Growth Of Ramets Research Articles

The effects of successional stage and size of gaps on recruitment of clonal plants in overgrowing Molinietum caeruleae meadows

<p>In majority of plant communities with a closed canopy, the disturbances created by abiotic factors and biotic agents contribute to origin of an area free of existing vegetation and considered as safe sites for seedling recruitment. Although the gaps are characterized by several features, the size is proposed to be the most important characteristic. The investigations of recruitment of clonal taxa in different–sized gaps were conducted in the years 2011–2012 in <em>Molinietum caeruleae</em> meadows representing various successional stages and dominated by different species. Patch ES, representing early-successional stage, was dominated by small meadow species, Patch MS, representing mid-successional stage, was prevailed by tall-growing macroforbs, while Patch LS representing late-successional stage was overgrown by macroforbs and willows. In the successive sites the mean height of plant canopy, as well as the period of spring inundation increased gradually.</p><p>The total number of species and seedlings decreased from the Patch ES, through the Patch MS, to the Patch LS. Almost all plants presenting positive correlation between seedling number and gap area created hypogeogenous stems with substantial lateral growth and considerable number of short-lived daughter ramets allowing the fast colonization of neighbourhood. The majority of species showing negative relationship formed epigeogenous stems with slight lateral growth, as well as low number of long-lived ramets contributing to slow colonization of area.</p><p>In light of performed studies, it might be concluded, that making disturbance in continuous plant canopy and litter might be very effective way of conservation of <em>Molinietum caeruleae</em> meadows. The creation of different-sized gaps seems to be especially valuable due to the maintenance of heterogeneity of clonal species, which is particularly important in advanced successional stages.</p>

竹类植物对异质生境的适应：表型可塑性

Since heterogeneity is ubiquitous,plant phenotypic plasticity is a vital ecological countermeasure to adapt to the heterogeneous habitat. Owing to the double modularity,the clonal plant has higher phenotypic plasticity and then acquires higher adaptability than other plants. Bamboo is a group of clonal plants,and mainly composed of woody plants. Bamboo could grow well in the difficult site and heterogeneous habitat where most plants hardly survive. Meanwhile,bamboo can expand rapidly to broad-leaved forest in the bamboo-forest ecotone. Compared with most plants,bamboo has stronger adaptability to heterogenous habitat due to its higher phenotypic plasticity. Thus,in order to advance the development of bamboo ecology, it is necessary to systematically summarize the bamboo phenotypic plasticity and adaptation countermeasures to heterogeneous habitat. Literature analysis shows that bamboo has obvious phenotypic plasticity to respond to heterogeneous habitat. Four realizing ways of phenotypic plasticity including morphological plasticity, selective placement,clonal integration and intraclonal division of labor,are exerted by bamboo to cope with heterogeneous habitat.Firstly,bamboo modifies the morphology,such as height,diameter,leaf area,spacer length,node number,branching angle,biomass etc,to adapt to the changes of above-ground or under-ground resources. The morphological modification is adapted to the resource level. In the poor resource habitat,energy is mainly invested in the constructing of absorbingstructures in order to increase resource absorption. In contrast,most energy is invested in the growth of ramet to increase plant biomass in the rich resource habitat. Secondly,bamboo grows more ramets in the fertile microhabitat than that of in the infertile microhabitat. Thus,bamboo can acquire more survival resources and adapt to the unfavorable habitat. The selective placement is achieved by altering the spacer length,branching angle and branching intensity. Clearly,it is an active behavior to adapt to the heterogeneous habitat. Thirdly,clonal integration behavior helps bamboo ramets in unfertile habitat gain resource from those in fertile habitat. Actually,bamboo shoot growth is a typical process of clonal integration,because the new shoot need obtain the nutrients from mother ramets. However,the direction and intensity of clonal integration could be altered with the variation of resource distribution in the heterogeneous habitat. Fourthly,intraclonal division of labor is another important countermeasure to deal with the heterogeneous habitat. Clonal integration and specialization of ramet are two basic prerequisites for intraclonal division of labor. Although many studies of intraclonal division of labor were developed in herbaceous plants,little is known about that in bamboo. Therefore,we need further confirm whether the intraclonal division of labor is commonly used by bamboo. Overall,the present studies focus on modular morphology and biomass allocation pattern,while little attention is paid on the mechanism of phenotypic plasticity. In the future,the researches on bamboo phenotypic plasticity shall be focused on the following 5 aspects: 1) pattern and mechanism of clonal integration;2) influence of clonal integration on ecosystem stability; 3) mechanism of intraclonal division of labor,and its relationship with environment; 4) hierarchical selection of phenotypic plasticity and the environmental effect; 5) differences of phenotypic plasticity in different types of clonal architecture,and their mechanisms.

