Ramet Height Research Articles

Field-based measurement tools to distinguish clonal Typha taxa and estimate biomass: a resource for conservation and restoration.

Two species of clonal Typha [T. latifolia (native) and T. angustifolia (exotic)] hybridize to form the highly invasive, heterotic (high vigor) T. × glauca in North American wetlands leading to increased primary production, litter accumulation, and biodiversity loss. Conservation of T. latifolia has become critical as invasive Typha has overwhelmed wetlands. In the field, Typha taxa identification is difficult due to subtle differences in morphology, and molecular identification is often unfeasible for managers. Furthermore, improved methods to non-destructively estimate Typha biomass is imperative to enhance ecological impact assessments. To address field-based Typha ID limitations, our study developed a predictive model from 14 Typha characters in 7 northern Michigan wetlands to accurately distinguish Typha taxa (n = 33) via linear discriminant analysis (LDA) of molecularly identified specimens. In addition, our study developed a partial least squares regression (PLS) model to predict Typha biomass from field collected measurements (n = 75). Results indicate that two field measurements [Leaf Counts, Longest Leaf] can accurately differentiate the three Typha taxa and advanced-generation hybrids. The LDA model had a 100% correct prediction rate of T. latifolia. The selected PLS biomass prediction model (sqrt[Typha Dry Mass] ~ log[Ramet Area at 30 cm] + Inflorescence Presence + Total Ramet Height + sqrt[Organic Matter Depth]) improved upon existing simple linear regression (SLR) height-to-biomass predictions. The rapid field-based Typha identification and biomass assessment tools presented in this study advance targeted management for regional conservation of T. latifolia and ecological restoration of wetlands impacted by invasive Typha taxa.

Evaluation of water depth and inundation duration on Typha domingensis sustainability in the Everglades Stormwater treatment areas: A test cell study

Typha domingensis is a dominant plant species in the Everglades Stormwater Treatment Areas, freshwater wetlands constructed to reduce phosphorus (P) levels in stormwater runoff prior to discharge into the Everglades. Water depth and duration of inundation can negatively affect the health of these plants. To determine the effect of water depth and inundation duration, Typha plants were grown in this study in a series of 15 test cells, 0.2 ha in area, and exposed to five water-depth treatments over 10 months: control (40 cm), shallow (61 cm), moderate (84 cm), deep (104 cm) and extremely deep (124 cm). Mean adult Typha densities declined from 14.1 shoots m−2 in the control to 10.9 and 10.5 shoots m−2 in the deep and extremely-deep treatments, respectively. However, only mean juvenile Typha densities were significantly different among water-level treatments, declining from 3.2 juveniles m−2 in the control to 1.2 and 0.6 juveniles m−2 in the deep and extremely-deep treatments, respectively. Typha leaf elongation rate (LER) was significantly higher in the deeper treatments, with the highest rates measured during the active growing season (July to October). LER increased from 6.84 cm day−1 during June baseline measurements to 8.89 cm day−1 in the deeper treatments after eight weeks of continuous inundation. Typha showed morphological plasticity to adapt to deep water through changes in morphology and biomass allocation. Typha grew significantly taller and heavier to adapt to deep-water conditions and facilitate gas exchange between the above and belowground tissues. Ramet height of Typha harvested at the end of the study averaged 343 and 374 cm in the deep and extremely-deep treatments, respectively, compared to 285 cm in the control. Likewise, the weight of individual adult ramets was significantly greater in the deeper treatments (256 g ramet−1) compared to the control (123 g ramet−1). Although none of the water-level treatments resulted in a total collapse of their Typha populations, increased LER in the deeper treatments resulted in less structural support in stems, causing substantial Typha lodging when water levels were lowered at the end of the study. These findings provide valuable insight into the effect of different water-level inundations on plant responses and overall health of Typha populations in the STAs.

