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Clonal integration increases growth performance and expansion of Eichhornia crassipes in littoral zones: A simulation study

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Abstract

Clonal integration can improve the spread and growth of invasive plants in response to various disturbances. However, little is known about its role in floating aquatic clonal plants that expand from aquatic into terrestrial habitats in littoral zones. Thus, in this study, we simulated the expansion of the invasive clonal aquatic plant Eichhornia crassipes from aquatic to terrestrial habitats through two modes of clonal integration. We subjected E. crassipes parent plants and offspring ramets to three levels of natural light in terrestrial habitats: 100%, 60%, and 10%. The stolon connections were either severed or kept intact. Our findings showed that clonal integration had positive effects on plants exposed to shade in the terrestrial habitats and produced negative effects on plants in the aquatic habitats. Overall, clonal integration significantly increased whole-plant growth performance. Parent plants and offspring ramets in the terrestrial environments can enhance their adaptability to shade by increasing the maximum quantum yield of photosystem II and chlorophyll content. Clonal integration can support the expansion of E. crassipes from aquatic into terrestrial habitats with limited light conditions through significantly elevated growth traits. Thus, E. crassipes has a high ability for clonal integration and may be a potential threat to littoral zone ecosystems.

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... Eckert et al., 2016;Fenollosa et al., 2016;Liu et al., 2006;Song et al., 2013). It has also been noted that many IAPS reproduce by clonal growth and that many of the most invasive plants in the world are clonal (Fenollosa et al., 2016;Liu et al., 2006;Yu et al., 2019). For instance, 2/3 of the most invasive plants in China and also about 2/3 of the world's worst invasive plants listed by the ISSG (Invasive Species Specialist Group) are clonal (Liu et al., 2006;Lowe et al., 2000). ...
... For instance, 2/3 of the most invasive plants in China and also about 2/3 of the world's worst invasive plants listed by the ISSG (Invasive Species Specialist Group) are clonal (Liu et al., 2006;Lowe et al., 2000). In addition to the ability to disperse by seeds, clonal plants can also spread their populations by clonal growth and may thus be less constrained by climate because they are not temperature-regulated regarding flowering and fruiting (Ye et al., 2014;Yu et al., 2019). Furthermore, clonal plants possess some distinguished characteristics that can assist them to quickly establish their populations in unexpectedly harsh environments (Negreiros et al., 2014). ...
... While clonality had little impact on the invasion risk in PAs medi- Aquatic ecosystems are prone to biological invasions, and many inland aquatic ecosystems in the world are heavily invaded by aquatic clonal plants (Eckert et al., 2016;Hussner et al., 2017;Santamaría, 2002;Teixeira et al., 2017). For some aquatics such as the common water hyacinth Eichhornia crassipes, the main way to spread and invade is by clonal growth, and the spread of clonal propagules is also much easier in such ecosystems (Herben & Klimešová, 2020;Yu et al., 2019). Hence, in the future, we need to pay much attention to clonal IAPS in PAs which function to conserve Inland Water. ...
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Aim Protected areas (PAs) play an important role in biodiversity conservation, but remain increasingly threatened by invasive alien plant species (IAPS) in conjunction with global climate change. The latter is modifying the distribution of the former, and the magnitude and direction of distributional changes are predicted to vary depending on species dispersal mode. Here, we address the question of whether clonality is expected to affect the future invasion pattern in PAs. Location Worldwide. Time period 1950–2100. Major taxa studied 36 invasive alien plant species. Methods We used ensembles of three species distribution models (GLM, GAM and Maxent) based on >70,000 occurrence records to project the distribution of 36 of the world's most invasive clonal and non‐clonal plants in >20,000 PAs. Projections were based on three greenhouse gas concentration scenarios (low, medium and high) for 2080. Results Climate change showed little impact on the global invasion pattern in PAs, and clonality showed little effect when all biomes were processed in concert. However, we discerned that the future invasion risk of clonal IAPS markedly increased in biomes located at high elevation and high latitude compared with non‐clonal IAPS, while the risk decreased in lower‐elevation tropical and subtropical biomes where asexual reproduction may be a less successful trait. We also showed that invasion hot spots overlapped with biodiversity hot spots and two realms (i.e. Nearctic and Palearctic), which calls for bridging the gap between invasion and conservation sciences and for more concerted management strategies. Main conclusions We suggest that effective management of IAPS in PAs should consider in which biomes PAs are located as well as the reproductive traits of IAPS that are present or may become so.
... clonal plasticity [35]; and IV. clonal integration [2,46]. For example, clonal plants can share resources (nutrients, water, etc.) among individual units through clonal integration, which increases plant survival and growth performance in habitats with different patterns of resource availability. ...
... Plants in natural habitats often experience heterogeneity in the spatial and temporal distribution of soil nutrients [21,46]. Wetland plants, especially emergent macrophytes, are sensitive to the distribution of soil pollutants and nutrients during their growth process [7,45]. ...
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Background Clonal plants are important in maintaining wetland ecosystems. The main growth types of clonal plants are the guerrilla and phalanx types. However, little is known about the effects of these different clonal growth types on plant plasticity in response to heterogeneous resource distribution. We compared the growth performance of clonal wetland plants exhibiting the two growth forms (guerrilla growth form: Scirpus yagara, Typha orientalis, Phragmites australis and Sparganium stoloniferum; phalanx growth form: Acorus calamus, Schoenoplectus tabernaemontani and Butomus umbellatus) grown in soil substrates that were either homogeneous or heterogeneous but had the same total amount of nutrients. Results We found that the morphological traits (plant height, ramet number, spacer diameter and length) and biomass accumulation of the guerrilla clonal plants (T. orientalis) were significantly enhanced by heterogeneity, but those of the phalanx clonal plants (A. calamus, S. tabernaemontani and B. umbellatus) were not. The results showed that the benefits of environmental heterogeneity to clonal plants may be correlated with the type of clonal structure. Conclusions Guerrilla clonal plants, which have a dispersed, flexible linear structure, are better suited to habitats with heterogeneous resources. Phalanx clonal plants, which form compact structures, are better suited to habitats with homogeneous resources. Thus, wetland clonal species with the guerrilla clonal structure benefit more from soil nutrient heterogeneity.
... E. crassipes often covers the water surface, obstructs rivers, decreases dissolved oxygen, reduces native aquatic plant diversity and even threatens human health by providing a refuge for mosquitoes (Chandra et al., 2006;Villamagna and Murphy, 2010;Zhou et al., 2017). Many recent studies on E. crassipes have mainly focused on topics such as its biological control and clonal integration, water purification and the interactions of E. crassipes with herbivores (Bownes et al., 2013;Pi et al., 2017;Yu et al., 2019); however, how abiotic factors and the biotic determinants of plant diversity affect the impact of E. crassipes is largely unknown. Given that E. crassipes shows superior abilities in terms of rapid growth, nutrient absorption, and environmental adaptation (You et al., 2014) and climate change is ongoing (e.g., warming and frequent floods), this invasive plant may expand its northern boundaries to higher latitudes and thus cause larger negative impacts on aquatic plant diversity in these regions (Hoveka et al., 2016;Liu et al., 2017;Wu and Ding, 2019). ...
... The vigorous asexual ramets (abundance) of aquatic invasive plants allow them to rapidly and fully occupy the available niche space, limiting the establishment of other native aquatic plants and, thus, dramatically decreasing aquatic plant diversity (Stiers and Triest, 2017;Yu et al., 2019). However, in our study, height did not contribute to E. crassipes invasiveness, likely because there were several tall hydrophytes in the invaded community (e.g., P. distichum, B. syzigachne, A. calamus, L. hexandra), which could disrupt the shading effect of E. crassipes. ...
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Rapid global environmental changes could exacerbate the impacts of invasive plants on indigenous plant diversity, especially for freshwater ecosystems characterized by relatively simple plant community structures with low bioresistance. However, the abiotic and biotic determinants of plant diversity in aquatic invaded habitats remain unclear. In this study, we measured four α-species diversity indices (the Patrick richness index, Shannon–Wiener diversity index, Simpson diversity index, and Pielou evenness index) in aquatic plant communities invaded by Eichhornia crassipes in southern China. We also recorded eight environmental parameters of these communities (longitude, latitude, elevation, dissolved oxygen, water conductivity, nitrate nitrogen, temperature, and precipitation), together with nine biotic traits of E. crassipes [abundance, invasion cover, height, total carbon (C) content of the leaves and stems, total nitrogen (N) content of the leaves and stems, and the C:N ratio of leaves and stems]. We then used regression analysis and redundancy analysis (RDA) to determine the dominant factors related to plant diversity. We found that the environment significantly affected E. crassipes abundance, height, coverage, stem carbon, and tissue nitrogen, while the leaf C:N stoichiometric ratio was relatively stable. Increasing longitude significantly increased plant diversity, while elevated dissolved oxygen and precipitation slightly improved plant diversity, but increased elevation caused negative effects. E. crassipes invasion significantly decreased all four diversity indices. Increases in E. crassipes coverage and leaf C:N strongly decreased plant diversity, and increased abundance slightly decreased diversity. Our study indicates that both the changing water environment and the properties of the aquatic invasive plants could have significant impacts on plant diversity. Thus, more attention should be paid to aquatic invasion assessment in lower longitudinal regions with lower native hydrophyte diversity.
... This study found that clonal integration significantly increased SPAD values of stressed ramets. These results align with previous research, which showed that clonal integration under heterogeneous environments increases chlorophyll levels [35][36][37]. ...
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Clonal plants can support the growth of their ramets in heterogeneous environments through clonal integration between the ramets. However, the role of clonal integration in modulating ramet photosynthesis under toxic stress, especially combined stress, is unclear. This study examines the impact of clonal integration on Zoysia japonica under three heterogeneous stresses (Pb, pyrene, and Pb+Pyrene) with two stolon connection conditions (connected and disconnected). Our results show that clonal integration significantly enhances PN, gs, Ci, E, and CE while reducing WUE. It also improves ΦPSII, Fv′/Fm′, Fv/Fm, Fv/F0, and qP while reducing NPQ. Clonal integration lowers MDA levels, increases SOD activity, and mitigates the decline in CAT and POD activity, resulting in increased biomass under stress. Furthermore, we observed that the synergistic effects of the Pb+Pyrene mixture negatively impacted the adaptability of clonal integration. Our study underscores the role of clonal integration in maintaining photosynthesis and supporting the success of clonal plants in toxic environments.
... Meanwhile, a significant increase was recorded in the contents of S, K, Ca, Mn and Zn against the stem and leaves. Simulation research for the expansion of invasive Eichhornia crassipes from aquatic habitats to land through two clone integration modes was also carried out [11], [12]. Based on the conducted simulation results, clone integration had significantly increased growth performance. ...
