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1.
Lynda J. Goff Larry Liddle Paul C. Silva Mary Voytek Annette W. Coleman 《American journal of botany》1992,79(11):1279-1285
The siphonous green alga Codium fragile occurs in many temperate marine regions and is composed of a number of distinct subspecies. Included in this taxon is the common open coast C. fragile subsp. fragile of the northeast Pacific and the weedy C. fragile subsp. tomentosoides which has invaded temperate marine communities in the Atlantic and Pacific oceans. The center of origin of this weedy subspecies is not known, although it is thought to have dispersed from the northwest Pacific. To examine the relationship of the weedy subspecies to the indigenous northeast Pacific form, chloroplast DNA was compared. Each of these subspecies has a restriction map that is uniform throughout its geographic distribution, and the patterns are distinct from each other and from other Codium species examined. However, the two share an almost identical genome size and arrangement of genes. A population in San Francisco Bay was found to be indistinguishable from the weed C. fragile subsp. tomentosoides from the Atlantic. The potential for using molecular data in solving systematic problems in Codium has been clearly demonstrated. 相似文献
2.
Emma Cebrian Fiona Tomas Paula López-Sendino Montserrat Vilà Enric Ballesteros 《Biological invasions》2018,20(10):2839-2848
The biotic resistance hypothesis predicts that more diverse communities should have greater resistance to invasions than species-poor communities. However for facultative and obligate epiphytic invaders a high native species richness, abundance and community complexity might provide more resources for the invader to thrive to. We conducted surveys across space and time to test for the influence of native algal species abundance and richness on the abundance of the invasive facultative epiphytic filamentous alga Lophocladia lallemandii in a Mediterranean Cystoseira balearica seaweed forest. By removing different functional groups of algae, we also tested whether these relationships were dependent on the complexity and abundance of the native algal community. When invasion was first detected, Lophocladia abundance was positively related to species richness, but the correlation became negative after two years of invasion. Similarly, a negative relationship was also observed across sites. The removal experiment revealed that more complex native communities were more heavily invaded, where also a positive relationship was found between native algal richness and Lophocladia, independently of the native algal abundance. Our observational and experimental data show that, at early stages of invasion, species-rich seaweed forests are not more resistant to invasion than species-poor communities. Higher richness of native algal species may increase resource availability (i.e. substrate) for invader establishment, thus facilitating invasion. After the initial invasion stage, native species richness decreases with time since invasion, suggesting negative impacts of invasive species on native biodiversity. 相似文献
3.
Annelise Sabine Chapman 《Helgoland Marine Research》1998,52(3-4):277-289
The green algaCodium fragile ssp.tomentosoides (Chlorophyta) has been introduced accidentally and successfully from Japan to many shores of the northern and southern hemispheres, including those of the Northeast and Northwest Atlantic Ocean. On most European coasts,Codium occurs regularly but at low abundances in the intertidal zone and is absent from subtidal habitats. In contrast,Codium is extremely abundant in subtidal kelp beds in the Northwest Atlantic Ocean where it often reaches nuisance proportions. This differential success cannot be accounted for by either the properties of the invader or by physico-chemical differences between invaded coasts. A theoretical comparison between two regions on opposite sides of the Atlantic Ocean, i.e. Eastern Nova Scotia, Canada, and south central Britain, illustrates how the resident benthic community may determine the difference in relative abundance ofCodium in subtidal habitats between northeast America and Europe. In this review, low floral species diversity, biological disturbance and facilitation by a previous species invasion are suggested as potential factors for the establishment, success and abundance ofCodium in the Northwest Atlantic Ocean, but these require testing in field experiments. 相似文献
4.
