Some Aspects of the Importance of Genetic Diversity in Phragmites australis (Cav.) Trin. ex Steudel for the Development of Reed Stands

Various sites of Phragmites australis in Germany (Uckermark and Mark Brandenburg) and sites in Hungary and Denmark were investigated by PCR fingerprinting in order to determine their genetic diversity. Genetic similarities were calculated and, based on this, a cluster analysis was performed. The genetic similarity of reed clones around one lake ranged from between 70 to 100%, that of clones from different lakes was clearly lower. The further apart the clones were situated from each other, the less similar they were. At a wetland site near the shore a sudden colonisation by several new Phragmites clones was observed. This site was located in front of a well established genetically almost homogenous stand within the eulittoral. All the results are discussed in connection with a proposed model of establishment and development of water reed stands: colonization, selection of best adapted clones by competition and the stability of stands.     

Phenotypic and genotypic variation of Phragmites australis: Comparison of populations in two human-made lakes of different age and history

Populations of Phragmites australis (CAV.) TRIN. ex STEUD. were studied in the littoral zones of two man-made lakes located in the Třeboň Basin (South Bohemia, the Czech Republic): (1) Opatovický fishpond, a shallow artificial lake constructed in 1510–1514 by damming a shallow valley and used since for carp production, and (2) Halámky sand pit, a new lake formed by sand extraction in 1970–1994. Phenotypic variability was assessed on the basis of shoot morphological and growth characteristics, measured at the time of seasonal maximum aboveground biomass. Genotypic variability was detected using RAPDs, which demonstrated a high clonal diversity in both habitats. The clonal diversity would be strongly underestimated if it were based only on morphological differences. Higher genotypic variability was found in the fishpond reed, not corresponding with low variability in its phenotype performance. Based on analysis of 160 samples, four patterns of genotypic variation were detected: (1) Some stands were genetically uniform and were therefore considered to be monoclonal in both populations studied. (2) Some stands consisted of several clones at the Halámky sand pit. However, these clones showed more similarity within the particular stands than with clones of adjacent stands. (3) In the Opatovický fishpond population, multiclonal stands consisted of clones with a low degree of similarity. (4) Identical clones were detected in several neighbouring stands separated by gaps in the Opatovický fishpond population. The findings support a model of colonization postulating that populations initiated by seeds are initially genetically diverse and over time become dominated by a few clones as a result of competition and selection. These processes then decrease both genetic and morphological variability.     

Lakeside reed border characteristics at Lake Constance (Untersee): A comparison between 1981–1983 and 1994

Eutrophication and the associated proliferation offilamentous algae were often considered importantcauses of reed die-back that occurred in the sixtiesand seventies at Lake Constance. According to thishypothesis the reduction in lake water nutrientconcentrations during the eighties and nineties shouldhave reduced the abundance of filamentous algae andwhich should have reduced the supposed mechanicalimpact of filamentous algae on the lakeside reedstands. To examine whether this had actually occurred,the condition of the lakeside reed border at LakeConstance (Untersee) was surveyed in 1994 and resultswere compared to those of similar surveys carried outin the years 1981–83. The extent of mechanical damageto reed stalks, the amount of macrophyte wash and thedegree of shoreline erosion were assessed forshoreline segments of 25 m along a total shorelinelength of 65 km. The results showed that mechanicaldamage to reed stalks was generally higher in 1994than in 1981–83, while macrophyte wash and shorelineerosion were generally less severe. The decreasedamount of macrophyte wash was associated with a changein macrophyte species composition from a dominance offloating filamentous algae to a dominance of rootedPotamogetonaceaeand fragile Characeae,and therefore probably was due to the lower nutrientconcentrations of the lake. The opposite trends foundfor mechanical damage to reed stands and the amount ofmacrophyte wash between 1981–83 and 1994, as well asthe absence of relation between the two variables in1994, suggested that macrophyte wash had only a minoreffect on the condition of lakeside reed stands atLake Constance. Highly damaged reed stands and erodedcliffs were often located at wind exposed sites orclose to highly frequented shipping routes in 1994,suggesting that mechanical stress from waves wasresponsible for the damage. Due to the lakewardprogression of reed stands during the early nineties,reed stalks were, on average, located in deeper waterin 1994 than in 1981–83. This might have strengthenedthe mechanical stress from wave action even more andhave caused the higher frequency of mechanical damageto reed stalks. Other causes of damage such asmacrophyte wash, roosts of birds or bird swarmsprobably played a minor and only local role.     