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Increase in science and technology development today has spurred environmental pollution in water, soil and air. Water pollution caused by the impact of industrial development must be controlled as quickly as possible. The study aimed to investigate the effect of Eichhornia crassipes plants at given metal concentrations. The Eichhornia crassipes plant was used as an observation material with varying concentrations of metal (Cr, Hg, and Pb). The method used in this study was Randomised Block Design (RBD) and continued with Duncan's Multiple Range Test analysis, or better known as the DMRT test. The study observations showed that the increase in Eichhornia crassipes seedlings was 3cm, 2cm and 2cm, respectively with the recorded concentrations of 20%, 40%, 60%, and 80%. Meanwhile, the leachate concentrations of 20%, 40%, 60%, and 80% could also increase the roots of Eichhornia crassipes plants by 3.5cm, 1.5cm and 1cm, respectively. However, the leaf growth of Eichhornia crassipes plants at concentrations of 20% and 40% recorded as much as three and two leaves only. Additionally, it can be noted that at leachate concentrations of 20% and 40%, there was an increase in the number of Eichhornia crassipes leaf petals during observation. Overall results showed that low concentrations could increase the Eichhornia crassipes plants. This was evident in the statistical test analysis, where the leachate concentration in the Eichhornia crassipes plant affected the overall test results.
... An emerging pattern in invasion biology is that many invasive alien plants and many of the world's worst invasive plants are capable of vegetative regeneration (Liu et al. 2006;Yu et al. 2009;Song et al. 2013). Indeed, vegetative regeneration is one of the characteristics of some highly invasive plants (Baker 1974;Sakai et al. 2001;Wang et al. 2017), including Eichhornia crassipes (Koutika & Rainey 2015;Yu et al. 2019), Spartina anglica (Castillo et al. 2017), Alternanthera philoxeroides (Chen et al. 2013;Wang et al. 2016aWang et al. , 2016b, Reynoutria japonica (Strgulc & Koce 2015), and Mikania micrantha (Li et al. 2013;Jiang et al. 2021). Also a considerable number of invasive plant species can perform vigorous means of vegetative regeneration that is frequently proposed to be related to their invasiveness (Kolar & Lodge 2001;Maurer & Zedler 2002;Liu et al. 2006). ...
Article
The capacity of vegetative regeneration can contribute to the invasion success of alien plant species in introduced ranges. Belowground bud bank is a trait closely related to vegetative regeneration, but it is still unknown whether belowground bud bank can help invasive alien plants to successfully invade into native plant communities. We measured bud bank density and aboveground biomass of invasive alien and native plants, and species diversity in four wetlands along a soil moisture gradient in Zhejiang Province in East China. Overall, bud bank density, aboveground biomass, and plant diversity differed significantly among the four wetlands along the soil moisture gradient. Bud bank density, aboveground biomass, and the relative dominance of invasive plants increased with increasing soil moisture, whereas bud bank density and the relative dominance of the native plants showed the opposite trend. For invasive plants, both the proportion of aboveground biomass and the relative dominance were significantly positively related to their bud proportion. These results suggest that belowground bud bank of invasive alien plant species can contribute to their successful invasion in native plant communities. Therefore, measures such as ploughing and raking could be taken to destroy or restrict belowground bud bank of invasive alien plants to prevent their invasion and to restore native vegetation. This article is protected by copyright. All rights reserved.
... Ramets growing in resource-rich patches can transfer resources (e.g., water, carbohydrates, nutrients) through stolons, rhizomes or horizontally growing roots to connected ramets growing in resource-poor patches (Hutchings and Wijesinghe 1997;You et al. 2013;Li et al. 2017;Duchoslavová and Jansa 2018). Therefore, clonal integration generally improves the growth performance of the recipient ramets in resource-poor patches and the whole clone (Xiao et al. 2011;Yu et al. 2019;Wang et al. 2020). Although this benefit of clonal integration has been extensively studied, most research has focused on the morphological, physiological and biomass characteristics (Evans 1992;He et al. 2011;Zhang et al. 2016;Xue et al. 2022), while few studies have investigated how clonal integration affects the underground dynamic characteristics of clonal ramets. ...
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Background Resource translocation among interconnected ramets can improve the growth performance of the recipient ramets and influence soil properties and microbial communities in the rooting zone. However, scanty attention has been paid to the effect of this clonal integration on soil biotic and abiotic characteristics of neighboring species around the recipient ramets.Methods We conducted a soil heterogeneous experiment in which the mother ramet of the ramet pair for Vallisneria natans was planted in a high-nutrient patch, and the daughter ramet was planted in a low-nutrient patch with conspecific neighbors V. natans or heterospecific neighbors Myriophyllum spicatum. The stolons between ramet pairs were severed or left intact.ResultsOur results showed that effects of clonal integration on growth of the daughter ramet depend on the identity of neighboring species. Overall growth of neighbors V. natans was not affected by clonal integration, while growth of neighbors M. spicatum was greatly reduced. Soil properties and microbial community composition (especially bacteria) in the rhizosphere of neighboring plants were significantly influenced by clonal integration, and these effects were more obvious in the rhizosphere of neighbor V. natans than those in the rhizosphere of neighbors M. spicatum.Conclusion Our study suggests that clonal integration may play a vital role in facilitating nutrient cycling, modifying habitat heterogeneity and affecting interspecific interactions and even the community structure.Graphical abstract
... Besides, due to the influence of fertilization, disturbance, and soil properties, the distribution of soil nutrients needed for plant growth is often heterogeneous in habitats Shen et al., 2019). In clonal plants, heterogeneous resources and colonization of habitats are moderated through clonal integration, where water, nutrients, and carbohydrates are translocated among ramets through a connecting rhizome or stolon, subsequently promoting their growth (Wei et al., 2019;Yu et al., 2019;Zhang et al., 2019;Franklin et al., 2020). ...
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Nitrogen (N) deposition significantly affects the growth and the function of invasive clonal plants. However, the effects of heterogeneous N supply with different frequencies on the growth and the potential contribution of clonal integration in invasion plants are still unclear, especially in the complex environment considering ramet damage. To address this question, apical and basal ramets of the clonal invader Hydrocotyle vulgaris were connected or disconnected, N was added to the basal ramets with a high frequency, a low frequency, or no supply, and the total N quantity was the same for the different frequency. Furthermore, 8 aphids were placed on the apical ramets, and 30% of each leaf was cut off to cause damage. The connection between ramets significantly increased the biomass, total carbon (C), and total N of the basal and apical ramets. Higher frequency N supply significantly increased the biomass, total C, and total N of the basal ramets and the entire clonal fragment biomass. The damage had no significant effect on the growth of basal and apical ramets. Especially, under the high N frequency and ramet damage condition, the connection between ramets more significantly increased the biomass, total C, and total N of the apical ramets and the entire clonal fragment biomass. In addition, the uptake rates of ¹⁵NH4+ and ¹⁵NO3- in H. vulgaris had no significant difference, and N supply increased the uptake rates of ¹⁵NH4+ and ¹⁵NO3- of the basal ramets. Our results suggest that both higher frequency N supply and clonal integration are beneficial to the growth of H. vulgaris. Moreover, the heterogeneous N supply with high frequency and ramet damage increases the benefits of clonal integration in H. vulgaris. These findings improve our understanding of the response of clonal invader H. vulgaris to nitrogen deposition and ramet damage.
... Previous studies have shown that the widespread invasive plants water hyacinth (Eichhornia crassipes) and alligator weed (Alternanthera philoxeroides) have caused severe effects in freshwater ecosystems in China (Wang et al. 2017;Wu et al. 2017;Yu et al. 2019). Recently, a newly introduced invasive plant, Carolina fanwort (Cabomba caroliniana), has become prevalent in an environmentally sensitive area, the Lake Taihu Basin (LTB), and has garnered considerable concern (Liu et al. 2018a;Zou et al. 2012). ...
Article
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Aims The submerged plant species Carolina fanwort (Cabomba caroliniana) has become a dominant invasive aquatic plant in the Lake Taihu Basin (LTB) in China. Introduced species may escape their original specialist enemies and encounter fewer enemies in their new environment. They were assumed to have suffered less herbivory than native species as they are relatively unpalatable (the enemy release hypothesis (ERH)). The objective of this study was to compare the responses of C. caroliniana with those of co-occurring native species to herbivory from native herbivores. Methods We conducted a mesocosm experiment to record the responses of C. caroliniana and two commonly co-occurring native submerged plant counterparts, water thyme (Hydrilla verticillata) and Eurasian watermilfoil (Myriophyllum spicatum), to herbivory by two native generalist gastropod snails, Radix swinhoei and Sinotaia quadrata. Plant morphological traits (total biomass, shoot/root (S/R) biomass ratio and relative growth rate (RGR)) and physiological traits (leaf total nonstructural carbohydrate (TNC), lignin, and cellulose) were recorded. Important Findings The snail S. quadrata rarely influences the plant traits of the three submerged plants. With the increasing numbers of R. swinhoei treatments, most of the plant traits of H. verticillata and M. spicatum changed, while those of C. caroliniana showed a relatively stable fluctuation. This result indicated that C. caroliniana was more resistant to herbivory by the snail R. swinhoei, which is consistent with the ERH hypothesis. This finding indicates that herbivorous snail species contributes the invasion of C. caroliniana, which potentially alters the species composition of submerged plants in the plant community.
... observ.). This assumption is supported by a simulation study, which has proved that clonal integration increases growth performance and expansion of P. crassipes in littoral zones (Yu et al. 2019). ...
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[OPEN ACCESS] Hydric fluctuations in the Pantanal comprise annual dry and wet seasons that modify local diversity and plant morphology and anatomy. Widespread in this wetland are the sympatric Pontederia azurea and P. crassipes, which, although primarily aquatic, can also develop in non-flooded environments. This study undertook a comparative investigation of the qualitative and quantitative phenotypic responses and strategies of these two species (regarding life-form and leaf morpho-anatomy) in moderately dry and aquatic environments in the Pantanal. Field observations, conventional methods in plant anatomy, and leaf biometry were performed, followed by statistical analyses. Phenotypic responses, such as the decreased size of lacunae, increased lignification of vessel elements, and storage of starch granules, are the most prominent responses associated with moderately dry environments. The ability of petioles to elongate and inflate seems to be closely related to specific morphological patterns of each species. In contrast, petiole length, leaf blade dimensions, size of lacunae, and lignification rates seem to be somewhat associated with water level fluctuations. Our results provide evidence of how plant structure can simultaneously reflect phylogeny and ecology, thus supporting further investigations into phenotypic plasticity.
... In the evening before harvest, the dark processing had been conducted for two hours to ensure that the photosystem II reaction centres had enough time to remain open (Yu et al., 2019), we chose mature and healthy leaves located at the same morphological positions (i.e., five leaves from the 3rd node to the 5th node of the apical end of the longest stolon) and used a portable chlorophyll fluorometer (DIVING-PAM, Walz, Effeltrich, Germany) to measure the fluorescence. Then, the saturation pulse method was used to measure the maximum (F m ) and minimum (F 0 ) fluorescence yields. ...