Incorporating herbivorous sea urchins in ramet culture of staghorn coral Acropora cervicornis

Since the 2006 listing of the staghorn coral Acropora cervicornis as threatened under the US Endangered Species Act, interest has increased in its culture for laboratory studies, resto- ration and ex situ conservation efforts. A pervasive problem in coral culture is substrate over- growth by algae and other spatial competitors. We conducted a laboratory study to examine the utility of introducing herbivores, juvenile variegated sea urchins Lytechinus variegatus, to tanks containing small (<1 cm 2 ) A. cervicornis ramets. Growth of coral ramets on ceramic tile substrates was monitored in recirculating seawater tanks over 210 d and measured in terms of area change under 3 treatment conditions: (1) presence of laboratory-reared, juvenile, variegated sea urchins; (2) weekly scraping of algal turfs from the tile substrate by means of a razor blade; and (3) absence of both urchins and manual turf removal (i.e. control). Over the course of the study, coral area decreased in the control treatment, but increased in the scraped and urchin-containing treat- ments. All 3 treatments differed significantly from one another, with the highest growth rate (3.1 mm 2 d �1 ) associated with the manual removal of algal competitors, followed by the urchin (1.9 mm 2 d �1 ) and control treatments (�0.8 mm 2 d �1 ). Given the relative ease of L. variegatus cul- ture, the incorporation of variegated sea urchins in the coral ramet production process appears to provide at least a partial substitute for manual algal removal. Although coral growth in the pres- ence of urchins was slower than with manual removal, human labor costs associated with the lat- ter may out-weigh any production rate improvements in large-scale operations.

Clonal integration facilitates invasiveness of the alien aquatic plant Myriophyllum aquaticum L. under heterogeneous water availability

Clonal plants benefit from the ability to translocate resources among interconnected ramets through clonal integration to colonise ubiquitous heterogeneous habitats, which may contribute to the invasiveness of exotic clonal plants. To test this hypothesis, a greenhouse experiment was conducted to investigate the effects of clonal integration on a non-native clonal plant, Myriophyllum aquaticum, subjected to spatial and temporal heterogeneity of water supply. The daughter ramets were grown with stolon connections either severed from or connected to the mother plant and subjected to different amounts or frequencies of water supply. Clonal integration significantly improved growth and photosynthetic performance of daughter ramets that were exposed to spatial and temporal heterogeneity of water supply. Biomass allocation to roots of offspring ramets changed with water supply to enhance the capacity for water uptake. The decrease of the maximum quantum yield of photosystem II (F v/F m) as a function of reduced water supply was greatly alleviated by stolon connection. Moreover, clonal integration facilitated stabilisation of foliar N concentration and C/N ratio to support healthy growth of the ramets. These results suggest that clonal integration may facilitate invasion of M. aquaticum when subjected to heterogeneity in resource supply under ever-changing environments.