The objective of this study was to quantify the spatial and temporal recolonization characteristics of Zostera marina beds in the lower Chesapeake Bay following large scale declines in the late summer of 2005. Transects were established and
monitored monthly for changes in eelgrass abundance at three sites (two downriver, one upriver) in the York River from April–October
2006 and 2007. Measurements included percent bottom cover, above ground biomass, shoot density, shoot origin (seedling or
vegetative), seed bank abundance and seed viability. During 2006, the eelgrass beds at all sites recovered with seedlings
providing the largest proportion of the total shoot abundance. This trend shifted in 2007 and surviving vegetative shoots
were the dominant component of shoot standing crop. A second consecutive decline related to low light conditions occurred
during the summer of 2006 in the upriver site and recovery there was minimal in 2007. These results highlight that after a
single die off event, seed germination with subsequent seedling growth is the principal method for revegetation in lower Chesapeake
Bay Z. marina beds. However, no viable seeds remain in the seed bank during this first year of recovery and shoots produced by the seedling
growth do not flower and produce seeds until their second year of growth. Therefore the seed-bank density is low and is not
immediately replenished. This suggests that the resiliency of perennial Chesapeake Bay Z. marina populations to repeated disturbances is restricted and repeated annual stress may result in much longer term bed loss. 相似文献
5.
Non-native grass invasion alters native plant composition in experimental communities 总被引:1,自引:0,他引:1
Invasions of non-native species are considered to have significant impacts on native species, but few studies have quantified
the direct effects of invasions on native community structure and composition. Many studies on the effects of invasions fail
to distinguish between (1) differential responses of native and non-native species to environmental conditions, and (2) direct
impacts of invasions on native communities. In particular, invasions may alter community assembly following disturbance and
prevent recolonization of native species. To determine if invasions directly impact native communities, we established 32
experimental plots (27.5 m2) and seeded them with 12 native species. Then, we added seed of a non-native invasive grass (Microstegium vimineum) to half of the plots and compared native plant community responses between control and invaded plots. Invasion reduced native
biomass by 46, 64, and 58%, respectively, over three growing seasons. After the second year of the experiment, invaded plots
had 43% lower species richness and 38% lower diversity as calculated from the Shannon index. Nonmetric multidimensional scaling
ordination showed a significant divergence in composition between invaded and control plots. Further, there was a strong negative
relationship between invader and native plant biomass, signifying that native plants are more strongly suppressed in densely
invaded areas. Our results show that a non-native invasive plant inhibits native species establishment and growth following
disturbance and that native species do not gain competitive dominance after multiple growing seasons. Thus, plant invaders
can alter the structure of native plant communities and reduce the success of restoration efforts. 相似文献
6.
A rhizomatous growth form of Codium fragile is described for the first time. Plants were collected in the Gulf of St. Lawrence in estuaries dominated by Zostera marina. Rhizomatous plants developed from propagules of whole plants that settled horizontally. Horizontal axes of C. fragile were up to 1 m long in plants collected in situ. Plants developed several to dozens of erect axes at right angle to the base. Horizontal growth of up to 0.2 m was found in field experiments where fragments were tied to plastic mesh and left in situ for 4 months. The unconsolidated filaments at the base of C. fragile often wrapped around the rhizomes of Z. marina and up to five separate attachment sites to eelgrass were found in single plants of C. fragile. In four estuaries, 57–100% of Codium plants with identifiable substratum were attached to shoots and rhizomes of Z. marina. The rhizomatous growth form was found in plants identified as C. fragile ssp. tomentosoides (Nova Scotia and Prince Edward Island) and C. fragile ssp. atlanticum (Prince Edward Island), suggesting that this is a phenotypic response to growth in soft bottom environments.Communicated by K Lüning 相似文献
7.
Variable responses of native eelgrass Zostera marina to a non-indigenous bivalve Musculista senhousia 总被引:6,自引:0,他引:6
The transport and establishment of non-indigenous species in coastal marine environments are increasing worldwide, yet few
studies have experimentally addressed the interactions between potentially dominant non-native species and native organisms.
We studied the effects of the introduced mussel Musculista senhousia on leaf and rhizome growth and shoot density of eelgrass Zostera marina in San Diego Bay, California. We added M. senhousia over a natural range in biomass (0–1200 g dry mass/m2) to eelgrass in transplanted and established beds. The effects of the non-indigenous mussel varied from facilitation to interference
depending on time, the abundance of M. senhousia, and the response variable considered. Consistent results were that mussel additions linearly inhibited eelgrass rhizome
elongation rates. With 800 g dry mass/m2 of M. senhousia, eelgrass rhizomes grew 40% less than controls in two eelgrass transplantations and in one established eelgrass bed. These
results indicate that M. senhousia, could both impair the success of transplantations of eelgrass, which spread vegetatively by rhizomes, and the spread of
established Z. marina beds to areas inhabited by M. senhousia. Although effects on leaf growth were not always significant, in August in both eelgrass transplantations and established
meadows leaf growth was fertilized by mussels, and showed a saturation-type relationship to sediment ammonium concentrations.
