Resource Translocation Research Articles

A theoretical framework for resource translocation during sexual reproduction in modular organisms

An individual of modular organisms, such as plants and fungi, consists of more than one module that is sometimes physically and physiologically connected with each other. We examined effects of translocation costs, resource–fitness relationships and original resource conditions for modules on the optimal resource translocation strategy for reproductive success in modular organisms with simple models. We considered two types of translocation cost: amount-dependent and ratio-dependent costs. Three optimal resource translocation strategies were recognized: all resource translocation (ART), partial resource translocation (PRT), and no resource translocation (NRT). These strategies depended on the translocation cost, shape of resource–fitness curve, and original resource condition for each module. Generally, a large translocation cost and a concave resource–fitness relationship promoted NRT or PRT. Meanwhile, a small translocation cost and convex resource–fitness relationship facilitated ART. The type of translocation cost did not strongly affect the optimal resource translocation patterns, although ART was never an optimal strategy when the cost was ratio-dependent. Resource translocation patterns found in modular plants were discussed in the light of our model results.

Nitrogen mediates above-ground effects of ozone but not below-ground effects in a rhizomatous sedge

Ozone and atmospheric nitrogen are co-occurring pollutants with adverse effects on natural grassland vegetation. Plants of the rhizomatous sedge Carex arenaria were exposed to four ozone regimes representing increasing background concentrations (background-peak): 10–30, 35–55, 60–80 and 85–105 ppb ozone at two nitrogen levels: 12 and 100 kg N ha −1 yr −1. Ozone increased the number and proportion of senesced leaves, but not overall leaf number. There was a clear nitrogen × ozone interaction with high nitrogen reducing proportional senescence in each treatment and increasing the ozone dose (AOT40) at which enhanced senescence occurred. Ozone reduced total biomass due to significant effects on root biomass. There were no interactive effects on shoot:root ratio. Rhizome tissue N content was increased by both nitrogen and ozone. Results suggest that nitrogen mediates above-ground impacts of ozone but not impacts on below-ground resource translocation. This may lead to complex interactive effects between the two pollutants on natural vegetation.

Reproduction of a Robinia pseudoacacia population in a coastal Pinus thunbergii windbreak along the Kujukurihama Coast, Japan

We investigated reproduction of the clonal tree Robinia pseudoacacia in a Pinus thunbergii windbreak. Microsatellite polymorphism analysis revealed that asexual reproduction through horizontal root elongation and ramet formation was the primary mode of reproduction in this population. Germination experiments indicated that the inability of established genets to produce viable seeds inhibited sexual reproduction. The boundaries between genet areas were relatively distinct, indicating that ramets within genets spatially excluded one another. Analyses of the number of annual rings and thickness of excavated horizontal roots provided new insight regarding photosynthate transfer through horizontal roots. The number of annual rings and thickness were highest for horizontal roots near the base of ramets and decreased along portions far from ramets. This result indicates that the new horizontal root is supplied with photosynthate from the mother ramet for a few years only, and that resource translocation between neighboring ramets within the same clone ceases after several years. Hypotheses about horizontal root expansion and cessation were considered to explain the exclusive distribution pattern of the horizontal root between genets.

Effects of leaf emergence on leaf lifespan are independent of life form and successional status

Abstract The longevity of a leaf is related to the benefit that the plant is able to derive from it. This benefit varies among seasons and as more leaves emerge, such that leaf lifespan can be limited by canopy position rather than physiological age. Using interval‐censored failure time analysis, we investigate leaf lifespan for 34 Mediterranean species in a previously published dataset involving species with different life forms and functional strategies. Failure time regression models were used to determine leaf lifespan, and to investigate how these effects varied among species. Median lifespan estimated for each species with two methods differed by less than 10% on average, but varied from 0.02–19.5% depending on the shape of the underlying failure time distribution. Within shoots, later‐emerging leaves had shorter lifespans for species with longer periods of leaf emergence, and the reverse was true for species with short emergence. Having accounted for the within‐shoot effect, leaves emerging in spring had shorter lifespans, particularly herbaceous species, whereas the reverse was true woody species. These effects were consistent among life forms and successional stages, and consistent with theories of within‐shoot translocation of resources following self‐shading.

