Use of stable isotopes to quantify nitrogen, potassium and magnesium dynamics in young Scots pine (Pinus sylvestris)

Two-yr-old Scots pine ( Pinus sylvestris ) seedlings were grown in sand culture for 1 yr with a generous supply of a balanced nutrient solution. Trees were repotted into clean sand in February 1998 and given either a reduced or adequate nutrient supply containing enriched ¹⁵N, ⁴¹K and ²⁶Mg to label nutrient uptake during spring 1998. Trees doubled their biomass during the experiment. Whole-tree net photosynthesis was reduced by 43% after 95 d in trees that received the lower nutrient supply ( P < 0.001), although differences in biomass between the two treatments were less pronounced. Remobilization contributed 83, 82 and 52% of the N, K and Mg, respectively, used to support growth of new tissues in trees that received reduced nutrient supply. Those receiving the higher nutrient supply still obtained 44–59% of nutrients used for spring growth of new tissues from remobilization. Current nutrient supply had no significant effect on the amount of N or Mg remobilized to new tissues but K remobilization was less in trees that received the lower nutrient supply ( P = 0.025). The importance of remobilization in young trees and problems associated with quantifying internal cycling of nutrients are discussed.     

Precision and accuracy of indole-3-acetic acid analyses performed with the 2-methylindolo-α-pyrone fluorescence assay and with a high performance liquid chromatography technique with spectrofluorimetric detection, exemplified on pine tissue (Pinus sylvestris L.)

The precision and accuracy of two versions of the 2-methylindolo-α-pyrone (2-MIP) assay and of a high performance liquid chromatography (HPLC) technique was assessed when applied to analysis of indole-3-acetic acid (IAA) in pine ( Pinus sylvestris ) tissue. In one version of the 2-MIP assay total fluorescence at wavelengths > 450 nm was recorded, whereas in the other version fluorescence spectra were recorded and analyzed. Such analysis revealed the occurrence in some samples of fluorescent contaminants that impaired both precision and accuracy. The precision and accuracy of the 2-MIP assay could be improved by additional sample purification, and the over-all accuracy of the assay was finally verified, at a high level of sample purity, by successive approximation. The precision of the assay was then 14%. Successive approximation also verified that the HPLC technique was accurate at a less advanced stage of sample purity than the 2-MIP assay, and had a precision of 14%.     

Schwankungen im Spektrum von Kriebelmückenarten und räumliche Konstanz der Eiablageplätze in einem Niederungsbach (Simuliidae,Diptera). Variation in Species Composition of Black Flies (Simuliidae,Diptera) and Spatial Stability of Oviposition Sites in a Lowland Stream

The species composition of black flies (Simuliidae, Diptera) in a lowland stream of Aller-Leineregion (northern Germany, FRG) is analysed in the course of several years. Normally, Odagmia ornata (MG .) is the dominating species. For a short sharply defined period Boophthora erythrocephala DE GEER appeared in a great number. Possible reasons and related research on spatial stability of oviposition sites are presented.     

Massenentwicklungen von Algen und Wasserlinsen in der Talsperre Bleiloch (Thüringen) — gegenwärtige Situation,Ursachenanalyse und erste Ergebnisse zu deren Verringerung Algal Blooms and Duckweed Covers in the Bleiloch Reservoir (Thuringia) — Actually Situation,Causal Analysis and First Results of its Overcome

The effects of a decreased sewage release from a cellulose mill on the hypertrophic Bleiloch reservoir were studied. The waste water treatment reduced the concentration of yellow substances in the reservoir and resulted in a more light-coloured waterbody. It is estimated that the changes in the light attenuation in the Bleiloch reservoir after 1989 can be described as eutrophication. Selected physical, chemical, and biological parameters from 1994 show the effect of changes. Three large pelagic enclosures (diameter 10 m, length 20 m) were installed in the reservoir to assess effects of artifical mixing on phytoplankton biomass and composition. Two circulation techniques have been used in the enclosures (relase of compressed air at the bottom of the enclosure and mechanical mixing, where water was pumped from the surface downward). The investigation demonstrate that the magnitude of seasonal peaks of chlorophyll were depressed in the mixed enclosures during circulation. The results were discussed in comparison with a reference enclosure without mixing and the waterbody of the reservoir. Cryptophytes and other flagellates achieved dominance during mixing in the “air”-enclosure, while diatoms were the most abundant species in the „pump”︁-enclosure. The development of filamentous cyanobacteria, which are significant indicators of eutrophication, was disturbed in the enclosures. They were outcompeted by cryptophytes, movable chlorophytes and diatoms. Both mechanical pump and compressed air can be used to control excessive algal growth. Further studies on the dynamics of phytoplankton to artifical mixing are suggested. The results of further studies should design an in situ experiment in the reservoir to reduce algal growth by light limitation. Further on a dense duckweed cover spreads over the surface of the Bleiloch reservoir, which influences the light regime in the waterbody. Therefore factors influencing the duckweed growth were analysed. Special attention was focused on the influence of the pH, consequences of the mixing in the waterbody and the role of resting stages.