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1.
We examined how dominance (% canopy cover) and invasion history of common reed, Phragmites australis, affected benthic macroinvertebrate diversity and density in 8 marshes along Lake Erie’s southern shoreline. We also compared
macroinvertebrate densities among patches (0.25 m2) of reed, cattail (Typha spp.), and native flora (e.g., Sagittaria, Sparganium) and epiphytic algal communities on submerged stems of reed and cattail. Narrow-leaf cattail (T. angustifolia) is also a common invasive plant to these wetlands, but does not greatly change plant community composition or ecosystem
conditions like reed. Macroinvertebrate diversity (Shannon–Weaver H′) was positively related to reed cover and was highest (4.6) in two marshes with ~35- and 5-year invasion histories. Shading
from high reed cover increased H′-diversity, in part, by reducing the abundance of floating duckweed, which harbored many Hyalella azteca amphipods. Percent Ephemeroptera, Odonata, and Trichoptera was low to moderate across marshes, regardless of reed cover and
invasion history. Macroinvertebrate density was not affected by reed cover or average plant stem density, and did not differ
among plant types. However, epiphyton densities and % diatoms were greater on reed than on cattail, suggesting reed provides
a better feeding habitat for microalgal grazers than Typha. Abundance rankings of common species in these diatom-dominated communities were also typically dissimilar between these
plant types. Although % grazers was unrelated to epiphyton densities and % diatoms, grazer identity (snails) differed between
natural and diked marshes, which had different microalgal food supplies. Our findings suggest that Phragmites does not necessarily adversely affect macroinvertebrate community structure and diversity and that invasion history alone
has little effect on the H′-diversity–reed dominance relationship. 相似文献
2.
Periphyton constitutes an important community that is useful for assessment of ecological conditions in lotic systems. The
objective of this study was to assess the effects of different mixtures of Cd and Pb on periphyton growth as well as Cd and
Pb mixtures toxicity to diatom assemblages in laboratory mesocosm experiments. A natural periphyton community sampled from
the Monjolinho River (South of Brazil) was inoculated into five experimental systems containing clean glass substrates for
periphyton colonization. The communities were exposed to mixtures of dissolved Cd and Pb concentrations of 0.01 and 0.1 mg l−1 Cd and 0.033 and 0.1 mg l−1 Pb. Periphyton ash-free dry weight, growth rate, diatom cell density and diatom community composition were analyzed on samples
collected after 1, 2 and 3 weeks of colonization. High Cd concentration (0.1 mg l−1) has negative effects on periphyton growth while high concentration of Pb (0.1 mg l−1) decreased the toxic effects of Cd on periphyton growth. Shifts in species composition (development of more resistant species
like Achnanthidium minutissimum and reduction of sensitive ones like Cymbopleura naviculiformis, Fragilaria capucina, Navicula cryptocephala, Encyonema silesiacum, Eunotia bilunaris, and Gomphonema parvulum), decreases in species diversity of diatom communities with increasing Cd and Pb concentrations and exposure duration have
been demonstrated in this study making diatom communities appropriate monitors of metal mixtures in aquatic systems. 相似文献
3.
The potential interactions of grazing, nutrients and light in influencing autotroph species diversity have not previously
been considered. Earlier studies have shown that grazing and nutrients interact in determining autotroph species diversity,
since grazing decreases species diversity when nutrients (i.e. N or P) limit autotroph growth, but increases it when nutrients
are replete. We hypothesized that increased light intensities would intensify the interactions between grazing and nutrients
on algal species diversity, resulting in even stronger reductions in algal species diversity through grazing under nutrient–poor
conditions, and to even stronger increases of algal species diversity through grazing under nutrient-rich conditions. We studied
the effects of grazing (absent, present), nutrients (ambient, N + P enriched) and light (low light, high light) on benthic
algal diversity and periphyton C:nutrient ratios (which can indicate algal nutrient limitation) in a factorial laboratory
experiment, using the gastropod grazer Viviparus viviparus. Grazing decreased algal biomass and algal diversity, but increased C:P and N:P ratios of periphyton. Grazing also affected
periphyton species composition, by decreasing the proportion of Spirogyra sp. and increasing the proportion of species in the Chaetophorales. Grazing effects on diversity as well as on periphyton N:P ratios were weakened when nutrients were added (interaction between
grazing and nutrients). Chlorophyll a (Chl a) per area increased with nutrient addition and decreased with high light intensities. Light did not increase the strength
of the interaction between grazing and nutrients on periphytic algal diversity. This study shows that nutrient addition substantially
reduced the negative effects of grazing on periphytic algal diversity, whereas light did not interact with grazing or nutrient
enrichment in determining periphytic algal diversity. 相似文献
4.