Are Annual Growth Intervals Independent Units in The Moss Pseudocalliergon Trifarium (Amblystegiaceae)

Evidence is accumulating that significant amounts of substances can move internally in ectohydric bryophytes, which lack specialized structures for internal water movement. This potential for resource translocation is likely to affect the productivity in individual shoot sections. We tested whether annual growth intervals in the pleurocarpous moss Pseudocalliergon trifarium were performing as independent units by comparing the biomass of annual increments within individual shoots from 13 populations from northern and central Sweden. Pseudocalliergon trifarium has a distinct shoot architecture with discrete annual segments and is therefore well suited to study annual biomass allocation patterns. Mass of the most recent growth interval was directly correlated with segment mass of at least two preceding years. The strength of the relationship between current growth and four consecutively older annual increments decreased linearly with age of the annual segments, suggesting that correlations within shoots were the result of resource translocation rather than of among-year correlations in local environmental factors. Our data suggest that interconnected segments are physiologically integrated, and that size relationships between successive increments are relatively independent of environmental conditions. We conclude that annual growth intervals cannot be considered as independent assimilatory units. Internal resource transfer across annual segments may buffer variation in external availability of or internal demands for resources, and has implications for the understanding of growth patterns and reproductive investments in ectohydric bryophytes.

Apical dominance and the importance of clonal integration to apical growth in the seagrass Syringodium filiforme

The existence of apical dominance and the importance of clonal integration to apical growth in the seagrass Syringodium filiforme were examined using field and mesocosm experiments. In the field, apical dominance was observed with proliferative branching resulting from the removal of rhizome apical meristems (RAMs). Rhizome internode length and branching increased when plants grew from a dense meadow into a bare patch, providing further evidence for the existence of apical dominance in S. filiforme. The results of the experiments indicated that growth of the RAM is dependent on the translocation of resources from older ramets. Removing 3 shoots from a rhizome runner lead to a significant reduction in the growth of the RAM, and removing 6 shoots had a greater effect. Apical growth was more significantly affected by cutting the rhizome, with the lowest growth observed in clonal fragments comprised of a RAM and the 4 youngest ramets. We conclude that clonal integration is an important factor regulating the growth form and productivity of S. filiforme. These results have implications for damage assessment and restoration projects, and indicate that future studies of meadow structure and plant production should consider RAM health and branch formation along with individual ramet growth.

E21 Habitat Connectivity and Ecosystem Productivity: Implications from a Simple Model

The import of resources (food, nutrients) sustains biological production and food webs in resource‐limited habitats. Resource export from donor habitats subsidizes production in recipient habitats, but the ecosystem‐scale consequences of resource translocation are generally unknown. Here, I use a nutrient‐phytoplankton‐zooplankton model to show how dispersive connectivity between a shallow autotrophic habitat and a deep heterotrophic pelagic habitat can amplify overall system production in metazoan food webs. This result derives from the finite capacity of suspension feeders to capture and assimilate food particles: excess primary production in closed autotrophic habitats cannot be assimilated by consumers; however, if excess phytoplankton production is exported to food‐limited heterotrophic habitats, it can be assimilated by zooplankton to support additional secondary production. Transport of regenerated nutrients from heterotrophic to autotrophic habitats sustains higher system primary production. These simulation results imply that the ecosystem‐scale efficiency of nutrient transformation into metazoan biomass can be constrained by the rate of resource exchange across habitats and that it is optimized when the transport rate matches the growth rate of primary producers. Slower transport (i.e., reduced connectivity) leads to nutrient limitation of primary production in autotrophic habitats and food limitation of secondary production in heterotrophic habitats. Habitat fragmentation can therefore impose energetic constraints on the carrying capacity of aquatic ecosystems. The outcomes of ecosystem restoration through habitat creation will be determined by both functions provided by newly created aquatic habitats and the rates of hydraulic connectivity between them.

