Harald Kühl

Investigation on the genetic diversity of Phragmites stands using genomic fingerprinting

Abstract The genetic diversity of stable and declining stands of Phragmites australis (Cav.) Trin. ex Steud. was investigated at various sites. DNA and polymerase chain reaction (PCR) fingerprinting were used to differentiate genotypes. Some sites are inhabited by homogeneous Phragmites stands, suggesting they consist of clones (genets, polycormones). Other sites are inhabited by several different clones. Reed stands at different lakes so far investigated exhibit different genotypes. The results support a new hypothesis about the causes of reed belt decline at many European lakes: it is supposed that the stability of reed stands is related to genetic diversity. Monoclonal stands should be limited in their adaptive response to changing site conditions. Recolonization of sites with changed conditions by well-adapted genotypes is difficult because of the preferentially vegetative propagation of littoral reed. The well-documented fact that reed belt decline is not restricted to eutrophic sites corresponds to the eutrophication hypothesis of reed belt decline if eutrophication is understood as a process of changing site conditions independent of the original status.

Seasonal nitrogen dynamics in reed beds (Phragmites australis (Cav.) Trin. ex. Steudel) in relation to productivity

Shoot biomass and nitrogen, accumulated within above-ground plant biomass in autumn, correlate with nitrogen availability indicated by nitrogen content (% DM) of several shoot parts during the height of the growth period.A higher nitrogen percentage of the shoots is correlated with a higher shoot loss and subsequent substitution by branching and tillering during and continuing toward the end of the growth period. A delayed switch from the vegetative to the generative phase reduces the translocation of reserve material to the rhizome. Increasing nitrogen load is at least one of the factors causing instability and reed-belt decline.

Seasonal changes in dissolved amino acids and sugars in basal culm internodes as physiological indicators of the C/N-balance of Phragmites australis at littoral sites of different trophic status

Abstract The nitrogen content of different internodes and the dissolved amino acids and sugars of the basal culm internodes of Phragmites australis (Cav.) Trin. ex Steud. were studied monthly in 1994 to estimate the carbon/nitrogen balance at eight sites and lakes. These stands had large differences in standing crop, with less than 400 g shoot dry weight m−2 in a mesotrophic lake and up to 1500 g dry weight m−2 in hypertrophic lakes. No significant differences were found between sites in the nitrate and ammonium concentration of the interstitial water because of very high variability in space and time. The relative nitrogen content (% of dry weight) of different leaves and culm internodes showed significant differences but only between the most different sites. The amount and composition of free amino acids and sugars of the basal culm internodes showed a clear association with the maximum standing crop of the sites. During the later shoot growth phase (July to September), plants of the high productivity sites exhibited a high content of dissolved amino acids in the basal culm internodes with asparagine as the main transport and storage compound, but a very low sugar content with sucrose as the main transport component in summer. At low productivity sites of mesotrophic to moderate eutrophic lakes, this relationship was inverse. The mean of the proportions of total sugars to total amino acids and asparagine to sucrose, respectively, were significantly correlated with the maximum standing crop of the eight sites. Alanine and serine were present in high concentration in early spring before outgrowth of the tiller without pressure induced ventilation of the subtending vertical rhizome parts. The results are discussed with respect to the indicatory value of the amino acid and sugar content of the basal shoot internodes to the productivity of the different stands and their limitation by the nitrogen availability of the plants.

