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1.
Recolonization dynamics from disturbance on a Philippine mixed seagrass meadow, containing species spanning more than 10-fold in rhizome elongation rates and reproductive effort, was examined by following the recovery of a 1,200 m2 gap over 2.5 yr. The objective was to assess the contribution of contrasting species to the recovery process and to evaluate the importance of sexual versus vegetative colonization. Large, slow-growing species,Thalassia hemprichii andEnhalus acoroides, that produce large, broadly-dispersed seeds dominated sexual colonization with a total of 2,643 and 210 seedlings, respectively, recruiting to the area. Despite very rapid turnover of sexual recruits, the high frequency of seedling establishment ensured successful development of new patches in areas devoid of vegetation, leading to a scattered and evenly distributed presence of vegetation inside the gap. The small seagrass speciesCymodocea rotundata andHalodule uninervis, characterized by fast rhizome elongation rates but low reproductive output and limited seed dispersal, were the major contributors to the overall 450 m2 increase in vegetation cover through fast lateral extension (144±6 cm yr−1) from meadow edge and surviving patches, forming a compact vegetation cover in one edge of the denuded area. We conclude that contrasting recruitment strategies in the mixed-species seagrass community examined have implications for colonization potential at different spatial scales. Fast clonal growth is only an efficient mechanism for colonization of disturbances within established meadows (small gaps), whereas the large species, which combined high reproductive output with high seed dispersal capacity, may act to accelerate the colonization process in large gaps or distant from established meadows.  相似文献   

2.
Patterns of seed dispersal and seed bank accumulation need to be known to predict the species that will recruit into restoration sites versus those that must be introduced. We assessed the temporal and spatial patterns of seed availability and seed accumulation on the salt marsh plain of an 8-ha resforation site, based on seedlings that emerged from tidal material, wrack, rabbit pellets, and soil samples (in controlled experiments). We compared results from the first 3 yr of restoration (2000–2002) with results from a 5-yr-old restoration and an extant marsh, all within Tijuana Estuary, California. Seed dispersal was limited for most marsh plain species. Tidal dispersal occurred mainly in winter; seedling density and richness were highest with high spring tides and after fruiting of the dominant species,Sarcocornia pacifica (>90% of emergent seedlings).S. pacifica was also common in the seedlings that emerged from soil seed banks (up to 63%) and wrack (60%), while other species common in the vegetation were present at much lower densities. Seed bank accumulation in restored sites was low and few species were abundant. Seedlings that emerged from soil samples from the youngest restoration were mostly invasive exotics (64%), those of the 5-yr restoration were mostlyS. pacifica (63%), and those from the nearby extant marsh were mostlyTriglochin concinna (70%), despite more diverse vegetation. No salt marsh seedlings emerged from rabbit pellets; all were invasives (Mesembryanthemum crystallimum andCarpobrotus edulis). Emerging seedlings were much sparser in soil from the younger restoration than from the 5-yr restoration and the extant site (32.9±5.7<4642.2±1131.5 and 4689.3±359.3 seedlings m−2, respectively). Because dispersal is limited for most species, restoring diverse vegetation will require seeding or planting. Natural recruitment could be facilitated by completing restoration by early winter, when seeds of native plants have maximum tidal dispersal.  相似文献   

3.
Schinus terebinthifolius (Brazilian pepper), a native of South America, is currently naturalized in 20 countries worldwide and can alter native systems by displacing flora and forming monotypic stands. The primary described mechanism of seed dispersal is through consumption of fruits by birds and mammals. We evaluated an alternative dispersal method by evaluating the potential for S. terebinthifolius growing in freshwater and estuarine environments to disperse via water currents. Specifically, we: (1) determined the duration fruits remained buoyant in three salinities, (2) estimated the viability of seeds after 7 days in water, (3) estimated the dispersal rate of floating solitary fruits, and (4) examined the role of boat wakes in moving seeds above mean high water at the shoreline. The length of time fruits floated in 0 ppt water (4.9 days) was significantly less than 15 ppt saltwater (6.2 days), and 30 ppt saltwater (6.9 days). After 7 days, over 13% of seeds remained viable in 0 ppt, 15 ppt, and 30 ppt water. By combining mean dispersal rates and the mean number of days fruits floated, we calculated individual fruits could be transported 16.9 km in 0 ppt and over 22 km in 15 and 30 ppt water. To increase germination, seeds must be stranded above the intertidal zone. Wind wakes alone never achieved this result; however, boat wakes plus wind wakes significantly increased the movement of fruits above the intertidal region into drier soils. The use of both vertebrate dispersal vectors and water dispersal may potentially increase the rate of invasion, establishment, and survival of S. terebinthifolius in freshwater and estuarine environments.  相似文献   