From simple metrics to cervid forage: Improving predictions of ericaceous shrub biomass

Common understory vegetation species such as the ericaceous shrubs bilberry (Vaccinium myrtillus), cowberry (V. vitis-idaea) and heather (Calluna vulgaris), are key forage plant species for moose and other large herbivores, as well as fulfilling many additional ecosystem functions and services. Here we developed models to predict above-ground biomass of these ericaceous species in coniferous forests, using data on their percentage cover, height, and different stand characteristics. We also built models to understand how the aforementioned variables affect the proportion of the shrubs commonly utilized as forage by large herbivores. We found that the percentage cover of shrubs was the most important explanatory variable when predicting above-ground biomass, explaining 51%, 47% and 71% of the variation (marginal R2) in bilberry, cowberry and heather biomass, respectively. By adding ramet height to the model with percentage cover, the variation explained increased to 77% for bilberry, 75% for cowberry and 87% for heather. The best outcome for candidate models was obtained by adding stand site index and spruce basal area to the model, improving the variation explained in bilberry to 83%, to 81% for cowberry, and 91% for heather. When modelling the proportion of the shrubs commonly utilized as forage by large herbivores, stand site index and spruce basal area often played important roles. Some of the best fitting models for forage biomass explained 51% of the variation in bilberry, 59% in cowberry and 30% in heather. Site location did not have a major role in improving the variability explained in either type of model, which indicated the applicability of the models regardless of study location. Our models therefore have a high potential to be implemented in forestry decision support systems. Their inclusion should provide better large-scale estimations of forage resources, aiding forest management, and thereby taking an important step forward to determine the ecosystem carrying capacity of large herbivores.

Temperature and flooding depth thresholds for early recruitment stages in a bulbous plant Bolboschoenus planiculmis

Early recruitment process dominated by vegetation reproduction for wetland plant is a key life-history stage affecting species distribution. Extreme climatic events, such as extreme temperature and heavy rainfall have been predicted to become more intense and frequent under future climate scenarios. To explore the effect of temperature and flooding depth on tubers sprouting and early growth of Bolboschoenus planiculmis, we conducted two artificial experiments in the incubator and greenhouse, including ten temperature regimes (8, 10, 12, 14, 16, 19, 22, 25, 28 and 31 °C), and ten flooding depth treatments (− 5, 0, 3, 6, 9, 12, 16, 20, 30 and 40 cm). The results showed that the temperature and flooding depth had significant effect on the tuber sprouting and ramet early growth. The estimated base temperature for the sprouting is 6.2 °C, the final sprouting percentage increased parabolically with increasing temperature and reached a maximum of 61.09% at 25.4 °C. The final sprouting percentage increased first and then decreased with increasing flooding depth, and reached a maximum of 96.04% at 3.92 cm. The ramet height increased first and then decreased with increasing flooding depth, and reached a maximum of 61.29 cm at 8.20 cm. Our study will provide a basis for understanding and predicting the influence of climate change on the distribution of B. planiculmis.

Herbivory, plant traits and nectar chemistry interact to affect the community of insect visitors and pollination in common milkweed, Asclepias syriaca.

Herbivory can alter plant fitness directly through changing reproductive allocation and indirectly through changing pollinator identity or behavior. Common milkweed is a plant of conservation concern with an inducible chemical defense that is also an important nectar resource. In this study, we aim to understand how herbivory severity and plant traits, including morphology and nectar chemistry, interact to affect insect visitation and pod production in common milkweed. We conducted pollinator watches on plants with experimentally varied herbivory severity and quantified insect frequency and visit length as a response to nectar chemistry, ramet height, number of inflorescences, number of flowers per inflorescence and percent tissue removed. We also quantified pollinator effectiveness and importance. Increased herbivory severity reduced floral displays, including fewer inflorescences and fewer flowers per inflorescence. A reduced floral display was correlated with reduced sucrose, fructose and glucose and resulted in a reduced number and species richness of insect visitors. Fewer flowers per inflorescence reduced the frequency of bumble bee and fly visitors, which were two important pollinators. Although honeybees, flies, small bees, soldier beetles and bumble bees were equally effective pollinators, only bumble bee frequency was positively correlated with pod production. The differences in pollinator visitation have the potential to create diversifying selection on plant floral traits, many of which are also affected by herbivores. This research demonstrates potentially conflicting selection pressures between native and non-native pollinators as well as non-native herbivores.