Habitat Connectivity and Ecosystem Productivity: Implications from a Simple Model

The import of resources (food, nutrients) sustains biological production and food webs in resource-limited habitats. Resource export from donor habitats subsidizes production in recipient habitats, but the ecosystem-scale consequences of resource translocation are generally unknown. Here, I use a nutrient-phytoplankton-zooplankton model to show how dispersive connectivity between a shallow autotrophic habitat and a deep heterotrophic pelagic habitat can amplify overall system production in metazoan food webs. This result derives from the finite capacity of suspension feeders to capture and assimilate food particles: excess primary production in closed autotrophic habitats cannot be assimilated by consumers; however, if excess phytoplankton production is exported to food-limited heterotrophic habitats, it can be assimilated by zooplankton to support additional secondary production. Transport of regenerated nutrients from heterotrophic to autotrophic habitats sustains higher system primary production. These simulation results imply that the ecosystem-scale efficiency of nutrient transformation into metazoan biomass can be constrained by the rate of resource exchange across habitats and that it is optimized when the transport rate matches the growth rate of primary producers. Slower transport (i.e., reduced connectivity) leads to nutrient limitation of primary production in autotrophic habitats and food limitation of secondary production in heterotrophic habitats. Habitat fragmentation can therefore impose energetic constraints on the carrying capacity of aquatic ecosystems. The outcomes of ecosystem restoration through habitat creation will be determined by both functions provided by newly created aquatic habitats and the rates of hydraulic connectivity between them.

Resource translocation within seagrass clones: allometric scaling to plant size and productivity

The allometric scaling of resource demand and translocation within seagrass clones to plant size (i.e. shoot mass and rhizome diameter), shoot production and leaf turnover was examined in situ in eight seagrass species (Cymodocea nodosa, Cymodocea serrulata, Halophila stipulacea, Halodule uninervis, Posidonia oceanica, Thalassodendron ciliatum, Thalassia hemprichii and Zostera noltii), encompassing most of the size range present in seagrass flora. One fully developed shoot on each experimental rhizome was incubated for 2-3 h with a pulse of NaH(13)CO(3) (235 micromol) and (15)NH(4)Cl (40 micromol). The mobilisation of incorporated tracers across the clone was examined 4 days later. Carbon and nitrogen demand for shoot production across seagrass species scaled at half of the shoot mass, whereas seagrass leaves incorporated tracers ((13)C and (15)N) at rates proportional to the shoot mass. The shoots of all seagrass species shared resources with neighbours, particularly with younger ones. The time scales of physiological integration and the absolute amount of resources shared by seagrass ramets scaled at 2.5 power of the rhizome diameter. Hence, the ramets of larger species were physiologically connected for longer time scales and share larger absolute amounts of resources with neighbours than those of smaller species. The different pattern of resource translocation exhibited by seagrasses helps explain the ecological role displayed by these species and the success of large seagrasses colonising nutrient-poor coastal areas, where they often dominate.

Bacterial motility: links to the environment and a driving force for microbial physics

Bacterial motility was recognized 300 years ago. Throughout this history, research into motility has led to advances in microbiology and physics. Thirty years ago, this union helped to make run and tumble chemotaxis the paradigm for bacterial movement. This review highlights how this paradigm has expanded and changed, and emphasizes the following points. The absolute magnitude of swimming speed is ecologically important because it helps determine vulnerability to Brownian motion, sensitivity to gradients, the type of receptors used and the cost of moving, with some bacteria moving at 1 mm s(-1). High costs for high speeds are offset by the benefit of resource translocation across submillimetre redox and other environmental gradients. Much of environmental chemotaxis appears adapted to respond to gradients of micrometres, rather than migrations of centimetres. In such gradients, control of ion pumps is particularly important. Motility, at least in the ocean, is highly intermittent and the speed is variable within a run. Subtleties in flagellar physics provide a variety of reorientation mechanisms. Finally, while careful physical analysis has contributed to our current understanding of bacterial movement, tactic bacteria are increasingly widely used as experimental and theoretical model systems in physics.

