Clonal diversity along a water depth gradient in a declining reed stand as detected by three different genetic methods

Isozyme, RAPD (random amplified polymorphic DNA) and microsatellite techniques were applied to determine the genetic diversity of a reed stand declining at the open water fringe for several decades and the accuracy of these methods was evaluated. Sampling was carried out along three transects parallel with and one transect at right angle to the lakeshore. In isoenzyme investigation, esterase and further 11 polymorphic loci of seven isozymes (with a total of 26 alleles) were analysed and 39 clones were distinguished. RAPD analysis involved 11 random decamer primers and, based on 141 repeatably amplifying and polymorphic RAPD fragments, 52 multilocus genotypes were differentiated. In microsatellite investigation, four primer pairs provided 47 polymorphic allelic variants that determined 37 multilocus phenotypes.Besides the differences, all the three methods revealed high number and intermingling (mixed) arrangement of clones at lower water depths, and low clone number and successive structure at the open water fringe of the stands. Only microsatellite analysis revealed different stages of colonization: old successful clone (colonizing the deeper water but almost completely disappearing at the lakeshore edge) and successful but young clone (with large extension at the lakeshore and just reaching the open water edge of the stand) were also distinguished. Finally, the present paper demonstrated that an appropriate data evaluation could make the result of RAPD comparable to that of microsatellite studies.     

Vertical differences in Phragmites australis culm anatomy along a water depth gradient

We reported on quantitative anatomical comparisons of reed culms grown under a wide range of water depth (from −10 to +230 cm). The study focused mainly on the above water parts of ramets, but also provided an insight into the submerged internodes. Investigated anatomical features were: radial thickness of the internode wall and that of each tissue constituting it (epidermis and subepidermal tissues, aerenchyma channels, cortical sclerenchyma and parenchyma); areas of aerenchyma channels and the summed transversal area of them; areas of the innermost vascular bundles involving the bundle sheath sclerenchyma, phloem and metaxylem vessels; the cross-sectional area of the pith cavity and that of the internode wall. After a 2–3% decrease below the uppermost internode, the thickness of internode tissues, except for cortical sclerenchyma, continuously increased downwards. Quantitative differences between the ramets grown at different water depths were observed only from the lower aerial internodes. Parenchyma taking part considerably in the mechanical stability of culms with its large extension and thick cell walls was more-layered and thicker (with the maximum thicknesses of approximately 1200 and 1000 μm) in ramets from 180–200 than from 20–30 cm water depth. Areas of the innermost vascular bundles increased downwards and decreased after a maximum value appearing in lower internodes of ramets grown in deeper than shallower water. Aerenchyma channels appeared farther up from the water surface in culms in shallower than deeper water: the top ends were found about 50 cm higher in culms from 20–30 than from 180–200 cm water depth. Along the transect at right angles to the shore, the radial thickness and area of aerenchyma channels were higher in ramets grown in medium water depth—the summed transversal area of them was greater than 4 mm² in internodes at the water surface, while plants from the two ends of the water depth gradient had smaller aerenchyma channels (with approximately 1 mm² total areas). In contrast, pith cavity area at the water surface continuously increased – up to 60 mm² – from shallower to deeper water. Therefore, oxygen transport in ramets grown at the open water fringe of stands may occur mostly in the pith cavity.     

Genetic diversity patterns in Phragmites australis at the population,regional and continental scales

Genetic diversity, population structure and interrelationships were investigated in eight populations of the common reed, Phragmites australis, in the Po Plain, Italy, by means of amplified fragments length polymorphisms (AFLPs) and random amplified polymorphic DNAs (RAPDs). Patterns of genetic diversity were analysed in relation to size, age and degree of human impact in the wetlands and compared with that of a distant population in Romania. Genetic distances between Po Plain clones and geographically distant clones were measured to determine the geographical extent of the gene pool.     

Genetic diversity and dispersal of Phragmites australis in a small river system

Even though the reed, Phragmites australis, is an extensively studied wetland species, little is known about reproduction and dispersal modes within and among reed populations at the scale of small river systems. Using microsatellite analysis of 189 individuals from three adjacent river catchments in the Czech Republic, we elucidated the role of the river corridors in the dispersal of P. australis. Using Bayesian clustering of individuals, we found that 19% of clusters were distributed only along one river, which implied dispersal by water (or by wind) along river corridors, whereas 38% of clusters were widely distributed and were likely the product of wind long-distance dispersal among rivers. Intensive exchange of propagules among river systems is further demonstrated by only 6% of total variance being attributed to the variance among rivers in the AMOVA-analysis. Spatial autocorrelation analysis revealed a decreasing pattern up to 5–10 km and no clear pattern over longer distances. This gives an evidence for pollen and seed dispersal at short distances (up to 1 km), whereas most likely only seed dispersal at longer distances up to 10 km. We found five multilocus genotypes distributed in two different populations. The distances between populations with the same genotype ranged from 0.5 to 10.8 km. This can be interpreted as long-distance vegetative dispersal.     