Effects of hydrologic and water quality drivers on periphyton dynamics in the southern Everglades 总被引:2,自引:2,他引:0
David M. Iwaniec Daniel L. Childers Damon Rondeau Christopher J. Madden Colin Saunders 《Hydrobiologia》2006,569(1):223-235
Everglades periphyton mats are tightly-coupled autotrophic (algae and cyanobacteria) and heterotrophic (eubacteria, fungi
and microinvertebrates) microbial assemblages. We investigated the effect of water column total phosphorus and nitrogen concentrations,
water depth and hydroperiod on periphyton of net production, respiration, nutrient content, and biomass. Our study sites were
located along four transects that extended southward with freshwater sheetflow through sawgrass-dominated marsh. The water
source for two of the transects were canal-driven and anchored at canal inputs. The two other transects were rain-driven (ombrotrophic)
and began in sawgrass-dominated marsh. Periphyton dynamics were examined for upstream and downstream effects within and across
the four transects. Although all study sites were characterized as short hydroperiod and phosphorus-limited oligotrophic,
they represent gradients of hydrologic regime, water source and water quality of the southern Everglades. Average periphyton
net production of 1.08 mg C AFDW−1 h−1 and periphyton whole system respiration of 0.38 mg C AFDW−1 h−1 rates were net autotrophic. Biomass was generally highest at ombrotrophic sites and sites downstream of canal inputs. Mean
biomass over all our study sites was high, 1517.30 g AFDW m−2. Periphyton was phosphorus-limited. Average periphyton total phosphorus content was 137.15 μg P g−1 and average periphyton total N:P ratio was 192:1. Periphyton N:P was a sensitive indicator of water source. Even at extremely
low mean water total phosphorus concentrations ( ≤ 0.21 μmol l−1), we found canal source effects on periphyton dynamics at sites adjacent to canal inputs, but not downstream of inflows.
These canal source effects were most pronounced at the onset of wet season with initial rewetting. Spatial and temporal variability
in periphyton dynamics could not solely be ascribed to water quality, but was often associated with both hydrology and water
source. 相似文献
5.
Dialysis cultures 总被引:8,自引:0,他引:8
Dialysis techniques are discussed as a means for effective removal of low-molecular-mass components from fermentation broth
to reach high cell density. Reactor systems and process strategies, the relevant properties of membranes and examples for
high-density fermentation with dialysis, and problems related to scale-up are addressed. The dialysis technique has turned
out to be very efficient and reliable for obtaining high cell densities. As in dialysis processes the membranes are not perfused,
membrane clogging is not a problem as it is for micro- and ultrafiltration. By applying a “nutrient-split” feeding strategy,
the loss of nutrients can be avoided and the medium is used very efficiently. The potential of dialysis cultures is demonstrated
on the laboratory scale in a membrane dialysis reactor with an integrated membrane and in reactor systems with an external
dialysis loop. In dialysis cultures with different microorganisms (Staphylococci, Escherichia coli, extremophilic microorganisms, Lactobacilli) the cell densities achieved were up to 30 times higher than those of other fermentation methods. The technique enables high
cell densities to be attained without time-consuming medium optimization. For animal cell cultures the concept of a fixed
bed coupled with dialysis proved to be very effective.
Received: 24 March 1998 / Received revision: 18 June 1998 / Accepted: 19 June 1998 相似文献
6.