Growth and Morphological Responses of Kentucky Bluegrass to Homogeneous and Heterogeneous Soil Water Availabilities

Understanding the effect of water heterogeneity on the growth and water integration of clonal plants is important for scientific water management. In controlled field plots, we conducted a study by creating three different soil water treatments comprising four patches with different soil water supplies using Kentucky bluegrass (Poa pratensis L.) as the materials. The objective was to explore the differences in the growth indices and morphological attributes, and the possible water integration in ‘Arcadia’ Kentucky bluegrass in plots and patches with different soil water availabilities. Soil water deficit resulted in the declined biomass, root/shoot ratio and leaf relative water content of the whole genet, decreased leaf length and height of mother ramet, reduced leaf width and height of daughter ramets, and significant changes in the structures of vascular bundles in rhizomes and leaves. However, the leaf length, leaf width, height and leaf relative water content of daughter ramets in heterogeneous water-poor patches were recovered to the levels in water-rich patches. In addition, the diameter of the vessel in the xylem and percentage of the xylem area in leaf vascular bundles of daughter ramets in the heterogeneous water-poor patch were insignificantly different from those in water-rich patches. These results demonstrated that water integration among interconnected ramets promoted the growth status of daughter ramets in heterogeneous water-poor patches. However, the water translocation in interconnected ramets subjecting to heterogeneous water supplies was not investigated using stable isotope labelling in this study. Thus, the directions and patterns of water translocation among ramets necessitate further research.

Estimation of temperature and flooding depth thresholds for Phragmites australis rhizome bud sprouting

AbstractCurrent climate models predict more intense rainstorms and temperature extreme events under future global climate change. Estimation of environmental factors thresholds might provide important information for the common patterns of species distributions and management of wetland ecosystems. The laboratory experiment and the greenhouse experiment examined separately the effects of temperature (10 constant temperature regimes of 8, 10, 12, 14, 16, 19, 22, 26, 30 and 35°C) and flooding depth (10 flooding depth treatments of −15, −10, −5, 0, +5, +10, +15, +20, +25 and +30 cm relative to the substrate surface) on rhizome bud sprouting and establishment of Phragmites australis. Our results revealed that the final sprouting percentage, relative growth rate and ramet height showed hump‐shaped relationships with temperature. Higher temperature led to shorter mean time to sprout, faster sprouting rate and greater ramet survival. The estimated base temperature for rhizome bud sprouting was 5.0 ± 1.27°C. The optimum temperature for rhizome bud sprouting and early growth might be the range of 23–30°C. The final sprouting percentage, relative growth rate and ramet height showed unimodal patterns with flooding depth. The mean time to sprout was increased with deeper flooding depth, while sprouting rate and ramet survival were decreased. The optimum flooding depth for rhizome bud sprouting and early growth might be the range of −7 to 0 cm. Our results will contribute to a better understanding of the influence of climate change on early plant recruitment processes and distribution of P. australis.

Water depth rather than substrate heterogeneity affects the clonal performance of the stoloniferous submerged plant, Vallisneria spiralis L

Environmental heterogeneity profoundly influences the performance of clonal plants. To evaluate the effects of substrate patchiness and different water depths on clonal performance, we subjected the stoloniferous submerged plant Vallisneria spiralis L. to different patchy substrates and water depths. We measured several growth traits. We found that ramet number, leaf number, and stolon length decreased, and ramet height, spacer thickness, and biomass increased with increasing water depth. We saw no significant trait variations across different substrates. Furthermore, the trait allocation – the distribution of trait values in different patches of heterogeneous substrates – was consistent in most treatments. Clonal integration homogenized the effects of substrate patchiness via resource exchange through interconnected ramets. The ability to use water nutrients may enable submerged plants to alleviate the uneven distribution of soil nutrients in patchy substrates. Additionally, the simple root structure and weak root functions curtail submerged plants in obtaining sufficient nutrients from soil. Water depth rather than substrate heterogeneity determined the plant performance of V. spiralis.