Secondary Branch Angles and Potential Topophytic Effects of Vegetatively Propagated Clones of Taxodium

Baldcypress [Taxodium distichum] branch angles were measured between the primary leader (1st order) and second order branches at three different positions (low, medium, high) in the canopy of 828 four-year-old, field-grown seedlings. Seedlings represented twenty-three open-pollinated families collected from Central Mexico to Alabama. Based on these measurements, six different representative families (three families with the most acute branch angles and three families with the most obtuse branch angles) were chosen to test 1) whether topophysis significantly affects the orientation and/or growth of ramets and 2) if branch angle divergence from the trunk of the ortet impacts the degree of topophysis observed on the ramets from rooted shoot tips. Cuttings from the six seedlings were harvested in June 2008 from basal (more horizontally oriented branches) and terminal (more erect upper branches) portions of the canopies in order to test topophytic effects. Rooted cuttings were oriented vertically upon transplanting and grown for approximately 8 months. Measurements included initial and final height and stem diameter and the final angle between the primary leader and the substrate surface. Branch angle data collected from field-grown seedlings revealed a significant interaction (P ≤ 0.0001) between family and location within the canopy. Most families measured had branch angles that were most obtuse at the bottom of the canopy becoming progressively more acute toward the tree apex. MX6D, TX3D, TX6D and EP7D were families that exhibited minimal to no branch angle differences in regard to position within canopy. Data analysis showed no significant main effect or interactions of cutting location within the canopy on vertical orientation during container production. A significant main effect (P ≤ 0.0001) of clone was observed for all measurements except initial stem diameter. Clone MX2MC31 cuttings displayed the greatest mean angle of divergence from vertical at 48° while cuttings of MX6MC14 diverted ≈12° from vertical. In this study neither initial branch angles on the ortet nor position within the canopy from which cuttings were taken was an accurate significant predictor of cutting orientation relative to vertical. Tendencies for clonal differences in vertical growth however, suggest the potential for selection of baldcypress clones that would have a reduced need for staking during production.

The Seasonality of Survival and Subsequent Growth of Common Reed (Phragmites australis) Rhizome Fragments

AbstractCommon reed [Phragmites australis (Cav.) Trin. ex Steud.] is an invasive plant that reproduces poorly by seed but regenerates vigorously by rhizomes. Because Phragmites australis propagates well through rhizome growth, invasion often occurs from transported rhizome tissue. We investigated both rhizome-fragment biomass and seasonal effects on survival and growth of ramets. Rhizomes were collected along roadside ditches during the fall of 2009 and 2010 and during the summer of 2010 and 2011. Fall and summer were chosen because the plants were either dormant or actively growing, respectively. Rhizomes were cut into fragments then grown in a greenhouse for 60 d in vermiculite with no added nutrients. Rhizomes collected in the fall had a survival rate of 71.1%, whereas only 15.6% of those collected in the summer survived. Within season, rhizomes with low initial biomass had lower survival rates and growth than did large rhizomes. There was no seasonal difference in the total biomass produced by the surviving plants; however, allocation of biomass did differ. Summer-collected rhizomes showed a higher belowground to aboveground biomass ratio than did those collected in the fall. Understanding the viability of Phragmites australis rhizome fragments provides land managers a greater awareness of the high-establishment risks of Phragmites australis. This information should be included in an integrated weed management program, and actions should be taken to reduce the spread of this weed during roadside maintenance. Although the risk of survival is lower during the summer, soil contaminated with Phragmites australis should not be transported or must be sifted with a screen to ensure all rhizome fragments are removed.

Inhibition effects of daughter ramets on parent of clonal plant Eichhornia crassipes

The aquatic invasive clonal Eichhornia crassipes was selected to study the effect of nutrients and stolon severing on clonal plants in less heterogenous aquatic environments. Under high nutrient conditions, parent ramets produced more daughter ramets and leaves with higher biomass, and, subsequent to severing daughter ramets, especially those in early stages; parents produced more daughter ramets and leaves with higher biomass. However, leaf number and biomass of individual daughter ramets did not differ from individuals with severed stolons and the control treatment. The biomass and leaves of the daughter ramets were lower than the control and other severing treatments that were carried out at later stages only when the nutrient level was low and the stolons of the daughter ramets were severed at early stages of growth. For this reason, the total number of ramets and leaves were lower in early stage severing treatments than severing treatments at later stages. After severing the connection with the daughter ramets, the root/shoot biomass ratio of the parent ramets increased, indicating that water hyacinths display morphological plasticity after stolon severing by increasing root growth. This study indicates that in aquatic environments where the nutrient distribution is less heterogenous in the same layer of water, daughter ramets of the water hyacinth can inhibit the growth and clonal reproduction of the parent, and this inhibition was strongest at early stages of ramet growth.

