pattern both in single-species and two-species stands was also highly parameter-dependent. Changes in architectural parameters and in translocation usually lead to pronounced change in the spatial pattern; change in growth and resource acquisition parameters generally had little effect on spatial pattern.

Potential and limitations of current concepts regarding the response of clonal plants to environmental heterogeneity

Plant ecologists have spent considerable effort investigating the physiological mechanisms and ecological consequences of clonal growth in plants. One line of research is concerned with the response of clonal plants to environmental heterogeneity. Several concepts and hypotheses have been formulated so far, suggesting that intra-clonal resource translocation, morphological plasticity on different organizational levels (e.g. leaves, ramets, fragments), and other features of clonal plants may represent potentially adaptive traits enabling stoloniferous and rhizomatous species to cope better with habitat patchiness. Although each of these concepts contributes substantially to our understanding of the ecology of clonal species, it is difficult to combine them into a consistent theoretical framework. This apparent lack of conceptual coherence seems partly be caused by an uncritical use of the term ‘habitat heterogeneity’. Researchers have not always acknowledged the fact that ‘heterogeneity’ may refer to a number of fundamentally different aspects of environmental variability (i.e. scale, contrast, predictability, temporal vs. spatial heterogeneity), and that each of these aspects may, on one hand, allow for the evolution of specific plant responses to heterogeneity and, on the other, severely constrain the viability of potentially adaptive traits. Since adaptive responses are operational only in a narrow range of conditions (delimited by external environmental conditions and constraints internal to plants) it seems imperative to clearly define the context and the limits within which concepts regarding clonal plants' responses to heterogeneity are valid. In this paper an attempt is made to review a number of these concepts and to try and identify the necessary conditions for them to be operational. Special attention is paid (1) to different aspects of environmental heterogeneity and how they may affect clonal plants, and (2) to possible constraints (e.g. sectoriality, perception of environmental signals, morphological plasticity) on plant responses to patchiness.

Nutrient Sharing in Natural Clonal Fragments of Fragaria Chiloensis

1 The potential advantages of clonal growth in plants include increased growth due to resource sharing between ramets in patchy environments. Net increases in the biomass and vegetative spread of clones attributable to resource sharing have been amply demonstrated in artificial environments, but little tested in natural ones. This study examines nutrient sharing in the stoloniferous perennial herb Fragaria chiloensis in a natural population on coastal sand dunes in California. The main questions asked were: (1) How extensive is nutrient sharing? (2) Do patterns of nutrient sharing change in response to nutrient patchiness? (3) Does nutrient sharing increase growth? 2 Three experiments were conducted, using clonal fragments in situ. Experiment 1 examined the extent of nutrient sharing when nutrient patchiness was minimal for the habitat, by tracing the movement of '5N within fragments that had all their ramets in low-nutrient microsites. Experiment 2 compared the extent of nutrient sharing when patchiness was maximal, by measuring the biomass and size of clonal fragments when a high-nutrient patch was artificially created around one of the ramets. Experiment 3 examined the effects of nutrient uptake without sharing, by measuring the growth of single ramets in high-nutrient patches. 3 Nitrogen was shared between all the ramets along a stolon, but large net transfers took place only from older to younger ramets. There was no evidence that these patterns changed in response to the degree of nutrient patchiness. Apparent effects of nutrient sharing on growth included a significant increase in the total biomass of younger ramets, a possible decrease in the biomass of some older ramets, and an increase in allocation to new stolons in ramets that imported nutrients. 4 These effects of nutrient sharing seem likely to speed the growth of fragments away from high-nutrient patches, and so, at first sight, may appear disadvantageous. However, the long term effect of accelerated spread away from good patches must be tested in relation to natural patterns of resource patch dynamics.

Reviews

Molecular Activities of Plant Cells. An Introduction to Plant Biochemistry. By J. W. Anderson and J. Beardell Clonal Growth in Plants. Ed. by Jan van Groenendael and Hans de Kroon Agricultural Plants, 2nd Edn. By G. D. Hill and R. H. M. Langer Photon–Vegetation Interactions. Applications in Optical Remote Sensing and Plant Ecology. Ed. by R. B. Myneni and J. Ross The Families and Genera of Vascular Plants, Volume I: Pteridophytes and Gymnosperms. Ed. by K. U. Kramer and P. S. Green The Illustrated Field Guide to Ferns and Allied Plants of the British Isles. By C. Jermy and J. CamusSerpula lacrymans: Fundamental Biology and Control Strategies. Ed. by D. H. Jennings and A. F. Bravery Seaweeds of the British Isles, Volume 2 – Chorophyta. By E. M. Burrows Quaternary Ecology : a Paleoecological Perspective. By Hazel R. Delcourt and Paul A. Delcourt

TRANSPORT OF CARBON AMONG CONNECTED RAMETS OF EICHHORNIA CRASSIPES (PONTEDERIACEAE) AT NORMAL AND HIGH LEVELS OF CO2

The floating, stoloniferous plant, Eichhornia crassipes, has high rates of productivity and rapidly invades new sites. Because the transport of carbon among connected ramets is known to increase the growth of clonal plants, we asked whether there is intraclonal carbon transport in E. crassipes. Because net photosynthesis of E. crassipes is significantly higher at high levels of atmospheric CO2, we also asked if high CO2 can change patterns of carbon transport in ways that might modify clonal growth. We exposed individual ramets within groups of connected ramets to 14CO2 for 15–45 min and measured the distribution of 14C in the group after 4 days of growth at 350, 700, 1,400, or 2,800 μ1 1−‐1 CO2. At 350 μ1 1−‐1 CO2, a parent ramet exported approximately 10% of the 14C that it assimilated to its first rooted offspring ramet. The offspring exported a similar percentage of the l4C it assimilated toward the parent; two‐thirds of this 14C was retained by the parent, and one‐third moved into new offspring of the parent. In all ramets, imported carbon moved into leaves as well as roots. At the higher levels of CO2, the percentage of assimilated carbon exported from a parent ramet to the leaf blades of its first offspring was lower by half. High CO2 had little other effect on carbon transport. E. crassipes maintains bidirectional transport of carbon between ramets even under uniform and favorable environmental conditions and when external CO2 levels are very high.