Article
Global warming and eutrophication are two important environmental issues facing freshwater ecosystems. Especially in winter and spring, freshwater ecosystems lacking large submerged plants are the most vulnerable. However, there is a paucity of research on the combined effects of global warming and eutrophication on the water quality of freshwater ecosystems and the growth characteristics of submerged plants in winter and spring. We therefore performed a mesocosm experiment examining the combined effects of nutrient (nitrogen and phosphorus) enrichment and warming (2.65 ± 0.07℃) on the submerged plant Potamogeton crispus. We found that warming affected the morphological characteristics of P. crispus, promoted plant height, accumulated more biomass, augmented the proportion of above-ground biomass and decreased the nitrogen content of the above-ground organs. Meanwhile, warming increased more resources for asexual reproduction (turions) and reduced the number of flowers. The addition of nitrogen or phosphorus alone could significantly augment the content of nitrogen or phosphorus in vegetative organs, respectively. In addition, the effects of different nutrient enrichment on the reproduction strategy of P. crispus were different. The addition of nitrogen reduced the number of flowers, while the addition of phosphorus augmented the number of flowers and turions. In contrast, the warming and co-addition of nitrogen and phosphorus treatments had a more negative effect on P. crispus, reducing biomass, maximum fluorescence and the number of ramets, flowers and turions. Although the leaf biomass allocation increased, the turion biomass allocation decreased. This may be due to the increase in algae, turbidity and total suspended solids caused by warming and the co-addition of nitrogen and phosphorus, which stressed the growth of P. crispus. Our results suggest that global warming and eutrophication can affect the structure and function of aquatic ecosystems by inhibiting the growth of submerged plants, which may lead to further fragile stability of freshwater ecosystems in winter and spring.
... Genera with clonal growth characteristics in aquatic higher plants in China account for 72% of the total number of aquatic plant genera in China (Song and Dong 2002). In a clonal network formed by clonal growth, ramets can transfer and share resources through the physical connections (e.g., stolons, rhizomes or horizontally growing roots) (Janeček et al. 2008;Xu et al. 2012;Yu et al. 2019). Such clonal integration has been widely studied in terms of phenotypic plasticity, risk spreading and capacity improvement of aquatic clonal plants in heterogeneous habitats or under stress (Wang et al. 2008(Wang et al. , 2016You et al. 2013;Dong et al. 2015). ...
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Many aquatic plants are characterized by clonal growth through which the mother ramet can support offspring ramets by providing resources. The capacities of exploring space, sampling environment and overcoming establishment risks for offspring ramets could be enhanced with the resource support of the mother plant, which may change over time. This study aimed to investigate whether there is a change of clonal integration between mother ramets and offspring ramets in the submerged macrophyte Vallisneria natans with growth time. The stolons between mother ramets and daughter ramets were severed or intact at different growth times (7th day, 17th day, or 27th day after planting). The anatomical structure of the stolons and the morphological, biomass and nitrogen traits of the plants were measured. The results showed that the anatomical structure of the stolon changed significantly over time. The growth and clonal reproduction of daughter ramets were markedly improved by clonal integration on the 14th day but not on the 24th day or 34th day. In addition, there was no significant cost to support daughter ramets in terms of the total biomass of mother ramets. Our results highlight that the growth and clonal reproduction of daughter ramets of V. natans relies on mother ramets in the early stage and support from mother ramets declines with increasing independence of daughter ramets.
... Eichhornia crassipes (Mart.) Solms which are listed as invasive alien species within the European Union (EU regulation No. 1143Xiao et al., 2007Xiao et al., , 2011You et al., 2013a;Wang et al., 2016bWang et al., , 2017Yu et al., 2019). Conversely, species like M. spicatum, S. ...
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Aquatic plant invasions pose a major threat to the biodiversity and functionality of freshwater ecosystems and harm human well-being and the economy. Most invasive alien aquatic plants predominantly reproduce through vegetative means in their introduced range, with unspecialized plant fragments being considered as the most important propagules. However, there is still a lack of knowledge about the species-specific dispersal capacity by plant fragments and the underlying dynamics in streams. According to the new EU Regulation 1143/2014 on the prevention and management of the introduction and spread of invasive alien species, information on a species’ reproduction and its spread patterns is mandatory. Thus, in order to comply with the EU Regulation, laboratory and field studies in lowland streams were conducted to assess the fragment dispersal capacity of native and invasive alien aquatic plants based on four key traits, comprising (i) fragmentation rate, (ii) drift distance, (iii) desiccation resistance relevant for overland dispersal to isolated waters and (iv) the regeneration and colonization potential of fragments. The findings of this thesis emphasize that fragment dispersal capacity is a major driving force behind the successful and rapid spread of many aquatic plant invaders worldwide. While the dispersal and invasion success of submerged species such as Myriophyllum spicatum, Potamogeton crispus, Elodea canadensis, Elodea nuttallii and Hydrilla verticillata can largely be attributed to a high fragment dispersal capacity, fragment dispersal seems to play only a minor role for the invasiveness of Lagarosiphon major and Myriophyllum heterophyllum. However, it was documented that fragment dispersal is strongly controlled by the hydrological and hydraulic stream properties and generally enhanced in streams characterized by high discharge and turbulent flow conditions. The spread of invasive alien aquatic plants therefore deserves particular attention in larger streams, as long as the degree of flow disturbance does not prevent the establishment and persistence of aquatic plants.
... For example, clonal integration can boost the growth of M. aquaticum when subjected to heterogeneity in resource supply in changing environments (You et al., 2013). Clonal plants can share photosynthates, mineral nutrients, or water among individual subunits through clonal integration, which increases the survival of clonal plants when they experience heterogeneous distribution of resources (Xiao et al., 2006;Yu et al., 2019). Thus, we predict that the positive response of clonal plants to environmental heterogeneity may be correlated with clonal integration and morphological plasticity. ...
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Spatial heterogeneity in soil nutrient availability is considered to play an important role in promoting plant invasion success and can affect interspecific competition. Although some clonal plants have been demonstrated to be correlated with resource heterogeneity in terrestrial systems, little is known about how soil nutrient heterogeneity affects the growth of invasive aquatic plants or their population structure. A greenhouse experiment was therefore conducted to study the response of the invasive aquatic plant Myriophyllum aquaticum to the spatial heterogeneity of soil nutrients under three plant densities (one, four, or twelve plants 0.28 m²) with a constant amount of soil nutrients. The results showed that soil nutrient heterogeneity significantly increased the number of shoots in the single-plant density treatment. However, heterogeneous soil nutrient treatment significantly increased the number of shoots at the expense of total biomass and aboveground biomass in the twelve-plant density treatment. The heterogeneous soil nutrient treatment had low effects on other growth traits and intraspecific competition under different plant density treatments. These results indicate that spatial heterogeneity in soil nutrient availability may facilitate the spread of M. aquaticum.
... Water hyacinth (Eichhornia crassipes (Mart.) Solms), is a tropical species belonging to the Pontederiaceae family (Ndimele et al., 2011;Gichuki et al., 2012;Marlin et al., 2013), free floating and rooted forms, perennial aquatic plant originated from Amazon river basin in South America (Sindhu et al., 2017), relies on asexual reproduction, vegetatively through the formation of stolons and also reproduced sexually through seeds (Adeyemi and Osubor, 2016;Yu et al., 2019). Rapid reproduction of water hyacinth making these weeds difficult to control. ...
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p>Batujai Reservoir locates in Batujai Village, Praya Barat, Central Lombok, West Nusa Tenggara. It is the primary source of irrigation water supply for agriculture in Central Lombok District with an area of around 3,235 ha. The problem is the bloom of water hyacinth weed ( Eichhornia crassipes ), which can cause reservoir water loss through evapotranspiration, affecting the amount of water reservoir available for the dry season. The objective was to identify the area of cover and estimate water loss through water hyacinth evapotranspiration for the period 2013 – 2017. This study used a descriptive method by analysis of secondary data which were meteorological data and landsat-8 satellite imagery. Evapotranspiration analyzes use CROPWAT 8.0, monitoring water hyacinth cover using landsat–8 satellite imagery processed using ENVI 5.3 and ArcGIS 10.4 software. The results show that the spatial distribution of water hyacinth can be detected and mapped accurately with an overall classification accuracy of 84.11% – 97.04% using Landsat 8 data, with a kappa coefficient of 0.80 – 0.96. The area of water hyacinth cover ranges from 38,400 m2 – 2,158,500 m2, with a cover area of more than 20%, causing water loss above 8,000 m3 day-1, which occurred in April 2013, April 2015, April 2016, February 2015, May 2014, May 2016 and July 2016, in those months it was seen that the amount of water loss was greater. Therefore, it is needed to suppress the growth of water hyacinth, in maintaining reservoir water storage capacity to support a systems of sustainable agriculture.</p
Article
Most aquatic plants applied to ecological restoration have demonstrated a clonal growth pattern. The risk-spreading strategy plays a crucial role in facilitating clonal plant growth under external environmental stresses via clonal integration. However, the effects of different concentrations of nanoplastics (NPs) on the growth traits of clonal aquatic plants are not well understood. Therefore, this study aimed to investigate the impact of NPs exposure on seedlings of parent plants and connected offspring ramets. A dose response experiment (0.1, 1, and 10 mg L–1) showed that the growth of Eichhornia crassipes (water hyacinth) was affected by 100 nm polystyrene nanoplastics after 28 days of exposure. Tracer analysis revealed that NPs are accumulated by parent plants and transferred to offspring ramets through stolon. Quantification analysis showed that when the parent plant was exposed to 10 mg L–1 NPs alone for 28 days, the offspring ramets contained approximately 13 ± 2 μg/g NPs. In the case of connected offspring ramets, leaf and root biomass decreased by 24%–51% and 32%–51%, respectively, when exposed to NP concentrations ranging from 0.1 to 10 mg L–1. Excessive enrichment of NPs had a detrimental effect on the photosynthetic system, decreasing the chlorophyll content and nonphotochemical quenching. An imbalance in the antioxidant defense systems, which were unable to cope with the oxidative stress caused by NP concentrations, further damaged various organs. The root system can take up NPs and then transfer them to the offspring through the stolon. Interference effects of NPs were observed in terms of root activity, metabolism, biofilm composition, and the plant’s ability to purify water. However, the risk-spreading strategy employed by parent plants (interconnected offspring ramets) offered some relief from NP-induced stress, as it increased their relative growth rate by 1 to 1.38 times compared to individual plants. These findings provide substantial evidence of the high NP enrichment capacity of E. crassipes for ecological remediation. Nevertheless, we must also remain aware of the environmental risk associated with the spread of NPs within the clonal system of E. crassipes, and contaminated cloned individuals need to be precisely removed in a timely manner to maintain normal functions.