Developmentally-programmed division of labour in the clonal invader Carpobrotus edulis

Invasive species are one of the main causes for the loss of global biodiversity. However, the mechanisms that explain the success of invasive species remain unsolved. Clonal growth has been pointed out as an attribute that could contribute to the invasiveness of plants, however little research has been conducted to determine the importance of clonal traits in successful invaders. One of the most interesting attributes related to clonal growth is the capacity for division of labour. In this experiment we investigated the capacity for division of labour in the aggressive invader Carpobrotus edulis, and how clonal integration can contribute to the expansion of this species. Division of labour was determined by studying the degree of morphological and physiological specialization of individual ramets to a specific activity: acquisition of soil or aboveground resources and aboveground expansion. Our results showed that there is division of labour in the clonal fragments, with older ramets increasing the biomass allocated to roots (specialization in the uptake of belowground resources) and younger ramets increasing the chlorophyll content and aboveground biomass (specialization in the uptake of aboveground resources). Physiological integration allows division of labour, and as consequence the overall performance of the clonal fragment was enhanced, with connected clonal fragments showing a higher total biomass than severed clonal fragments. Division of labour increased the aboveground growth of apical ramets of C. edulis, and therefore could contribute to an effective colonization of the surrounding area by this aggressive invader. Our study is the first exploring the role of division of labour in the expansion of an invader, and supports the idea that clonal traits could increase the invasiveness of plant species.

异质性光照下匍匐茎草本狗牙根克隆整合的耗益

In a pot experiment,the clonal ramets of Cynodon dactylon,the stolon herbaceous plant,were treated with heterogeneous lighting. Shade stress was carried out on the distal ramets( younger ramets) to three different degrees,and the stolons between the proximal ramets and distal ramets of each pair were treated in an intact or severed manner. The results show that in moderate shade stress,the stolons severed significantly decreased the biomass and net photosynthetic rate( Pn) of distal ramets,and that in serious shade stress,the stolons severed significantly reduced the number of ramets,the number of leaves,biomass,net photosynthetic rate( Pn),the maximal quantm yield of the photosystemⅡ( Fv / Fm)and the effective quantum yield of PSⅡ( ФPSⅡ) of the distal ramets,and that clonal integration alleviated the negative effects of shade stress on the growth of distal ramets. In moderate shade stress,the stolons being intact significantly increased the net photosynthetic rate( Pn) of proximal ramets. In the serious shade stress,the stolons being intact effectively improved the maximal quantm yield of the photosystem Ⅱ( Fv / Fm) and the effective quantum yield of PS Ⅱ( ФPSⅡ) of the proximal ramets. Thus,clonal integration drove the photosynthetic rate of the unstressed proximal ramets to compensatory increase. In contrast to the treatment of the stolons severed,clonal integration would significantly reduce the biomass of the unstressed ramets,but result in no significant change of the whole clonal fragments when the distal ramets were treated with serious shade stress. Therefore,when the distal ramets suffer from serious shade stress,Cynodon dactylon,the stolon herbaceous plant,may take a risk-spreading strategy to reduce the death of genets,which is of vital importance to maintain the fitness of the genets of clonal plants in heterogeneous environments.

Differences in clonal integration between the sexes: long-term demographic patterns in the dioecious, multi-stemmed shrub Lindera triloba

In clonal plants, ramets connected within a genet can share resources through clonal integration, and clonal integration often facilitates the growth and survival of young ramets. However, in dioecious plants, it is not fully understood whether female and male genets differ in their integration patterns affecting the demographic processes. To test between-sex differences in the demographic process in relation to clonal integration, we conducted a long-term census for the dioecious sprouting shrub Lindera triloba (Sieb. et Zucc.) Blume. In an old-growth forest, we selected 73 female and 82 male genets, and the recruitment, growth, and mortality of ramets within those genets were monitored over six years. Ramet recruitment was greater in males than in females, whereas ramet growth and survival rates did not differ, on average, between sexes. Females and males showed different sensitivities to factors affecting their ramet dynamics. The ramet recruitment, growth, and survival within male genets were significantly positively affected by the largest main ramet size, whereas females were not sensitive to the effect. This suggested that demographic patterns of ramets within male genets were more sensitive to assimilates translocated from the main ramets than those within female genets, and the role of clonal integration worked differently on ramet dynamics between sexes.