Clone specific differences in a Phragmites australis stand: I. Morphology, genetics and site description

Abstract A selected reed stand ( Phragmites australis ) at a shallow lake near Berlin was investigated from 1992 to 1995. This reed stand is clearly divided into four visually distinguishable clusters. The study focuses on the clonal distribution within the whole reed stand in relation to morphological characteristics. Furthermore, it should be proved if the clustered stand structure is caused by different site conditions. Genotypic variability was detected by using the RAPD-technique. The parameters shoot length, leaf area, number of internodes and leaves, diameter of culms, shoot density and percentages of shoots with panicles were measured once a year at the end of the vegetation period. The concentrations of ammonium, nitrate, nitrite, o-phosphate and sulphate in interstitial water and sediment extracts were determined. Four adjacent clones were found, which showed differences in morphology. These differences in shoot architecture were observed in spite of uniform site conditions. This suggests a large clonal difference in expression of morphological features. First conclusions are drawn regarding the relationship between genotypes within a reed stand and the expression of morphological characteristics.

To the importance of genetic diversity of Phragmites australis in 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 stands ability to adapt tochanging site conditions and eventually for itssurvival or die-back.

Internal and external nutrient cycles in stands of Phragmites australis – a model for two ecotypes

Two genetically different stands of Phragmites australis differing in their trophic status were investigated regarding seasonal changes in shoot morphology, stand structure, standing crop and N-, P-content in the above-ground and below-ground biomass. A model was developed describing internal and external nutrient cycles of two distinct ecotypes — translocation type and assimilation type. In adaptation to high nutrient availability in littoral sediments, the assimilation type is characterized by a higher productivity and standing stock (N, P), lower fertility, lower translocation rates (N, P), and higher N-, P-contents in the remaining standing dead culms, which leads to a more pronounced external nutrient cycle as compared to the translocation type situated at nutrient poor sites. Furthermore, the duration of heterotrophic and autotrophic growth phase, translocation and dormancy of buds differs between the both types.

Evaluation of the ventilation resistance to convective gas-flow in the rhizomes of natural reed beds of Phragmites australis (Cav.) Trin. ex Steud.

Abstract The ventilation resistance of the internal gas-space system of common reed rhizomes (Phragmites australis (Cav.) Trin. ex Steud.) to convective gas through-flow was studied at reed stands of different lakes with respect to reed die-back. Some parameters for evaluating the contribution of the culms in ventilating the rhizomes are calculated. This involves the culms own pressure development (Pc), the counter-pressure within the rhizomes measured at the bottom of the culm (stubble; Ps), and the resistance of the connected rhizome against gas-flow. The advantage of the relation between counter-pressure of rhizomes to the potential pressure differential of the culms ( P s P c ) and the ventilation resistance parameter (VRP) is that they are not dependent on the actual pressurization due to changing weather conditions. A comparison of different sites is possible even when measured at different times. Most of the reed stands so far investigated show low resistances to convective gas-flow during summer but an increase in resistance was measured during the later vegetation season. Low numbers of old culms functioning as efflux culms can at least partly be compensated by the functional change of living shoots to efflux culms. The gas composition of these green shoots and the dead efflux culms is lower in oxygen and higher in carbon dioxide than influx culms, and additionally methane is present. Very high resistances against gas through-flow could only be detected at sites where the formerly homogeneous distribution of the shoots was changed to a cluster-like distribution with only few or no old culms.

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.

Differences in morphology and C/N-balance between clones of Phragmites 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.

Transfer of results from reed research into practice as illustrated by reed protection measures in Berlin

Abstract There is great interest in solving the question of how far the successful establishment of common reed for shore restoration is influenced by genetically determined characteristics of different reed clones. For this purpose, ten reed clones were planted at six artificial sand banks in 1995, according to a special planting design. The growth and expansion performance of the clones was compared. The reed plants grew without significant stress in the first vegetation period, resulting in newly established reed stands in a very good condition at the end of the season. Despite the same site conditions at the experimental plots, the planted clones differed significantly in their morphology and stand structure. By comparison, reed plants of the same clone exhibited strong similarity on all experimental plots. These results appear to justify the assertion that, at least during the initial phase of establishing a reed stand, the development of stand structure is determined more by genetically controlled programmes than by site conditions. Only long-term investigations will be able to clarify to what extent stable stand structures are formed by genetically controlled programmes after polycormons reach maturity.