Seasonal dynamics of resource translocation between the aboveground organs and age-specific rhizome segments of Phragmites australis

This study aims to test the hypothesis that resource translocation patterns between rhizomes and the aboveground organs depend not only on the season but also on rhizome age. Changes in rhizome biomass and storage reserves of Phragmites australis were therefore investigated to explore the age specificity of rhizomes in resource translocation patterns. Above and belowground biomass were harvested six times between April and December from an undisturbed monospecific stand, and analyzed to give rhizome age-specific dry mass and total non-structural carbohydrate (TNC) contents. Seven rhizome age-classes were recognized, from <1 to 6-year-old. Changes in dry weight and in TNC per unit area of each rhizome age-class were used to describe seasonal patterns in growth and mortality, translocation and movement of assimilates on an areal basis. TNC budgets were prepared based on these data and estimates of losses due to tissue mortality and respiration for each age-class. The seven age-classes had similar growth patterns but differed when translocation occurred, with older rhizomes translocating a substantial amount in spring to the aboveground organs to establish new shoots. Before summer, the photosynthates were evenly allocated to each age-class, while the recovery of TNC in segments was earlier with younger ones. The allocation in autumn was mainly to young rhizome segments. Older segments became severely depleted during winter, with high mortality; however, the youngest rhizome segments survived, which can be interpreted as an internal re-distribution of resources. This study clearly showed that there is a clear variation between rhizome age-classes in belowground resource translocation patterns depending on the season.

Resource transport between ramets alters soil resource pattern: a simulation study on clonal growth

Clonal plants spread horizontally, and can transport nutrients between ramets. Decaying biomass feeds back nutrients into the soil, but importantly, the place of deposition may differ from the place of uptake. To our knowledge, the present model is the first attempt to couple population dynamics with resource dynamics with the consideration of lateral transport. The simulations start from various initial resource patterns. Six types of clonal plants are compared, which differ in the birth and survival rates of ramets. Size of the ramet population and the amount of translocated resource are recorded over time. In addition, we consider the pattern of gaps in the canopy of the clonal plant from the aspect of two colonizer species: a strong and a weak competitor. The results suggest that the most important factor determining the impact of a clonal plant on its environment is ramet survival; the rate of ramet production is only secondary. Phenotypic plasticity in the production of ramets does not appear to be important: it has only minor effect on resource translocation and on the availability of colonizable gaps.

Ecological role of vegetative sprouting in the regeneration of Dryobalanops rappa, an emergent species in a Bornean tropical wetland forest

Dryobalanops rappa (Dipterocarpaceae), a dominant tree in wetland forests in Borneo, often produces vegetative sprouts in its juvenile stages (trees less than 25 m in height), a characteristic that is believed to be rare in tropical forest trees. We investigated the growth characteristics of this species in a tropical forest in Merimbun Heritage Park, Brunei, to verify the hypothesis that the vigorous sprouting ability enables it to grow in a wetland forest with soft soils that promote stem decumbency and to assess the adaptive significance of vegetative sprouting in the context of its regeneration. Reproductively mature trees developed buttresses and were rarely decumbent. However, if they became decumbent, they died without sprouting. Juvenile trees were frequently decumbent, and their decumbent shoots sprouted vegetatively. Therefore, vegetative sprouting acted as a countermeasure to decumbency and death on the soft wetland soil. A decumbent shoot produced only one sprout in most cases. Decumbent shoots grew little and eventually died, but new sprouts showed rapid growth. This suggests that there is translocation of resources from decumbent shoots to sprouts. If decumbency occurs, a D. rappa genet ramifies into sprouts, and helps sustain the population in the wetland environment. This vegetative life history strategy is important for regeneration in wetland forests with soft soil.

Polyp oriented modelling of coral growth

The morphogenesis of colonial stony corals is the result of the collective behaviour of many coral polyps depositing coral skeleton on top of the old skeleton on which they live. Yet, models of coral growth often consider the polyps as a single continuous surface. In the present work, the polyps are modelled individually. Each polyp takes up resources, deposits skeleton, buds off new polyps and dies. In this polyp oriented model, spontaneous branching occurs. We argue that branching is caused by a so called “polyp fanning effect” by which polyps on a convex surface have a competitive advantage relative to polyps on a flat or concave surface. The fanning effect generates a more potent branching mechanism than the Laplacian growth mechanism that we have studied previously (J. Theor. Biol. 224 (2003) 153). We discuss the application of the polyp oriented model to the study of environmentally driven morphological plasticity in stony corals. In a few examples we show how the properties of the individual polyps influence the whole colony morphology. In our model, the spacing of polyps influences the thickness of coral branches and the overall compactness of the colony. Density variations in the coral skeleton may also be important for the whole colony morphology, which we address by studying two variants of the model. Finally, we discuss the importance of small scale resource translocation in the coral colony and its effects on the morphology of the colony.