To the importance of genetic diversity of Phragmites australisin the development of reed stands

Reed stands in Germany and Europe were investigatedwith respect to their genetic diversity by means ofRandom Amplified Polymorphic DNA (RAPD) via thePolymerase Chain Reaction (PCR-fingerprinting).Different types of clonal distribution could bedistinguished: monoclonal reed stands and polyclonalreed stands, and among the latter, stands with low orhigh numbers of different clones as well as standswith mosaic-like coexisting or intermingling clones.Furthermore, clonal distribution and the expansion ofdifferent clones was observed within a newlydeveloping reed population. The findings appear tosupport a model of colonization postulating thatpopulations initiated by seeds are initiallygenetically diverse, but over time become dominated byone or a few clones adapted to the prevailing siteconditions. Thus, low genetic diversity seems to bethe result of a natural selection process. Clonaldiversity within a reed population and the type ofclonal distribution are discussed with regard to theirimportance for the reed stand's ability to adapt tochanging site conditions and eventually for itssurvival or die-back.     

Genetic survey on a reed-bed in Central Italy showing early die-back symptoms

Phragmites australis die-back is a well known phenomenon in Central Europe and rather recently observed also in some Mediterranean wetlands. In this study we analyze the genetic structure of a reed-bed in a protected wetland in N-W Tuscany (Italy) recently showing some clear symptoms of die-back, in particular the clumped growth-form, searching for any possible relationships with the ecological condition or the health status of common reed stands. After a diachronic analysis of vegetation maps (from 1988 to 2013) and a field survey, we have sampled four temporarily emerged and four permanent submerged reed stands, being the submersion regime a crucial trigger of reed die-back. Aquatic plots showed two clear conditions, with the presence of clumped and non-clumped stands. Emerged stands have been sampled in areas showing temporarily stable, increasing and decreasing reed-bed surface. In order to investigate the genetic structure of the population, the AFLP technique was applied on 69 individuals. The total reedbed surface showed a decrease in the observed time, partly due to the human activities and partly attributable to the RDBS. In several areas of the Lake the reed-bed appeared clumped and fragmented. The genetic analysis put in evidence a rather high level of genetic diversity, compared to the results of previous international studies on other populations of the same species. No significant differences between temporarily and permanently submerged stands were found. The major portion of genetic variation appeared within sampling sites rather than between sampling sites, indicating the absence of isolation between the different reed stands of the lake and a negligible role of genetic diversity in the occurrence of die-back symptoms.     

Differences in morphology and C/N-balance between clones ofPhragmites australis within a plantation at a degraded fen

The morphology, productivity and C/N-balance of 9 different clones ofPhragmites australis planted in 1997 in a degraded fen area of 40,000 m² was investigated in order to estimate the degree of variation between the genotypes. The planted reed clones showed significant differences in morphology, standing crop and stand structure at the same site. The above-ground biomass of some reed clones was due to high culms and large leaf areas, while among others it was due to high shoot densities and small culms. The productivity of the individual clones also differed. At the end of the 1998 growing season the standing crop of the clones ranged from about 700 to 2,000 g of dry matter per m². Differences were found in the C/N-dynamics as in the standing stock of total nitrogen in the above-ground biomass (ranging from 15 to 50 g N/m²) and the relative nitrogen content of the shoots. Furthermore, seasonal changes in the amount of free amino acids and carbohydrates in the basal internodes of the different clones were compared. The patterns are discussed with respect to the nutritional status of the reed plants. In conclusion, the results suggest high genotypic variation despite the comparable site conditions and thus a strong influence of genetically determined differences in growth and resource exploitation on the characteristics of reed clones.     