Zhen-Ming Ge Seppo Kellomäki Xiao Zhou Heli Peltola Kai-Yun Wang Pertti J. Martikainen 《Bioenergy Research》2012,5(3):637-648
We investigated the seasonal variability of effects of elevated temperature (+3.5°C), CO2 elevation (700 μmol mol−1) and varying water regimes (high to low water content) on physiological responses and biomass growth of reed canary grass (Phalaris arundinacea L., local field-grown cultivar) grown in a boreal environment. In controlled environment greenhouses, various physiological and growth parameters of grass, i.e., light-saturated net photosynthetic rates (P nmax), water use efficiency (WUE) and optimal photochemical efficiency of photosystem II (F v/F m), and leaf area development and biomass of plant organs (leaf, stem, coarse, and fine root) were measured. During the early measurement periods, elevated temperature enhanced leaf photosynthesis and above-ground biomass of reed canary grass; however, this resulted in earlier senescence and lower biomass at the end of measurement period, compared to ambient temperature. This effect was more pronounced under water limitation. Elevated CO2 enhanced P nmax, WUE, and leaf area and total plant biomass (above- and below-ground) over growing season. The explanation for imbalance between stimulated photosynthesis and increase in above-ground biomass was that CO2 enrichment causes a greater increase in the plant’s root system. The combination of elevated temperature and CO2 slightly increases the growth of plant. Adequate water availability favored photosynthesis and biomass growth of reed canary grass. The temperature- and drought-induced stresses were partially mitigated by elevated CO2. Other cultivars should be tested in order to identify those that are better adapted to elevated temperatures and CO2 and variable water levels. 相似文献
7.
Rusznyák A Vladár P Szabó G Márialigeti K Borsodi AK 《Extremophiles : life under extreme conditions》2008,12(6):763-773
Bacterial diversity of reed (Phragmites australis) periphyton communities of Kelemen-szék and Nagy-Vadas (two Hungarian soda ponds) was investigated using molecular cloning
and cultivation-based techniques. The majority of the 80 Kelemen-szék and 72 Nagy-Vadas bacterial isolates proved to be moderately
halophilic and alkaliphilic. A great proportion of the isolates showed phosphatase and urease activity, utilized aesculin,
citrate and certain biopolymers (e.g., gelatine and tween 80). Partial 16S rDNA sequence analysis of 33 Kelemen-szék and 20
Nagy-Vadas ARDRA group representatives showed Gram-positive (Nesterenkonia, Cellulomonas, Dietzia, Bacillus and Planococcus) dominance at both sampling sites. Species of the genera Acidovorax, Hydrogenophaga (β-Proteobacteria) and Flavobacterium, Sphingobacterium (Bacteroidetes) were represented only from Kelemen-szék. Altogether 16 isolates showed low sequence similarity with yet described
bacteria and may represent novel taxa. Screening of the 16S rRNA gene libraries of 129 Kelemen-szék and 158 Nagy-Vadas clones
resulted in 30 and 28 different ARDRA groups, respectively. Sequence analysis revealed a Gram-negative (Rheinheimera, Aquimonas, Cellvibrio, Flavobacterium and Sphingobacterium) dominated phylogenetic diversity. A high number of the clones were affiliated with uncultured bacterial clones described
from diverse environmental samples. 相似文献
8.
Invasive species pose a serious threat to native plant communities and are an important contributor to loss of biodiversity. In the case of Phalaris arundinacea, L. (Poaceae), reed canary grass, a cool-season, long-lived perennial plant native to Eurasia and North America, nonnative agronomically important genotypes were introduced to North America for numerous uses such as forage and soil stabilization. Following repeated introductions, reed canary grass became an aggressive invader that takes over natural wet prairies, stream-banks and wetlands. Reed canary grass can outcompete native plant species, resulting in monospecific stands with concomitant loss of plant and insect diversity and ultimately to alteration in ecosystem function. Abiotic factors such as disturbance, changes in hydrological regime, and particularly nutrient runoff to wetlands can enhance reed canary grass establishment and vegetative spread. In addition, the species' capacity for early season growth, rapid vegetative spread, high stem elongation potential, wide physiological tolerance, and high architectural plasticity make the species highly aggressive under a wide range of ecological conditions. The change in life-history and environmental conditions responsible for the enhanced aggressiveness observed between native and invasive genotypes are not yet understood. Hence, reed canary grass provides an ideal study system to test a number of ecological and genetic hypotheses to explain why some plant species become extremely aggressive when transported into a new geographical area. To date, genetic studies have found that invasive populations have high genetic diversity and that genotypes differ in their phenotypic plasticity and response to ecological conditions, which may contribute to their invasion success. Finally comparative studies currently underway on European native and American invasive genotypes of reed canary grass should shed light on the mechanisms responsible for reed canary grass's aggressiveness and should provide an experimental protocol to test ecological and genetic hypotheses about what makes a species invasive. 相似文献
9.