Ammonium concentrations and sediment organic content were linear functions of mussel biomass. We found only small, non-consistent
effects of M. senhousia on shoot density of eelgrass over 6-month periods. In established eelgrass beds, but not in transplanted eelgrass patches
(≈0.8 m in diameter), added mussels suffered large declines. Hence, eelgrass is likely to be affected by M. senhousia primarily where Z. marina beds are patchy and sparse. Our study has management and conservation implications for eelgrass because many beds are already
seriously degraded and limited in southern California where the mussel is very abundant.
Received: 31 May 1997 / Accepted: 4 September 1997 相似文献
8.
In assessments of ecological impact in invasion ecology, most studies compare un‐invaded sites with highly invaded sites, representing the ‘worst‐case scenario’, and so there is little information on how impact is modified by the population density of the invader. Here, we assess how ecological impact is modified by population density through the experimental development of density‐impact curves for a model invasive fish. Using replicated mesocosms and the highly invasive Pseudorasbora parva as the model, we quantified how their population density influenced their diet composition and their impacts on invertebrate communities and ecosystem processes. The density–impact curves revealed both linear and non‐linear density–impact relationships. The relationship between P. parva density and zooplankton body mass was represented by a low‐threshold curve, where their impact was higher at low densities than predicted by a linear relationship. In contrast, whilst the relationship between density and zooplankton biomass and abundance was also non‐linear, it was high‐threshold, indicating a lower impact than a linear relationship would predict. Impacts on diversity and phytoplankton standing stock were linear and impacts on benthic invertebrate abundance and decomposition rates were represented by s‐shaped curves. These relationships were underpinned by P. parva dietary analyses that revealed increasing reliance on zooplankton as density increased due to depletion of other resources. We caution against the common assumption that ecological impact increases linearly with invader density and suggest that increased understanding of the relationship between invader population density and ecological impact can avoid under‐investment in the management of invaders that cause severe problems at low densities. 相似文献
9.
Paula V. Fernández Marina Ciancia Alicia B. Miravalles José Manuel Estevez 《Journal of phycology》2010,46(3):456-465
Cell walls in the coenocytic green seaweed Codium vermilara (Olivi) Chiaje (Bryopsidales, Chlorophyta) are composed of ~32% (w/w) β‐(1→4)‐d‐mannans, ~12% sulfated polysaccharides (SPs), and small amounts of hydroxyproline‐rich glycoprotein‐like (HRGP‐L) compounds of the arabinogalactan proteins (AGPs) and arabinosides (extensins). Similar quantities of mannans and SPs were reported previously in the related seaweed C. fragile (Suringar) Hariot. Overall, both seaweed cell walls comprise ~40%–44% of their dry weights. Within the SP group, a variety of polysaccharide structures from pyruvylated arabinogalactan sulfate and pyruvylated galactan sulfate to pyranosic arabinan sulfate are present in Codium cell walls. In this paper, the in situ distribution of the main cell‐wall polymers in the green seaweed C. vermilara was studied, comparing their arrangements with those observed in cell walls from C. fragile. The utricle cell wall in C. vermilara showed by TEM a sandwich structure of two fibrillar‐like layers of similar width delimiting a middle amorphous‐like zone. By immuno‐ and chemical imaging, the in situ distribution of β‐(1→4)‐d‐mannans and HRGP‐like epitopes was shown to consist of two distinct cell‐wall layers, whereas SPs are distributed in the middle area of the wall. The overall cell‐wall polymer arrangement of the SPs, HRGP‐like epitopes, and mannans in the utricles of C. vermilara is different from the ubiquitous green algae C. fragile, in spite of both being phylogenetically very close. In addition, a preliminary cell‐wall model of the utricle moiety is proposed for both seaweeds, C. fragile and C. vermilara. 相似文献
10.
