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ABSTRACT: Invasive species are one of the main causes for the loss of global biodiversity. However, the mechanisms that explain the success of invasive species remain unsolved. Clonal growth has been pointed out as an attribute that could contribute to the invasiveness of plants, however little research has been conducted to determine the importance of clonal traits in successful invaders. One of the most interest-ing attributes related to clonal growth is the capacity for division of labour. In this experiment we investi-gated the capacity for division of labour in the aggressive invader Carpobrotus edulis, and how clonal integration can contribute to the expansion of this species. Division of labour was determined by studying the degree of morphological and physiolog-ical specialization of individual ramets to a specific activity: acquisition of soil or aboveground resources and aboveground expansion. Our results showed that there is division of labour in the clonal fragments, with older ramets increasing the biomass allocated to roots (specialization in the uptake of belowground resources) and younger ramets increasing the chlorophyll content and aboveground biomass (spe-cialization in the uptake of aboveground resources). Physiological integration allows division of labour, and as consequence the overall performance of the clonal fragment was enhanced, with connected clonal fragments showing a higher total biomass than severed clonal fragments. Division of labour increased the aboveground growth of apical ramets of C. edulis, and therefore could contribute to an effective colonization of the surrounding area by this aggressive invader. Our study is the first exploring the role of division of labour in the expansion of an invader, and supports the idea that clonal traits could increase the invasiveness of plant species.
Dataset: The effects of physiological integration on biomass partitioning in plant modules: an experimental study with the stoloniferous herb Glechoma hederaceaSergio R Roiloa, Michael J Hutchings[show abstract] [hide abstract]
ABSTRACT: Morphological and physiological plastic-ity are crucial attributes enabling plants to acquire resources from heterogeneous habitats. Although physiological integration can modify biomass parti-tioning in modules, especially when connected mod-ules experience different conditions, its ecological importance has been largely overlooked. This exper-iment examined its effects on above-and belowground biomass partitioning by modules in the stoloniferous herb Glechoma hederacea. We studied how biomass allocation to roots by younger ramets was affected by connection to older ramets, and by nutrient conditions. A lower proportion of biomass was allocated to roots by younger ramets growing under low nutrient (LN) conditions when connected to older ramets in high nutrient (HN) conditions than when they were iso-lated, demonstrating localised modification of bio-mass partitioning due to physiological integration. The proportion of biomass allocated to roots by younger ramets was also lower when connected to older ramets in HN conditions than when connected to older ramets in LN conditions. Thus, the effect of integration on biomass partitioning depended on the nutrient condi-tions experienced by connected ramets. Such changes in biomass partitioning would result in more extensive stolon growth, and greater lateral displacement of new ramets. Understanding the ecological implications of phenotypic plasticity in plants will require further examination of the effects of physiological integration when connected modules experience contrasting growing conditions. This study demonstrates that such integration affects the biomass allocation strategy of connected ramets, enhancing resource acquisition in heterogeneous habitats. The widespread success of clonality in many communities is likely to be strongly promoted by this characteristic.
Dataset: The effects of rooting frequency and position of rooted ramets on plasticity and yield in a clonal species: an experimental study with Glechoma hederaceaSergio R Roiloa, M.J. Hutchings[show abstract] [hide abstract]
ABSTRACT: Clonal plants produce numerous ramets that can be distributed over a considerable area. Resources are translocated between ramets, especially when they occupy microsites of different quality, or places where leaves or roots cannot be deployed. It is common for a proportion of the ramets of clones and clonal fragments to lack roots. We conducted a greenhouse study using clonal fragments of Glechoma hederacea to examine the effects of differences in the number and position of rooted ramets on yield and plasticity of clonal frag-ments. We hypothesized that (1) mass of roots and root mass ratio would increase as the number of rooted ra-mets decreased, (2) plasticity in rooted ramets would buffer the clonal fragment against reduction in yield as the number of rooted ramets declined, (3) ramet plas-ticity in response to the absence of rooting, and the beneficial effects of this plasticity, would be greater when older ramets were rooted. The same yield was achieved in clonal fragments with only one out of four ramets rooted as in clonal fragments with all four of their ra-mets rooted, regardless of whether rooting was confined to older or younger ramets. Plasticity in biomass allo-cated to roots was greater in older rooted ramets suc-ceeded by unrooted ramets than in younger rooted ramets preceded by unrooted ramets. Modular plastic-ity, involving both direct responses to local conditions, and indirect responses to the conditions experienced by connected modules, buffered performance against vari-ation in rooting ability, enabling clonal fragments to maintain their yield and lateral expansion even when a high proportion of their ramets lacked roots.
Dataset: Clonal integration in Fragaria vesca growing in metal-polluted soils: parents face penalties for establishing their offspring in unsuitable environmentsSergio R Roiloa, Rubén Retuerto[show abstract] [hide abstract]
ABSTRACT: Clonal plants often establish descendent ramets in sites with contrasting presence of favourable and unfavourable factors. Connections between ramets allow translocation of essential resources from established ra-mets to developing ramets and, as consequence, integra-tion confers net benefits to ramets growing under unfavourable conditions. Therefore, integrated ramets may survive in habitat patches that would be lethal to independent ramets or non-clonal plants. This experiment aimed to investigate the physiological and morphological responses of the clonal plant Fragaria vesca growing in heterogeneous substrate with patches of contrasting quality (i.e. uncontaminated or heavy-metal-contami-nated). We observed that parents reduced their photo-synthetic efficiencies and growth as consequence of maintaining their offspring. This cost did not affect sur-vival of the parents. Physiological integration brings about benefits to offspring ramets growing both at uncontaminated and heavy-metal-contaminated soils. The benefits of integration were detected in both physio-logical and morphological traits, enhancing the survi-vorship of offspring ramets in the Cu-polluted soils. We conclude that integration improves the performance of developing ramets of F. vesca growing in heavy-metal-contaminated habitats, allowing clone systems to over-come the establishment risks and maintain their presence in these less favourable sites.
Article: Physiological integration increases the survival and growth of the clonal invader Carpobrotus edulis[show abstract] [hide abstract]
ABSTRACT: Clonal growth seems to be a common trait for many of the most aggressive invasive plant species. However, little research has been conducted to determine the role of clonality in the successful invasion of new areas by exotic species. Carpobrotus edulis (L.) N.E. Br. is a mat-forming succulent plant, native to South Africa that is invasive in coastal dunes of Australia, New Zealand, USA and Southern Europe. Although Carpobrotus edulis is a clonal plant, there is no information on the role of clonality for the invasion by this species, therefore the objective of this study was to test whether or not physiological integration improves the performance of C. edulis invading coastal sand dunes. To do that, a 6-month field experiment was designed in which the stolon connections between the apical ramets and the C. edulis mats were severed to prevent physiological integration. This treatment was applied to ramets growing under high and low competition with the native species. Apical ramets with intact stolon connections were used as control. Integration improved the survivorship and growth of apical ramets, both in high and low competition. Connected ramets showed a more pronounced increase of clonal growth (estimated as stolon length) during the experimental period and a higher total biomass and number of ramets at the completion of the experiment. In terms of survivorship, the benefit of integration was greater under high competition. Physiological integration can therefore be considered an important factor in the invasiveness of C. edulis, both in open space and in direct competition with the native plants.01/2009; 12:1815–1823.