Effects of sand burial in integrated clonal systems of the invasive Carpobrotus edulis

ABSTRACT Sand burial represents one of the most common stresses for plant performance in coastal sand dunes. Clonal plants inhabiting sand dunes frequently experience situations in which the sand can bury part of the clone while other modules remain unburied. Here we present a field experiment in a coastal sand dune testing the effect of sand burial in the clonal Carpobrotus edulis. In the experiment, apical ramets were either or not subjected to burial in sand to a depth of 90% ramet height, and connected basal ramets were not subjected to sand burial. Sand burial significantly reduced survival and growth of apical ramets. Interestingly, we found a non-local plastic response in basal ramets that was dependent on the conditions experienced by their apical ramets. Thus, when apical ramets remained unburied a developmentally programmed division of labour was found. In this situation, basal ramets specialized in the acquisition of soil-based resources while apical ramets specialized in aboveground expansion. On the contrary, when apical ramets were subjected to sand burial, basal ramets increased the production of photosynthetic structures. This response could alleviate the light stress suffered by the buried apical ramets. We demonstrate that burial stress suffered by apical ramets of C. edulis triggered a compensatory response in their connected unburied ramets. This result highlights the importance of considering modular plasticity to understand plant responses to sand burial stress.

Shade Avoidance and Light Foraging of a Clonal Woody Species, Pachysandra terminalis.

(1) Background: A central subject in clonal plant ecology is to elucidate the mechanism by which clones forage resources in heterogeneous environments. Compared with studies conducted in laboratories or experimental gardens, studies on light foraging of forest woody clonal plants in their natural habitats are limited. (2) Methods: We investigated wild populations of an evergreen clonal understory shrub, Japanese pachysandra (Pachysandra terminalis Siebold & Zucc.), in two cool-temperate forests in Japan. (3) Results: Similar to the results of herbaceous clonal species, this species formed a dense stand in a relatively well-lit place, and a sparse stand in a shaded place. Higher specific rhizome length (i.e., length per unit mass) in shade resulted in lower ramet population density in shade. The individual leaf area, whole-ramet leaf area, or ramet height did not increase with increased light availability. The number of flower buds per flowering ramet increased as the canopy openness or population density increased. (4) Conclusions: Our results provide the first empirical evidence of shade avoidance and light foraging with morphological plasticity for a clonal woody species.

Clonal performance of Scirpus yagara in multiple levels of substrate heterogeneity and submergence

Abstract Aims Environmental heterogeneity affects the performance of clonal aquatic plants. Few researchers integrated two aspects of heterogeneity into the study of clonal plant ecology. The aims of the present study are to (i) test whether different substrate heterogeneity and submergence exert similar effects on plant performance and (ii) explore the foraging behaviour. Methods In this study, Scirpus yagara was subjected to multiple levels of substrate heterogeneity and submergence. Substrate treatments included one homogeneous substrate and three heterogeneous substrates (two-patch, four-patch and eight-patch). Water level treatments included 0, 10 and 30 cm. Traits including ramet number, generation number, leaf number, bulb number, ramet height, culm length, rhizome length, clonal radius, spacer length, spacer thickness, total biomass, biomass of bulbs and biomass per bulb were measured. Important Findings Deeper water levels significantly reduced variables associated with growth such as ramet number, generation number, leaf number and bulb number, while substrate patchiness induced significant variations in traits such as spacer length and spacer thickness. Significant interactive effects of the two factors were found for ramet number, leaf number and spacer length. Scirpus yagara showed colonization towards the lake sediment patch in two-patch and four-patch substrates, and more structures were placed in the lake sediment patch. Especially for the two-patch substrate, all structures occupied the lake sediment patch. Two-sided intrusion was observed in the eight-patch substrate, which induced an even allocation of structures in different patches. The foraging behaviour was correlated with the patch size.