4.
The purpose of this study was to investigate the concentration levels of heavy metals in different species of the main three marine algal divisions from the Gulf of Aden coastal waters, Yemen. The divisions included Chlorophyta—green plants (Halimeda tuna, Rhizoclonium kochiamum, Caldophora koiei, Enteromorpha compressa, and Caulerpa racemosa species), Phaeophyta—brown seaweeds (Padina boryana, Turbinaria elatensis, Sargassum binderi, Cystoseira myrica, and Sargassum boveanum species), and Rhodophyta—red seaweeds (Hypnea cornuta, Champia parvula, Galaxaura marginate, Laurencia paniculata, Gracilaria foliifere, and species). The heavy metals, which included cadmium (Cd), cobalt (Co), copper (Cu), chromium (Cr), Iron (Fe), manganese (Mn), nickel (Ni), lead (Pb), zinc (Zn), and vanadium (V) were measured by Atomic Absorption Spectrophotometer (AAs). The concentrations of heavy metals in all algal species are in the order of Fe >> Cu > Mn > Cr > Zn > Ni > Pb > Cd > V > Co. The results also showed that the uptake of heavy metals by different marine algal divisions was in the order of Chlorophyta > Phaeophyta > Rhodophyta. These heavy metals were several order of magnitude higher than the concentrations of the same metals in seawater. This indicates that marine alga progressively uptake heavy metals from seawater.  相似文献   

5.
The role of positive and indirect interactions is often crucial in communities with intense abiotic stress such as salt marshes. The burrowing crab, Neohelice (=Chasmagnathus) granulata, is the dominant benthic macroinvertebrate of southwest Atlantic marshes (southern Brazil to Northern Argentinean Patagonia), having strong direct and indirect effects on marsh soil and, in consequence, on marsh vegetation and primary consumers. In this work, we investigate if this crab indirectly modifies habitat use by the granivorous rodents, Akodon azarae and Oligoryzomys flavescens, by increasing nutrient availability and thus enhancing seed production by the marsh plant Spartina densiflora. The study was conducted at the Mar Chiquita Coastal Lagoon, Argentina (37°32′ S). Rodent frequencies in S. densiflora were positively correlated with crab densities throughout the low and middle marsh. Additionally, the highest quality of S. densiflora and inflorescence density was recorded at the highest crab densities. Experimental manipulation of crab densities shows that N. granulata indirectly enhances the performance of S. densiflora (e.g., decreased fiber content and C/N ratios) and increases density of seeds. Moreover, N. granulata also facilitates S. densiflora seed availability to rodents by concentrating them in sediment mound at their burrows entrances. Experimental rodent exclusions showed that rodent species used S. densiflora seeds, a variable positively related to crab burrow density. Thus, our results show that N. granulata drives the granivorous rodent distribution and the intensity of seeds–rodent interaction trough facilitative and indirect interactions in marsh community.  相似文献   

6.
The formation of gas bubbles byZostera marina immediately prior to seed release is described together with evidence for its role as a seed dispersal mechanism. The gas bubbles, ranging in volume from 1.1 to 3.4 mm3, escape from the funiculus and adhere to the seed coat. As a bubble expands, the seed is pushed clear of the ovary and rises to the water surface with the bubble attached. Field data suggest that approximately 5–13% of the seeds produced are released with gas bubbles, and in some cases are transported more than 200 m (float time≥40 min).  相似文献   

