Johannes-Günter Kohl

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.

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.

Assessment of the long-term effectiveness of sediment dredging to reduce benthic phosphorus release in shallow Lake Müggelsee (Germany)

Two series of laboratory experiments mimicking dredging of the uppermost phosphorus (P) rich sediment layers of the shallow eutrophic L. Müggelsee were carried out to study the extent of P release from deeper sediment layers, and changes in P mobility by means of fractional P composition of the in 10 cm steps ‘dredged’ sediment cores. In the first run over 38 days, the aerated controls reached 55%, and the ‘dredged’ cores from 18.1% (−10 cm) down-core to 0.4% (−50 cm) of the non-aerated control (50.82 mg P m−2 d−1 = 100%). In the second run over one year, the fractional P composition in the revealed sediment layers changed slightly. The water-soluble P (H2O-P) increased for the respective ‘dredged’ horizon by between 1.5 and 5.6% TP. The redox-sensitive P (BD-P) increased in each horizon from the intact core to the situation following ‘dredging’, as well as with depth in each horizon from 4.9% TP (−10 cm) to 11.4% TP (−40 cm). The organic bound P portion (NaOH-NRP) decreased least (1.7% TP) in the uppermost layer and most (15.6% TP) in the deepest horizon exposed to water after ‘dredging’. Based on the changes in P pools following dredging at the future sediment–water interface, it is predictable that dredging without reduction of the external loading may give only temporary improvement followed by a slow return to the present situation.

Physiological consequences of mowing and burning of Phragmites australis stands for rhizome ventilation and amino acid metabolism.

Mowing and burning of Phragmitesaustralis-stands have been recommended in the recentliterature as management tools for both protection andcontrol, and both favourable and detrimental effectsof these treatments were actually observed. This studyaims to clarify this apparent contradiction using anew physiological approach. Reed stands in thebiosphere reserves of Trebon (Czech Republic) and theDanube Delta (Romania) were investigated usingparameters of convective ventilation and amino acidpatterns. Flooded mown reed and unflooded burned reedwas compared to unmanaged control stands withcomparable hydrology and trophic level. Managementtook place in winter. The elimination of old culmsthrough mowing resulted in a lower ventilationefficiency due to a high counterpressure of rhizomes.The corresponding gas flow rates were reduced to 38%of the value in control stands, indicating a stronglyimpaired oxygen supply to basal and below-ground plantparts after mowing. Concomitantly, significantlyincreased levels of alanine and gamma-aminobutyricacid in basal culm internodes of shoots were measuredas signs of a metabolic shift due to hypoxic stress.Conversely, shoot loss by burning (without flooding)did not diminish ventilation efficiency and gas flowrate, i.e. oxygen supply to buried organs wasunaffected. Correspondingly, the level ofhypoxia-indicating amino acids (alanine,gamma-aminobutyric acid) did not indicate more severeoxygen deficiency in basal and below-ground plantparts of burned reed. It is concluded that the impactof mowing and burning on P. australisstronglydepends on the water level and on whether or notflooding occurs after the treatment. The mechanismresponsible for detrimental effects is probablyimpaired convective ventilation followed by hypoxia inbasal plant parts. This aspect should be taken intoaccount when mowing or burning in winter are used asmanagement tools for wetlands.

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.

Zur Rolle der Milchsäure im Stoffwechsel der Keimpflanzenwurzeln von Zea mays L.

Summary The occurrence of ultradian oszillations in the malate pool with a period of 2 h is confirmed by experiments with isolated root tips of plants of Zea mays L., also when they are cultivated on non-rhythmic conditions. From the beginning of incubation an inversion of pool-sizes of malate on the one hand and of lactate and of pyruvate on the other hand is observed. On partially anaerobic conditions lactate is accumulated and the pool of malate is decreasing. These results and the proof of an active LDH mak be considered as an indicator of a fermentation of lactate in the root of Zea mays L. On aerobic conditions lactate transgressing the maximum within the oscillations is not surrendered to the medium of incubation but is endogenly metabolized.