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Glyphosate and microplastics are widely found in marine, terrestrial, and freshwater environments due to their globally widespread application. Further, they have proved to have specific ecotoxicity effects on aquatic plants. However, few studies have focused on the effects of small plastic particles and glyphosate, or especially, their combined effect on vascular plants in freshwater ecosystems. This study aimed to conduct a simulated greenhouse experiment to investigate the ecotoxicity of polystyrene microplastics and glyphosate on the floating plant Salvinia cucullata by exposure to fluorescent polystyrene microplastics (width, 1 μm; concentration, 3, 15, and 75 mg/L), glyphosate (5, 25, and 50 mg/L), and a mixture of the two (3 + 5, 15 + 25, and 75 + 50 mg/L) for seven days. Glyphosate significantly reduced the relative growth rate, photosynthetic capacity, and root activity of S. cucullata. Polystyrene microplastics did not significantly influence photosynthesis or leaf morphological characteristics but they significantly reduced relative growth rate and root activity in S. cucullata, indicating that the effects of microplastics on aquatic plants are potentially associated with different organs exposed to pollution. Polystyrene microplastics and glyphosate activated the plant antioxidant defense systems by increasing antioxidative enzyme activities including, superoxide dismutase, ascorbate peroxidase, and catalase to cope with oxidative stress. Synergistic effects (only observed in percent leaf yellowing) were observed when S. cucullata was exposed to a high concentrations (≥15 + 25 mg/L) of glyphosate and microplastics. Our results indicate that pervasive microplastics and herbicide contamination in freshwater may potentially affect the growth of aquatic plants.
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Invasive alien aquatic plant species (IAAPs) cause serious ecological and economic impact and are a major driver of changes in aquatic plant communities. Their invasive success is influenced by both abiotic and biotic factors. Here, we summarize the existing knowledge on the biology of 21 IAAPs (four free-floating species, eight sediment-rooted, emerged or floating-leaved species, and nine sediment-rooted, submerged species) to highlight traits that are linked to their invasive success. We focus on those traits which were documented as closely linked to plant invasions, including dispersal and growth patterns, allelopathy and herbivore defence. The traits are generally specific to the different growth forms of IAAPs. In general, the species show effective dispersal and spread mechanisms, even though sexual and vegetative spread differs strongly between species. Moreover, IAAPs show varying strategies to cope with the environment. The presented overview of traits of IAAPs will help to identify potential invasive alien aquatic plants. Further, the information provided is of interest for developing species-specific management strategies and effective prevention measures.
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The vegetative spread potential of aquatic plant species is largely based on the quantity of dispersed plant fragments (propagule pressure) and their potential for regrowth and establishment, i.e., fragment regeneration and colonization. In streams, fragment dispersal is of particular significance as the exposure of plants to flow facilitates fragmentation and downstream drift of fragments. We conducted field investigations to quantify the relevance of fragment dispersal and the species-specific propagule pressure due to fragmentation in five small to medium-sized German streams. These field surveys were combined with determination of the potential for regeneration/colonization of fragments collected in the field indicated by relative root formation under standardized conditions. In general, the number of drifting fragments tended to increase with larger stream size. We documented species-specific differences in fragmentation rate, which contributed to weak correlations between the number of drift units and specific plant cover within four streams. The overall likelihood for root formation increased significantly with increasing fragment size and was highest for the invasive Elodea nuttallii (70% of fragments). We conclude that the fragment dispersal capacity in streams is highly species-specific and that propagule pressure alone cannot explain the successful spread of invasive species like Myriophyllum heterophyllum.
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Premise of the study: Physiological integration between connected ramets is well known to increase performance of clonal plant species. However, no direct evidence appears to exist that integration can increase the ability of clonal species to compete with other species within mixed communities. We tested this hypothesis using two floating, invasive, aquatic species in which fragmentation-and thus extent of integration-is likely to vary between habitats and times. Methods: Individual ramets of Pistia stratiotes and Eichhornia crassipes were grown in monoculture or in mixture, and new stolons bearing new offspring were severed or left intact. After 6 wk, the numbers of offspring and second-generation (2°) offspring produced by each original ramet, or parent, were counted; and the final dry mass of each parent, its stolons, its offspring, and its 2° offspring were measured. Key results: Fragmentation decreased the relative competitive ability of Pistia, but not that of Eichhornia. This was mainly because Pistia accumulated ∼30% less dry mass of offspring when fragmented and grown with Eichhornia than in other treatments. Offspring of Pistia were smaller than those of Eichhornia in all treatments. Conclusions: Our results show that clonal integration can increase competitive ability in some clonal species. In this case, integration appeared to enable the small offspring of Pistia to compete more effectively with the large offspring of Eichhornia. Lower rates of fragmentation may select for production of more numerous, smaller vegetative offspring in clonal species.
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Many notorious invasive plants are clonal, living in heterogeneous or homogeneous habitats. To understand how clonal integration affects the performance of these plants in different habitat conditions, an 8-week greenhouse experiment was conducted: ramet pairs of A. philoxeroides were grown in two habitats, either heterogeneous or homogeneous in water availability, with the stolon connections either severed or kept intact. Under heterogeneous water availability, compared with ramets in homogeneous habitats, clonal integration significantly promoted the growth and photosynthetic performance of water-stressed apical ramets, whereas it only increased the photosynthetic performance but did not affect the growth of water-stressed basal ramets. Moreover, clonal integration markedly increased the root/shoot ratios of ramets grown in habitats with high water supply but decreased it under low water availability. Under homogeneous water availability, stolon connection (clonal integration) did not influence the growth, photosynthetic performance and biomass allocation of water-stressed ramets, but it significantly promoted the growth of well-watered ramets in both apical and basal sections. These findings deepen our understanding of the bidirectional and differentiated (mainly acropetal) clonal integration of A. philoxeroides, suggesting that the invasive plant A. philoxeroides can benefit from clonal integration in both heterogeneous and homogeneous habitats.
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Aims Foraging behavior was concerned less in plants especially for clonal aquatic species. The goal of this study was to test the foraging behavior and the function of phenotypic plasticity of a clonal submerged plant, Potamogeton maackianus A. Benn in variable manipulative environments. Methods To explore the foraging behavior of a clonal submerged plant, clones of P. maackianus were cultivated in variable environments of different substrate types and light conditions. We measured biomass, specific root area (SRA), specific root length (SRL), branching angle of the ramet, chlorophyll content of apical leaves (CCAL), Fv/Fm (Chlorophyll fluorescence parameter which indicates maximal photosystem II (PS II) efficiency) and biomass distribution in soil- and light-contrast treatments after harvest. Important findings We found that the atypical non-clonal-like foraging behavior homogenized the performance of the stoloniferous clonal species, P. maackianus in the measurement of biomass in our study. Substrate type had significant effects on most traits of P. maackianus, except on total biomass, shoot biomass distribution and chlorophyll content of apical leaves (CCAL). Patchy substrate mediated more root distribution into sand patch rather than into clay patch. Increase of specific root area (SRA), specific root length (SRL) and Fv/Fm might be adaptive to substrate heterogeneity. Moreover, substrate heterogeneity induced ‘sidewalk’- stolon lineage on the edge of sand patch along the patch border. Light condition only had significant effects on branching angle, shoot biomass distribution and Fv/Fm. Shade led to more shoot assignment in light-rich zone than in light-poor zone. P. maackianus adjusted the branching angle of ramet rather than clonal exploitation in heterogeneous substrates with patchy shade. Moreover, shade led to higher Fv/Fm. A compromising foraging strategy promoted P. maackianus to escape unfavorable environments. Phenotypic plasticity, which maximized the performance of P. maackianus in the measurement of biomass in variable environments, may explain its domination in some shallow lakes of the middle and lower reaches of Yangtze River.
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Eichhornia crassipes is a noxious weed and is cold sensitive. Water level treatments may affect its overwintering and regrowth capability during warming winter. To test this hypothesis, an experiment was conducted to analyze the effects of different water levels on the survival rates and regrowth of E. crassipes under experimental warm winter conditions. Three water levels were set up including drawdown with rooted, shallow submergence with rooted and floating. Regrowth characters including number of ramets, Fv/Fm, biomass and biomass allocation were surveyed. The results showed that warming significantly increased survival, ramet numbers and the biomass of plants. Warming also significantly increased Fv/Fm in drawdown plants. Water level only impacted plants under warming conditions. Compared to floating plants, drawdown significantly decreased survival but increased total biomass, while submergence led to 100 % survival, significantly higher ramet numbers and increased total biomass. In terms of biomass allocation, the effects of warming were similar for drawdown and submergence cases; it resulted in increased shoot biomass allocation and a lower root mass ratio. Warming only significantly increased the stem mass ratio of floating plants. Our findings suggested that warming help E. crassipes successfully overwinter and regrow during the next growing season. Drawdown or shallow submergence cannot effectively control this species but rather promotes its regrowth during warm winters. Thus, this species has the potential to spread with warm winters and frequent water level fluctuations caused by future climate change.
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Many notorious invasive plants are clonal, and clonal integration may improve their ability to cope with disturbances such as herbivory. We hypothesize that clonal integration positively affects the growth, physiology and biomass allocation of the invasive aquatic plant Eichhornia crassipes and thus improves its performance in response to defoliation. In a 7-week greenhouse experiment, we subjected E. crassipes ramets to three levels of experimental defoliation, i.e., 20 % (mild), 50 % (moderate) and 80 % (heavy) leaf clipping and an unclipped control, and the stolon connections to the mother plants were either severed or kept intact. Compared with the control, defoliation significantly decreased the growth (total biomass and ramet number), but increased the maximum quantum yield of photosystem II (F v/F m) and chlorophyll content of the target ramets. Stolon connection (clonal integration) greatly increased the growth, F v/F m and contents of non-structural carbohydrates (soluble sugar and total non-structural carbohydrates) of E. crassipes, and these effects were larger under heavier defoliation. Moreover, stolon connection significantly reduced the shoot/root ratio of E. crassipes ramets, and such effects were greater under heavier leaf clipping. These results support our hypothesis that E. crassipes can benefit from clonal integration in response to defoliation, suggesting that clonal integration may enhance the invasion potential of E. crassipes and potentially reduce the efficacy of biological control.
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Studies of clonal plant foraging generally focus on growth responses to patch quality once rooted. Here we explore the possibility of true plant foraging; the ability to detect and respond to patch resource status prior to rooting. Two greenhouse experiments were conducted to investigate the morphological changes that occur when individual daughter ramets of Fragaria vesca (woodland strawberry) were exposed to air above live (non-sterilized) or dead (sterilized) substrates. Contact between daughter ramets and substrate was prohibited. Daughter ramet root biomass was significantly larger over live versus dead substrate. Root:shoot ratio also increased over live substrate, a morphological response we interpret as indicative of active nutrient foraging. Daughter ramet root biomass was positively correlated with mother ramet size over live but not dead substrate. Given the choice between a live versus a dead substrate, primary stolons extended preferentially toward live substrates. We conclude that exposure to live substrate drives positive nutrient foraging responses in F. vesca. We propose that volatiles emitted from the substrates might be effecting the morphological changes that occur during true nutrient foraging.
