Clonal Fragments Research Articles

Does clonal fragmentation of the floating plant Eichhornia crassipes affect the growth of submerged macrophyte communities?

Few studies have tested the effect of clonal fragmentation at the community level. Floating plants and submerged macrophytes can coexist, and the presence of floating plants may greatly restrict the growth of submerged macrophyte communities. Clones of floating plants are frequently fragmented by disturbance, but little is known about how clonal fragmentation of floating plants affects the growth of submerged macrophyte communities and whether such effect depends on the intensity (frequency) of fragmentation. We assembled experimental aquatic communities consisting of four submerged macrophytes (Hydrilla verticillata, Ceratophyllum demersum, Chara fragilis and Myriophyllum spicatum), and grew them without the floating plant Eichhornia crassipes, with an intact clone of E. crassipes, or with a clone fragmented every 5, 10 or 15 days. Clonal fragmentation, irrespective of the frequency, did not significantly affect the growth of the floating plant. Consequently, it did not significantly affect the growth of the submerged macrophyte community or that of each of the four submerge macrophytes. However, compared to the treatment without E. crassipes, the presence of E. crassipes significantly decreased the biomass of the macrophyte community because it greatly decreased the biomass of the most abundant species H. verticillata. Therefore, the presence of floating plants can influence the establishment of submerged macrophyte communities, but clonal fragmentation of floating plants may not. To restore submerged macrophyte communities, measures should be taken to restrict the spread of floating plants, and breaking clones of floating plants may not be an effective measure.

Growth strategies of an abundant reef-building coral in the southern Caribbean (Undaria tenuifolia)

The Caribbean coral community structure is changing, particularly species dominance. The Acropora die-off, at many southern and western Caribbean reefs, has allowed the branching scleractinian coral Undaria tenuifolia Dana to become one of the dominant species in these shallow reefs. In this study, colonies of U. tenuifolia were followed for a year using digital imagery. We developed a size class model that allowed us to estimate population fluctuation and growth strategies (colony growth rates and clonal processes). Growth rates varied with colony size; mid-sized colonies doubled their size in a year, while larger colonies often undergo fission. The clonal strategies, i.e., fusion and fission, allow U. tenuifolia to compensate for the low survival rates of early larval post-settlement thus being able to become a dominant coral species in the current reef scenario. The size matrix model formulated on the basis of a relative colony growth rate offered a practical approach for a short-term observation situation, generating a time- invariant transition model. Mortality patterns were not correlated to size classes and were variable by location and time. Overall, population abundance was stable over the monitored period of time. The high survivorship of U. tenuifolia after clonal fragmentation, as well as its high growth rate, suggests that this is a potential species to be cultured, which could be a solution given that this species has become the most common coral being extracted and sold as a souvenir in Cartagena, Colombia.

Does clonal resource translocation relate to invasiveness of Typha taxa? Results from a common garden experiment

Plant species traits such as leaf and seed characteristics are increasingly used to understand drivers of species dominance and invasiveness. Because many plants are clonal, traits that influence the connectivity of clonal ramets might also be important in community assembly, species dominance, and invasion. We investigated the resource translocation (both amount of translocation and translocation distance) in three different native and non-native cattail (Typha) taxa that differ in their invasiveness by varying the initial amount of maternal resources available to clonal fragments and measuring their growth response in a field experiment. We found the non-native invasive taxa Typha angustifolia and Typha x glauca responded most strongly to increased maternal resource availability, and grew significantly more than the native Typha latifolia. T. angustifolia translocated resources to the largest number of daughter ramets, while T. latifolia translocated resources to the fewest and their hybrid (T. x glauca) was intermediate. These results are consistent with the hypothesis that resource translocation confers advantages for invasion and that the invasiveness of Typha taxa is related to clonal traits. Future studies and meta-analyses relating invasiveness to plant traits should consider clonal traits in addition to leaf and seed traits.

Clonal integration in homogeneous environments increases performance of Alternanthera philoxeroides.

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.