Changes in leaf gas exchange, water relations, biomass production and solute accumulation in Phragmites australis under hypoxic conditions

The physiological responses to hypoxic stress were studied in the common reed, Phragmites australis (Cav.) Trin. ex Steudel. Growth, leaf gas exchange, water (and ion) relations and osmotic adjustment were determined in hydroponically grown plants exposed to 10, 20 and 30 days of oxygen deficiency. The highest growth of reed seedlings was found in normoxic (aerobic) conditions. Treatment effects on biomass production were relatively consistent within each harvest. Leaf water potential and osmotic potential declined significantly as hypoxia periods increased. However, leaf turgor pressure showed a consistent pattern of increase, suggesting that reed plants adjusted their water status by osmotic adjustment in response to root hypoxia. After 20 and 30 days in the low oxygen treatment, net CO₂ assimilation and stomatal conductance were positively associated and the former variable also had a strong positive relationship with transpiration. Short-term hypoxic stress had a slight effect on the ionic status (K⁺, Ca²⁺ and Mg²⁺) of reed plants. In contrast, soluble sugar concentrations increased more under hypoxic conditions as compared to normoxia. These findings indicate that hypoxia slightly affected the physiological behavior of reed plants.     

Decomposition of Phragmites australis rhizome in a shallow lake

Decomposition of Phragmites australis (Cav. Trin ex Steudel) rhizome was studied at Lake Fert?/Neusiedler See using the litter bag technique. Samples were analysed for rhizome dry mass, fibre (cellulose, hemicellulose, lignin) and nutrient content (C, N, P and S), litter-associated fungal biomass, potential microbial respiration (electron transport activity: ETS) and cellulolitic bacteria. The mass loss of decomposing rhizome was rapid in the initial period and only 13.6% of the dry mass remained at the end of the experiment during 953 days. Substantial quantities of C, N, S and P were lost during 99 days; only 18% C, 19% N, 14% S and 6.4% of the P remained after 953 days. Hemicellulose degraded more rapidly than the other fibres whilst the lignin had the slowest rate of decomposition. Bacteria were found to be the primary colonizers of plant detritus, which was followed by fungal growth. An antagonistic relationship was observed between bacteria and fungi. Fungal biomass as determined by ergosterol concentrations ranged between 4.1 and 420 μg g⁻¹ and peaked every year in September. The number of cellulolitic bacteria varied from 0 to 22 MPN g⁻¹ with higher values in summer. The ETS-activity ranged between 0.1 and 1.6 mg O₂ g⁻¹ h⁻¹. The changes in ETS-activity varied almost in parallel with the in situ temperature of the lake water.     

Effects of abiotic conditions on Phragmites australis along geographic gradients in Lake Burullus, Egypt

Stand structure and biomass production of Phragmites australis (Cav.) Trin. ex Steud. were analyzed along north-south and east-west transects in the Burullus coastal lagoon (N Egypt, 410 km²) at monthly intervals over a period of 1 year (February 2003 until January 2004). For this purpose, young and old stands were selected at eight different locations in the lagoon. It was found that the north-south transect mainly represented a fertility gradient (207-286 mg l⁻¹ TN, 30-106 mg l⁻¹ TP), while the east-west transect was associated with significantly decreasing salinity (7-4 ppt). All morphological and biomass variables of P. australis were significantly different between young and old stands. On average, the old (7.3 ± 0.2 kg DW m⁻²) accumulated three times more total above-ground biomass than the young stands (2.5 ± 0.1 kg DW m⁻²). Shoot height, diameter and shoot dry weight significantly increased by 25-50% with increasing fertility along the north-south transect. Shoot density significantly decreased from north to south, while it almost doubled in the north sites from 109 ± 6 to 216 ± 7 shoots m⁻² along the west-east transect. In separate stepwise multiple regressions, variation in water quality explained 34-63% of the variation in morphology and total above-ground biomass in the old stands (salinity and water level were most important for biomass, transparency also for height and density) while it explained 16-42% of variation in young stands (mainly transparency).     