Morphological plasticity could facilitate invasions of wetland plants into areas that experience increased durations of flooding
and eutrophication. We explored canopy plasticity of Phalaris arundinacea, an aggressive invader of wetlands, as it differentially invaded wet prairie mesocosms under 3 flooding durations and 3 levels
of nutrient addition. Phalaris grew as a sward with intermittent and early-season flooding but shifted to tussocks under constant flooding. These two growth
forms differed by >20% in several canopy ratios. Clones that formed tussocks produced 45% more shoots per unit biomass (P = 0.007) and a 25% higher ratio of total shoot length to biomass (P = 0.04). Lighter-weight shoots supported 33% fewer leaves and, consequently, had 35% less leaf area per shoot height (P < 0.002). Tussocks developed a continuous mat of adventitious roots, with root mats reaching 20.9 ± 0.6 cm in diameter and
4.7 ± 0.3 cm in height over two growing seasons. While forming tussocks, Phalaris tolerated longer durations of flooding and more than doubled its aboveground biomass. Invasions occurred rapidly, with Phalaris exceeding 75% canopy cover and accounting for 66% of the total aboveground biomass under constant flooding. Early-season
flooding increased the lateral spread of individual shoots. High nutrient addition produced shoots that were 27% taller and
50% heavier (P < 0.02), with 81% more leaf area (P < 0.0003) than shoots that received no nutrients. Consequently, under early-season flooding with high nutrient additions,
Phalaris was primed to invade, nearly doubling its proportion of the total aboveground biomass and exceeding 50% canopy cover during
year two. 相似文献
11.
Ant invasions exert a range of effects on recipient communities, from displacement of particular species to more complex community
disruption. While species loss has been recorded for a number of invasion events, a little examined aspect of these invasions
is the mechanisms for coexistence with resident ant species.The yellow crazy ant, Anoplolepis gracilipes (Smith), is considered one of the world’s worst ant invaders and has recently undergone rapid population growth in Tokelau.
We surveyed the ground-dwelling ant fauna in two plots on each of five invaded and three uninvaded islands across two atolls
in Tokelau to examine community characteristics of the ant fauna in areas with and without yellow crazy ants. We also used
three types of food bait (tuna, jam and peanut butter) to experimentally test if species are able to coexist by consuming
different food resources. Anoplolepis gracilipes was found to coexist with two to six other ant species at any one site, and coexisted with a total of 11 ant species. Four
species never co-occurred with A. gracilipes. Non-metric multidimensional scaling showed significant differences in community composition and the relative abundance of
species between areas that had, and had not, been invaded by A. gracilipes. The number of other ant species was significantly lower in communities invaded by the yellow crazy ant, but did not decline
with increasing A. gracilipes abundance, indicating that impacts were independent of population density. The yellow crazy ant dominated all tuna and jam
baits, but had a low attendance on peanut butter, allowing four other ant species to access this resource. Our results demonstrate
community level impacts of an ant invader on a tropical oceanic atoll and suggest that differing use of food resources can
facilitate coexistence in ant communities.
Received 11 September 2006; revised 15 January 2007; accepted 22 February 2007. 相似文献
12.
Nathan R. Geraldi Ashley R. Smyth Michael F. Piehler Charles H. Peterson 《Biological invasions》2014,16(9):1819-1831
The introduction of non-native species occurs within a context of other anthropogenic impacts: thus a holistic approach is needed to understand interactive effects. Installation of shoreline protection structures is increasing in response to rising sea levels and increasing frequency of intense storms. Shoreline hardening structures can facilitate establishment of non-native species with multiple potential consequences. We measured abundances of both native and non-native Codium, a green macroalga, on natural hard substrates (oyster reefs) and artificial substrates (bulkheads and revetments) in two estuaries and assessed the effects of each Codium species on nitrogen fixation and net N2 fluxes. Native C. decorticatum was the most abundant (86 %) Codium on oyster reefs, while exotic C. fragile dominated (99 %) artificial substrates. N2 production via denitrification was greater than nitrogen fixation for both species and the net N2 production associated with non-native C. fragile was greater than with native C. decorticatum. Comparing our results with surveys conducted in the 1940s before C. fragile had invaded, indicates that non-native Codium has outcompeted native Codium on artificial substrates, but that natural substrate provided by oyster reefs remains a refuge for native Codium. Although shoreline hardening with artificial structures can reduce ecosystem services provided by coastal marsh and other habitats, an unexpected beneficial consequence was the N2 production associated with the non-native Codium, which has the potential to mitigate anthropogenic nutrient loading. Our results illustrate that the interaction between multiple anthropogenic impacts can be positive, and indicate that non-ephemeral macroalgae could be an overlooked component in nitrogen removal from marine ecosystems by enhancing denitrification. 相似文献
13.