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All around the globe, humans have greatly altered the abiotic and biotic environment with ever-increasing speed. One defining feature of the Anthropocene epoch is the erosion of biogeographical barriers by human-mediated dispersal of species into new regions, where they can naturalize and cause ecological, economic and social damage. So far, no comprehensive analysis of the global accumulation and exchange of alien plant species between continents has been performed, primarily because of a lack of data. Here we bridge this knowledge gap by using a unique global database on the occurrences of naturalized alien plant species in 481 mainland and 362 island regions. In total, 13,168 plant species, corresponding to 3.9% of the extant global vascular flora, or approximately the size of the native European flora, have become naturalized somewhere on the globe as a result of human activity. North America has accumulated the largest number of naturalized species, whereas the Pacific Islands show the fastest increase in species numbers with respect to their land area. Continents in the Northern Hemisphere have been the major donors of naturalized alien species to all other continents. Our results quantify for the first time the extent of plant naturalizations worldwide, and illustrate the urgent need for globally integrated efforts to control, manage and understand the spread of alien species.
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The distribution of the invasive aquatic plant Eichhornia crassipes is considered to be limited by winter survival. Therefore, winter warming, as well as characteristics of overwintering organs, are expected to affect its distribution and survival. An experiment was conducted to analyze the effects of winter warming and stem base treatments (size or burial) on winter survival, regrowth and thus performance of floating or rooted plants of E. crassipes using a simulated warming system in a greenhouse. Winter warming significantly increased the percentage survival in both forms of the plant and facilitated its regrowth and clonal propagation. Stem base size played an important role in determining survival, regrowth and vegetative propagation. Moreover, water cover and sediment burial of stem bases facilitated overwintering. After winter survival, a larger fraction of the biomass of E. crassipes was allocated to shoots. These results suggest that, with climate warming, the invasive ability of E. crassipes will be enhanced, with distribution spreading to the north into central and north China, favouring plants with large stem bases.
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Physiological integration between connected ramets can increase the performance of clonal plants when ramets experience contrasting levels of resource availabilities in heterogeneous environments. It has generally been shown or assumed that clonal integration has little effect on clonal performance in homogeneous environments. However, a conceptual model suggests that integration could increase performance in a homogeneous environment when connected ramets differ in uptake ability and external resource supply is high. We tested this hypothesis in a greenhouse experiment with the amphibious plant Alternanthera philoxeroides. Ramets in clonal fragments containing three rooted and two unrooted ramets were either left connected or divided into a basal part with two rooted ramets and an apical part with the other ramets. To simulate realistic, homogeneous environments of the species with different levels of resource supply, plants were grown at 0, 20, or 40 cm of water depth. Water depth had a positive effect on most measures of growth, indicating that resource supply increased with depth. Connection had negative to neutral effects on total growth of fragments at a water depth of 0 cm, and neutral to positive effects at 20- and 40-cm depths; effects on the apical part were generally positive and larger at greater depth; effects on the basal part were generally negative and smaller at greater depth. Results largely supported the hypothesis and further suggest that clonal integration of allocation and reproduction may modify benefits of resource sharing in homogeneous environments.
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Enhanced availability of photosynthates increases nitrogen (N) mineralization and nitrification in the rhizosphere via rhizodeposition from plant roots. Under heterogeneous light conditions, photosynthates supplied by exposed ramets may promote N assimilation in the rhizosphere of shaded, connected ramets. This study was conducted to test this hypothesis. Clonal fragments of the stoloniferous herb Glechoma longituba with two successive ramets were selected. Mother ramets were subjected to full sunlight and offspring ramets were subjected to 80 % shading, and the stolon between the two successive ramets was either severed or left intact. Measurements were taken of photosynthetic and growth parameters. The turnover of available soil N was determined together with the compostion of the rhizosphere microbial community. The microbial community composition in the rhizosphere of shaded offspring ramets was significantly altered by clonal integration. Positive effects of clonal integration were observed on NAGase activity, net soil N mineralization rate and net soil N nitrification rate. Increased leaf N and chlorophyll content as well as leaf N allocation to the photosynthetic machinery improved the photosynthetic capability of shaded offspring ramets when the stolon was left intact. Clonal integration improved the growth performance of shaded, connected offspring ramets and whole clonal fragments without any cost to the exposed mother ramets. Considerable differences in microbial community composition caused by clonal integration may facilitate N assimilation in the rhizosphere of shaded offspring ramets. Increased N content in the photosynthetic machinery may allow pre-acclimation to high light conditions for shaded offspring ramets, thus promoting opportunistic light capture. In accordance with the theory of the division of labour, it is suggested that clonal integration may ameliorate the carbon assimilation capacity of clonal plants, thus improving their fitness in temporally and spatially heterogeneous habitats. © The Author 2014. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com.
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1. To test whether clonal macrophytes can select favourable habitats in heterogeneous environments, clonal fragments of the stoloniferous submerged macrophyte Vallisneria spiralis were subjected to conditions in which light intensity and substratum nutrients were patchily distributed. The allocation of biomass accumulation and ramet production of clones to the different patches was examined. 2. The proportion of both biomass and ramet number of clones allocated to rich patches was significantly higher than in poor patches. The greatest values of both clone and leaf biomass were produced in the heterogeneous light treatment, in which clones originally grew from light‐rich to light‐poor patches, while clones produced the most offspring ramets in the treatments with heterogeneous substratum nutrients. Similarly, root biomass had the highest values in nutrient‐rich patches when clones grew from nutrient‐rich to nutrient‐poor patches. 3. The quality of patches in which parent ramets established significantly influenced the foraging pattern. When previously established in rich patches, a higher proportion of biomass was allocated to rich patches, whereas a higher proportion of ramet number was allocated to rich patches when previously established in poor patches. 4. Results demonstrate that the clonal macrophyte V. spiralis can exhibit foraging in submerged heterogeneous environments: when established under resource‐rich conditions V. spiralis remained in favourable patches, whereas if established in adverse conditions it could escape by allocating more ramets to favourable patches.
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Whole-plant energy capture depends not only on the photosynthetic response of individual leaves, but also on their integration into an effective canopy, and on the costs of producing and maintaining their photosynthetic capacity. This paper explores adaptation to irradiance level in this context, focusing on traits whose significance would be elusive if considered in terms of their impact at the leaf level alone. I review traditional approaches used to demonstrate or suggest adaptation to irradiance level, and outline three energetic tradeoffs likely to shape such adaptation, involving the economics of gas exchange, support, and biotic interactions. Recent models using these tradeoffs to account for trends in leaf nitrogen content, stornatal conductance, phyllotaxis, and defensive allocations in sun v. shade are evaluated. A re-evaluation of the classic study of acclimation of the photosynthetic light response in Atriplex, crucial to interpreting adaptation to irradiance in many traits, shows that it does not completely support the central dogma of adaptation to sun v. shade unless the results are analysed in terms of whole-plant energy capture. Calculations for Liriodendron show that the traditional light compensation point has little meaning for net carbon gain, and that the effective compensation point is profoundly influenced by the costs of night leaf respiration, leaf construction, and the construction of associated support and root tissue. The costs of support tissue are especially important, raising the effective compensation point by 140 µmol m⁻² s⁻¹ in trees 1 m tall, and by nearly 1350 µmol m⁻² s⁻¹ in trees 30 m tall. Effective compensation points give maximum tree heights as a function of irradiance, and shade tolerance as a function of tree height; calculations of maximum permissible height in Liriodendron correspond roughly with the height of the tallest known individual. Finally, new models for the evolution of canopy width/height ratio in response to irradiance and coverage within a tree stratum, and for the evolution of mottled leaves as a defensive measure in understory herbs, are outlined.
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Disturbance is common and can fragment clones of plants. Clonal fragmentation may affect the density and growth of ramets so that it could alter intraspecific competition. To test this hypothesis, we grew one (low density), five (medium density) or nine (high density) parent ramets of the floating invasive plant Pistia stratiotes in buckets, and newly produced offspring ramets were either severed (with fragmentation) or remained connected to parent ramets (no fragmentation). Increasing density reduced biomass of the whole clone (i.e. parent ramet plus its offspring ramets), showing intense intraspecific competition. Fragmentation decreased biomass of offspring ramets, but increased biomass of parent ramets and the whole clone, suggesting significant resource translocation from parent to offspring ramets when clones were not fragmented. There was no interaction effect of density x fragmentation on biomass of the whole clone, and fragmentation did not affect competition intensity index. We conclude that clonal fragmentation does not alter intraspecific competition between clones of P. stratiotes, but increases biomass production of the whole clone. Thus, fragmentation may contribute to its interspecific competitive ability and invasiveness, and intentional fragmentation should not be recommended as a measure to stop the rapid growth of this invasive species.
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Background and aims Plant root placement is highly plastic in order to acquire patchily distributed nutrients and to ensure their survival, growth and reproduction. Considering the spatial extension of clonal organs, we selected two clonal plants (Leymus chinensis (Trin.) Tzvel. and Hierochloe glabra Trin.) to determine the spatio-temporal effects of environmental heterogeneity on belowground organs and newly-born ramets. Methods Small-scale and multi-patch heterogeneous environments were manipulated by creating four patches filled with different types of soil in a same pot. The four patches were composed of sandy soil, sandy loam, loam soil and humus soil, respectively. Ramet number, bud number, mean spacer length, rhizome length, and biomass allocation within each patch were measured to identify plant foraging responses. Results The preferential patch of L. chinensis was humus soil patch which was the highest in nutrient availability, whereas H. glabra preferred to place ramets in sandy loam and loam soil patches. When growing in homogeneous environments, both species randomly rooted their offspring ramets in the four compartments. In heterogeneous environments, foraging responses were detected in ramet placement, aboveground biomass and total rhizome length. However, there were no differences in bud number or belowground biomass among four types of patches in heterogeneous environments, which might suggest that there would be no inter-patch differences in seedling establishment in the next year. Conclusions Plants show selective allocation of offspring ramets to preferential patches in the presence of multi-patch environmental heterogeneity. Responses of H. glabra to multi-patch heterogeneity were faster than those of L. chinensis, demonstrating that the foraging patterns are species-specific. Clonal plants can rapidly respond to environmental heterogeneity, whereas foraging responses are potentially reversible over a longer temporal scale.