Effect of rhizome exposure to contrasting abiotic conditions on the performance of the invasive macrophyte Hedychium coronarium J. Koenig (Zingiberaceae)

Although invasive species are often better competitors than native species, broad environmental tolerance may also drive invasion success. Tolerance to abiotic heterogeneity in riparian ecosystems tends to favour the establishment of alien clonal species, as well as their dispersion by vegetative fragments. Hedychium coronarium J. Koenig is a rhizomatous emergent macrophyte native to Asia and has invaded Neotropical riparian ecosystems. We assessed the effect of H. coronarium rhizome exposure to distinct abiotic conditions on ramet growth. We exposed rhizomes to different desiccation periods (1–90 days), temperatures (15, 25 and 35 °C), and light regimes (0, 12, 16 h) and then assessed the effect of each of these variables on subsequent clonal growth (aboveground biomass production per plant and per ramet, and number and height of ramets) under ambient conditions. While no rhizome survived desiccation periods longer than 30 days, ramet growth among surviving rhizomes was not affected by the period of desiccation. Biomass production per rhizome, ramet biomass, and ramet height were significantly lower at 35 °C than at 25 °C. Constant darkness increased rhizome survival, but decreased ramet growth. Although rhizome exposure to extremes of each abiotic variable may hinder the invasion success of H. coronarium, the subsequent aboveground biomass production of surviving rhizomes did not decrease strongly in response to any treatment. This resilience may contribute to successful establishment of H. coronarium after dispersal through rhizome fragments and to varying abiotic conditions.

Integrating management techniques to restore subtropical forests invaded by Hedychium coronarium J. Köenig (Zingiberaceae) in a biodiversity hotspot

The restoration of areas invaded by non‐native plants is challenging as invasive plants may affect both biotic and abiotic components of ecosystems, leading to impacts that constrain recolonization by native species after invaders are eliminated. In such a scenario, restoration techniques as topsoil transposition might accelerate colonization by native species in forests. Hedychium coronarium J. Koenig (Zingiberaceae) is a Himalayan herbaceous rhizomatous plant recognized as invasive in several countries. This study aimed to experimentally evaluate the response of plant assemblages to topsoil transposition on a site invaded by H. coronarium after chemical control. Four treatments were applied: chemical control integrated with topsoil transposition, chemical control of H. coronarium alone, topsoil transposition alone, and no intervention (control). Plots were evaluated prior to the application of treatments and then monthly for 11 months after treatments. Parameters were measured for H. coronarium (number of ramets, ramet height, and cover) and other species (species richness, abundance, and cover). Plots treated with chemical control (regardless of topsoil transposition) were similar in terms of all parameters measured and species composition, with dominance of herbs and shrubs. Plots managed solely with topsoil transposition had lower species richness, abundance, and cover, but more diverse life‐forms, being equally rich in climbers, trees, and herbs. Chemical control was effective to control invasion by H. coronarium and increase species richness and abundance on the managed site. Topsoil transposition promoted colonization by species that might accelerate restoration.

Litter accumulation and biomass dynamics in riparian zones in tropical South America of the Asian invasive plant Hedychium coronarium J. König (Zingiberaceae)

ABSTRACTBackground: Promoting changes in abiotic conditions and ecosystem processes, such as decomposition, is a mechanism by which some exotic plant species displace native plants and become invasive.Aims: We monitored ramets of Hedychium coronarium over 30 months to estimate the litter decay rate, biomass dynamics and litter accumulation over time in riparian sites invaded by the species in southeastern Brazil.Methods: We measured the number, height, emergence and mortality of ramets in three environments invaded by H. coronarium (natural, rural and urban). We also measured litter decay in situ and in in vitro experiments. We used sinusoidal models to describe height fluctuation and exponential models to simulate litter decay and litter accumulation.Results: Ramets of H. coronarium showed high seasonal variation in terms of height and emergence, as well as low litter decay. Accordingly, our models predicted high litter production and a seasonal pattern of litter accumulation in invaded sites.Conclusions: H. coronarium produces a great amount of litter, which shows slow decay and hence seems to affect decomposition processes. Investigating seasonal variation on the effects of invasive species on ecosystem functioning shed light on the factors driving the success and impact of invasive plants.