Inter-ramet water translocation in natural clones of the rhizomatous shrub, Hedysarum laeve, in a semi-arid area of China

The patterns of resource translocation among interconnected ramets within a clone may show diversity. In order to understand the pattern of inter-ramet water translocation in natural clones of the rhizomatous shrub Hedysarum laeve (Leguminosae), which frequently dominates inland dunes in semi-arid areas of China, acid fuchsin dye application combined with spectrometric analysis was employed. Dye solutions were fed to the base of plants (near the parent ramet) and to the apical portions (near one of the youngest shoots) and the amount of dye in shoots and rhizomes was measured spectrometrically after 24 h. The total amount of dye translocated from the base in the acropetal direction was approximately four times as high as that of basipetal translocation from cut sections near the apex. Most of the dye was detected in the shoots with very little found in the rhizomes. The average percentage allocation of dye from donor ramet transferred to recipient ramets in the ramet hierarchy closer, due to acropetal and/or basipetal translocation, was significantly greater than those in the ramet hierarchy less close to it. The ramet-hierarchy order had a great influence on dye translocation in either the acropetal or basipetal direction. It is inferred that the donor ramet would transport water towards its recipient ramets in different ramet hierarchies in unequal proportions in this species.

Within‐Alga Integration and Compensation: Effects of Simulated Herbivory on Growth and Reproduction of the Brown Alga, Fucus vesiculosus

We investigated the level of within‐alga integration, the consequent ability to compensate for simulated herbivory, and the effect of nutrient availability on the ability to compensate in Fucus vesiculosus (L.). Although F. vesiculosus lacks vascular connections, resource translocation occurs on a local scale. Vegetative apical parts and reproductive structures were dependent on the resources provided by the mature thallus. Thus, damage from herbivory has the potential to decrease the growth and reproductive success of F. vesiculosus. In contrast to vascular plants, F. vesiculosus did not show any plasticity in response to different types of damage. Removal of an apical part terminated the growth of the focal branch but had no effect on the growth of the neighboring branch. Removal of the older part of the thallus had no effect on the branching of the apical meristems. Thus, the within‐alga growth pattern remained similar whether the old thallus or an apical part was damaged. Increased resource availability did not enhance the ability of algae to compensate for lost thallus. The strong dependence of the apical part on the older thallus and the low plasticity in the type of response to damage indicate that in F. vesiculosus the tolerance of herbivory may be low.

Induced sink strength as a prerequisite for induced tannin biosynthesis in developing leaves of Populus.

Induced defenses occur predominately in young, developing plant tissues that rely upon carbohydrate import to support their growth and development. To test the hypothesis that the induced production of carbon-based defenses is dependent upon photoassimilate import, we examined the response of developing leaves of hybrid poplar (Populus deltoides × P. nigra) saplings to wounding by gypsy moth caterpillars (Lymantria dispar L.) and exogenous jasmonic acid (JA). Growth rates, condensed tannin contents and acid invertase activities were measured for individual leaves and the translocation of 13C-labeled resources between orthostichous source-sink pairs was quantified. Results showed a substantial increase in the activity of cell wall invertase in sink leaves wounded by gypsy moth caterpillars and treated with JA. JA-induced sink leaves also imported 3-4 times as much 13C-labeled carbon from orthostichous source leaves relative to controls and allocated a significant portion of this imported 13C to condensed tannin biosynthesis. Reduced carbohydrate flow to these leaves, caused by source leaf removal, resulted in reduced condensed tannin levels and the emergence of a growth-defense tradeoff. These results indicate that (1) induced sink strength is elicited by insect wounding and JA application in hybrid poplar foliage, (2) imported resources are allocated to the production of carbon-based defenses, and (3) the level of induced defense in leaves can be constrained by the ability of leaves to import carbohydrates from source tissues. Together, these results suggest that within-canopy variations in induced resistance may arise in part because of uneven distribution of resources to induced foliage.