Cultivable bacterial composition and BIOLOG catabolic diversity of biofilm communities developed on Phragmites australis

Biofilm samples formed on submerged young and old stems of reed, Phragmites australis (Cav.) Trin ex Steudel were taken during summer at different sites of Lake Velencei, Hungary. BIOLOG GN microplates were used to analyze the patterns of sole carbon source utilizations by microbial communities. From the carbon sources, carbohydrates and amino acids were preferred by all microbial communities. In the case of the old reed stem samples, higher number of carbohydrates, carboxylic acids and polymers were used than in young samples. Biofilm bacterial communities from the old reed samples of the nature conservation area of the lake used the highest number of (≥50% of the available) substrates. In principal component analysis (PCA), the metabolic potential of the microbial communities from the middle open water region of the lake showed the smallest variability. The variability within metabolic potential of the reed stem microbial communities from a given sampling site was the largest in the case of samples originating from the western, reed-covered nature conservation area. A total of 251 bacterial isolates obtained after serial dilutions and plating onto different media were characterized by traditional phenotypic tests. The strains showed high activities mainly in the hydrolysis of certain biopolymers (gelatine and casein). PCA was used to evaluate the phenotypic variability of strain groups of different sampling sites. The two open water regions were similar to each other, and separated from the western reed covered part of the lake. Similarly to the BIOLOG community-level physiological profiles, strain groups of the young and old reed stem samples originating from the nature conservation area had the largest metabolic potential. On the basis of 16S rDNA sequence analysis, 23 representative strains with different ARDRA patterns were identified. The cultivation-based investigations of bacterial diversity showed characteristic differences in the number of identified taxa in connection with the sampling sites. No characteristic differences could be observed according to medium or sample type (young, first year and more than 1-year old stems) among the identified species. 16S rDNA sequence comparisons resulted in the identification of the genera Aureobacterium, Arthrobacter, Kocuria, Microbacterium, Micrococcus, Rhodococcus, Bacillus, Marinibacillus, Rhodobacter, Defluvibacter, Pseudomonas, Klebsiella, Serratia and Aeromonas. The results of the cultivation-based and BIOLOG investigations revealed characteristic differences in the bacterial community composition and activities of the open water region and the reed covered nature conservation part of the lake.     

Genetic diversity of the endangered and endemic species Psathyrostachys huashanica natural populations using simple sequence repeats (SSRs) markers

Psathyrostachys huashanica Keng., a species endemic to China, is only distributed in Huashan Mountain in Shaanxi Province. It has been listed as “national first-class protected rare species.” In this study, the microsatellites of barley were used to analyze genetic diversity of P. huashanica populations sampled from three valleys (Huangpu, Xian and Huashan Valleys) in Mt. Huashan. A total of 33 alleles of 11 loci were detected from 266 individuals. The observed average number of alleles (A) is 2.75; the effective number of alleles (Ae) is 1.67. The percentage of polymorphic loci (PPB) is 58.33% in Huangpu Valley, 75% in Xian Valley, 83.33% in Huashan Valley, and the total PPB is 83.33%. About 77.6% of (F_ST = 0.324) genetic diversity was observed within the subpopulations. Genetic differentiation within each subpopulations was higher than that among the subpopulations. Mean genetic distance is 0.17 (range: 0.010–0.401). Correlation analysis detected significant correlation between genetic distance and vertical distance of altitude in Huashan Valley. Differentiation mainly occurred between the higher altitude subpopulations and the lower altitude subpopulations, suggesting that altitude might be the major factor that restricted the gene flow between different altitude subpopulations and resulted in differentiation of subpopulations.     

Different sensitivity of Phragmites australis and Glyceria maxima to high availability of ammonium-N

The ability to cope with NH₄⁺-N was studied in the littoral helophytes Phragmites australis and Glyceria maxima, species commonly occupying fertile habitats rich in NH₄⁺ and often used in artificial wetlands. In the present study, Glyceria growth rate was reduced by 16% at 179 μM NH₄⁺-N, and the biomass production was reduced by 47% at 3700 μM NH₄⁺-N compared to NO₃⁻-N. Similar responses were not found in Phragmites. The amounts (mg g⁻¹ dry wt) of starch and total non-structural carbohydrates (TNC) in rhizomes were significantly lower in NH₄⁺ (8.9; 12.2 starch; 20.1; 41.9 TNC) compared to NO₃⁻ treated plants (28.0; 15.6 starch; 58.5; 56.3 TNC) in Phragmites and Glyceria, respectively. In addition, Glyceria showed lower amounts (mg g⁻¹ dry wt) of soluble sugars, TNC, K⁺, and Mg²⁺ in roots under NH₄⁺ (5.6; 14.3; 20.6; 1.9) compared to NO₃⁻ nutrition (11.6; 19.9; 37.9; 2.9, for soluble sugars, TNC, K⁺, and Mg²⁺, respectively), while root internal levels of NH₄⁺ and Ca²⁺ (0.29; 4.6 mg g⁻¹ dry wt, mean of both treatments) were only slightly affected. In Phragmites, no changes in soluble sugars, TNC, Ca²⁺, K⁺, and Mg²⁺ contents of roots (7.3; 14.9; 5.1; 17.3; 2.6 mg g⁻¹ dry wt, means of both treatments) were found in response to treatments. The results, therefore, indicate a more pronounced tolerance towards high NH₄⁺ supply in Phragmites compared to Glyceria, although the former may be susceptible to starch exhaustion in NH₄⁺-N nutrition. In contrast, Glyceria's ability to colonize fertile habitats rich in NH₄⁺ is probably related to the avoidance strategy due to shallow rooting or to the previously described ability to cope with high NH₄⁺ levels when P availability is high and NO₃⁻ is also provided.     