Andrew J. Rodusky 《Aquatic Ecology》2010,44(4):797-815
The abundance, community structure and nutrient content of periphyton, and the host plant taxa Chara, Hydrilla, Potamogeton, Vallisneria and Scirpus were studied in Lake Okeechobee, USA. Water levels were generally high during the study period (August 2002–January 2006),
but substantial fluctuations occurred. All host plant biomass was seasonally variable but only Vallisneria biomass was spatially variable. All submerged plant beds disappeared after the passage of two hurricanes in September 2004,
and a third hurricane passed over the lake in October 2005. Periphyton assemblages were statistically separated most by substrate
and then by season. Prior to the hurricanes, annual maxima of periphyton biovolumes and those of summer submerged plant coverage
coincided. During all study years, the diatom taxa dominated periphyton total biovolumes. Periphyton biomass was generally
highest during the summer or prior to the hurricanes (in the case of epiphytes) and was spatially variable in the case of
both Scirpus and Vallisneria. Epiphytic nutrient contents within each host plant group seasonally varied except for nitrogen and carbon in the Vallisneria epiphytes. Epipelic nutrient contents were spatially variable and seasonally variable for carbon. Nutrient contents in epipelon
were significantly higher than that in Scirpus epiphytes and were similar but lower among all epiphytic communities. The total annual areal potential epiphytic phosphorus
storage extrapolated during this study (2.0 × 10−4 metric tons ha−1 year−1) was underestimated because storage estimates for epipelon, Chara and Hydrilla-associated epiphytes were omitted. The Chara and Hydrilla-associated epiphytic nutrient storage values were omitted because of limited data, whereas the epipelic data may have not
been spatially representative. For periphyton biovolume, host substrate type, water level fluctuation and hurricane impacts
on host substrates appear to be more important than seasonal variation in such factors as temperature and nutrients. Epiphytic
nutrient storage appears to be influenced most by water level fluctuation and hurricane-related impacts, while the host substrate
type appears to be a less important factor than it is for periphyton biovolume. Maximum periphyton biomass and high nutrient
storage in shallow subtropical and tropical eutrophic lakes may only occur at consistently lower water levels and during infrequent
periods of disturbance, which enhance host substrate colonizable area. 相似文献
10.
11.
A temporal temperature gradient gel electrophoresis (TTGE) method was developed to determine the diversity of methanogen populations
in the rumen. Tests with amplicons from genomic DNA from 12 cultured methanogens showed single bands for all strains, with
only two showing apparently comigrating bands. Fingerprints of methanogen populations were analyzed from DNA extracted from
rumen contents from two cattle and four sheep grazing pasture. For one sheep, dilution cultures selective for methanogens
were grown and the culturable methanogens in each successive dilution examined by TTGE. A total of 66 methanogen sequences
were retrieved from bands in fingerprints and analyzed to reveal the presence of methanogens belonging to the Methanobacteriales, the Methanosarcinales, and to an uncultured archaeal lineage. Twenty-four sequences were most similar to Methanobrevibacter ruminantium, five to Methanobrevibacter smithii, four to Methanosphaera stadtmanae, and for three, the nearest match was Methanimicrococcus blatticola. The remaining 30 sequences did not cluster with sequences from cultured archaea, but when combined with published novel
sequences from clone libraries formed a monophyletic lineage within the Euryarchaeota, which contained two previously unrecognized clusters. The TTGE bands from this lineage showed that the uncultured methanogens
had significant population densities in each of the six rumen samples examined. In cultures of dilutions from one rumen sample,
TTGE examination revealed these methanogens at a level of at least 105 g−1. Band intensities from low-dilution cultures indicated that these methanogens were present at similar densities to Methanobrevibacter ruminantium-like methanogens, the sole culturable methanogens in high dilutions (106–10−10 g−1). It is suggested that the uncultured methanogens together with Methanobrevibacter spp. may be the predominant methanogens in the rumen. The TTGE method presented in this article provides a new opportunity
for characterizing methanogen populations in the rumen microbial ecosystem. 相似文献
12.