Water depth and biotic insulation: Major determinants of back-swamp plant community composition

Based on phytosociological data, a polythetic divisive classification technique resulted in the delineation of eight broad vegetation types in the back-swamp areas of the Maunachira River System of the Okavango Delta, Botswana. A detrended correspondence analysis indicated that water depth was the major environmental factor influencing the distribution of submerged, floating-leaved and tall, emergent species dominated communities. The remaining communities, with relatively distinct boundaries between each of them, were of short emergent species assemblages rooted in peat deposits with a water depth of less than 0.7 m. Their species composition was not related to water depth, conductivity, pH, redox potential, water temperature or total nitrogen or phosphorus concentrations in the water. The relationship between the present day wetland plant community composition and its environment may be masked by long term, biotic, ‘insulating’ processes such as the accumulation of resources during peat formation and clonal plant growth. This insulation process does not lead necessarily to long term community stability as has been previously suggested (Mitsch and Gosselink 1986).

Nitrogen Sharing Among Ramets Increases Clonal Growth in Fragaria Chiloensis

Transport of resources among connected ramets can increase the growth of clonal plants when ramets are located in microsites with contrasting light, water, or total soil nutrient availability. To test whether this is also true for soil nitrogen availability alone, two greenhouse experiments were conducted using the stoloniferous herb Fragaria chiloensis (beach strawberry). First, pairs of ramets were prepared in which the two ramets were connected by a stolen but rooted in separate pots. Ramets in a pair were: (1) severed from each other and given contrasting levels of soil nitrogen (high vs. low); (2) left connected and given contrasting levels of soil nitrogen; or (3) left connected and given a uniform level of soil nitrogen (both high or both low). Second, single ramets were given the high, the low, or one of three intermediate levels of soil nitrogen. Maintaining the vascular connection between ramets given contrasting levels of the soil nitrogen resulted in a greater production of new stolons and new ramets by the ramet given low nitrogen level, and in slightly greater leaf growth of the ramet given the low nitrogen level if it was also younger than the connected ramet. However, a ramet given high soil nitrogen grew much more than a ramet given low soil nitrogen, even when connected. Maintaining the vascular connection between ramets given a uniform level of soil nitrogen had no significant effect on growth. Single ramets given a higher soil nitrogen had greater total and component masses, more stolons and new ramets, higher nitrogen concentrations, higher specific leaf area, and a higher proportional mass of leaves and of stolons and new ramets. Experiments suggested that: (1) transport of nitrogen among ramets can increase growth in F. chiloensis, but to a limited extent; (2) transport of nitrogen through a stolon may be either acropetal or basipetal but tends to promote the growth of younger ramets; (3) higher soil nitrogen availability alters plant architecture by increasing allocation to leaves and to new stolons and ramets; and (4) physiological integration among ramets modifies colonal architecture because nitrogen acquire by roots promotes growth of both a rooted ramet and its new ramets, whereas nitrogen acquired from another ramet promotes the growth of new ramets almost exclusively.

Models of Clonal Plant Growth Based on Population Dynamics and Architecture

The branching pattern of Lycopodium annotinum, a modular and clonal vascular cryptogam with a stoloniferous/rhizomatous growth form, was simulated using a combination of architectural and population dynamics models. Data on morphology, survival and fecundity were collected in the field in Swedish Lapland and used to generate a series of growth rules in two models. An initial, simple, deterministic growth model reflected the growth form of L. annotinum in a homogeneous environment. From this model, conclusions were drawn that apical dominance and branching angles are two important internal controls which optimize the balance between ground exploitation and the avoidance of competition for light, water and nutrients within plants (plants being defined as the aggregations of branches physically connected by living tissues). The introduction of stochastic elements into the model, based on field data, produced a wide range of simulated plant forms, clearly comparable to those in the field. Lateral spread in simulated plants varied greatly in shape, from compact, dense forms with short annual segments to loose widely spread forms with long annual segments. Both guerilla and phalanx growth forms occurred in the simulations simply as part of a stochastic process. Survival of clones (i.e. aggregations of plants from a common ancestor) varied from 1 yr to the duration of the simulation, indicating their potential for indefinite growth, although a substantial number (51%) survived for only 2 to 5 yr. The architectural model based on population dynamics was robust and a sensitivity analysis showed that survival probabilities had to be changed by 20% before the clone reacted, while a much greater degree of change of fecundity values was required (-100% to +50%) to overcome the stochastic element of the model. This reflects the robustness suggested for clonal plants also indicated by their low sensitivity values from transition probability matrices, but is in marked contrast to the great sensitivity of transition probability matrices in general. The sensitivity analysis also showed that the most sensitive age classes were 2 to 6 yr. A major limitation of the stochastic model is that the population processes of age-specific death and fecundity, the growth processes of root production and segment elongation, and the geometry of the plant all vary unintelligently. A mechanistic approach is now required to relate these processes to environmental variables and internal feedback.