7.
The distribution pattern of the Acacia tortilis in several sites in Qatar was investigated using the Greig-Smith-Kershaw method of pattern analysis. Neither random nor regular dispersion were detected and the distribution of the species was of the contagious type in almost every site. Pattern analyses showed two consistent scales: a smaller scale pattern attributed to an intrinsic factor of restricted dispersal of seeds and a larger scale pattern related to past and present biotic interference.  相似文献   

8.
The dominant plant in Humboldt Bay salt marshes in Spartina densiflora, a species of cordgrass apparently introduced from South America. At several salt marshes and restoration sites around Humboldt Bay, distribution of this plant has increased significantly. We investigated the relative contributions of vegetative tiller production and seed germination to the establishment and expansion of S. densiflora. Lateral spread of plants surrounded by competitors were compared to areas without competing plant species. Plants growing in areas without competitors had significantly higher rates of vegetative expansion (p<0.0001). Viable seed production, germination rates, seedling survivorship, and growth of adult plants were measured in six salinity treatments. Approximately 1,977±80 viable seeds are produced per plant (0.25–0.5 m2). The number of germinating seeds was inversely related to increases in salinity. Salinity treatments between 19‰ and 35‰ produced significantly lower germination rates than salinities of 0–18‰ (p<0.0001). Seedling survivorship was 50% at ≤4‰ and 8–14% at ≥11‰. Lateral expansion of adult, greenhouse-grown plants occurred in all salinity treatments, with modest decreases in the highest salinity treatments (p<0.05). Our findings indicate that S. densiflora expands primarily by vegetative expansion, and lateral tillers are produced by throughout the year. Spartina densiflora produces prolific amounts of seed, but recruitment in mature salt marshes may be limited by competitors and higher salinities. At restoration sites, planting of native species such as Salicornia virginica, Distichlis spicata, or Jaumea carnosa may prevent monospecific stands of S. densiflora from developing.  相似文献   

9.
Sophora moorcroftiana, an endemic leguminous shrub in Tibet, is found in valleys, slopes, terraces from 3,000 to 3,900 m above sea level along the middle reaches of the Yarlung Zangbo River. S. moorcroftiana is more tolerant of sand burial than other species in the valleys and is regarded as an ideal species for studying acclimatization to climatic factors. Stem basal diameter showed decline as altitude increased from 3,039 to 3,928 m in the Yarlung Zangbo River valley. Population density increased with the rise of altitude. However, seed bank density, seed germination and seed weight of S. moorcroftiana did not change with changing elevation. Plants responded to altitude variances with remarkable sensitivities. Stem basal diameter size declined along the vertical gradient between plateau and mountainside. Both in alpine and plateau areas, plants similarly adapted growth to altitude, but displayed different responses with respect to reproductive parameters, such as seed bank density, dry weight of seed, seed germination, seedling density and sapling density. Sand accretion remarkably reduced seed bank density and seedling density of the total population of S. moorcroftiana, but could promote shoot sprouting and shoot growing on the individual scale that stimulated the overall development of the population. The results suggested that this particular foredune species did not merely tolerate sand burial, but actually responded positively to sand accumulation.  相似文献   

10.
Paul J. Richards   《Earth》2009,96(1-2):92-106
Australian ants belonging to the genus Aphaenogaster excavate dense and frequently relocated nest systems in topsoil and deposit ephemeral, highly erodible (type-I) mounds at their funnel-shaped nest entrances. Rates of mounding are generally higher for this genus than for other Australian ant species, and are amongst the highest rates recorded for ant mounding anywhere in the world. Furthermore, tentative analysis of subsurface mixing suggests that overall rates of Aphaenogaster bioturbation are higher than indicated by mounding alone. This bioturbation has pronounced implications for soil and landscape processes, particularly in modifying soil fabric and texture and in impacting on soil hydrology and erosion. Aphaenogaster bioturbation may also be viewed as a form of ecosystem engineering, and affects the distribution of soil nutrients and the dispersal of seeds. This can lead to localized increases in soil fertility, although Aphaenogaster are notorious as a nuisance in agricultural landscapes.  相似文献   