The phylogenetic diversity and axial distribution of microorganisms in three sections of the gastrointestinal tracts of the
polychaete Neanthes glandicincta was evaluated using both most probable number method and cloning analyses of 16S rRNA genes in this study. Quantification
of the density of microorganisms in the gut showed that aerobic microorganisms decreased from anterior to posterior, while
anaerobic ones showed a reverse trend. The total numbers of microorganisms decreased significantly (p < 0.05, analysis of variance) but more rapidly from the anterior to the middle segment. Phylogenetic analysis showed that
the dominating phylogenetic groups included Methanomicrobiales I: Methanosaetaceae (up to 66% of archaeal clones), δ-Proteobacteria (up to 42% of bacterial clones), and γ-Proteobacteria (up to 30% of bacterial clones) widely distributed throughout the entire gut. Other microbiota distributed in different gut
sections were Methanomicrobiales II: Methanospirillaceae, Methanomicrobiales III, Thermoplasmatales, Crenarchaea, Methanobacteriaceae, and Methanosarcinales for archaea; and α-Proteobacteria, β-Proteobacteria, Fusobacteria, Clostridia, Chloroflexi, and Planctomycetes for bacteria. The results reveal a difference in microbial community structure along the gut of N. glandicincta. The various phylogenetic diversity and axial distribution of microbes along the gut might indicate an environmental gradient
from anterior to posterior sections affecting the structure of the microbial community. 相似文献
13.
Comparative study of periphyton community structure in long and short-hydroperiod Everglades marshes 总被引:1,自引:0,他引:1
The Florida Everglades is a mosaic of short and long-hydroperiod marshes that differ in the depth, duration, and timing of
inundation. Algae are important primary producers in widespread Everglades’ periphyton mats, but relationships of algal production
and community structure to hydrologic variability are poorly understood. We quantified differences in algal biomass and community
structure between periphyton mats in 5 short and 6 long-hydroperiod marshes in Everglades National Park (ENP) in October 2000.
We related differences to water depth and total phosphorus (TP) concentration in the water, periphyton and soils. Long and
short-hydroperiod marshes differed in water depth (73 cm vs. 13 cm), periphyton TP concentrations (172μg g−1 vs. 107 μg g−1, respectively) and soil TP (284 μg g−1 vs. 145 μg g−1). Periphyton was abundant in both marshes, with short-hydroperiod sites having greater biomass than long-hydroperiod sites
(2936 vs. 575 grams ash-free dry mass m−2). A total of 156 algal taxa were identified and separated into diatom (68 species from 21 genera) and “soft algae” (88 non-diatom
species from 47 genera) categories for further analyses. Although diatom total abundance was greater in long-hydroperiod mats,
diatom species richness was significantly greater in short- hydroperiod periphyton mats (62 vs. 47 diatom taxa). Soft algal
species richness was greater in long-hydroperiod sites (81 vs. 67 soft algae taxa). Relative abundances of individual taxa
were significantly different among the two site types, with soft algal distributions being driven by water depth, and diatom
distributions by water depth and TP concentration in the water and periphyton. Periphyton communities differ between short
and long-hydroperiod marshes, but because they share many taxa, alterations in hydroperiod could rapidly promote the alternate
community.
Electronic supplementary material Electronic supplementary material is available for this article at
and accessible for authorised users. 相似文献
14.