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The Valsequillo reservoir, located near the city of Puebla, Mexico, is a hard-water eutrophic subtropical system, with minimum temperatures in winter (November–December), and marked dry-rain seasons with fluctuating depth. The reservoir has been infested with water hyacinth for over three decades. A management program involving the use of triturating machines was applied from December 1996 to February 1997. After trituration, remains were allowed to settle to the bottom. The purpose of this study was to monitor the changes in the water quality and the biological communities before and after physical control of weeds. A monthly sampling of surface water was performed at four stations one year before the treatment. After trituration, one year sampling was also carried out. Variables measured included temperature, Secchi disk transparency, depth, pH, dissolved oxygen, oxygen saturation, hardness, nitrate content, nitrite content, ammonia, orthophosphates, and numerical abundance of phytoplankton, zooplankton, and nekton.Weed control affected changes in all variables measured, as a result of residual decomposition of triturated matter. Secchi transparency and oxygen levels decreased and pH became slightly more alkaline. More important changes occurred for nutrients. Orthophosphate concentration increased, for nitrate and nitrite, increase was about 320% and 450% respectively. Ammonia reached lethal values for at least four months after trituration. As a result, phytoplankton decreased initially, and when it flourished again, the Bacillariophyta were replaced by Cyanophyta. Euglenophyta were important in both years. Of zooplankton, calanoids decreased, but cyclopoids and cladocerans maintained similar numbers, although the latter group changed in composition in that Ceriodaphnia was replaced by Moina. Fish disappeared from the system after weed trituration. In the second year a small recovery of water quality occurred, but water hyacinth also started to develop again. At present, Valsequillo is again covered by water hyacinth.
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Trembling aspen (Populus tremuloides Michx.) as a clonal tree species possesses a complex root system through which trees of the same or different clones are connected. Root connections have been studied with respect to resource sharing, but the nature, quantities or extent of what is shared between trees is relatively unknown. In this study, we posed the hypothesis that systemic defense induction signals could also spread through these root networks and trigger defenses in neighboring ramets before arrival of pests. Temporal expression pattern of Kunitz trypsin inhibitor (KTI) and dihydroflavonol reductase (DFR) genes, two markers of poplar defense, was followed by quantitative real-time polymerase chain reaction. The expression was quantified in systemic leaves of wounded and healthy plants that shared the same parental root and in untreated controls grown in separate pots. Untreated interconnected plants did not show induced resistance upon herbivore-simulated attack. Although wound-treated ramets induced defense genes, untreated interconnected plants produced an expression pattern similar to non-connected controls. Root connections do not automatically lead to induction of defensive traits that are expressed in plants directly under damage thought to simulate herbivory. Rather, it seems that other communication means such as airborne volatiles can serve as signal transmission pathways among neighboring plants.
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Availability of food and habitat complexity are two factors generally invoked to explain the high density of fish in vegetated habitats. The role of food resources (zooplankton) and habitat complexity (expressed by a vegetation structural index) in determining juvenile fish abundance and fish species richness in three morphologically contrasted macrophyte types (Sagittaria, Ceratophyllum and Nuphar) was studied for a large, lowland river. Our results showed that fish abundance increased with food availability, and was maximal for intermediate values of vegetation complexity. Food resources and vegetation complexity did not, however, explain the higher juvenile fish abundance observed in Sagittaria beds. We suggested that plant growth form, acting on fish foraging success and risk of predation, might influence patterns of juvenile fish distribution. Species-abundance relationships were similar among the three macrophyte types, but relationships between number of fish species (fish richness) and number of samples differed. Fish richness in terms of total number of fish species found at each sampling point showed the same pattern as for fish abundance: it increased with food availability and was highest at intermediate vegetation complexities. However, since both fish abundance and fish richness responded in the same manner to food availability and vegetation complexity, we were not able to distinguish statistically any effect for the specific fish richness formulated by the number of fish species per unit fish abundance. The current paradigm that structural complexity of vegetation provides a wider range of niches, increasing species diversity, was thus not verified. This finding indicates a simple species-abundance relationship (the passive sampling hypothesis), and suggests that no special mechanism acts directly on fish species richness.
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Resource sharing between ramets of clonal plants is a well-known phenomenon, which allows stoloniferous and rhizomatous species to internally translocate water, mineral nutrients and carbohydrates from sites of high supply to sites of high demand. The mechanisms and implications of resource integration in clonal plants have extensively been studied in the past. Vascular ramet connections are likely to provide an excellent means to share substances other than resources, such as systemic defence signals and pathogens. The aim of this paper is to propose the idea that physical ramet connections of clonal plants can be used (1) to transmit signals, which enable members of clonal plant networks to share information about their biotic and abiotic environments, and (2) to facilitate the internal distribution of systemic pathogens in clonal plant networks and populations. We will focus on possible mechanisms as well as on potential ecological and evolutionary implications of clonal integration beyond resource sharing. More specifically, we will explore the role of physiological integration in clonal plant networks for the systemic transmission of direct and indirect defence signals after localized herbivore attack. We propose that sharing defence induction signals among ramets may be the basis for an efficient early warning system, and it may allow for effective indirect defence signalling to herbivore enemies through a systemic release of volatiles from entire clonal fragments. In addition, we will examine the role of clonal integration for the internal spread of systemic pathogens and pathogen defence signals within clonal plants. Clonal plants may use developmental mechanisms such as increased flowering and clone fragmentation, but also specific biochemical defence strategies to fight pathogens. We propose that clonal plant networks can act as stores and vectors of diseases in plant populations and communities and that clonal life histories favour the evolution of pathogens with a low virulence.
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Non-marine aquatic vascular plants generally show broad distributional ranges. Climatic factors seem to have limited effects on their distributions, besides the determination of major disjunctions (tropical–temperate–subarctic). Dispersal should have been frequent enough to assure the quick colonisation of extensive areas following glacial retreat, but dispersal limitation is still apparent in areas separated by geographic barriers. Aquatic vascular plants also show limited taxonomic differentiation and low within-species genetic variation. Variation within populations is particularly low, but variation among populations seems to be relatively high, mainly due to the persistence of long-lived clones. Ecotypic differentiation is often related to factors that constrain clonal reproduction (salinity and ephemeral inundation). Inland aquatic habitats are heterogeneous environments, but this heterogeneity largely occurs at relatively small scales (within waterbodies and among neighbouring ones). They also represent a stressful environment for plants, characterised by low carbon availability, shaded conditions, sediment anoxia, mechanical damage by currents and waves, significant restrictions to sexual reproduction, and sometimes also osmotic stress and limited nutrient supply. I propose that the generality of broad distributions and low differentiation among the inland aquatic flora is best explained by a combination of: (1) selection for stress-tolerant taxa with broad tolerance ranges. (2) The selective advantages provided by clonal growth and multiplication, which increases plant tolerance to stress, genet survivorship and population viability. (3) Long-distance dispersal of sexual propagules and high local dispersal of asexual clones. (4) The generality of broad plastic responses, promoted by the combination of clonal growth, high local dispersal, small-scale spatial heterogeneity and temporal variability.
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Examines the features of the surface-floating plant regime, the adaptations of the plants to survive and proliferate in the habitat, and the nature and extent of problems caused by floating aquatic plants in Africa. -from Author
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Clonal integration plays an important role in clonal plant adapting to heterogeneous habitats. It was postulated that clonal integration could exhibit positive effects on nitrogen cycling in the rhizosphere of clonal plant subjected to heterogeneous light conditions. An in-situ experiment was conducted using clonal fragments of Phyllostachys bissetii with two successive ramets. Shading treatments were applied to offspring or mother ramets, respectively, whereas counterparts were treated to full sunlight. Rhizomes between two successive ramets were either severed or connected. Extracellular enzyme activities and nitrogen turnover were measured, as well as soil properties. Abundance of functional genes (archaeal or bacterial amoA, nifH) in the rhizosphere of shaded, offspring or mother ramets were determined using quantitative polymerase chain reaction. Carbon or nitrogen availabilities were significantly influenced by clonal integration in the rhizosphere of shaded ramets. Clonal integration significantly increased extracellular enzyme activities and abundance of functional genes in the rhizosphere of shaded ramets. When rhizomes were connected, higher nitrogen turnover (nitrogen mineralization or nitrification rates) was exhibited in the rhizosphere of shaded offspring ramets. However, nitrogen turnover was significantly decreased by clonal integration in the rhizosphere of shaded mother ramets. Path analysis indicated that nitrogen turnover in the rhizosphere of shaded, offspring or mother ramets were primarily driven by the response of soil microorganisms to dissolved organic carbon or nitrogen. This unique in-situ experiment provided insights into the mechanism of nutrient recycling mediated by clonal integration. It was suggested that effects of clonal integration on the rhizosphere microbial processes were dependent on direction of photosynthates transport in clonal plant subjected to heterogeneous light conditions.
Article
Ramets of some clonal plant species alter their internode lengths or their frequency of lateral branching in response to their immediate microenvironment. Such “plant foraging” responses are thought to allow clones to concentrate in favorable portions of their environment. Despite widespread interest among ecologists in plant foraging, few realistic models have been developed to examine conditions under which plant foraging responses are likely to provide clones with ecological benefit. In this paper, we develop spatially explicit, stochastic simulation models to examine consequences of both empirical and hypothetical plant foraging responses. We construct a hierarchical series of models in which we incorporate effects of resource heterogeneity on spacer lengths, angles of growth, and lateral branch production. We also vary the number, size, and arrangement of patches, and the presence or absence of ramet mortality. Simulations based on hypothetical data demonstrated the potential importance of shortening spacer lengths in favorable habitat. In these simulations, ramet crowding increased significantly, implying a potential cost to plant foraging responses whose magnitude is large enough to cause ramets to concentrate in favorable patches. Models calibrated with empirical data suggest that when clonal plants were able to concentrate in favorable habitat, this was usually caused by increased daughter ramet production in the favorable habitat. Variation in clonal growth angles had little impact on the ability of ramets or clones to locate favorable patches, but did increase the ability of clones to remain in favorable patches once found. Alterations in the number and size of patches strongly influenced the effectiveness of the foraging response. The spatial arrangement of patches also was important: clumped distributions of patches decreased the success with which plants located favorable patches, especially at the genet level and when the number of patches was low. Finally, when ramet mortality varied with patch quality, there was an increase in the percentage of ramets located in favorable patches; differential ramet mortality also lessened the impact of other effects, such as the decreased success of clones when patches are clumped. Overall, our models indicate that the effectiveness of plant foraging responses is variable and is likely to depend on a suite of environmental conditions.
Article
 What confers invasive alien plants a competitive advantage over native plants remains open to debate. Many of the world’s worst invasive alien plants are clonal and able to share resources within clones (clonal integration), particularly in heterogeneous environments. Here, we tested the hypothesis that clonal integration benefits invasive clonal plants more than natives and thus confers invasives a competitive advantage.  We selected five congeneric and naturally co-occurring pairs of invasive alien and native clonal plants in China, and grew pairs of connected and disconnected ramets under heterogeneous light, soil nutrient and water conditions that are commonly encountered by alien plants during their invasion into new areas.  Clonal integration increased biomass of all plants in all three heterogeneous resource environments. However, invasive plants benefited more from clonal integration than natives. Consequently, invasive plants produced more biomass than natives.  Our results indicate that clonal integration may confer invasive alien clonal plants a competitive advantage over natives. Therefore, differences in the ability of clonal integration could potentially explain, at least partly, the invasion success of alien clonal plants in areas where resources are heterogeneously distributed.
