Clonal Parental Effects on Offspring Growth of Different Vegetative Generations in the Aquatic Plant Pistia stratiotes.

Parental (environmental) effects can modify the growth of offspring, which may play an essential role in their adaptation to environmental variation. While numerous studies have tested parental effects on offspring growth, most have considered offspring growth of only one generation and very few have considered offspring growth of different generations. We conducted a greenhouse experiment with an aquatic clonal plant Pistia stratiotes. We grew a single ramet of P. stratiotes under low or high nutrients, the initial (parent) ramets produced three different generations of offspring ramets, and these offspring ramets were also subjected to the same two nutrient levels. High nutrients currently experienced by the offspring increased biomass accumulation and ramet number of all three offspring generations of P. stratiotes. However, these positive effects on biomass were greater when the offspring ramets originated from the parent ramets grown under low nutrients than when they were produced by the parent ramets grown under high nutrients. These results suggest that parental effects can impact the performance of different offspring generations of clonal plants. However, heavier offspring ramets produced under high nutrients in parental conditions did not increase the subsequent growth of the offspring generations. This finding indicates that parental provisioning in favorable conditions may not always increase offspring growth, partly depending on root allocation but not ramet size such as ramet biomass.

Capacity for clonal integration in introduced versus native clones of the invasive plant Hydrocotyle vulgaris.

Clonal plants can make up a disproportionately high number of the introduced, invasive plant species in a region. Physiological integration of connected ramets within clones is a key ecological advantage of clonal growth. To ask whether clonal integration underlies the invasiveness of clonal plants, we tested the hypothesis that introduced clones of an invasive species will show higher capacity for integration than native clones of the same species. We conduct a greenhouse experiment on the widespread, perennial herb Hydrocotyle vulgaris. Clonal fragments consisting of pairs of connected ramets from seven sites in northwestern Spain where the species is native and seven sites in southeastern China where the species is introduced and invasive were grown for 79 days with the younger, apical ramet shaded to 30% of ambient light and the connection between ramets either severed or left intact. Severance decreased the final dry mass and ramet number of the apical ramet and its offspring in nearly all clones and increased the mass or ramet number of the basal portion of the fragment in about half of the clones, but these effects did not differ consistently between native and introduced clones. Severance did affect allocation more in introduced than in native clones, decreasing root/total mass more in apical portions and increasing it more in basal portions. Maintaining the connection between ramets caused introduced, but not native, clonal fragments to produce more leaf and less root mass and thus to lower allocation to roots. Regardless of severance, introduced clones accumulated about twice as much mass as native clones. Results suggest that introduced clones of a species can show greater effects of integration on allocation than native clones. In species such as H. vulgaris, this might increase competitiveness for light.

A dynamic model-based framework to test the effectiveness of biocontrol targeting a new plant invader- the case of Alternanthera philoxeroides in the Iberian Peninsula.

Biological invasions are one of the major threats to biodiversity at the global scale, causing numerous environmental impacts and having high direct and indirect costs associated with their management, control and eradication. In this work, we present a system-dynamic modelling approach for the biocontrol of the invasive plant species Alternanthera philoxeroides using its natural predator, Agasicles hygrophila, as a biocontrol agent. We have simulated different scenarios in the Finisterre region (Spain), where a single population of the invasive plant has been recently described. To assess the effectiveness of A. hygrophila as a biocontrol agent in the region, a population dynamic model was developed in order to include the life-cycle of both species, as well as the interaction among them. The results of the simulations indicate that the control of this new invasive plant is possible, as long as several releases of the biocontrol agent are made over time. The proposed model can support the control or even the eradication of the population of A. philoxeroides with a minimal impact on the environment. Additionally, the proposed framework also represents a versatile dynamic tool, adjustable to different local management specificities (objectives and parameters) and capable of responding under different contexts. Hence, this approach can be used to guide eradication efforts of new invasive species, to improve the applicability of early management measures as biocontrol, and to support decision-making by testing several alternative management scenarios.

Soil resource heterogeneity competitively favors an invasive clonal plant over a native one.