Assessment of aquatic and terrestrial reed (Phragmites australis) stands

A survey of recent publications shows that research on Phragmites australishas oftenapplied character because of the considerableecological and economic significance of the species.The main applications are water treatment, agriculture(food production or weed control) and natureconservation. In Europe, most research on natural reedstands has been motivated by reed die-back and effortstowards protection or restoration. Reed progressionand reed control have been the main concerns in otherparts of the world, and reed progression has alsoreceived increasing attention in Europe. While reeddie-back generally affects aquatic stands, progressioncan occur at both terrestrial and aquatic sites, andit can be desired (e.g. lake shore restoration)or unwanted (e.g. in species-rich fens ormarshes). Therefore, reed stands need to be assessedindividually to decide on management aims andappropriate methods. The varying status of Phragmites australisformed the background of the`European Reed Conference' held in Zürich/Switzerlandin October 1998. The seven contributions published inthis special issue are introduced with particularreference to differences between aquatic andterrestrial reed stands and to approaches used in theirassessment.     

Phenotypic and genotypic variation of Phragmites australis: A comparative study of clones originating from two populations of different age

Populations of common reed (Phragmites australis [Cav.] Trin. Ex Steud.) were studied in the littoral zones of two human-made lakes in the Třeboň Basin (South Bohemia, Czech Republic): (1) Opatovický fishpond, a 500-year-old fishpond, and (2) Halámky sand pit, a new lake formed by sand extraction in the 1970–1990s. Clones were identified using the RAPD method within morphologically different stands. The clones were propagated vegetatively and cultivated under comparable conditions in a common garden experiment for one vegetation season. Morphological and growth characteristics of the cultivated plants were recorded and compared with those found in the original reed stands. The younger (30-year old) population was genotypically more diverse than the older (500-year old) population. In addition, the younger population demonstrated correspondence of genotypic and phenotypic variation, while the older did not. The results indicate that the genetically determined morphological features (especially shoot length) are manifested more fully in the phenotype of the plants of the younger (Halámky) population, whereas environmental factors affect the phenotype to a greater extent in the older (Opatovický) population.     

Reedbed structure and habitat preference of reed passerines during the post-breeding period

Post-breeding habitats of nine passerine species were studied in the permanently flooded reed beds of ponds near the village Pusté úlany (SW Slovakia) in 2002. Structural features of reed beds and the abundance of all birds studied were sampled at two sites and eight study plots. The reed bed structure and abundance of four passerines differed considerably between the individual study plots. The variations in vegetation structure were also caused by winter reed burning in the SE part of study area. Stems in burnt reed beds were smaller and thinner than unburnt. Abundance of the reed warbler and to a lesser extent sedge warbler was higher in tall reed beds, while the bearded tit preferred thick reed stems. Position of reed beds along the shore — open water gradient was an important factor in terms of abundance at the study plots in the case of the reed bunting. This species showed a strong preference for the reed bed edge with open water. Horizontal distribution of other species seems to be random, however, the birds with the exception of Savi’s warbler preferred the upper stratum of reed bed in vertical distribution. Our field data corroborate with those found in experimental studies concerning with ecomorphological characteristics of birds. Some inconsistencies, however, could also be caused by other factors (e.g. foraging preferences). Comparison of breeding and post-breeding habitat requirements of the studied bird species confirmed a more or less random distribution of the majority of species in the post-breeding period. Some variation was found in the cases of only the reed warbler and bearded tit.     

Effects of seasonal temperature on shoot growth dynamics and shoot morphology of common reed (Phragmites australis)

The shoot growth during the vegetation period andshoot morphology at the end of the season wereinvestigated in four monoclonal aquatic reed stands(Phragmites australis) with differentproductivity in Berlin and Brandenburg. Investigationswere conducted over a period of six years (1991–96) toascertain the effects of differences in temperatures.All clones showed significant year-to-year variationin shoot morphology. The mean final shoot length ofthe two clones with highest variation ranged from252 cm (1991) to 388 cm (1993; Templiner See), andfrom 170 cm (1993) to 229 cm (1994; Parsteiner See).In spite of this considerable variation, morphologicalparameters measured at the end of the growing seasonshowed only a slight relation to the average airtemperature either during the main growth phase (Aprilto June) or during the period of bud formation (Augustto October of the previous year). Contrary to meanshoot length at the end of the growing season, shootelongation during the main growth phase (from April toJune) was clearly related to the sum of daily averagetemperatures. Thus, taking into account temperaturemay enhance the accuracy of studies on reed growthwhenever these studies are carried out at localitiesdiffering in temperature or in different years.     