Clonality strongly affects the spatial genetic structure of the nurse speciesAechmea nudicaulis(L.) Griseb. (Bromeliaceae)

Aechmea nudicaulis is a clonal bromeliad common to the Brazilian Atlantic forest complex and is found abundantly in the sandy coastal plain vegetation (restinga) on the north coast of Rio de Janeiro state, Brazil. This restinga site is structured in vegetation islands, and the species plays a key role as a nurse plant, much favoured by its clonality. We studied the clonal structure and consequences of clonality on the population spatial genetic structure (SGS) of this species using six nuclear microsatellites. Spatial autocorrelation analysis was performed to study the effects of sexual and clonal reproduction on the dispersal of A. nudicaulis. Analyses were performed at the genet (i.e. excluding clonal repeats) and ramet levels. Genotypic richness was moderate (R = 0.32), mostly as a result of the dominance of a few clones. The spatial distribution of genets was moderately intermingled, the mean clone size was 4.9 clonal fragments per genet and the maximum clonal spread was 25 m. Expected heterozygosities were high and comparable with those found in other clonal plants. SGS analyses at the genet level revealed significantly restricted gene dispersal (Sp = 0.074), a strong SGS compared with other herbaceous species. The clonal subrange extended across 23 m where clonality had a significant effect on SGS. The restricted dispersal and SGS pattern in A. nudicaulis, coupled with high levels of genetic diversity, indicated a recruitment at windows of opportunity (RWO) strategy. Moreover, the spatial distribution of genetic variation and the habitat occupation pattern in A. nudicaulis were dependent not only on the intrinsic biological traits of the species (such as spacer size and mating system), but also on biotic interactions with neighbouring species that determined suitable habitats for germination and the establishment of new genets. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 178, 329–342.

Physiological Integration Ameliorates Negative Effects of Water Stress in Salt-sensitive ‘C198’ Common Bermudagrass

Clonal plants can consist of connected individual ramets that enhance resource sharing through physiological integration. This integration enables the whole clone to tolerate environmental stresses. The objective of this research was to investigate the effects of physical ramet connections on the integration of antioxidant enzymes in clonal common bermudagrass (Cynodon dactylon) growing under heterogeneously distributed water; i.e., nonuniform distribution of water due to 20% polyethylene glycol (PEG 6000) treatment on some ramets and not others. The bottom, middle, upper and three fragments of clonal common bermudagrass were subjected to 20% PEG 6000 with water potential of −1.8 MPa to induce heterogeneous and homogeneous drought stress. The control was not treated with 20% PEG 6000. Within the heterogeneous treatment, water stressed clonal fragments generally had higher leaf and root antioxidant enzyme activities with respect to superoxide dismutase, catalase, peroxidase (except for root peroxidase). There was no difference in antioxidant enzyme activity within the connected clonal ramets for homogeneous treatment; i.e., three connected ramets treated with 20% PEG 6000. Osmotically stressed clonal fragments under heterogeneous environments had a lower level of malonaldehyde (MDA) compared with those in homogeneous regimes. The antioxidant enzyme integration was affected by directionality and water availability contrast. This was indicated by significant decline in MDA levels within the heterogeneous treatments as compared with homogeneous treatment, which suggested reduced lipid peroxidation. These results suggested that ramet connections facilitate integration of antioxidant enzymes within clonal plants growing in heterogeneously available water. Enzymes were integrated from clonal fragments growing in water sufficient environment to those in water stressed regimes. This enhanced reactive oxygen species scavenging capacity of the entire clone hence improved drought tolerance.

Testing for disconnection and distance effects on physiological self-recognition within clonal fragments of Potentilla reptans.