11.
Avai'o'vuna Swamp, a small coastal wetland in Vava'u, Kingdom of Tonga, produced a 4500-year pollen and sediment record. Results are: (1) a mid-Holocene sea level highstand is confirmed for Tonga between about 4500 and 2600 14C yr B.P.; marine clay contains pollen from mangroves (Rhizophora mangle), coastal forest trees (Barringtonia asiatica and Cocos nucifera), and rainforest trees (Alphitonia, Rhus, Hedycarya and Calophyllum). (2) Microscopic charcoal first appeared at 2600 14C yr B.P., coincident with the arrival of Polynesians. (3) Cocos, Pandanus, Excoecaria, Macaranga, and Elaeocarpaceae pollen reflects the establishment of a mixed coastal-lowland rainforest in the last 2500 years. (4) The loss of Hedycarya, Elaeocarpus, Calophyllum, and Guettarda and the reduction of Terminalia and taxa in the Papilionaceae family by about 1000 years ago may be due to habitat destruction and the loss of dispersal capabilities of some species through the extinction of the two largest pigeons in Tonga.  相似文献   

12.
The burrowing crab,Chasmagnathus granulatus, is the dominant benthic macroinvertebrate of southwest Atlantic salt marshes and tidal flats, having strong ecosystem engineering effects by direct and indirect effects on soil, vegetation, invertebrates, fishes, and birds. Vegetation structure is a main component for bird habitat selection, since greater habitat complexity generates higher niche diversity. This environmental complexity can be modified by species interactions or disturbance events (i.e., by crabs), in turn modifying the associated community. The bird species of salt marshes of the southwest Atlantic are highly dependent on these ecosystems. We assessed the effects of the burrowing crab on the structure of the cordgrass,Spartina densiflora, marshes, and how these changes affected the composition and diversity of birds. This study was conducted at the Mar Chiquita Coastal Lagoon, Argentina (37°40′S, 57°23′W).S. densiflora marshes were classified within three categories: marshes without burrowing crabs, marshes with low burrow densities, and marshes with high burrow densities. We made vegetation and bird surveys during spring beforeS. densiflora produce seeds and in summer when seeds are abundant. We also manipulated inflorescence (i.e., spike) density (a variable affected by crabs) to assess the effect on bird habitat use. The highest inflorescence density ofS. densiflora and highest bird diversity were recorded at low burrow densities. Cover and height ofS. densiflora were negatively correlated with burrow density. The number of bird species and the number of red-capped wren-spinetail,Spartonoica maluroides, were negatively related with cover and height ofS. densiflora. Experiments confirmed that granivorous species used areas with higher spike densities, a variable related to crab burrow density. Burrowing crabs directly and indirectly affect the cover, height, spike density, and morphologic characteristic of seeds ofS. densiflora marshes. These effects indirectly affect the bird community that uses these marshes, being negatively related toS. maluroides and total bird abundance, and positively related to bird diversity.  相似文献   

13.
Plants are frequently moved around the world, creating new regional landscapes and environmental imaginaries. Building on previous work in environmental history and geography, we develop a three-part approach to analyzing plant movements and apply it to trees from the Acacia genus (sens. lat.) exchanged between Australia and the rest of the world. First, we investigate the agents, circuits, and frequencies of acacia movements, including transoceanic transfers, regional diffusion, and ecological dispersal. Second, we trace bundles of knowledge or technology that accompany the acacias, highlighting how they help shape regional biogeographies. Finally, we analyze how different societies, with distinct economies, politics, and environmental sensibilities, receive introduced plants. This approach allows us to see transferred plants as active agents in region-forming processes, and to avoid normative tropes like ‘miracle plants’ or ‘alien invasives’. The highlighted species include Acacia colei, Acacia melanoxylon, Acacia mearnsii, Acacia farnesiana, Acacia nilotica, Acacia mangium, and their close relatives.  相似文献   