Effect of eutrophication on culm architecture of lakeshore Phragmites reeds

The eutrophication of lakes in central Europe has been assumed to be at least partly responsible for a widespread die-back of fringing Phragmites australis reeds. To test the ‘eutrophication hypothesis’ on a broad data basis, lakeshore reed stands at 41 lakes of known trophic status and 10 stands in waste water and sludge treatment plants in Denmark and north Germany (North data subset, n=26), and south Germany, Switzerland and Austria (South data subset, n=25) were investigated. A total of 24 culm performance variables in three different shoot classes were analyzed by two-way ANOVA with the geographic origin and the ‘relative trophic index’ as factors. The geographic origin had a pronounced influence on culm architecture, whereas the effect of the trophic level mostly failed to be significant in the ANOVA. The culms from the North reed stands showed a weaker performance throughout than those from the South stands for a given trophic level. However, some of the morphometric traits in the North stands were significant positively correlated with the trophic level but very few significant cases were observed in the South data subset. Three hypotheses are discussed to explain the geographic effect: climatic effects, geochemistry of lake water and sediments, and trophic history of the lakes. It is concluded that lake eutrophication does not influence the culm performance negatively and that eutrophication cannot be regarded as a general cause in reed decline.     

Genetic diversity of riverine reed stands indicating the water regime of the habitat

Although genetic diversity of reed stands developing in habitats with unchanged water levels have been frequently investigated, little is known about reed propagation along rivers, where fluctuating water levels may provide various conditions for germination and seedling development.The present paper evaluates genetic diversity of reed stands grown in (i) an oxbow with significant water level fluctuations related to the flood events in the main river; (ii) a separated oxbow which has lost connection to the main channel; and (iii) artificially controlled running water with low water level fluctuation. At each site, reed stands were investigated along transects parallel to the shore and multilocus phenotypes were determined by microsatellite analysis.The results demonstrated that genetic diversity of riverine reed stands can indicate the water regime of the habitat. Reed colonizes mostly by vegetative propagation where regular inundation can impede germination and seedling development and, therefore, genetic diversity is low in the whole stand. If a former oxbow becomes practically a lake, the clonal diversity and colonization processes are similar to those observed in regular lakes; clone number decreases toward the open water. When reed forms floating mats (i.e. the effect of water level fluctuation is excluded), generative reproduction prevails in the entire stand, resulting in high genetic diversity even at the open water edge of the stand.     

Patterns of spatial resource use in lotic invertebrate assemblages

Spatial resource overlap by benthic invertebrates was investigated between stones in 11 freshwater habitats (10 streams and a wind-swept lake shore) of similar physicochemical nature but different thermal and hydrologic stability in the Cass-Craigieburn region, New Zealand. Both overlap and breadth of stone use by the invertebrate taxa decreased as stability declined, in part because of the lower number of species available with which to share resources at unstable sites. Although there was no evidence for resource partitioning of stones, communities at stable sites and on more stable substrates differed from those that would have been expected to accumulate by chance colonisation alone. Stone assemblages at unstable sites are dominated by the same general suite of species well suited to surviving disturbances, while conditions at stable sites allow more specialised taxa to colonise individual stones differentially.     

Early Holocene environmental change, the presence and disappearance of early Mesolithic habitation near Zutphen (The Netherlands)

The Early Holocene landscape near Zutphen (The Netherlands) is reconstructed by means of microfossil, macroremain and bone analyses. In this area early Mesolithic sites were found on a river dune along a former river channel. AMS¹⁴C dating provided a detailed chronology for the sites and river channel deposits. Between ca. 9800–9600 B.P. open herbaceous vegetation was present on the river dunes. The residual channels were fringed by reed swamps and willow shrubs, with birch and poplar woodlands inland. During this period there are indications of natural or man-made burning of the reed swamp vegetation along the residual channel. Also trampling zones along the lake edge were more abundant. However, no archaeological sites were discovered in the vicinity. From ca. 9600 B.P. on, the area became more densely forested; willow, birch and poplar replaced the reed swamps along the residual channels, while pine colonised the river dunes. Archaeological finds show that early Mesolithic people inhabited the area between ca. 9400 and 9200 B.P. and between ca. 8900–8700 B.P. During the earlier period, records of Urtica, Plantago and coprophilous fungi may point to trampling and/or eutrophication as a result of the presence of large herbivores and people along the channel shores. After ca. 8700 B.P. people probably left the area when open water was no longer available in the vicinity.     