Article
Many naturalized non-native plants pose ecological and economic threats. A quantitative analysis of the global distribution of naturalized plants confirms some anticipated trends and exposes new patterns. See Letter P.100
Article
1. The economic principle of spatial division of labour comprises two basic features, specialization in the performance of specific tasks and close co-operation by potentially independent, spatially separated subunits of a higher-level organizational system. Space-economic theory predicts large benefits from such a spatial division of labour if essential resources are heterogeneously distributed and if high-availability zones for these resources do not spatially coincide. In this paper, evidence is provided that a spatial division of labour may also occur in clonal plants growing in spatially heterogeneous environments. 2. Clonal fragments of the stoloniferous herb Trifolium repens L., consisting of two interconnected groups of ramets, were exposed to contrasting levels of light and water supply. Ramet groups specialized morphologically in the uptake of the locally most abundant resource and they exchanged both water and assimilates. This division of labour significantly increased the performance of the entire plant in terms of fitness-related traits such as biomass and clonal offspring production. 3. It is concluded that spatial division of labour may contribute to the apparent success of clonal plant species in many natural habitats by enabling them to efficiently exploit environmental patchiness. The implications of these results for the understanding of foraging strategies of clonal plants and the general notion of habitat heterogeneity in plant ecology are discussed.
Article
Many notorious alien invasive plants have the capacity for vigorous clonal growth, and clonal integration may contribute to their invasiveness in response to various disturbances. Here, it is hypothesized that clonal integration affects the growth, biomass allocation, physiology, and compensatory response of the alien invasive clonal plant Alternanthera philoxeroides when faced with defoliation. To test these hypotheses, a growth experiment was conducted to investigate the effect of clonal integration on the responses of A. philoxeroides to different levels of defoliation. Daughter ramets that had been grown with stolon connections that were either severed from or connected to the mother plant were subjected to four defoliation levels: 0 (control), 30% (mild), 60% (moderate) and 90% (heavy) removal of leaf tissue. Defoliation greatly decreased growth (total biomass, number of ramets and total stolon length) but increased the maximum quantum yield of photosystem II (Fv/Fm) of daughter ramets. Clonal integration significantly increased growth, Fv/Fm and contents of non-structural carbohydrates (soluble sugars and total non-structural carbohydrates) of A. philoxeroides, and these effects were larger under heavier defoliation. Moreover, clonal integration markedly reduced the shoot/root ratio of A. philoxeroides, and these effects tended to increase with increasing levels of defoliation. These results support our hypothesis that A. philoxeroides benefits from clonal integration in response to defoliation, suggesting that clonal integration may be closely related to the invasiveness of A. philoxeroides in natural habitats with frequent disturbances.
Article
Alternanthera philoxeroides (Mart.) Griseb. is one of many aggressive invasive plants that can grow in diverse habitats. Aquatic A. philoxeroides forms dense floating mats over the water surface. However, when water levels decrease during winter, some mats become stranded on exposed sediments and are thus exposed to air. Do the stems of these mats possess the capacity to develop new shoots during the next growing season? In this study, we examined the sprouting of sediment-stranded over-wintering mats of A. philoxeroides. Stems of the over-wintering mats were divided into three types (dry, withered, and fresh stems) depending on moisture content and were immersed in water for 4 weeks to observe the sprouting of axillary buds and roots. The results showed that withered stems yielded much more biomass than dry or fresh stems. Stem moisture content significantly affected the sprouting rate and the length growth rate of buds and roots. Dry stems lacked reproductive capacity. The sprouting rate and length growth rate of the buds and roots were higher in fresh stems than in withered stems. Furthermore, the mean values of the bud sprouting rate and the bud length growth rate were highest during the first week, i.e., most of buds sprouted within 1 week or less. Our results suggest that more than 70% (on a dry weight basis) of the stems in stranded mats possessed rapid sprouting capacity even after over-wintering on the sediment for more than 2 months. This strategy may be an adaptation to the fluctuations inherent in many aquatic habitats, and it possibly explains why A. philoxeroides can flourish even after a dry winter.
Article
1. Clonal plants benefit from the ability to translocate resources among interconnected ramets to colonize heterogeneous habitats. Clonal integration affects the resource level and morphological traits of ramets, and thus may influence their physiology and general performance. Although leaf gas exchange and its associated physiological adjustments are key traits to assess plant fitness, the effect of clonal integration on these functional traits is insufficiently understood. 2. In a glasshouse experiment, we addressed how clonal integration affects gas exchange properties, leaf characters and growth of ramets in two invasive plants, Alternanthera philoxeroides and Phyla canescens, under full sun and 85% shade. We also used stable-isotope labelling to assess the maternal subsidy to daughter ramets. 3. Similar effects of connection were observed in both species for most gas exchange parameters and leaf characters. Clonal integration did not affect photosynthetic capacity and respiratory rates of ramets. When grown in shade, ramets connected with an unshaded mother plant displayed higher area-based leaf nitrogen and chlorophyll content than severed ramets, but the additional nitrogen and chlorophyll was not translated to increased photosynthetic capability. Overall, severed ramets displayed significant light response for leaf nitrogen (area-based), photosynthetic nitrogen use efficiency, chlorophyll to nitrogen ratio, and nitrogen stable-isotope signature, but the light response was eliminated by clonal integration in connected ramets. 4. Both species displayed substantial maternal carbohydrate subsidy that benefited the growth of daughter ramets, but species-specific patterns were observed in the growth of daughter ramets and the amount of subsidy. The amount of subsidy was independent of ramet growth light levels for P. canescens, but shaded, connected ramets of A. philoxeroides received more subsidy than unshaded controls, facilitating a larger growth improvement relative to severed counterparts than P. canescens. 5. Synthesis. We observed increased leaf nitrogen and chlorophyll in shaded, connected ramets of two clonal invasive plants. Clonal integration may facilitate nitrogen assimilation and allow pre-acclimation to high-light conditions for shaded, connected ramets, thus promoting the opportunistic expansion of these invaders on site scale. The species-specific maternal subsidy pattern demonstrated that clonal plants possess different strategies to subsidize ramets under light-limited conditions.
Article
Summary • Clonal integration in plants can improve their ability to cope with habitat heterogeneity. Integration may increase in response to damage, such as herbivore attack, if undamaged ramets support damaged ones. To test this, we studied the effects of apex removal and substantial defoliation on the performance of the clonal perennial herb Linaria vulgaris Mill. in a common-garden growth experiment and a 13C-labelling study. • In the growth experiment, contrary to expectations, the target ramet could compensate for damage better when the other ramets in the clone were also damaged, indicating within-clone competition for resources rather than support to damaged ramets. • In the 13C-labelling experiment, 5·7% of the label moved to a neighbour ramet in controls. Apex removal resulted in a negative net translocation of 13C in the damaged ramet, but defoliation led to zero net translocation. • The observed lack of support to damaged ramets in Linaria suggests that plasticity of clonal integration in this species includes competition between sibling ramets. Although young ramets may be supported, resources are not directed towards a single damaged ramet if there are more viable intact ramets in the clone. Our main results are consistent with the notion that resource allocation among ramets depends on their relative value in terms of expected fitness profits in heterogeneous environments. Functional Ecology (2006) 20, 413–420 doi: 10.1111/j.1365-2435.2006.01115.x
Article
Lake Chilwa (Malawi) is a shallow tropical lake surrounded by an extensive zone of littoral swamp mainly composed of Typha domingensis. The data produced show that the physical and chemical conditions are different and more varied in the littoral region when compared with the open lake. Primary production in the littoral is confined almost entirely to Typha domingensis, which also acts as a nutrient pump by absorbing nutrients from the soils and eventually releasing them into the lake waters. Long term and short term exchanges in organic and inorganic materials between the littoral swamps and the open lake are described. These, as well as available evidence on the distribution, reproductive habits and diet of certain faunal groups, indicate that the littoral region of Lake Chilwa has an important regulating influence on the functioning of the whole lake.
Article
1. Water hyacinth (Eichhornia crassipes) is one of the world’s most invasive aquatic plants and is known to cause significant ecological and socio-economic effects. 2. Water hyacinth can alter water clarity and decrease phytoplankton production, dissolved oxygen, nitrogen, phosphorous, heavy metals and concentrations of other contaminants. 3. The effects of water hyacinth on ecological communities appear to be largely nonlinear. Abundance and diversity of aquatic invertebrates generally increase in response to increased habitat heterogeneity and structural complexity provided by water hyacinth but decrease due to decreased phytoplankton (food) availability. 4. Effects of water hyacinth on fish are largely dependent on original community composition and food-web structure. A more diverse and abundant epiphytic invertebrate community may increase fish abundance and diversity, but a decrease in phytoplankton may decrease dissolved oxygen concentrations and planktivorous fish abundance, subsequently affecting higher trophic levels. 5. Little is known about the effects of water hyacinth on waterbird communities; however, increases in macroinvertebrate and fish abundance and diversity suggest a potentially positive interaction with waterbirds when water hyacinth is at moderate density. 6. The socio-economic effects of water hyacinth are dependent on the extent of the invasion, the uses of the impacted waterbody, control methods and the response to control efforts. Ecosystem-level research programmes that simultaneously monitor the effects of water hyacinth on multiple trophic-levels are needed to further our understanding of invasive species.
Article
Herbaceous species possess several mechanisms to compensate for tissue loss. For clonal herbaceous species, clonal integration may be an additional mechanism. This may especially hold true when tissue loss is very high, because other compensatory mechanisms may be insufficient. On inland dunes in northern China, we subjected Bromus ircutensis and Psammochloa villosa ramets within 0.5 m×0.5 m plots to three clipping treatments, i.e., no clipping, moderate (50% shoot removal) and heavy clipping (90% shoot removal), and kept rhizomes at the plot edges connected or disconnected. Moderate clipping did not reduce ramet, leaf or biomass density of either species. Under moderate clipping, rhizome connection significantly improved the performance of Psammochloa, but not that of Bromus. Heavy clipping reduced ramet, leaf and biomass density in the disconnected plots of both species, but such negative effects were negated or greatly ameliorated when the rhizomes were connected. Therefore, clonal integration contributed greatly to the compensatory growth of both species. The results suggest that clonal integration is an additional compensatory mechanism for clonal plants and may be important for their long-term persistence in the heavily grazed regions in northern China.
Article
The Laurentian Great Lakes have been successfully invaded by at least 182 nonindigenous species. Here we report on two new species, water hyacinth Eichhornia crassipes and water lettuce Pistia stratiotes, that were found at a number of locations in Lake St. Clair and Detroit River during autumn 2010. Both species are commonly sold in the water garden and aquarium trade in southern Ontario and elsewhere. While it is not clear whether these species are established or can establish in the Great Lakes, the historic assumption that neither of these subtropical to tropical plants pose an invasion risk must be questioned in the light of changing environmental conditions associated with climate warming that may render Great Lakes' habitats more suitable for these species and increase the likelihood of their successful establishment.