Soil resource heterogeneity can affect plant growth and competitive ability. However, little is known about how soil resource heterogeneity affects competitive interactions between invasive and native plants. We conducted an experiment with an invasive clonal plant Alternanthera philoxeroides and a coexisting native one Alternanthera sessilis. The experiment was a randomized design with three factors, i.e. two species (A. philoxeroides and A. sessilis), two interspecific competition treatments (with and without) and five soil treatments (three homogeneous treatments and two small-scale heterogeneous treatments consisting of two patches of 10 cm × 15 cm and with different initial planting positions). Irrespective of competition, increasing soil resource availability increased the growth of A. philoxeroides. Increasing soil resource availability also increased the growth of A. sessilis without competition, but had no impact with competition. Irrespective of competition, soil resource heterogeneity increased biomass and ramet production of A. philoxeroides, and such effects were independent of initial planting position. For A. sessilis, however, soil resource heterogeneity only increased ramet production when the initial plant was grown in the low-resource patch without competition. Our results suggest that both high soil resource availability and small-scale soil resource heterogeneity can increase the relative competitive ability of the invasive plant A. philoxeroides when grown with its native congener A. sessilis. These findings may partly explain the invasion success of this clonal species in area with high soil resource availability and heterogeneity caused by e.g. nitrogen deposition, fertilization and disturbance.

Ecophysiological differentiation between two invasive species of Carpobrotus competing under different nutrient conditions.

PREMISE: Hybridization between the South African invasive species Carpobrotus edulis and C. acinaciformis in Europe has led to the formation of highly aggressive morphotypes referred to in the scientific literature as the new large "hybrid swarm" C. aff. acinaciformis. In the present study, we aimed to determine whether the taxonomic differentiation between taxa coincides with ecophysiological differentiation. With this aim, we tested for differences between both morphotypes in functional traits related to competitive ability and resource-use efficiency. Assuming that the complex hybrid C. aff. acinaciformis is more vigorous, depends more strongly on vegetative reproduction, and invests less in sexual reproduction than C. edulis, we predicted that the hybrid would show higher competitive ability and better physiological performance compared with the species. METHODS: We used a comparative ecophysiological approach to assess the extent to which two Carpobrotus morphotypes coexisting in northwestern Spain differ in physiological, reproductive, and growth traits when competing under different soil nutrients in controlled greenhouse conditions. RESULTS: C. aff. acinaciformis had a greater relative growth rate and water-use and photochemical efficiencies compared to C. edulis. However, C. edulis appeared to be more responsive to incremental change in soil nutrients than C. aff. acinaciformis. They also differed in the amount of resources invested in reproduction. CONCLUSIONS: The study findings demonstrate that the taxonomic differentiation between taxa corresponds to ecophysiological differentiation, warranting a detailed examination of all existing trades-offs to predict the long-term outcomes of the interaction between these taxa.

Herbivory induced non-local responses of the clonal invader Carpobrotus edulis are not mediated by clonal integration.

The anthropogenic displacement of species around the world results in new environmental situations where native and exotic species coexist. Exotic plants have to face native herbivores, and interactions between introduced plants and native herbivores seem to play an important role in the invasiveness of some exotic plant species. We studied the role of clonal integration in induce morphological, physiological, and biochemical responses in the clonal invader Carpobrotus edulis against the attack of the native snail Theba pisana. Our results demonstrated the presence of labour division mediated by physiological integration, with a significant increase of photosynthesis potential (both at morphological and physiological) in un-attacked integrated ramets. This response could be especially important under herbivory, as the negative impact of T. pisana on the photosynthetic structures of attacked C. edulis ramets could be buffered by transferring the dependence of photosynthetic activity to the un-attacked ramets. Our results also showed a constitutive resistance in un-attacked apical ramets, showing a similar amount of defence compounds to those exhibited in the basal branches attacked by snails. Results reported a non-local compensatory response, which there was an increase of total biomass in apical ramets when their basal ramets were attacked by the herbivore. We interpret this result as a compensatory response, with these apical ramets increasing shoot biomass to compensate for the biomass loss due to a potential attack from herbivores. However, this non-local response was not mediated by physiological integration but probably due to belowground communication, with the presence of alarm signals released by root exudates. We conclude that the attack of this snail is not enough to be a possible biological control due to the compensatory response to this snail by C. edulis, favouring their expansion. Future studies should focus on unravelling the role of belowground communication in the defensive responses of C. edulis.

Clonal integration facilitates the colonization of drought environments by plant invaders.

Biological invasion represents one of the main threats for biodiversity conservation at the global scale. Identifying the mechanisms underlying the process of biological invasions is a crucial objective in the prediction of scenarios of future invasions and the mitigation of their impacts. In this sense, some plant attributes might better explain the success of invasive plant species than others. Recently, clonal growth has been identified as an attribute that could contribute to the invasiveness of plants. In this experiment, we aim to determine the effect of physiological integration (one of the most striking attributes associated with clonal growth) in the performance (at morphological and physiological levels) of the aggressive invader Carpobrotus edulis, when occupying stressful environments. To achieve this objective we performed a greenhouse experiment in which apical ramets of C. edulis were water-stressed and the connection with the basal ramets was either left intact (physiological integration is allowed) or severed (physiological integration is impeded). Our results show that clonal integration allowed apical ramets to buffer drought stress in terms of photochemical activity, and as a consequence, to increase their growth in comparison with severed apical ramets. Interestingly, this increase in biomass was mainly due to the production of aboveground structures, increasing the spread along the soil surface, and consequently having important implications for the colonization success of new environments by this aggressive invader.