Development of 1,030 genomic SSR markers in switchgrass 总被引:1,自引:0,他引:1
Wang YW Samuels TD Wu YQ 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2011,122(4):677-686
Switchgrass, Panicum virgatum L., a native to the tall grass prairies in North America, has been grown for soil conservation and herbage production in
the USA and recently widely recognized as a promising dedicated cellulosic bioenergy crop. A large amount of codominant molecular
markers including simple sequence repeats (SSRs) are required for the construction of linkage maps and implementation of molecular
breeding strategies to develop superior switchgrass cultivars. The objectives of this study were (1) to identify SSR-containing
clones and to design PCR primer pairs (PPs) in SSR-enriched genomic libraries, and (2) to validate and characterize the designed
SSR PPs. Five genomic SSR enriched libraries were constructed using genomic DNA of ‘SL93 7 × 15’, a switchgrass genotype selected
in an Oklahoma State University (OSU) southern lowland breeding population. A total of 3,046 clones from four libraries enriched
in (CA/TG)n, (GA/TC)n, (CAG/CTG)n and (AAG/CTT)n SSR repeats were sequenced at the OSU Core Facility. From the sequences,
we isolated 1,300 unique SSR-containing clones, from which we designed 1,398 PPs using SSR Locator V.1 software. Among the
designed PPs, 1,030 (73.7%) amplified reproducible and strong bands with expected fragment size, and 802 detected polymorphic
alleles, in SL93 7 × 15 and ‘NL94 16 × 13’, two parents of one mapping population. All of the four libraries contained a high
rate of perfect SSR repeat types, ranging from 62.7 to 76.2%. Polymorphism of the effective SSR markers was also tested in
two lowland and two upland switchgrass cultivars, encompassing ‘Alamo’ and ‘Kanlow’, and ‘Blackwell’ and ‘Dacotah’, respectively.
The developed SSR markers should be useful in genetic and breeding research in switchgrass. 相似文献
15.
V. R. Bommineni P. P. Jauhar T. S. Peterson R. N. Chibbar A. B. Almouslem 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1997,95(5-6):757-763
The objective of this study was to detect the presence of alien chromatin in intergeneric hybrids of durum wheat (Triticum turgidum, 2n=4x=28; AABB genomes) with the perennial grass Thinopyrum junceiforme (2n=4x=28; J1J1J2J2) using RAPD markers. The first step was to identify amplification of species-specific DNA markers in the parental grass species
and durum wheat cultivars. Initially, the genomic DNA of five grass species (Thinopyrum junceiforme, Th. bessarabicum, Lophopyrum elongatum, Leymus karataviensis and Elytrigia pycnantha) and selected durum cultivars (‘Langdon’, ‘Durox’, ‘Lloyd’, ‘Monroe’, and ‘Medora’) was screened with 40 oligonucleotide
primers (nano-mers). Three oligonucleotides that amplified DNA fragments specific to a grass species or to a durum cultivar
were identified. Primer PR21 amplified DNA fragments specific to each of the five durum cultivars, and primers PR22 and PR23
amplified fragments specific to each of the grass species. Intergeneric hybrids between the durum cultivars ‘Langdon’, ‘Lloyd’
and ‘Durox’ and Th. junceiforme, and their backcross (BC) progeny were screened with all 40 primers. Six primers amplified parent-specific DNA fragments
in the F1 hybrids and their BC1 progeny. Three primers, PR22, PR23 and PR41, that amplified Th. junceiforme DNA fragments in both F1 and BC1 were further analyzed. The presence of an amplified 1.7-kb Th. junceiforme DNA fragment in the F1 hybrids and BC1 progeny was confirmed using Southern analysis by hybridization with both Th. junceiforme genomic DNA and Th. junceiforme DNA amplified with primer PR41. With the exception of line BC1F2 no. 5, five selfed progeny of BC1 and a BC2 of line 3 (BC1F2 no. 3בLloyd’) from a cross of ‘Lloyd’×Th. junceiforme showed the presence of the 1.7-kb DNA fragment. All selfed BC1 and BC2 lines retained the 600-bp fragment that was confirmed after hybridization with Th. junceiforme DNA amplified with primer PR22. Other experiments using RFLP markers also showed the presence of up to seven Th. junceiforme DNA fragments in the F1 hybrids and their BC progeny after hybridization with Th. junceiforme DNA amplified with primer PR41. These studies show the usefulness of molecular markers in detecting alien chromatin/DNA fragments
in intergeneric hybrids with durum wheat.