14.
H. Tagawa Dr. 《GeoJournal》1992,28(2):175-183
The three Krakatau islands in Indonesia were completely denuded by the great eruption in 1883. One century after the eruption, the vegetation of Rakata on the one hand and of Panjang and Sertung on the other are quite different. Indigenous or exogenous Neonauclea seeds successfully formed Neonauclea forest on Rakata island but compltely failed to do so on Panjang and Sertung islands. The dispersal of seeds, soil conditions and volcanic activity of Anak Krakatau were all found to be contributing factors.The Timonius and Dysoxylum forests found on Panjang and Sertung originated on both islands after the appearance of Anak Krakatau. These dominants have larger seeds than Neonauclea and were able to germinate and grow under the regenerated mixed forest canopy but it was not so easy for them to colonize the Neonauclea forest. At the present time, their invasion progresses only gradually on Rakata. Ardisia scrub on steep coastal slopes on the Satsunan islands, SW Japan, is thought to be a somewhat parallel case of the retarding effect on the subsequent development of communities of the first arrivals. Ardisia scrub in these habitats appears to be a stable community, withstanding salt-laden wind. This shrub produces a number of stem and root sprouts, in a mop-headed growth. Their drupes are carried by birds and few seedlings were found in the scrub. The scrub floor was heavily shaded when its canopy was covered by lianes. The deep shade and frugivore activity prevent the invasion of other dominant species which would change the scrub into another type of forest. In milder habitats the scrub gradually becomes tall and the number of sprouts decreases, the forest then changes into another type such as Persea or Castanopsis forest.  相似文献   

15.
Contamination of soil with heavy metals is one of the important concerns of public health and food production. Nickel is a heavy metal whose toxic properties have been confirmed. In some plants, nickel has also been known as a useful metal for their growth. In this research, the response of two chamomile species to different levels of nickel was investigated in two stages of germination and callogenesis in vitro conditions in factorial experiment based on completely randomized design. In the first experiment, the effect of different concentrations of nickel sulfate (0, 60, 120, and 180 µM) was examined on germination of German (Matricaria chamomilla) and Aurea (M. aurea) chamomile seeds in the MS culture medium. The results indicated that at high levels of nickel sulfate, the speed and percentage of germination increased in both types of chamomile. In M. chamomilla, with the increase in the concentration of nickel sulfate, the length of the seedling decreased, but the seed weight vigor, length of the radicle, and dry weight of the seedling increased. M. aurea showed elevation in most indices. The results of the second experiment indicated that the M. chamomilla leaf explants had callogenesis and its callogenesis indices showed a significant decrease at high levels of nickel, when compared with the control In M. aurea, the calluses did not grow sufficiently, suggesting the sensitivity of M. aurea’s callogenesis to the presence of different levels of nickel. In conclusion, chamomile appears to be tolerant to nickel stress.  相似文献   

16.
The objective of the present study is to evaluate the absorption efficacy of H. fusiformis biochar (HFB) for the removal of phenol and heavy metals from single and mixed solute systems of these species under different experimental conditions. The effects of contact time, pH change, initial phenol concentration, and heavy metal concentration on the adsorption capacity of HFB were investigated. The kinetics and equilibrium models of sorption of the components of the single and mixed solute systems on HFB were also studied. The experimental data were fitted to kinetic and equilibrium models. The batch experiments revealed that 360 min of contact time was sufficient to achieve equilibrium for the adsorption of both phenol and heavy metals. The adsorption of phenol and nickel by HFB followed the pseudo-second-order kinetic model, which was quite adequate for describing the adsorption mechanism. The equilibrium data for the adsorption of phenol and heavy metals fit well to the Langmuir model with regression coefficients of R 2 > 0.819. The maximum Langmuir adsorption capacities were 10.39, 12.13, 22.25, 2.24, 2.89, and 22.03 mg/g for phenol, Ni2+, Zn2+, Cu2+, Pb2+, and Cd2+, respectively. Moreover, HFB exhibited optimal sorption under slightly acidic conditions at pH 6. The HFB used in the present study exhibited higher adsorption capacity for the removal of phenol and heavy metals from aqueous solutions compared to documented sorbents. These results demonstrate that HFB is potentially useful for alleviating the harmful effects of phenol and heavy metal in wastewater treatment systems.  相似文献   