Competitive effects of Phragmites australis on the endangered artesian spring endemic Eriocaulon carsonii

We investigated the relative importance of above- and below-ground competition by reeds (Phragmites australis (Cav.) Trin. ex Steud) on the growth rate of Eriocaulon carsonii F.Muell. subsp. carsonii, an endangered plant threatened by reeds on artesian springs in Australia. Soil-filled buckets containing E. carsonii were frequently watered to simulate artesian spring conditions and subject to three treatments: (1) no Phragmites (control), (2) Phragmites (ABG), and (3) Phragmites with shoots tied back (BG). After thirteen months, Phragmites mean below-ground biomasses had increased to c. 3 kg m⁻² and mean above-ground biomasses to c. 1 kg m⁻². After the same period, mean root biomass of E. carsonii plants was significantly lower in buckets subject to both Phragmites treatments compared with control plants, as was E. carsonii foliage area. Comparison of the two Phragmites treatments indicated that below-ground competition was the primary cause of this reduced growth in E. carsonii. The vulnerability of E. carsonii to competitive exclusion by P. australis is in part due to the highly synchronized phenologies of the two species.     

Clonal diversity and structure related to habitat of the marine angiosperm Thalassia testudinum along the Atlantic coast of Mexico

The clonal structure of the tropical seagrass Thalassia testudinum was studied at 16 sites along the Mexican Atlantic coast, situated in back-reef, shallow coastal and lagoon habitats. Thalassia testudinum was highly clonal, with an overall average clonal richness (R) of 0.55. The largest genet found in this study extended throughout the sampling area (∼230 m), with an estimated max age almost reaching 600 years. Lagoons with higher nutrient availability reflected by nutrient content of leaves (mean leaf C:N ratio 11.4) and lower hydrodynamic regimes reflected by the percentage of fine sediments (on average 23%), sustained larger genets of T. testudinum (mean of the largest genets over populations was 167.3 m) than the shallow coastal areas (C:N 12.3, 6.2% fine sediment, mean largest genet 10.3 m) and the more oligotrophic back-reefs (C:N 16.3, 2.7% fine sediment, mean largest genet 6.5 m). Population genetic analysis showed different levels of clonality, genotypic diversity and spatial genetic relatedness for this seagrass per habitat, with the lagoons presenting much lower levels of clonal diversity than the other two habitats.     

预处理方式对香蒲和芦苇种子萌发的影响

有性繁殖是植物种群形成与维持的主要方式。为探索退化湿地的快速恢复方法,为松花江下游退化湿地恢复提供科学依据,本研究开展了香蒲和芦苇种子快速发芽的有性繁殖实验。研究采用滤纸为发芽基质,通过变温培养试验,以未浸种处理为参照,分析了蒸馏水、双氧水(H₂O₂)、硝酸钾(KNO₃)和高锰酸钾(KMnO₄)溶液浸种的预处理方式对香蒲、芦苇种子发芽率和发芽速率的影响。结果表明:不同预处理方式对香蒲、芦苇种子的发芽率和发芽速率均具有显著影响。KMnO₄溶液浸种再清洗处理条件下,香蒲种子发芽率和发芽速率均显著高于其他处理,平均发芽率可达未浸种处理条件下的3.1倍,发芽速率为16.17±0.80。芦苇种子的发芽率和发芽速率在经KNO₃溶液浸泡再清洗处理后效果最佳,种子发芽率达96%-99%,发芽速率达28.43±0.71。因此,分别对香蒲、芦苇种子采用KMnO₄和KNO₃溶液浸泡再清洗的预处理方式可以缩短出苗时间,提高发芽率,从而加速湿地植被恢复进程。     