Evidence suggests that belowground self-recognition in clonal plants can be disrupted between sister ramets by the loss of connections or long distances within a genet. However, these results may be confounded by severing connections between ramets in the setups. Using Potentilla reptans, we examined severance effects in a setup that grew ramet pairs with connections either intact or severed. We showed that severance generally reduced new stolon mass but had no effect on root allocation of ramets. However, it did reduce root mass of younger ramets of the pairs. We also explored evidence for physiological self-recognition with another setup that avoided severing connections by manipulating root interactions between closely connected ramets, between remotely connected ramets and between disconnected ramets within one genet. We found that ramets grown with disconnected neighbors had less new stolon mass, similar root mass but higher root allocation as compared to ramets grown with connected neighbors. There was no difference in ramet growth between closely connected- and remotely connected-neighbor treatments. We suggest that severing connections affects ramet interactions by disrupting their physiological integration. Using the second setup, we provide unbiased evidence for physiological self-recognition, while also suggesting that it can persist over long distances.

Regeneration capacity of the small clonal fragments of the invasive Mikania micrantha H.B.K.: effects of the stolon thickness, internode length and presence of leaves

Mikania micrantha H.B.K., one of the top 10 worst weeds in the world, is now spreading quickly in southern China. Disturbance can fragment and spread the stolons of M. micrantha. A greenhouse experiment was conducted in order to assess the regeneration capacity of single‐node fragments with varying stolon thickness (diameters of 3.01, 2.49 and 1.96 mm), internode lengths (2 and 8 cm) and leaf presence status (with and without leaves). The results indicated that an increasing stolon thickness, internode length and the presence of leaves all increased the survival rate of the clonal fragments. An increasing stolon thickness, internode length and the presence of leaves also increased the growth of the clonal fragments and the presence of leaves exhibited the strongest effect. An increasing internode length and the presence of leaves also reduced the amount of time that was needed for emergence, while the effect of the stolon thickness was not significant. None of the effects of the interactions was significant, although the interaction between the stolon thickness and the internode length was nearly significant for fragment survival. These results suggest that M. micrantha has developed a strategy to cope with disturbance by storing reserves in the stolons and leaves, which could increase its regeneration capacity after fragmentation. Currently, the management of M. micrantha (such as manual or mechanical control) should avoid the generation of the small clonal fragments of M. micrantha, while repeated control with short time intervals is necessary in order to prevent reinvasion from the stolon fragments.

Clonal integration ameliorates the carbon accumulation capacity of a stoloniferous herb, Glechoma longituba, growing in heterogenous light conditions by facilitating nitrogen assimilation in the rhizosphere.

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.

Contrasting light spectra constrain the macro and microstructures of scleractinian corals.

The morphological plasticity of scleractinian corals can be influenced by numerous factors in their natural environment. However, it is difficult to identify in situ the relative influence of a single biotic or abiotic factor, due to potential interactions between them. Light is considered as a major factor affecting coral skeleton morphology, due to their symbiotic relation with photosynthetic zooxanthellae. Nonetheless, most studies addressing the importance of light on coral morphological plasticity have focused on photosynthetically active radiation (PAR) intensity, with the effect of light spectra remaining largely unknown. The present study evaluated how different light spectra affect the skeleton macro- and microstructures in two coral species (Acropora formosa sensu Veron (2000) and Stylophora pistillata) maintained under controlled laboratory conditions. We tested the effect of three light treatments with the same PAR but with a distinct spectral emission: 1) T5 fluorescent lamps with blue emission; 2) Light Emitting Diodes (LED) with predominantly blue emission; and 3) Light Emitting Plasma (LEP) with full spectra emission. To exclude potential bias generated by genetic variability, the experiment was performed with clonal fragments for both species. After 6 months of experiment, it was possible to detect in coral fragments of both species exposed to different light spectra significant differences in morphometry (e.g., distance among corallites, corallite diameter, and theca thickness), as well as in the organization of their skeleton microstructure. The variability found in the skeleton macro- and microstructures of clonal organisms points to the potential pitfalls associated with the exclusive use of morphometry on coral taxonomy. Moreover, the identification of a single factor influencing the morphology of coral skeletons is relevant for coral aquaculture and can allow the optimization of reef restoration efforts.