Received: 21 November 1996 / Accepted: 21 March 1997 相似文献
16.
A preliminary analysis of the correlation of food-web characteristics with hydrology and nutrient gradients in the southern Everglades 总被引:2,自引:2,他引:0
We estimated trophic position and carbon source for three consumers (Florida gar, Lepisosteus platyrhincus; eastern mosquitofish, Gambusia holbrooki; and riverine grass shrimp, Palaemonetes paludosus) from 20 sites representing gradients of productivity and hydrological disturbance in the southern Florida Everglades, U.S.A.
We characterized gross primary productivity at each site using light/dark bottle incubation and stem density of emergent vascular
plants. We also documented nutrient availability as total phosphorus (TP) in floc and periphyton, and the density of small
fishes. Hydrological disturbance was characterized as the time since a site was last dried and the average number of days
per year the sites were inundated for the previous 10 years. Food-web attributes were estimated in both the wet and dry seasons
by analysis of δ15N (trophic position) and δ13C (food-web carbon source) from 702 samples of aquatic consumers. An index of carbon source was derived from a two-member
mixing model with Seminole ramshorn snails (Planorbella
duryi) as a basal grazing consumer and scuds (amphipods Hyallela azteca) as a basal detritivore. Snails yielded carbon isotopic values similar to green algae and diatoms, while carbon values of
scuds were similar to bulk periphyton and floc; carbon isotopic values of cyanobacteria were enriched in C13 compared to all consumers examined. A carbon source similar to scuds dominated at all but one study site, and though the
relative contribution of scud-like and snail-like carbon sources was variable, there was no evidence that these contributions
were a function of abiotic factors or season. Gar consistently displayed the highest estimated trophic position of the consumers
studied, with mosquitofish feeding at a slightly lower level, and grass shrimp feeding at the lowest level. Trophic position
was not correlated with any nutrient or productivity parameter, but did increase for grass shrimp and mosquitofish as the
time following droughts increased. Trophic position of Florida gar was positively correlated with emergent plant stem density. 相似文献
17.
Sugar Beet-Associated Bacterial and Fungal Communities Show a High Indigenous Antagonistic Potential Against Plant Pathogens 总被引:1,自引:0,他引:1
The aim of this study was to analyze microbial communities in/on sugar beet with special focus on antagonists toward plant
pathogens. For this purpose, the composition of microorganisms isolated from the rhizosphere, phyllosphere, endorhiza, and
endosphere of field-grown sugar beet plants was analyzed by a multiphasic approach at three different plant development stages
at six locations in Europe. The analysis of microbial communities by Single Strand Conformation Polymorphism (SSCP) of 16S/18S
rRNA clearly revealed the existence of discrete microenvironment- and site-specific patterns. A total of 1952 bacterial and
1344 fungal isolates screened by dual testing for antagonism toward the pathogens Aphanomyces cochlioides, Phoma betae, Pythium ultimum, and Rhizoctonia solani resulted in 885 bacterial (=45%) and 437 fungal (=33%) antagonists. In general, the indigenous antagonistic potential was
very high and influenced by (a) the location, (b) the plant developmental stage, and (3) the microenvironment. Furthermore,
we showed for the first time that the antagonistic potential was highly specific for each target pathogen. The majority of
antagonistic microorganisms suppressed only one pathogen (bacteria: 664 = 75%; fungi: 256 = 59%), whereas the minority showed
a broad host range (bacteria: 4 = 0.5%; fungi: 7 = 1.6%). The bacterial communities harbored the highest antagonistic potential
against P. ultimum, whereas the fungal communities contained more antagonists against A. cochlioides and R. solani. In contrast to their high proportion, only a low diversity of antagonists at genotypic and species level was found. Novel
antagonistic species, e.g., Subtercola pratensis or Microbacterium testaceum were found in the internal part of the sugar beet body. 相似文献
18.