Physiological integration ameliorates negative effects of drought stress in the clonal herb Fragaria orientalis.

Clonal growth allows plants to spread horizontally and to establish ramets in sites of contrasting resource status. If ramets remain physiologically integrated, clones in heterogeneous environments can act as cooperative systems – effects of stress on one ramet can be ameliorated by another connected ramet inhabiting benign conditions. But little is known about the effects of patch contrast on physiological integration of clonal plants and no study has addressed its effects on physiological traits like osmolytes, reactive oxygen intermediates and antioxidant enzymes. We examined the effect of physiological integration on survival, growth and stress indicators such as osmolytes, reactive oxygen intermediates (ROIs) and antioxidant enzymes in a clonal plant, Fragaria orientalis, growing in homogenous and heterogeneous environments differing in patch contrast of water availability (1 homogeneous (no contrast) group; 2 low contrast group; 3 high contrast group). Drought stress markedly reduced the survival and growth of the severed ramets of F. orientalis, especially in high contrast treatments. Support from a ramet growing in benign patch considerably reduced drought stress and enhanced growth of ramets in dry patches. The larger the contrast between water availability, the larger the amount of support the depending ramet received from the supporting one. This support strongly affected the growth of the supporting ramet, but not to an extent to cause increase in stress indicators. We also found indication of costs related to maintenance of physiological connection between ramets. Thus, the net benefit of physiological integration depends on the environment and integration between ramets of F. orientalis could be advantageous only in heterogeneous conditions with a high contrast.

Differential influence of clonal integration on morphological and growth responses to light in two invasive herbs.

Background and aimsIn contrast to seeds, high sensitivity of vegetative fragments to unfavourable environments may limit the expansion of clonal invasive plants. However, clonal integration promotes the establishment of propagules in less suitable habitats and may facilitate the expansion of clonal invaders into intact native communities. Here, we examine the influence of clonal integration on the morphology and growth of ramets in two invasive plants, Alternanthera philoxeroides and Phyla canescens, under varying light conditions.MethodsIn a greenhouse experiment, branches, connected ramets and severed ramets of the same mother plant were exposed under full sun and 85% shade and their morphological and growth responses were assessed.Key resultsThe influence of clonal integration on the light reaction norm (connection×light interaction) of daughter ramets was species-specific. For A. philoxeroides, clonal integration evened out the light response (total biomass, leaf mass per area, and stem number, diameter and length) displayed in severed ramets, but these connection×light interactions were largely absent for P. canescens. Nevertheless, for both species, clonal integration overwhelmed light effect in promoting the growth of juvenile ramets during early development. Also, vertical growth, as an apparent shade acclimation response, was more prevalent in severed ramets than in connected ramets. Finally, unrooted branches displayed smaller organ size and slower growth than connected ramets, but the pattern of light reaction was similar, suggesting mother plants invest in daughter ramets prior to their own branches.ConclusionsClonal integration modifies light reaction norms of morphological and growth traits in a species-specific manner for A. philoxeroides and P. canescens, but it improves the establishment of juvenile ramets of both species in light-limiting environments by promoting their growth during early development. This factor may be partially responsible for their ability to successfully colonize native plant communities.