Trait and density responses of Spartina alterniflora to inundation in the Yellow River Delta, China

Understanding plant traits in response to physical stress has been an important issue in the study of coastal saltmarshes. For plants that reproduce both sexually and asexually, whether and how seedlings (sexual reproduction) and clonal ramets (asexual reproduction) may differentially respond to tidal inundation is still unclear. We investigated the growth and morphology of sexual and asexual propagules of an exotic saltmarsh plant (Spartina alterniflora) along a gradient of tidal submergence in the Yellow River Delta. Our results showed that the density, height and basal diameter of clonal ramets or sexual seedlings increased with tidal inundation. The patch amplification edge clonal ramets are superior than patch center plants. The differences response of plants to tidal inundation highlight the sensitivity of S. alterniflora to future tidal regime shifts and can help predict and evaluate the impacts of changes in inundation conditions due to sea level rise, coastal erosion and human activities.

Is phenotypic plasticity an explanation for the invasiveness of goldenrods (SolidagoandEuthamia) in Europe?

AbstractHigh phenotypic plasticity contributes to invasiveness of alien species. Goldenrods of American origin (Solidago canadensis,S. giganteaandEuthamia graminifolia) have successfully invaded Europe, and this success can be related to their high phenotypic plasticity. The aim of our study was to test the hypothesis of higher phenotypic plasticity of invasive goldenrods by comparing them with native taxa: closely relatedSolidago virgaureaand similar ecologically, invasive in other regionsTanacetum vulgare. The species studied were grown in a common garden on three different substrates with different fertilizers. After 3 years, the height and number of ramets, biomass production and allocation, phenology and nitrate reductase activity (NRA) were measured. The highest level of phenotypic plasticity was exhibited by the competitively weak native speciesS. virgaurea. The invasive species produced relatively high biomass and exhibited a moderate level of phenotypic plasticity. Variability in the studied traits did not always correlate with differences in substrates. The invasion success of non‐native goldenrods is not caused by their having a higher phenotypic plasticity than native species. Rather, the non‐natives should be considered as “Jack of all traits, and master of some”.

The importance of sexual, asexual and mixed ramet clusters in production of descendant ramets in populations of Solidago \xd7niederederi (Asteraceae)

In this study, we focused on the potential production of descendant ramets in sexual, asexual, and mixed ramet clusters of Solidago ×niederederi Khek (Asteraceae), a natural hybrid between the North American S. canadensis and the European S. virgaurea. We selected eight populations of the hybrid occurring in southern Poland. The ANOVA results proved the significant effect of cluster type and population on the number of descendant ramets in sexual, asexual, and mixed ramet clusters. The post-hoc Tukey test showed that the number of descendant ramets in sexual and mixed ramet clusters differs significantly (p < 0.001). The number of descendant ramets was positively correlated with the number of maternal ramets in sexual, asexual, and mixed ramet clusters, reaching the coefficient values of 0.78, 0.64, and 0.82, respectively. Moreover, the number of descendant ramets was positively correlated with the height of maternal ramets in mixed ramet clusters, reaching the coefficient value of 0.25. The post-hoc Tukey test revealed the significant differences between the height of ramets originating from sexual and asexual ramet clusters (p < 0.001). Our results complemented the current state of knowledge and brought evidence that the number of descendant ramets might be influenced by a type of ramet cluster.