Effects of Nitrogen Enrichment and Clonal Integration on the Expansion of <i>Alternanthera p</i><i>hiloxeroides</i> in Aquatic Habitats

This study examined the effects of nitrogen enrichment and clonal integration on the growth and expansion process from terrestrial to aquatic habitats of the amphibious and invasive plant Alternanthera philoxeroides. The clonal fragments of A. philoxeroides were subjected to three nitrogen levels of 10/3, 10 and 30 mg/l N with the stolon connections either severed or left connected. The results suggested that nitrogen enrichment increased the clonal growth and expansion of A. philoxeroides in aquatic habitats. Clonal integration supports the expansion of A. philoxeroides from terrestrial to aquatic environments. And A. philoxeroides will be more invasive in nitrogen enriched waters due to the synergistic effects of nitrogen enrichment and clonal integration.

Responses of rhizomatous grass Phragmites communis to wind erosion: effects on biomass allocation

The ability of modifying biomass allocation to deal with different environmental stress is an important mechanism for plant population expansion and maintenance in the unstable dune environment where wind erosion persists. However, how biomass is partitioned between horizontal rhizome extension and vertical ramet growth in response to wind erosion has not been fully understood. The objective of this study was to explore how wind erosion affected the relationship between horizontal rhizome extension and vertical ramet growth using a common rhizomatous perennial grass, Phragmites communis. We dug 300 cm × 200 cm, 80 cm deep pits in a garden experiment plot. Clonal fragments of P. communis were planted individually at a depth of 40 cm in these pits for 4 weeks before treatments. Surface sand was gradually removed to the final depth of 0 (control), 10, 20, 30 and 40 cm (maximum sand removal). Ramet emergence time, rhizome-based and tiller-based ramet number, rhizome number and length, biomass of vertically and horizontally oriented structures were monitored at the end of the experiment. With increasing erosion depth, the proportion of tiller-based ramets (in total number of ramets) increased, whereas that of rhizome-based ramets decreased. With increasing erosion depth, the percentage of vertically oriented structures biomass in total biomass increased significantly, whereas that of horizontally oriented structures biomass decreased. The changes in biomass allocation (i.e., more allocation in vertical than horizontal biomass) together with a trade-off in tiller-based and rhizome-based ramets may enable P. communis to make better use of the resources in erosion conditions and maximize plant population expansion and maintenance.

Conservation assessment of an extremely restricted bromeliad highlights the need for population-based conservation on granitic inselbergs of the Brazilian Atlantic Forest

Inselbergs support highly specialized vegetation with many endemic species. Here we studied by an integrated approach a rare and threatened species from Brazilian inselbergs. Pitcairnia encholirioides (Bromeliaceae) is included in the Red Book of Brazilian Flora, in the ‘Endangered’ category. Only one single population on unprotected private property was known at the beginning of our study. We studied several life-history traits including clonal growth, reproductive biology, seed germination and cryopreservation, and genetic diversity. Pitcairnia encholirioides has the phalanx type of clonal growth strategy. Its self-incompatible flowers are successfully pollinated by hummingbirds. However, less than 5% of clonal fragments produced flowers. Seeds can be wind-dispersed, but most of them are dispersed by gravity and fall close to the mother plant. The percentage and speed of germination were significantly affected by different temperatures, water potential, and red:far-red light ratios, although more than 80% of seeds germinated under optimal physiological conditions. The genetic diversity was very low (Hsp=0.09) and the population was highly structured (ΦST=0.51). The combination of dispersal mode and environmental conditions seems to be the main factor leading to the rarity of P. encholiroides. Low genetic diversity combined with small population size and low reproductive capacity suggest that the species is highly susceptible to environmental disturbance. Similarly to P. encholiroides, many species from Brazilian inselbergs are restricted to only a few localities. For more widely distributed species, a higher genetic diversity among populations has been consistently detected. The pattern of low gene flow of many species with small distributions highlight the importance of population-based conservation strategies for such taxa the areas of occurrence of which being naturally fragmented at inselberg sites. We discuss some strategies that may help in conservation of such species.

Effects of clonal fragmentation on intraspecific competition of a stoloniferous floating plant

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.

Flooding and fragment size interact to determine survival and regrowth after fragmentation in two stoloniferous Trifolium species.