17.
The purpose of this study was to determine the levels of heavy metals namely cadmium (Cd), copper (Cu) and lead (Pb) in the five aquatic plants. For this purpose, the concentration of heavy metals were measured in water and in the five aquatic plant species, Lepironia articulata, Pandanus helicopus, Scirpus grossus, Cabomba furcata and Nelumbo nucifera, in 15 sites from Tasik Chini. The concentrations were different among the plant species as well as among the parts of plants. The highest concentration of heavy metals among the aquatic plants and plant parts was found in the roots of S. grossus. The concentrations of Cd in the leaves and stems of submerged aquatic plant, C. furcata, were higher than concentration of Cd in the leaves and stems of emergent aquatic plant and floating leaf plant. The concentration of Cu in the stem of C. furcata was greater than that in the leaf, while the concentration of Cd was more in the leaf than in the stem. The heavy metal contents of the aquatic plants were in descending order of Pb > Cu > Cd. The metal concentration quotient of leaves/roots and stems/roots (ML/MR and MS/MR) were calculated. The highest internal translocation was found in P. helicopus, while the lowest internal translocation was found in S. grossus.  相似文献   

18.
A sequence of Triassic rocks is exposed near the town of Concepción, Chile. These clastic strata are interpreted as the deposits of rivers, lakes, playas, and alluvial fans. The deposits comprise conglomerates, arkosic sandstones, and sand-, silt- and mudstones. Four facies associations comprising eight sedimentary facies can be distinguished. Plant fossils from the sedimentary sequence of the Santa Juana Formation indicate a Carnian age. The flora includes ferns (Gleichenites, Cladophlebis, Dictyophyllum, Thaumatopteris, Asterotheca, Saportaea) and seed ferns (Kurtziana, Antevsia, Dicroidium), ginkgophytes (Sphenobaiera), cycads (Pseudoctenis), conifers (Heidiphyllum, Telemachus, Rissikia), and gymnosperms of uncertain affinities (Linguifolium, Gontriglossa). Two new species are presented: Pseudoctenis santajuanensis and Gontriglossa reinerae.  相似文献   

19.
The temperature (T) evolution of the barium carbonate (BaCO3) structure was studied using Rietveld structure refinements based on synchrotron X-ray diffraction and a powdered synthetic sample. BaCO3 transforms from an orthorhombic, Pmcn, α phase to a trigonal, R3m, β phase at 811°C. The orthorhombic BaCO3 structure is isotypic with aragonite, CaCO3. In trigonal R3m BaCO3, the CO3 group occupies one orientation and shows no rotational disorder. The average <Ba–O> distances increase while the <C–O> distances decrease linearly with T in the orthorhombic phase. After the 811°C phase transition, the <Ba–O> distances increase while C–O distances decrease. There is also a significant volume change of 2.8% at the phase transition.  相似文献   

20.
Eco-restoration of mine overburden (OB) or abandoned mine sites is a major environmental concern. In the present investigation, an integrated approach was used to rejuvenate a high-sulphur mine OB dumping site in the Tirap Collieries, Assam, India, which is situated in the Indo-Burma mega-biodiversity hotspot. A mine OB is devoid of true soil character with poor macro and micronutrient content and contains elevated concentrations of trace and heavy metals. Planting of herbs, shrubs, cover crops and tree species at close proximity leads to primary and secondary sere state succession within a period of 3 to 5 years. A variety of plant species were screened for potential use in restoration: herbs, including Sccharum spontaneum, Cymbopogon winterianus Jowitt (citronella), and Cymbopogon flexuosus (lemon grass) cover plants, including Mimosa strigillosa, M. striata, and M. pigra; shrubs, including Sesbania rostrata (dhaincha) and Cassia streata (cassia); and tree species, including Gmelina arborea (gomari) and Dalbergia sissoo (sissoo). Amendment with unmined soil and bio-organic matter was required for primary establishment of some plant species. Management of these plant species at the site will ensure long term sustainable eco-restoration of the coal mine-degraded land.  相似文献   

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