The spatial ecology of sex ratios in a dioecious plant: Relations between ramet and genet sex ratios

Abstract In clonal dioecious plants, the frequency and spatial distribution of flowering ramets contains information on the underlying genet sex ratio. These measures can also provide insight on potential ecological mechanisms causing variation and bias in sex ratios among populations. We used a novel likelihood‐based approach and spatial clustering model to estimate the genet sex ratios from flowering ramet data collected from 32 populations of dioecious Thalictrum pubescens, a clonal species from eastern N. America that occupies moist wetland and forested environments. We investigated sex ratios of seed families, clone size, patterns of flowering and plant height to determine potential causes of sex‐ratio bias. Flowering ramet sex ratios varied considerably among populations but were significantly male‐biased. Seed families grown to flowering also exhibited the same degree of male bias. Both models predicted close correspondence between ramet and genet sex ratios. The likelihood model revealed that sex differences in ramet production could not account for biased ramet sex ratios. The spatial clustering model indicated that ramets were significantly clustered at two spatial scales and estimated similar cluster sizes and densities for both sexes. There was no evidence for spatial segregation of the sexes. Both sexes were equally likely to flower in consecutive years and repeated bouts of flowering had no effect on ramet height. Synthesis. Our analyses suggest that the widespread occurrence of male‐biased sex ratios in Thalictrum pubescens is unlikely to result from sexual differences in clonal growth or habitat preferences. The bias appears to become established early in the life cycle, perhaps at the seed stage as a consequence of local resource competition.

An invasive population of Solidago canadensis is less sensitive to warming and nitrogen-addition than its native population in an invaded range

Native and invasive populations might behave differentially due to contrasting genetics and histories of environmental pressures. Here we attempted to understand how climate warming and atmospheric nitrogen (N) deposition influence native and invasive populations, and thus conducted an experiment to address their effects on the nine invasiveness-related traits (leaf dry matter content, specific leaf area, leaf lifespan, ramet height, ramet number, the first inflorescence buds, the first flowering, the first seed-setting, and the first dieback) of Solidago canadensis populations from the USA and China. Solidago canadensis from the USA had shorter leaf lifespan and ramet height, smaller ramet number, and earlier phenology than that from China. Warming and N addition extended leaf lifespan but failed to influence leaf dry matter content and specific leaf area; warming decreased ramet height and delayed the onset of inflorescence and flowering but N addition increased ramet height and advanced the onset of inflorescence and flowering. Six traits were more sensitive to warming or N addition in the native population than in the invasive population, and the other traits were similar; warming and N addition together had stronger effects on six traits of the native population than those of the invasive population, and the opposite was true for ramet height. Our results suggest that climate warming and N deposition might promote S. canadensis invasion, as indicated by enhanced growth, and could influence its native populations to a greater extent than its invasive populations.

Responses of the native species Sparganium angustifolium and the invasive species Egeria densa to warming and interspecific competition.

Climate change, especially warming temperatures, may increase invasion and modify the ecological impacts of invasive species by enhancing their ability to compete. To test the effects of warming on invasive plants, a mesocosm experiment was conducted to study competition between the invasive plant Egeria densa and the native hygrophyte Sparganium angustifolium under simulated warming conditions in a greenhouse. These two species were grown in monoculture (no competitor control) or mixed culture (competitor control) for two months under different temperature conditions (warming treatment or no-warming treatment). In S. angustifolium, the higher temperatures led to a shorter root length and significantly increased the aboveground traits of ramets, the total biomass, and the RGR (relative growth rate) but had no effect on the aboveground traits of genets. Growth in mixed culture significantly decreased the S. angustifolium ramet height under warmer conditions and significantly reduced the ramet root length, ramet number, genet biomass, root-to-shoot ratio and RGR of S. angustifolium under natural temperature conditions. All the morphological, biomass and growth traits of E. densa except for the root-to-shoot ratio were significantly increased by the warmer temperatures and decreased by growth in mixed culture. The RCI and RII of E. densa in both the no-warming and warmer environments were two and three times greater than those of S. angustifolium, whereas the ACI values for the two species were similar. Thus, S. angustifolium was a better competitor than E. densa under both temperature conditions. These results suggest that although the superior competitive ability of native species can inhibit E. densa growth, the performance of this species will be enhanced under future climate warming in cold regions.