Habitat-specific pigmentation in a freshwater isopod: adaptive evolution over a small spatiotemporal scale

Pigmentation in the freshwater isopod Asellus aquaticus (Crustacea) differed between habitats in two Swedish lakes. In both lakes, isopods had lighter pigmentation in stands of submerged vegetation, consisting of stoneworts (Chara spp.), than in nearby stands of reed (Phragmites australis). Experimental crossings of light and dark isopods in a common environment showed that pigmentation had a genetic basis and that genetic variance was additive. Environmental effects of diet or chromatophore adjustment to the background had minor influence on pigmentation, as shown by laboratory rearing of isopods on stonewort or reed substrates, as well as analyses of stable isotope ratios for isopods collected in the field. In both study lakes, the average phenotype became lighter with time (across generations) in recently established stonewort stands. Taken together, these results indicate that altered phenotype pigmentation result from evolutionary responses to local differences in natural selection. Based on the assumption of two generations per year, the evolutionary rate of change in pigmentation was 0.08 standard deviations per generation (haldanes) over 20 generations in one lake and 0.22 haldanes over two generations in the other lake. This genetic change occurred during an episode of population growth in a novel habitat, a situation known to promote adaptive evolution. In addition, stonewort stands constitute large and persistent patches, characteristics that tend to preserve local adaptations produced by natural selection. Results from studies on selective forces behind the adaptive divergence suggest that selective predation from visually oriented predators is a possible selective agent. We found no indications of phenotype-specific movements between habitats. Mating within stonewort stands was random with respect to pigmentation, but on a whole-lake scale it is likely that mating is assortative, as a result of local differences in phenotype distribution.     

Effects of winter harvest on water and sediment chemistry in a stand of reed (Phragmites australis)

An investigation of the effects of repeated winter harvest and removal of dry reed culms on water and sediment chemistry was made in a shallow lake dominated by closed, monospecific reed stands. The oxygen concentration and redox potential in the water, as well as temperature, showed regular diurnal fluctuations inside the reed stands. Ammonium and nitrate + nitrite did not exhibit diurnal fluctuations and differences between a harvested and an unharvested reed area were small. Molybdate reactive phosphorus (MRP) concentration was higher in the unharvested area.Because the winter harvest caused an almost doubling of shoot production compared to the unharvested area, net addition of reed litter (leaves, stubble and culms) to the sediment of the harvested area was similar to that of the unharvested area. It is concluded that removal of reed culms in winter has the largest effect on microclimate in spring, and that the rate of mineralization and reducing intensity in the substrate are not immediately affected. Significantly higher summer standing crop of reed after harvest may have caused lower phosphate concentration in the water column and sediment interstitial water.     

Seeds contribute strongly to the spread of the invasive genotype of the common reed (<Emphasis Type="Italic">Phragmites australis</Emphasis>)

The introduced subspecies of the common reed (Phragmites australis (Cav.) Trin. ex Steud. subsp. australis; Poaceae) is considered one of the most invasive plants in North American wetlands. Given its relatively low seed set and its tremendous capacity to spread via stolons or rhizomes, it has generally been thought that the spread of vegetative diaspores was responsible for the establishment of new populations. To test this hypothesis, we sampled a single plant from each of 345 visually-distinct common reed stands located along the shores of Lake St. François (southern Quebec, Canada). With a set of six nuclear microsatellite markers, we distinguished 134 different genotypes. The number of individuals sharing the same genotype ranged from one to 16, and averaged 2.1. Most genotypes were encountered only once. We examined the spatial distribution of the most frequent genotypes and found little evidence of clusters along the lakeshore. These data contradict the hypothesis that a common reed invasion is initiated by the introduction of vegetative diaspores from a few clones. Rather, they clearly support the alternative hypothesis that seeds were the primary diaspores responsible for the establishment of common reed populations.     