Effects of fragment size and water depth on performance of stem fragments of the invasive, amphibious, clonal plant Ipomoea aquatica

Many aquatic, clonal plants spread by vegetative fragments consisting of one to several ramets. Fragment size and physiological integration between ramets are likely to affect the establishment and growth of these fragments, and water depth is likely to affect the success of fragments in aquatic species that root in the sediment, but these effects have been little studied. To test the hypotheses that larger fragments perform better, that fragments perform better in shallower water, and that integration produces differences in the growth of ramets within fragments, we grew stem fragments of the cultivated, invasive, amphibious, floating, rooting plant Ipomaea aquatica with 1, 2, 3, or 4 nodes, which function as ramets, in water depths of 5, 20, or 40cm for 8 weeks in the greenhouse. Final mean mass and leaf area per node were greater in larger fragments (e.g., 0.46g and 49.3cm2 in 4-node versus 0.16g and 18.5cm2 in 2-node fragments). Fragments accumulated about 3 times more mean biomass and leaf area in 5cm (1.78g and 196.7cm2) than in 20cm (0. 49g and 49.9cm2) or 40cm (0.36g and 34.9cm2) deep water. Within larger fragments, most of the mean final mass was contained in the youngest ramet (66% in 3-node and 67% in 4-node fragments). Results supported all three hypotheses, and suggest that only stem fragments with 2 or more nodes are likely to promote vegetative reproduction in I. aquatica, and that physiological integration may concentrate growth in younger ramets.

火炬树雌雄母株克隆生长差异及其光合荧光日变化

Because resources are limited,plants must allocate resources between growth and reproduction to maximize lifetime fitness.The clonal reproduction pattern of male plants may be different from that of females: the female plants may have to allocate resources to both seed production and clonal reproduction,while the male plants may have to allocate resources only to clonal growth.The Staghorn sumac(Rhus typhina Linn.) is an exotic tree species in China;it is dioecious and grows clonally.We hypothesized(1) that the clonal growth of male plants of R.typhina is greater than that of the female plants and(2) that this ecological difference can be explained by male plants either allocating a high proportion of photosynthetic products to clonal growth or males having a higher net photosynthetic rate.Finally,we hypothesized that(3) female and male plants of R.typhina may differ in the number of the clonal ramets,their photosynthetic physiological parameters,and their fluorescence parameters. In order to explore whether male and female plants of R.typhina had different colonization abilities and to analyze their diurnal changes in photosynthesis and chlorophyll fluorescence,we measured growth indicators and used a CIRAS-2 portable photosynthesis system and a FMS-2 PAM-2100 Chlorophyll Fluorometer.Growth indicators,chlorophyll content,and diurnal changes in photosynthetic parameters of both female and male plants growing in a sample plot were compared and analyzed. Based on the above,we can reveal the resources utilization efficiency of male and female plants of R.typhina and the buffering abilities to strong light between the male and female plants of R.typhina at noon.The results showed that: 1) Male plants were superior to females in clonal growth as indicated by ramet size and ramet number,and they produced clonal ramets one year earlier than females.2) Males used light energy,water,and CO2 more efficiently than females,and their net photosynthetic rate(Pn) was higher.This observation explains why male plants of R.typhina were better able to use resources than females.3) Under natural conditions,the potential efficiency of primary conversion of light energy of PS Ⅱ(Fv/Fm) for the male plants decreased smoothly and the non-photochemical quenching coefficient(qN) increased slowly in measuring period.However,the minimum value of the Fv/Fm for the female plant occurred at 11:00,and the peak value of qN occurred at the same time.Therefore,although the male plant did not show obvious light photoinhibition,but female did.Based on the diurnal changes of the nonphotochemical quench(qN) under high light intensity,female plants were better able to dissipate heat than male plants. Our results demonstrated that the light utilization efficiency,water use efficiency,carbon utilization efficiency,and net photosynthetic rate of male plants of R.typhina were all higher than those of female plants.Thus,male plants are able to allocate more resources to clonal growth.Male plants exhibit greater clonal growth and higher numbers of ramets than female plants,which suggests that male plants of R.typhina are dominant in monodominant communities of this plant.