Article
Different views exist as to what traits will lead to dominance when plants compete for light. One view is that taller plants with better relative positions in the canopy will exclude shorter plants because they intercept almost all light and thus can achieve a higher carbon gain. Alternatively, resource competition models predict that plants that are capable of positive net photosynthesis at the lowest light level will win. In a 5‐year‐old dense competition experiment with 10 genotypes of the clonal plant Potentilla reptans , both these views were tested to see if either of them could explain the dominance of one of the genotypes, or the possible coexistence of several others. Using a combination of measured morphological and physiological traits, a canopy model was constructed to calculate whole‐shoot daily photosynthetic rates of the genotypes in the different layers of the canopy in relation to the invested mass. Results show that the dominant genotype exhibited characteristics of relative shade tolerance: low rates of light‐saturated photosynthesis and respiration. This resulted in a calculated daily carbon gain at the bottom of the canopy, where other genotypes could not achieve that. However, the dominant genotype did not have the highest photosynthetic rates throughout the whole canopy. Some genotypes that persisted in the stand in coexistence with the dominant one achieved greater daily carbon gain at the top of the canopy. Synthesis . The dominant genotype had characteristics similar to those predicted by resource competition models such as the ability to have positive growth at lower light levels. The persistence of several other genotypes, in contrast, may be explained by traits that allowed them to achieve higher carbon gains at the top of the canopy. This suggests that the light gradient formed by the plants themselves creates enough heterogeneity for strategies for dealing with different light requirements to coexist, even within a single species.
Article
1Carex arenaria forms large clonal fragments (up to 12 m long) in environments in which soil-bound resources limit growth. 2 We hypothesized that extensive integration of C. arenaria would facilitate the exploitation of scarce and patchily distributed soil resources and that the continued functioning of old roots would enable exploitation of resources that are temporally variable. 3 We used labelling with 14C and acid fuchsin to study the degree and extent of physiological integration and root function of intact clonal systems of C. arenaria in a sand dune area in south Sweden. 4 The uptake and translocation of dye suggests that old roots remain capable of taking up water and nutrients, in contrast with negative reports from previous studies. Water was translocated both acropetally and basipetally. 5 Thirty per cent of the assimilated carbon was found to be translocated towards the growing apex. Smaller, but significant, amounts of carbon were translocated basipetally throughout the fragments (17–74 ramet generations). 6 The results are discussed in terms of the source–sink relations of large clonal systems in the field. The translocation patterns are considered in relation to soil moisture and nutrient availability.
Article
Plant canopy shade reduces photosynthetic photon flux density (PPFD) and ratio of red to far-red light (z). Both effects can cause plants to increase potential for light acquisition through vertical growth and leaf area expansion. Clonal plants such as Eichhornia crassipes might alternatively increase light interception via horizontal growth of stolons or rhizomes and placement of new ramets in less shaded microsites. Effect of simulated canopy shade and component effects of PPFD and z were tested by filtering or adding light uniformly, to a whole group of connected ramets, or locally, to individual ramets within a group. In uniform treatments, low PPFD reduced total growth but low z did not. Low PPFD and low z independently reduced stolon and ramet production and caused etiolation of petioles; effect of low PPFD plus low z on ramet production was greater than that of either factor alone. Lateral clonal growth thus did not seem to be a response to uniform shading; instead, uniformly low PPFD or low z increased partitioning to established ramets. Low z changed partitioning without changing total growth. In local treatments, reduction of growth of individual ramets due to low PPFD and inhibition of new ramet production attributable to spectral composition of light were mitigated when connected ramets were unshaded; plants may respond differently to patchy than to uniform shade.
Article
In plants, only species with clonal growth are able to directly transfer resources between otherwise independent units of the same genetic individual. A simple conceptual model of plant performance as a function of internal resource supply and environmental resource availability suggests that resource sharing between ramets within clones is likely to be disadvantageous in uniform habitats and advantageous in patchy ones. It was therefore hypothesized that clones in populations from relatively uniform habitats will have been selected for low rates of resource sharing between ramets compared to clones in populations from patchier habitats. In coastal northern California, the clonal herb Fragaria chiloensis is common both in grasslands, where resources are relatively uniform, and on sand dunes, where resources are more patchy. It was predicted that clones from a grassland population of Fragaria would have “selfish” ramets with low rates of resource sharing compared to clones from an adjacent dune population. Ramets were subjected to contrasting light levels with and without connection between ramets. Patterns of biomass accumulation were consistent with the prediction. This appears to be the first report of genetically based variation in patterns of resource sharing in clonal plants. It supports the idea that these patterns are locally selected to increase plant performance in habitats with different patterns of resource availability.
Article
Interconnected ramets of the submersed macrophyte Vallisneria spiralis were subjected to two homogeneous treatments (shading or not shading whole plants) and two heterogeneous treatments (only shading basal or apical ramets of plants). The benefits and costs of clonal integration between connected ramets grown in heterogeneous treatments were examined. Results showed that shading apical ramets induced significant benefits to the performance of whole plant in terms of dry weight per plant (P < 0.01) and number of ramets per plant (P < 0.05). Especially for the unshaded basal ramets, their dry weight, number of ramets, number of branches and total stolon length were 89%, 30%, 29% and 58% higher than the corresponding ramets in homogeneous treatment, respectively. Compared to their controls in homogeneous treatments, unshaded basal ramets produced more leaf mass (0.15 g versus 0.11 g) whereas shaded apical ramets produced more root mass (0.012 g versus 0.008 g). However, there was a different pattern of integration when basal ramets were shaded. Shading basal ramets led to a significant decrease in stolon growth, but the individual performance of shaded ramets improved. Cost-benefit analyses revealed that dry weight per ramet of basal shaded ramets was 31% greater than that of basal shaded ramets in the homogeneous treatment. We can conclude that V. spiralis can benefit from clonal integration in heterogeneous light environments, but that the scale of these benefits is related to the quality of light environments where the clone become established.
Article
Above- and below-ground clonal growth architecture was compared for two neighbouring patches of Potamogeton perfoliatus L. in Lake Constance, representing typical sparse and dense growth types. A detailed map of individual ramets and their corresponding rhizome network was produced and the seasonal development of ramet sprouting and rhizome growth was reconstructed. Rhizomes extended at rates ranging between 40 and 63 cm per year, and added a new shoot for every 1–20 cm of rhizome produced. The main rhizome axis grew in a semi-linear fashion, with deviation means of 15 and 24°, and developed 0–0.5 branches per plant, with an insertion angle from 15–90°. Total rhizome length of all plants amounted to 5 and 11 m m−2 at the two sites. The total biomass produced at the two sites differed by 10-fold. The neighboring patches also showed different allocation patterns which are interpreted as foraging.Contrary to the prediction of the foraging hypothesis, there was only a small difference in mean spacer length between sites. On the other hand, the spacer length was plastic relatively to total biomass. We propose that spacer length is not an independent part of the foraging strategy, but rather a result of overall productivity and biomass allocation. Phosphorus content of plant tissue at the more productive site was two-fold higher than that at the less productive site which suggests that the different growth types may be due to differences in sediment nutrient availability: in situ fertilization of a less productive site increased the P content to those levels of the productive site. In situ fertilization also resulted in higher ramification, lower root allocation and decreased spacer length and confirmed the foraging capability of P. perfoliatus.
Article
Light gradients are ubiquitous in nature, so all plants are exposed to some degree of shade during their lifetime. The minimum light required for survival, shade tolerance, is a crucial life-history trait that plays a major role in plant community dynamics. There is consensus on the suites of traits that influence shade tolerance, but debate over the relative importance of traits maximizing photosynthetic carbon gain in low light versus those minimizing losses. Shade tolerance is influenced by plant ontogeny and by numerous biotic and abiotic factors. Although phenotypic plasticity tends to be low in shade-tolerant species (e.g., scant elongation in low light), plasticity for certain traits, particularly for morphological features optimizing light capture, can be high. Understanding differential competitive potentials among co-occurring species mediated by shade tolerance is critical to predict ecosystem responses to global change drivers such as elevated CO2, climate change and the spread of invasive species.
Article
Vegetative multiplication allows clonal systems to spread horizontally and to establish (descendents) ramets in sites of contrasting resource status. Stolon or rhizome connections between ramets permit the transport of resources within the clone. As a result of such physiological integration, clones can act as cooperative systems, enabling buffering of any differences in resource supply among ramets due to local heterogeneity. This study tests the hypothesis that parent ramets of Fragaria vesca L. enhance their photosynthetic activity when connected to shaded or drought-stressed offspring ramets as result of the assimilate demand from those ramets. The study also investigated the extent to which small-scale topographic heterogeneity (i.e. offspring ramets at higher or lower level than parents) may influence the physiological integration, in terms of photosynthetic efficiencies, biomass and production of new ramets. Results showed that the photosynthetic efficiencies of parent ramets were increased in response to the assimilate demand made by drought-stressed offspring ramets, especially under shade conditions. We attribute this response to a mechanism of feed-back regulation in line with the source–sink hypothesis. We also found that offspring ramets at a raised topographic position with respect to parents showed a significant decline in the production of new ramets and a reduction in total biomass relative to offspring at a lower level or the same level. We conclude that microtopographic aspects of environmental heterogeneity may involve additional costs for ramet establishment of ramets.
Article
1) Unlike non-clonal plants, clonal plants can develop a division of labour in which connected ramets specialize to acquire different, locally abundant resources. This occurs as a plastic response to a patchy environment where two resources tend not to occur together and different ramets experience high availabilities of different resources. We hypothesized that if division of labour is an important advantage of clonal growth in such environments in nature, then clones from habitats where resource availabilities are negatively associated should show a greater capacity for division of labour than clones from habitats where resource availabilities are more uniform. 2) To test this, we collected clones of Fragaria chiloensis from sand dune and grassland sites in each of three regions of the central coast of California, grew pairs of connected or severed ramets under low light and high N or under high light and low N, and measured leaf area, chlorophyll content and final dry mass. Given that previous work has indicated that high availabilities of light and N show a stronger tendency not to occur together in the dune than in the grassland sites, we expected that clones from dunes would show greater capacity for division of labour than clones from grasslands. 3) Clones from dunes showed a greater capacity than clones from grasslands to specialize for acquisition of abundant N via high proportional mass of roots. Clones from the two types of habitats showed similar capacity to specialize for acquisition of abundant light via high leaf area and chlorophyll content of leaves. Specialization via leaf area and chlorophyll content took place mainly within the first half of the 60-day experiment. 4) These results provide evidence that division of labour in a clonal plant has been selected for in natural habitats where high levels of different resources tend to be spatially separated. Results also show that division of labour can occur, not just via allocation of mass, but also via physiological traits, and that both morphological and physiological specialization can take place within a few weeks. 5) Clonal plants dominate many habitats and include many highly invasive species. Division of labour is one of the most striking potential advantages of clonal growth, and is a remarkable instance of phenotypic plasticity in plants. This study further suggests that division of labour in clonal plants is an instance of adaptive plasticity and could therefore play a part in their widespread ecological success.
Article
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 15N 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.