A comparison of symbiotic nitrogen fixation in Scotland inAlnus glutinosa andAlnus rubra

Summary Alnus glutinosa andAlnus rubra growing in the field in Scotland show specific nitrogenase activities of the same order of magnitude. The period of maximum potential nitrogenase activity coincides with that of maximum growth in late Spring and Summer. It is suggested that the retention of nitrogenase activity into the Autumn when growth has virtually ceased may be important as a contribution to the nitrogenous reserves of the tree.Bioassay of different Scottish soils, all collected from the locality of natural stands ofAlnus glutinosa, showed wide variation in the nodulation of seedlings, although generally a soil poor for nodulation ofAlnus glutinosa generally gave poor nodulation ofAlnus rubra. Soils of pH 4.5 to 6.5, best suited for growth and nitrogen fixation of the two species, often gave nodules showing highest specific nitrogen fixing activity. Young (2 to 3 year old) plants in glasshouse or controlled environment cabinet, inoculated withAlnus glutinosa endophyte, differed from mature field grown plants, however, sinceAlnus rubra required a much larger (up to 2.5 times) mass of root nodules to fix a unit quantity of N. Microscopic comparison of the nodules of glasshouse plants showed that the proportion of cells containing the vesicular (nitrogen fixing) form of the endophyte was only slightly lower inAlnus rubra than inAlnus glutinosa and it is suggested that the differences in specific nitrogen fixing activity between the two species may reflect some incompatibility of function of theAlnus glutinosa endophyte when in symbiosis withAlnus rubra.     

Rhizome age structure of three populations ofPhragmites australis (Cav.) Trin. ex Steud.: Biomass and mineral nutrient concentrations

The rhizome age structure for populations ofPhragmites australis (Cav.) Trin. exSteud. was determined at three sites of the T?eboň Biosphere Reserve (Czech Republic). These sites were classified according to plant species composition and phosphorus availability as oligotrophic (Branná), mesotrophic (Ro?mberk East) and hypertrophic (Ro?mberk West).P.australis stands at these sites were expanding, stabilized and retreating, respectively. Rhizomes were sampled within the terrestrial parts of the reed stands (at a water depth of about 10 cm). The rhizomes were dated according to the position in the branching hierarchy and to supplementary morphological criteria. The analysis of the branching pattern revealed that at the sites studied, the rhizomes typically branch only once a year. The longest life span of rhizomes (six years) was found for the stable reed population at Ro?mberk East. The reduced rhizome life span at Ro?mberk West (four to five years), accompanied by a reduced branching frequency of horizontal rhizomes, was ascribed to a greater incidence of anaerobic conditions associated with the permanent flooding of the hypertrophic organic soil. The maximum life span of the Branná population (four years) probably corresponds to the total age of the reed population. The concentrations of nitrogen, phosphorus, and potassium in the tissue decreased with rhizome age while those of calcium and magnesium increased. The effect of rhizome age on mineral-nutrient concentrations was more pronounced than the effect of site on these concentrations. The mineral nutrient concentrations were not closely associated with reed performance.     

芦苇生态型研究进展

芦苇生态幅极广,适生于多种生境类型。不同的环境选择压力如水深、盐度、养分、气候等交互影响致使芦苇个体及种群间发生不同程度的分化和变异,形成了形态、生理或遗传上互有差异、异地性的不同生态型。尽管基于芦苇表型变异以及遗传变异进行生态型划分的研究已开展很多,但针对芦苇生态型变异规律及其可能的形成机制的认知仍存在较多分歧。在总结近年来有关芦苇生态型研究文献的基础上,通过对影响芦苇生态型变异的主要因素——环境因素和遗传因素的分析,以期为芦苇生态型的划分及其可能的形成机制提供新的研究思路。(1)空间尺度的选择应成为研究者分析、划分芦苇生态型的首要定位。在较大的地理空间尺度上,高度异质性的生境导致某些性状的变异式样具有相对的不连续性,可作为不同芦苇生态型鉴别与描述的主要依据;(2)在合理的尺度定位、取样设计和统计分析的基础上开展的表型变异研究,及进一步基于种群水平的分子标记研究(分子指纹特征或特有等位基因),可为芦苇生态型的鉴定、划分提供更为可靠的参考数据,并且可以甄别生境差异(环境响应)和遗传变异对芦苇不同生态型分化的贡献;(3)应同时进行不同生态型的特定性状与功能(株高、茎粗、生物量、生理抗逆性、水体污染物净化能力等)的定位,推动优良基因型的选育与扩繁。