Long-term population demography of Trillium recurvatum on loess bluffs in western Tennessee, USA

Understanding the demography of long-lived clonal herbs, with their extreme modularity, requires knowledge of both their short- and long-term survival and ramet growth patterns. The primary objective of this study was to understand the dynamics of a clonal forest herb, Trillium recurvatum, by examining temporal and small-scale demographic patterns. We hypothesized: (i) there would be more variability in the juvenile age class compared with non-flowering adult and flowering adult classes due to year-to-year fluctuations in recruitment; (ii) rates of population growth (λ) and increase (r) would be highest in non-flowering ramets due to a combination of transitions from the juvenile stage and reversions from flowering adults; and (iii) inter-ramet distances would be most variable between flowering and juvenile ramets due to a combination of clonal growth, seed dispersal by ants and ramet death over time. Census data were collected on the total number of stems in the population from 1990 to 2007, and placed within one of three life stages (juvenile, three-leaf non-flowering and three-leaf flowering). Modified population viability equations were used to assess temporal population viability, and spatial structure was assessed using block krigging. Correlations were performed using current and prior season weather to current population demography. The first hypothesis was rejected. The second hypothesis was supported: population increase (r) and growth rate (λ) were highest in non-flowering ramets. Finally, the third hypothesis was rejected: there was no apparent density dependence within this population of Trillium and no apparent spatial structure among life stages. Overall population density fluctuated over time, possibly due to storms that move soil, and prior year's temperature and precipitation. However, density remained at some dynamic stable level. The juvenile age class had greater variability for the duration of this study and population growth rate was greatest for non-flowering ramets.

Impact of attack by Gnorimoschema gallmakers on their ancestral and novel Solidago hosts

Interactions between insect herbivores and host plants can involve herbivore-host pairs that are evolutionarily ancient or only recently associated. Novel herbivore-host species pairs are continually being formed via host shifts, dispersal, and increasingly via anthropogenic introductions. Conceptual models of enemy-victim coevolution (specifically, the evolution of plant tolerance and of insect virulence) suggest that the impact of an herbivore on its novel host should, at least at first, be more intense than its impact on its ancestral host. We tested this hypothesis for the specialist gallmaking caterpillar Gnorimoschema gallaesolidaginis (Lepidoptera: Gelechiidae) on its ancestral and novel hosts, Solidago altissima and S. gigantea. We measured aboveground ramet mass for paired attacked and unattacked ramets of each species at two sites (Fredericton, NB, and Toronto, ON, Canada), and also measured allocation of tissue mass to stems, leaves, and flowers in galled and ungalled ramets. G. gallaesolidaginis attack reduced ramet growth considerably more on S. gigantea, the novel host, consistent with the coevolutionary hypothesis. We were unable to detect reallocation of tissues in galled ramets as a mechanism for tolerance, and found no intraspecific difference in the impact of gallmaking on allocation patterns. Herbivore host shifts between alternative native hosts will provide an excellent opportunity to understand the evolutionary history of novel herbivore-host associations, particularly (as in the Solidago system) when multiple insect herbivores have host-shifted across the same plant pair.

Effects of stolon severing on the expansion ofAlternanthera philoxeroidesfrom terrestrial to contaminated aquatic habitats

AbstractFew studies have examined the effects of clonal integration (translocation of resources between interconnected ramets) during the expansion of amphibious clonal plants from terrestrial to aquatic habitats. We conducted a greenhouse experiment to simulate the expansion of plants from terrestrial to contaminated aquatic habitats in the amphibious stoloniferous herbAlternanthera philoxeroides(alligator weed). The proximal ramets (i.e. relatively old) of clonal fragments grown in uncontaminated soils were connected to (allowing clonal integration) or disconnected from (preventing clonal integration) distal ramets (i.e. relatively young) grown either in uncontaminated water (control, no CuSO4) or in four copper‐contaminated water treatments containing 31.25, 62.5, 125 and 250 mg/L CuSO4, respectively. When a stolon connection was severed, all distal ramets grown in the contaminated water died. When the stolon connection was intact, however, the survival rate of the distal ramets was 85–100% when they were grown at the three lower levels of contamination and 43.75% at the highest level. Moreover, the survival rate and growth of the distal ramets grown in the three lower levels of contamination treatments did not differ from those in the control (uncontaminated water). These results suggest that clonal integration could greatly improve the survival and growth of alligator weed subjected to moderate levels of copper stress. Although clonal integration could also increase the survival rate of the connected distal ramets subjected to the highest level of copper stress (250 mg/L CuSO4) compared with that of disconnected distal ramets, the survival rate and growth measures were still significantly lower than those in the control. This suggests that clonal integration plays a limited role in the survival and growth of alligator weed when it is subjected to severe stress by high levels of copper contamination.