Clonal plants, which reproduce by means of stolons and rhizomes, are common in frequently flooded habitats. Resilience to disturbance is an important trait enabling plants to survive in such highly disturbed habitats. Resource storage is thought to enable clonal plants to resume growth after clonal fragmentation caused by disturbance. Here we investigated if submergence prior to disturbance reduces survival and regrowth of clonal fragments and whether or not genotypes originating from highly disturbed riverine habitats are more resistant to mechanical disturbance than genotypes from less disturbed coastal dune slack habitats. We further tested if variation in survival and regrowth was affected by internode size. Clones from contrasting habitats of two closely related Trifolium species were first genotypically characterized by amplification fragment length polymorphism and then subjected to soil flooding and subsequent clonal fragmentation. These species differ with respect to their abundance in riverine and dune slack habitats, with Trifolium repens mainly occurring in riverine grasslands and Trifolium fragiferum in coastal dune slacks. Soil flooding decreased survival and regrowth by up to 80 %. Plants originating from riverine grasslands were less negatively affected by fragmentation than plants from dune slack habitats. Surprisingly, ramets did not always benefit from being attached to a larger internode, as internode size was often negatively correlated with survival after fragmentation. Regrowth, on the other hand, was generally positively correlated with internode size. These unexpected results indicate that there may be contrasting selection pressures on internode size in stoloniferous species growing in severely disturbed habitats.

UV-B辐射方向对白三叶克隆整合的影响

增强UV-B辐射会对植物生长和生理生化过程产生有害效应。克隆植物中，相连的克隆分株对经常共享资源和激素，然而鲜有关于异质性UV-B辐射下UV-B辐射方向对克隆整合的影响及克隆植物形态结构变化的报道。模拟同质（克隆分株片段均处于自然背景辐射）和异质（克隆分株一端处于自然背景辐射，另一端处于补加的UV-B辐射）UV-B辐射，以克隆植物白三叶为材料，进行连接和隔断处理，研究UV-B辐射方向对克隆整合强度变化、叶片形态结构特化及生理可塑性的影响。结果表明：异质性UV-B辐射下，¹⁵N同位素标记端保留的¹⁵N百分比高于同质UV-B辐射处理，转移到无标记相连端的¹⁵N含量则降低，紫外辐射处理和同位素标记是否处于同一分株端对结果无显著性影响，说明克隆植物白三叶生理整合存在但整合强度降低，辐射方向与克隆整合强度无关；隔断处理组气孔长度增加，栅栏组织增厚，但连接处理组却无此变化，表明生理整合在白三叶叶片形态结构特化中发挥作用。UV-B辐射下，最小荧光、电子传递速率及光化学淬灭系数降低但非光化学淬灭系数升高，而生理整合却使结果相反；叶绿素和紫外吸收物可在异质性UV-B辐射相连的两端运输分享。以上均表明异质UV-B辐射环境中，UV-B辐射胁迫端克隆分株通过生理整合从非胁迫端获益，并以此提高胁迫环境中克隆植物对资源的利用效率。;Clonal plants are widely distributed in all types of ecosystems, and dominate in many of them. Vascular connections (e.g. stolons or rhizomes) of clonal plants can transport resources such as carbohydrates, water and nutrient between interconnected ramets. This feature has been long considered to be adaptive in all types of ecosystems, particularly in environments where resources or stressful factors are patchily distributed in both time and space. Many studies have shown that the stressed ramets of clonal fragments can be supported by resource translocation from the connected unstressed ramets, for example, clonal integration can alleviate local stress caused by shading, drought, salinity, serpentine soils, mechanical stimulation and sand burial. Ultraviolet-B (UV-B) radiation (280-315 nm) can result in deleterious effects on many plant growth processes because it is strongly absorbed by many macromolecules and causes their conformational changes, especially proteins and nucleic acids. Environmental UV-B radiation is highly variable in spatial and temporal distributions. It is controlled by a great deal of factors, such as changes in the solar elevation with latitude, time of day, season and clouds. Little is still known about the response of physiological integration in clonal plants to heterogeneous ultraviolet-B radiation. In this study, pairs of connected and severed ramets of the stoloniferous herb <em>Trifolium repens </em>were grown under the homogeneity (both of ramets received only natural background radiation) and heterogeneity of UV-B radiation (one of the ramet received only natural background radiation and the other was exposed to supplemental UV-B radiation). Changes in intensity of nutrient integration were followed with ¹⁵N-isotope labeling of the xylem water transport. Stomata density, length, the thickness of wax, cuticle epidermal cell and palisade tissue were observed to study leaf anatomic characters. The effects of heterogeneous UV-B radiation on chlorophyll fluorescence of a clonal plant <em>T. repens</em> were evaluated. In order to assess the patterns of physiological integration contents of chlorophyll and UV-B absorbing compounds were determined. When ramets were connected and exposed to heterogeneous UV-B radiation, the percentage of ¹⁵N left in labeled ramets that suffered from enhanced UV-B radiation was higher and their transfer to unlabeled ramets lower. The intensity of physiological integration of <em>T. repens </em>for resources decreased under heterogeneous ultraviolet-B radiation in favor of the stressed ramets. Severing groups under UV-B radiation had more closed stomas (according to stomatal length) and the thickness of palisade tissue, results were reversed in connecting groups, indicating physiological integration plays a role in anatomic characters. Additive UV-B radiation resulted in a notable decrease of the minimal fluorescence of dark-adapted state (<em>F</em>_o), the electron transport rate (<em>ETR</em>) and photochemical quenching coefficient (<em>q</em>_P) and an increase of non-photochemical quenching (<em>NPQ</em>) under heterogeneous UV-B radiation, while physiological connection reverse the results. Chlorophyll and UV-B absorbing compounds were shared between connected ramets under heterogeneous UV-B radiation. Ultraviolet-B stressed ramets benefited from unstressed ramets by physiological integration, improving resource efficiency on clonal plants in less favorable sites.