Division of Labor Brings Greater Benefits to Clones of Carpobrotus edulis in the Non-native Range: Evidence for Rapid Adaptive Evolution.

Why some species become invasive while others do not is a central research request in biological invasions. Clonality has been suggested as an attribute that could contribute to plant invasiveness. Division of labor is an important advantage of clonal growth, and it seems reasonable to anticipate that clonal plants may intensify this clonal attribute in an invaded range because of positive selection on beneficial traits. To test this hypothesis, we collected clones of Carpobrotus edulis from native and invasive populations, grew pairs of connected and severed ramets in a common garden and under negative spatial covariance of nutrients and light to induce division of labor, and measured biomass allocation ratios, final biomass, and photochemical efficiency. Our results showed that both clones from the native and invaded range develop a division of labor at morphological and physiological level. However, the benefit from the division of labor was significantly higher in apical ramets from the invaded range than in ramets from the native area. This is a novel and outstanding result because it provides the first evidence that the benefit of a key clonal trait such as division of labor may have been subjected to evolutionary adaptation in the invaded range. The division of labor can therefore be considered an important trait in the invasiveness of C. edulis. An appropriate assessment of the influence of clonal traits in plant invasions seems key for understanding the underlying mechanisms behind biological invasions of new environments.

Adaptive plasticity to heterogeneous environments increases capacity for division of labor in the clonal invader Carpobrotus edulis (Aizoaceae).

UNLABELLED: • PREMISE OF THE STUDY: Clonality has been proposed as an important mechanism favoring plant invasions, but few studies have been conducted to determine the role of clonal traits on successful invaders. An interesting trait associated with clonality is the capacity for division of labor. Division of labor requires a negative spatial correlation between the availabilities of two essential resources and ramet specialization for locally abundant resources to increase the overall performance of the clone. We hypothesized that the capacity for division of labor in the clonal invader Carpobrotus edulis will be selected in those clones from patchy environments where this trait could be an advantage.• METHODS: Morphological and physiological division of labor was compared between clones from coastal sand dunes (where nutrients and light show a negative spatial covariance) and from rocky coasts (where nutrients and light are homogenously distributed).• KEY RESULTS: Clones from coastal sand dunes showed a greater capacity than clones from rocky coasts for division of labor. Specialization for abundance was found at the morphological (biomass allocated to roots) and the physiological (photochemical efficiency) level.• CONCLUSIONS: The greater ability for division of labor in the patchy environment where the presence of this trait would be more beneficial demonstrates the existence of local adaptation and suggests that rapid evolution in clonal traits could be contributing to the success of the invader C. edulis. This study is one of the few showing that division of labor is under selection and is the first reporting adaptive division of labor of an aggressive invader.

Development, photosynthetic activity and habitat selection of the clonal plant Fragaria vesca growing in copper-polluted soil.

The ability of clonal systems to spread by ramet production may expose the clone to spatial heterogeneity. This study explored the physiological and morphological responses in the clonal plant Fragaria vesca L. growing in homogeneous (Cu-contaminated or uncontaminated) or in heterogeneous environments with patches of contrasting quality (Cu-contaminated or uncontaminated). We also investigated the potential of this species to selectively establish ramets within a heterogeneous environment. In heterogeneous environments, plants expanded ramets randomly, but selectively established ramets in the favourable patches. We discuss whether the selective establishment of ramets is a consequence of direct suppression of plant growth due to copper toxicity. The assimilate demand from offspring ramets in unfavourable environments increased the chlorophyll content and photosynthetic efficiency of parents by a feedback regulation process. Integration ameliorated the effects of copper on the photochemical efficiency of the offspring ramets. We did not observe integration costs, in terms of total biomass, for parents supporting ramets in Cu-contaminated environments, although we did detect costs in terms of ramet production. Parents with offspring ramets in Cu-contaminated environments produced 25 times more reproductive biomass than parents with offspring ramets in uncontaminated environments. We interpret this as a strategy for escaping from stressful environments. In this study, we extend the concept of physiological integration in clonal plants to include photochemical responses.