The Florida Everglades is a naturally oligotrophic hydroscape that has experienced large changes in ecosystem structure and
function as the result of increased anthropogenic phosphorus (P) loading and hydrologic changes. We present whole-ecosystem
models of P cycling for Everglades wetlands with differing hydrology and P enrichment with the goal of synthesizing existing
information into ecosystem P budgets. Budgets were developed for deeper water oligotrophic wet prairie/slough (‘Slough’),
shallower water oligotrophic Cladium jamaicense (‘Cladium’), partially enriched C. jamaicense/Typha spp. mixture (‘Cladium/Typha’), and enriched Typha spp. (‘Typha’) marshes. The majority of ecosystem P was stored in the soil in all four ecosystem types, with the flocculent
detrital organic matter (floc) layer at the bottom of the water column storing the next largest proportion of ecosystem P
pools. However, most P cycling involved ecosystem components in the water column (periphyton, floc, and consumers) in deeper
water, oligotrophic Slough marsh. Fluxes of P associated with macrophytes were more important in the shallower water, oligotrophic
Cladium marsh. The two oligotrophic ecosystem types had similar total ecosystem P stocks and cycling rates, and low rates
of P cycling associated with soils. Phosphorus flux rates cannot be estimated for ecosystem components residing in the water
column in Cladium/Typha or Typha marshes due to insufficient data. Enrichment caused a large increase in the importance of
macrophytes to P cycling in Everglades wetlands. The flux of P from soil to the water column, via roots to live aboveground
tissues to macrophyte detritus, increased from 0.03 and 0.2 g P m−2 yr−1 in oligotrophic Slough and Cladium marsh, respectively, to 1.1 g P m−2 yr−1 in partially enriched Cladium/Typha, and 1.6 g P m−2 yr−1 in enriched Typha marsh. This macrophyte translocation P flux represents a large source of internal eutrophication to surface
waters in P-enriched areas of the Everglades. 相似文献
19.
Isoetes yunguiensis is an endangered and endemic fern in China. Field survey indicated that only one population and no more than 50 individuals
occur in the wild. The genetic variation of 46 individuals from the population remaining at Pingba (Guizhou Province, China)
was assessed by Random Amplified Polymorphic DNA (RAPD) finger-printing. Twelve primers were screened from sixty ten-bp arbitrary
primers, and a total of 95 DNA fragments were scored. Of these, 62.1% were polymorphic loci, which indicated that high level
genetic variation existed in the natural population. The accumulation of genetic variation in the history of the taxon and
the apparent minimal reduction effect on genetic diversity following destruction of habitat might be responsible for the high
level genetic diversity presently remaining in the I. yunguiensis population. However, with the continuing decrease of population size, the genetic diversity will gradually be lost. We suggest
that the materials from the extant population should be used for re-establishment of the populations.
Translated from Journal of Wuhan University (Natural Sciences Edition), 2005, 51(6): 767–770 [译自: 武汉大学学报 (理学版)] 相似文献
20.
Methyl tert-butyl ether (MTBE) is a prevalent groundwater contaminant. In this study, three distinct MTBE-degrading, anaerobic cultures
were derived from MTBE-contaminated aquifer material: cultures NW1, NW2 and NW3. The electron acceptors used are anthraquinone-2,6-disulfonate
(AQDS; NW1), sulfate (NW2) and fumarate (NW3), respectively. About 1–2 mM MTBE is consistently degraded within 20–30 days
in each culture. The 16S rDNA-based amplified ribosomal DNA restriction analysis (ARDRA) was used to analyze the microbial
community in each culture. Results indicate novel microorganisms (i.e. no closely related known genera or species) catalyze
anaerobic MTBE biodegradation, and microbial diversity varied with different electron acceptors. Tert-butyl alcohol (TBA) accumulated to nearly stoichiometric levels, and these cultures will be critical to understanding the
factors that influence TBA accumulation versus degradation. The cultures presented here are the first stable anaerobic MTBE-degrading
cultures that have been characterized with respect to taxonomy. 相似文献