Restoring Eelgrass (Zostera marina L.) Habitats Using a Simple and Effective Transplanting Technique
Eelgrass beds in coastal waters of China have declined substantially over the past 30 years. In this study, a simple new transplanting technique was developed for eelgrass (Zostera marina L.) restoration. To assist in anchoring single shoots, several rhizomes of rooted shoots were bound to a small elongate stone (50–150 g) with biodegradable thread (cotton or hemp), and then the bound packet was buried at an angle in the sediments at a depth of 2–4 cm. This stone anchoring method was used to transplant eelgrass in early November 2009 and late May 2010 in Huiquan Bay, Qingdao. The method led to high success. Three month survivorship of the transplanted shoots at the two transplant sites was >95%. From April 20 to November 19, 2012, the following characteristics of the 2009 and 2010 transplanted eelgrass beds were monitored: morphological changes, shoot density, shoot height, leaf biomass, and sediment particle size. Results showed that the sexual reproduction period of the planted eelgrass was from April to August, and vegetative reproduction reached its peak in autumn. Maximum shoot height and biomass were observed in June and July. After becoming established, the transplanted eelgrass beds were statistically equal to natural eelgrass beds nearby in terms of shoot height, biomass, and seasonal variations. This indicates that the transplant technique is effective for eelgrass restoration in coastal waters. 相似文献
14.
Dilli P. Rijal Torbjørn Alm Lennart Nilsen Inger G. Alsos 《Ecology and evolution》2017,7(13):4936-4950
The impact of invasion on diversity varies widely and remains elusive. Despite the considerable attempts to understand mechanisms of biological invasion, it is largely unknown whether some communities’ characteristics promote biological invasion, or whether some inherent characteristics of invaders enable them to invade other communities. Our aims were to assess the impact of one of the massive plant invaders of Scandinavia on vascular plant species diversity, disentangle attributes of invasible and noninvasible communities, and evaluate the relationship between invasibility and genetic diversity of a dominant invader. We studied 56 pairs of Heracleum persicum Desf. ex Fisch.‐invaded and noninvaded plots from 12 locations in northern Norway. There was lower native cover, evenness, taxonomic diversity, native biomass, and species richness in the invaded plots than in the noninvaded plots. The invaded plots had nearly two native species fewer than the noninvaded plots on average. Within the invaded plots, cover of H. persicum had a strong negative effect on the native cover, evenness, and native biomass, and a positive association with the height of the native plants. Plant communities containing only native species appeared more invasible than those that included exotic species, particularly H. persicum. Genetic diversity of H. persicum was positively correlated with invasibility but not with community diversity. The invasion of a plant community by H. persicum exerts consistent negative pressure on vascular plant diversity. The lack of positive correlation between impacts and genetic diversity of H. persicum indicates that even a small founder population may cause high impact. We highlight community stability or saturation as an important determinant of invasibility. While the invasion by H. persicum may decrease susceptibility of a plant community to further invasion, it severely reduces the abundance of native species and makes them more vulnerable to competitive exclusion. 相似文献
15.