Regeneration capacity of small clonal fragments of the invasive Mikania micrantha H.B.K.: effects of burial depth and stolon internode length.

The perennial stoloniferous herbaceous vine Mikania micrantha H.B.K. is among the most noxious exotic invaders in China and the world. Disturbance can fragment stolons of M. micrantha and disperse these fragments over long distances or bury them in soils at different depths. To test their regeneration capacity, single-node stolon fragments with stolon internode lengths of 0, 3, 6 and 12 cm were buried in soil at 0, 2, 5 and 8 cm depths, respectively. The fragments were growing for nine weeks, and their emergence status, growth and morphological traits were measured. The results indicated that increasing burial depth significantly decreased survival rate and increased the emergence time of the M. micrantha plants. At an 8-cm burial depth, very few fragments (2.19%) emerged and survived. Burial did not affect the total biomass and root to shoot ratio of the surviving M. micrantha plants that emerged from the 0- and 2-cm burial depths. Increasing internode length significantly increased survival rate and growth measures, but there was no interaction effect with burial depth for any traits measured. These results suggest that M. micrantha can regenerate from buried stolon fragments, and thus, disturbance may contribute to the spread of this exotic invader. Any human activities producing stolon fragments or facilitating dispersal should be avoided.

Combined effects of resource heterogeneity and simulated herbivory on plasticity of clonal integration in a rhizomatous perennial herb