Growth-mortality trade-offs along a depth gradient in Cancer borealis

Intertidal and shallow subtidal ecosystems experience steep environmental gradients over short distances. Individual foraging rate, predation risk, and physiologic stress vary along these gradients, resulting in growth-mortality trade-offs with depth. In the summer, Cancer borealis commonly forage in the shallow subtidal in the Gulf of Maine. C. borealis are the favored invertebrate prey of the Herring Gull and the Great Black-backed Gull, which consume 25%-50% of available C. borealis (those in < 1 m water) during each daytime low tide. We investigated three possible explanations for the presence of C. borealis in the risky gull-predation zone. First, we tested whether predation risk in the gull-predation zone was matched at deeper depths by subtidal predators; we found predation risk decreases with depth. Second, we tested whether water temperatures were warmer in the gull-predation zone and whether these warmer temperatures resulted in increased growth rates. We found that, while waters were warmer in the gull-predation zone, crabs grew at similar rates above and below the thermocline when fed similar diets. Finally, we tested for differences in food availability with depth and whether these differences influenced C. borealis growth rates. Our results suggest a growth-mortality trade-off, where increased food availability provides sufficient growth benefit to outweigh the risk of foraging at shallower depths.     

Differences in rhizome aeration of Phragmites australis in a constructed wetland

Waterlogged soils are a challenging environment for plants due to anoxic conditions and enrichment of phytotoxic substances in the rhizosphere. High contents of organic matter in the substrate as present in constructed wetlands (CW) may amplify these effects. The influence of substrate organic matter on the rhizome aeration of Phragmites australis (common reed) was investigated in a CW for sewage treatment on two sites with different organic concentrations: (a) inflow part of the bed with a high organic charge (high-organic site) and (b) outflow zone of the bed with a lower organic charge (low-organic site). Several diurnal oxygen (O₂) courses were recorded inside the rhizomes using micro-optodes. Maximum O₂ percentages in the rhizomes were generally the same at both sites, but minimum O₂ values were lower in the low-organic site than in the high-organic site, leading to higher amplitudes at the low-organic site. The results suggest that oxygen release from the roots is hampered under high-organic compared to low-organic conditions. This observation might be explained by changes in gas conductivity of the roots, but also by alterations in microbial oxygen demand, under different organic burden.     

莫莫格湿地芦苇对水盐变化的生理生态响应

认识湿地植物对不同水盐环境的生理生态响应特征和规律,是确定湿地生态需水阈值的关键,为湿地生态需水量计算及生态恢复提供科学依据.通过对莫莫格湿地水盐环境因子与芦苇生理生态特征指标进行调查研究,并利用国际通用植被数量分析软件CANOCO4.5对其关系进行了冗余度分析(RDA).结果表明:湿地水深、Na+,HCO(3)含量3个环境因子组合对芦苇生理生态特征变异的解释量达到54.7％,说明这3个变量是影响芦苇生理生态特征变异的重要因子,水深是关键驱动因子.水深与芦苇株高、生物量、叶绿素含量、最大光化学效率Fv/FM以及光化学性能指数PIABS成显著正相关,随着水深的增加,芦苇株高、生物量以及叶绿素含量等逐渐增加.Na+含量、HCO(3)含量与芦苇生理生态特征的相关性没有达到显著水平.因此,中轻度盐碱湿地生态恢复需要重点考虑水深条件对湿地生态的影响,其次是水质( Na+/HCO(3))因素的影响作用,确保适宜生态水位,满足生态恢复需要.     

Detection of genetic diversity in closely related bread wheat using microsatellite markers

Wheat microsatellites (WMS) were used to estimate the extent of genetic diversity among 40 wheat cultivars and lines, including mainly European elite material. The 23 WMS used were located on 15 different chromosomes, and revealed a total of 142 alleles. The number of alleles ranged from 3 to 16, with an average of 6.2 alleles per WMS. The average dinucleotide repeat number ranged from 13 to 41. The correlation coefficient between the number of alleles and the average number of repeats was only slight (r _s = 0.55). Based on percentage difference a dendrogram is presented, calculated by the WMS-derived data. All but two of the wheat cultivars and lines could be distinguished. Some of the resulting groups are strongly related to the pedigrees of the appropriate cultivars. Values for co-ancestry (f) of 179 pairs of cultivars related by their pedigrees (f0.1) averaged 0.29. Genetic similarity (GS) based on WMS of the same pairs averaged 0.44. The rank correlation for these pairs was slight, with r _s = 0.55, but highly significant (P<0.001). The results suggest that a relatively small number of microsatellites can be used for the estimation of genetic diversity and cultivar identification in elite material of hexaploid bread wheat.