Differential response of the homoploid hybrid speciesIris nelsonii(Iridaceae) and its progenitors to abiotic habitat conditions

Homoploid hybrid speciation involves the evolution of reproductive isolation between a hybrid lineage and its progenitors without a change in chromosome number. Ecological divergence presumably plays a large role in the stabilization of hybrid lineages, as all homoploid hybrid species described to date are reported to be ecologically divergent from their progenitors. However, the described ecological divergence in most systems is anecdotal and has not been empirically tested. We assessed the vegetative response of Iris nelsonii, a homoploid hybrid species, and its three progenitor species, I. brevicaulis, I. fulva, and I. hexagona, to different abiotic conditions (i.e., varied sunlight availability and flooding conditions) that largely characterize the habitats of these four species in their natural habitats in Louisiana, USA. The species differed in their responses to the water-level treatment for many of the response variables, including rhizome weight, ramet growth, plant height, and two principal components used to characterize the data. The species differed in their response to the light-level treatment for root allocation and the principal component used to characterize plant size. Iris nelsonii significantly differed from its progenitors, including its most closely related progenitor species, in response to many of the treatments. The differential response to abiotic habitat conditions of I. nelsonii suggests that this species is ecologically divergent from its progenitor species.

Salinity stress modulates habitat selection in the clonal plant Aeluropus sinensis subjected to crude oil deposition1,2

Environmental stresses and disturbances are common in terrestrial ecosystems. Clonal integration and foraging behavior are often, but not always, beneficial for clonal plants grown in heterogeneous stressful environments. In this study, clonal fragments of the clonal perennial herb, Aeluropus sinensis (Debeaux) Tzvel (Poaceae), were grown with stolons connected or severed at five salinity levels (0, 50, 100, 200, and 400 mmol L−1 NaCl). In each clonal fragment, the apical ramet was exposed to crude oil on the sediment surface while the basal ramet was not. We proposed three possible scenarios: growth of the apical ramet subjected to crude oil would be (1) enhanced, (2) limited, or (3) not affected by clonal integration. Results supported scenario (2). Responses to crude oil differed between plants grown at low and high salinity levels. For A. sinensis, at high salinity levels, clonal integration promoted habitat selection by decreasing biomass of apical parts to escape the oil polluted habitats and increasing clonal growth of basal parts to select the unpolluted habitats, while at low salinity levels, connection did not influence growth of the basal or apical parts. Salinity modulates the behavior of a clonal plant subjected to heterogeneous crude oil contamination, at least in A. sinensis.

Effects of salinity and clonal integration on growth and sexual reproduction of the invasive grass Spartina alterniflora

The purpose of this study was to explore clonal integration of Spartina alterniflora under gradually changing substrate salinity conditions. We hypothesized that there might be a trade-off between growth and sexual reproduction influenced by soil salinity and, that clonal integration would change this trade-off. The experiment consisted of three levels of substrate salinity (5‰, 20‰ and 35‰), two clonal integration treatments (rhizomes severed or not), and three growth stages of daughter ramets (21, 40 and 60 cm tall). Both growth and sexual reproduction of S. alterniflora greatly decreased with increasing salinity. Clonal integration enhanced the survival, growth and sexual reproduction of daughter ramets experiencing salt stress, especially for young ramets, whereas the performance of mother ramets was reduced by clonal integration. Therefore, clonal integration did not affect performance of the whole clones. Contrary to expectations, there was no evidence for a trade-off between growth and sexual reproduction associated with salinity. In addition, clonal integration did not change the effect of salinity on the growth and sexual reproduction of mother and daughter ramets nor of the whole clones.