Previous lines of investigation assuming potential advantage of clonal integration generally have neglected its plasticity in complex heterogeneous environments. Clonal plants adaptively respond to abiotic heterogeneity (patchy resource distribution) and herbivory-induced heterogeneity (within-clone heterogeneity in ramet performance), but to date little is known about how resource heterogeneity and simulated herbivory jointly affect the overall performance of clones. Partial damage within a clone caused by herbivory might create herbivory-induced heterogeneity in a resource-homogeneous environment, and might also decrease or increase the extent of heterogeneity under resource-heterogeneous conditions. We conducted a greenhouse experiment in which target-ramets of Leymus chinensis segments within homogeneous or heterogeneous nutrient treatments were subject to clipping (0% or 75% shoot removal). In homogeneous environments with high (9:9) nutrient availability, ramet biomass of L.chinensis with intact or severed rhizomes is 0.70 or 0.69g. Conversely, target-ramet biomass with intact rhizomes is obviously lower than that of the severed target-ramets in the homogeneous environments with medium (5:5) and low (1:1) nutrient availability. High resource availability and the presence of herbivory can alleviate negative effects of rhizome connection under homogeneous conditions, by providing copious resource or creating herbivory-induced heterogeneity respectively. Herbivory tolerance of clonal fragments with connected rhizomes was higher than that of fragments with severed rhizomes under heterogeneous conditions. These findings confirmed the unconditional advantage of clonal integration on reproduction under the combined influence of resource heterogeneity and simulated herbivory. Moreover, our results made clear the synergistically interactive effects of resource heterogeneity and simulated herbivory on costs and benefits of clonal integration. This will undoubtedly advance our understanding on the plasticity of clonal integration under complex environmental conditions.

Clonal integration of Fragaria orientalis in reciprocal and coincident patchiness resources: cost-benefit analysis.

Clonal growth allows plants to spread horizontally and to experience different levels of resources. If ramets remain physiologically integrated, clonal plants can reciprocally translocate resources between ramets in heterogeneous environments. But little is known about the interaction between benefits of clonal integration and patterns of resource heterogeneity in different patches, i.e., coincident patchiness or reciprocal patchiness. We hypothesized that clonal integration will show different effects on ramets in different patches and more benefit to ramets under reciprocal patchiness than to those under coincident patchiness, as well as that the benefit from clonal integration is affected by the position of proximal and distal ramets under reciprocal or coincident patchiness. A pot experiment was conducted with clonal fragments consisting of two interconnected ramets (proximal and distal ramet) of Fragaria orientalis. In the experiment, proximal and distal ramets were grown in high or low availability of resources, i.e., light and water. Resource limitation was applied either simultaneously to both ramets of a clonal fragment (coincident resource limitation) or separately to different ramets of the same clonal fragment (reciprocal resource limitation). Half of the clonal fragments were connected while the other half were severed. From the experiment, clonal fragments growing under coincident resource limitation accumulated more biomass than those under reciprocal resource limitation. Based on a cost-benefit analysis, the support from proximal ramets to distal ramets was stronger than that from distal ramets to proximal ramets. Through division of labour, clonal fragments of F. orientalis benefited more in reciprocal patchiness than in coincident patchiness. While considering biomass accumulation and ramets production, coincident patchiness were more favourable to clonal plant F. orientalis.

Phenotypic Responses of a Stoloniferous Clonal Plant Buchloe dactyloides to Scale-Dependent Nutrient Heterogeneity

Clonal plants could modify phenotypic responses to nutrients heterogeneously distributed both in space and time by physiological integration. It will take times to do phenotypic responses to modifications which are various in different growth periods. An optimal phenotype is reached when there is a match between nutrient conditions and foraging ability. A single plantlet of Buchloe dactyloides with two stolons was transplanted into heterogeneous nutrient conditions. One stolon grew in homogeneous nutrient patch, while the other cultured in different scales of heterogeneous nutrient patches. As compared to the other nutrient treatment, heterogeneous nutrient treatments with small scale of 25×25 cm resulted in a higher biomass, and larger number of ramets, clumps and stolons in B. dactyloides at both genet and clonal fragment levels. Significant differences of number of ramets, clumps and stolons were detected at the rapid growth stage, but not in the early stage of the experiment. Foraging ability was more efficient in heterogeneous than in homogeneous nutrient conditions as assessed by higher root mass and root to shoot ratio. Different nutrient treatments did not prompt significant differences in internode and root length. Physiological integration significantly increased biomass, but did not influence other growth or morphological characters. These results suggest that physiological integration modifies phenotypic plasticity of B. dactyloides for efficient foraging of nutrients in heterogeneous nutrient conditions. These effects are more pronounced at genet and clonal fragment levels when the patch scale is 25×25 cm. Time is a key factor when phenotypic plasticity of B. dactyloides in heterogeneous nutrient conditions is examined.