Ross Meffin Alice L. Miller Philip E. Hulme Richard P. Duncan 《Diversity & distributions》2010,16(5):804-815
Aim There is debate over whether alien plants necessarily alter the communities they invade or can coexist with native species without discernable impacts. We followed the fate of montane plant communities in response to the experimental sowing of the alien weed Hieracium lepidulum, looking for changes in plant community composition and structure over 6 years. Location Craigieburn Range, New Zealand. Methods We used a replicated randomised block design, with 30 × 30 cm plots (n = 756) subdivided into 5 × 5 cm cells to examine and compare the effects of H. lepidulum at 0.09 m2 (plot) and 0.0025 m2 (cell) scales. Plots were sown with between 0 and 15,625 H. lepidulum seeds in 2003, forming gradients of invader density and cover. Measurements comprised community richness, evenness and diversity along with H. lepidulum density and cover at both scales. The relationships between the invader and local community attributes were modelled using hierarchical mixed‐effect models. Results Plant communities differed in the extent to which they became invaded, with H. lepidulum cover in the plots ranging from 0% to 52%, with a mean of only 1.89%. Plot species richness increased from 2003 to 2009, with a component of this increase (+0.002 species per year) associated with increasing H. lepidulum density. Other relationships between the plant community and H. lepidulum were generally non‐significant. Main conclusions In these montane plant communities, it appears H. lepidulum coexists with the native community with no measurable negative effects after 6 years on species richness, evenness or diversity, even where density and cover of the invader are highest. We suggest H. lepidulum has persisted preferentially at those sites with abiotic conditions sufficient to support a species‐rich assemblage. 相似文献
16.
Ana Luísa Cazetta 《Plant Ecology & Diversity》2020,13(1):85-91
ABSTRACTBackground: Invasive plants can negatively impact native communities, but the majority of the effects of these invasions have been demonstrated only for temperate ecosystems. Tropical ecosystems, including the Cerrado, a biodiversity hotspot, are known to be invaded by numerous non-native species, but studies of their impacts are largely lacking.Aims: Our research aimed at quantifying how Pinus spp. presence and density affected Cerrado plant communities.Methods: We sampled areas invaded and non-invaded by Pinus spp. to determine if pine invasion affected native tree richness, diversity, evenness, and density. We also evaluated if community composition differed between invaded and non-invaded sites.Results: We found invaded plots had lower native tree densities than non-invaded plots and that Pinus spp. invasions changed native tree communities by reducing native species abundances.Conclusion: Invasive pines had negative impacts on the native Cerrado tree community by reducing native plant density and changing species abundances. Reduced density and abundance at early invasion stages can result in reduction in biodiversity in the long term. 相似文献
17.
Variation in the impact of non‐native seaweeds along gradients of habitat degradation: a meta‐analysis and an experimental test
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Laura Tamburello Elena Maggi Lisandro Benedetti‐Cecchi Giuseppe Bellistri Alex James Rattray Chiara Ravaglioli Luca Rindi Jason Roberts Fabio Bulleri 《Oikos》2015,124(9):1121-1131
Biological invasions are acknowledged among the main drivers of global changes in biodiversity. Despite compelling evidence of species interactions being strongly regulated by environmental conditions, there is a dearth of studies investigating how the effects of non‐native species vary among areas exposed to different anthropogenic pressures. Focusing on marine macroalgae, we performed a meta‐analysis to test whether and how the direction and magnitude of their effects on resident communities and species varies in relation to cumulative anthropogenic impact levels. The relationship between human impact levels and non‐native species impact intensity emerged only for a reduced subset of the response variables examined. Yet, there was a trend for the effects of non‐native species on community biomass and abundance and on species abundance to become less negative at heavily impacted sites. By contrast, the magnitude of negative effects of seaweed on community evenness tended to increase with human impact levels. The hypothesis of decreasing severity of invader’ impacts along a gradient of habitat degradation was also tested experimentally at a regional scale by comparing the effects of the removal of non‐native alga, Caulerpa cylindracea, on resident assemblages among rocky reefs exposed to different anthropogenic pressures. Assemblages at urban and pristine site did not differ when invaded, but did so when C. cylindracea was removed. Our results suggest that, despite the generally weak relationship between human impacts levels and non‐native species impacts, more negative impacts can be expected in less stressful environments (i.e. less degraded or pristine sites), where competitive interactions are presumably the driving force structuring resident communities. Implementing strategies for controlling the establishment of non‐native seaweeds should be, thus, considered a priority for preserving biodiversity in relatively pristine areas. On the other hand, control of invaders at degraded sites could be warranted to lessen their role as propagule sources. Synthesis Local anthropogenic stressors that severely alter biotic and abiotic conditions may underpin context‐dependency in the impacts of biological invasions. We used a meta‐analysis and an experimental test to examine the relationship between cumulative human impacts and ecological impact of non‐native seaweeds on resident assemblages. Our results suggest that more negative impacts of non‐native seaweeds on the abundance and biomass of resident assemblages can be expected in less degraded or pristine sites. Possibly, stronger impacts prevail at pristine sites, where assemblages are mainly structured by biotic interactions. Hence, management efforts should be mostly directed to prevent the establishment and spread of non‐native seaweeds in pristine areas. On the other hand, weak, but positive effects of seaweeds at the most degraded sites add to the ongoing debate on the role of non‐native species in rehabilitation plans. 相似文献
18.