Bleaching effect on regeneration and resource translocation in the coral Oculina patagonica

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 234:119-125 (2002) - doi:10.3354/meps234119 Bleaching effect on regeneration and resource translocation in the coral Oculina patagonica M. Fine, U. Oren, Y. Loya* Department of Zoology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel *Corresponding author. E-mail: yosiloya@post.tau.ac.il ABSTRACT: Bleaching of corals is the result of the loss of their symbiotic algae (zooxanthellae) and/or their pigments. The supply of photoassimilates provided by the zooxanthellae to the corals declines during bleaching and reduces their ability to activate energy-costly processes. In the present study we compared regeneration capabilities of unbleached Oculina patagonica colonies (an encrusting Mediterranean stony coral) with those of bleached and partly bleached colonies. Using the 14C point-labelling technique on coral tissue, we examined possible intra-colonial translocation of photosynthetic products from the site of tissue labelling to recuperating lesions in partly bleached versus unbleached intact colonies. The percentage recovery of 2 cm2 lesions inflicted on unbleached O. patagonica colonies was significantly higher than the percentage recovery of similar lesions within the bleached area of the partly bleached colonies. Totally bleached colonies showed no regeneration of lesions. Lesion regeneration in unbleached O. patagonica resulted in oriented intra-colonial translocation of 14C products towards recuperating lesions located up to 4-5 cm away. In partly bleached colonies (40 to 80%), such translocation did not occur, probably explaining the reduced recovery rates of lesions in these colonies. Our findings suggest a bleaching threshold of ca. 30% within O. patagonica colonies that determines the levels of colony integration and intra-colonial translocation of resources to regions of maximal demand. KEY WORDS: Coral bleaching · Lesion recovery · 14C-labelling · Colony integration · Resource translocation · Oculina patagonica Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 234. Online publication date: June 03, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.

Carbon and nitrogen translocation between seagrass ramets

The spatial scale and the magnitude of carbon and nitrogen translocation was examined in 5 tropical (Cymodocea serrulata, Halophila stipulacea, Halodule uninervis, Thalassodendron cilia- tum, Thalassia hemprichii) and 3 temperate (Cymodocea nodosa, Posidonia oceanica, Zostera noltii) seagrass species using 13 Carbon ( 13 C) and 15 Nitrogen ( 15 N) as tracers in experiments conducted in situ. Seagrass leaf and rhizome production during the study period varied from <0.001 to 0.015 g DW shoot -1 d -1 and 0.002 to 0.017 g DW rhizome apex -1 d -1 , respectively. Based on measured leaf and rhi- zome growth rates, the demand of resources for leaf production varied from 0.19 to 4.99 mgC shoot -1 d -1 , and from 0.01 to 0.24 mgN shoot -1 d -1 , while the demand for rhizome production varied from 0.62 to 5.57 mgC rhizome apex -1 d -1 and from 0.02 to 0.12 mgN rhizome apex -1 d -1 . Seagrass leaves incor- porated the isotopes at rates ranging from 0.04 to 0.63 µg 13 C g DW -1 h -1 , and <0.01 to 0.35 µg 15 N g DW -1 h -1 . After 4 d, all incubated shoots had shared part of the incorporated 13 C and 15 N with ram- ets placed at maximum distances ranging from 2.7 (H. stipulacea) to 81 cm (C. nodosa), indicating that seagrass clonal integration may be maintained between 1.6 d (H. stipulacea) and 5.4 yr (P. ocean- ica). Resource translocation within seagrass clones was stimulated towards horizontal rhizome apices. Seagrass ramets, in 4 d, shared with their neighbours between 0.37 and 390 µg 13 C and between 0.02 and 178 µg 15 N. During the study period, resource translocation would supply <5% and up to 40% of the leaf carbon and nitrogen required by a neighbouring developing ramet, respec- tively, and <5% and up to 36% of the carbon and nitrogen required for rhizome growth; provided that the incorporated resources over 1 d were mobilised at similar rates over 4 d. These results con- clusively demonstrate physiological integration between seagrass ramets, and that resource translo- cation may be an important mechanism for young seagrass ramets to acquire resources and for sea- grass clones to expand and persist.

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.