Eupatorium adenophorum is one of the more noxious invasive plants worldwide. However, the mechanisms underlying its invasiveness are still not well
elucidated. In this study, we compared the invader with its two native congeners (E. heterophyllum and E. japonicum) at four irradiances in terms of growth, biomass allocation, morphology, and photosynthesis. The higher light-saturated photosynthetic
rate (P
max) and total leaf area of the invader may contribute to its higher relative growth rate (RGR) and total biomass compared with
its native congeners. Total biomass and RGR increased significantly with the increase of P
max and total leaf area. The higher support organ mass fraction and the lower root mass fraction of the invader may also contribute
to its higher RGR and biomass through increasing carbon assimilation and reducing respiratory carbon loss, respectively. The
higher growth rate of the invader increased its total leaf area, ramet number, and crown area. These traits may help the invader
to form dense monoculture, outshading native plant species. However, consistently higher leaf area ratio, specific leaf area,
and leaf mass fraction were not found across irradiances for the invader compared with its native congeners. Higher plasticity
in response to irradiance was also not found for the invader. The invader retained advantages over the natives across irradiances,
while its performance decreased with lower irradiance. The results indicate that the invader may be one of the few super invaders.
Reducing irradiance may inhibit its invasions. 相似文献
19.
Most of North America’s northern Great Plains have been cultivated for crop production, leaving remnants of natural mixed-grass prairie fragmented and threatened by alien plant invasions. The region’s most widespread alien perennial forage crop, crested wheatgrass (Agropyron cristatum sensu amplo), has invaded native grassland and raised concerns regarding its ecological impact. To evaluate impacts at multiple scales of organization, adjacent invaded and uninvaded mixed-grass prairie were sampled at eight widely separated locations. At the population level, native C3 mid-grasses and forbs were less abundant in invaded grasslands, while native C3 and C4 short-grass abundance was not different. At community and landscape levels, diversity was lower in invaded grasslands largely because of lower forb species richness and cover, and crested wheatgrass dominance of both cover (14% basal cover) and seedbank (404 seeds m−2). At the ecosystem level, both vegetation and litter biomass were greater in invaded grasslands, however, below ground organic matter (roots and litter), soil organic carbon, total nitrogen and phosphorus were not different. Crested wheatgrass invasion of mixed-grass prairie was associated with lower diversity within and among plant communities, and appears to simplify the composition of mixed-grass prairie landscapes. Hypotheses for crested wheatgrass dominance and persistence following invasion are suggested. 相似文献
20.
The macroalgal assemblages at the low intertidal zone were studied at three localities on the north coast of Spain between 1977 and 2002. Two of these localities were invaded at the end of the 1980s by the brown seaweed Sargassum muticum (Yendo) Fensholt (Phaeophyta, Sargassaceae), whereas the third locality remained free of the invader. In 2002, distinct algal assemblages were noticed in invaded and noninvaded localities. No major changes were detected in the noninvaded locality. Apart from the obvious presence of S. muticum, the changes observed in the invaded localities included a significant reduction in abundance of the previous dominant species (the red alga Gelidium spinosum (S. G. Gmelin) P. C. Silva) as well as an increased number of species and diversity, increased primary productivity, and variations in the seasonal abundance patterns of some species. We speculate that the arrival of S. muticum had a negative effect on the dominant native G. spinosum, probably related to competition for light. This resulted in indirect positive effects on other species of the assemblage (such as Bifurcaria bifurcata R. Ross). Other small epiphytic opportunistic species might also have been benefited from the presence of S. muticum, because the invader has a rich associated epiphytic assemblage. 相似文献