Long-term pattern of alternative stable states in two shallow eutrophic lakes

• 1 Lake Tåkern and Lake Krankesjön, two moderately eutrophic, shallow lakes in southern Sweden, have during the past few decades shifted several times between a clear-water state with abundant submerged vegetation and a turbid state with high phytoplankton densities.
• 2 Between 1985 and 1991, Lake Takern was in a clear state, whereas Lake Krankesjon shifted from a turbid to a clear state. During this shift, the area covered by submerged macrophytes expanded, followed by an increase in water transparency, plant-associated macroinvertebrates, and piscivorous fish. Nutrient concentrations, phytoplankton biomass and abundance of planktonic cladocerans decreased.
• 3 In both lakes, water level fluctuations were the most common factor causing shifts, affecting submerged macrophytes either through changes in light availability or through catastrophic events such as dry-out or mechanical damage by ice movement.
• 4 Our data give further support for the existence of two alternative stable states in shallow lakes maintained by self-stabilizing feedback mechanisms.

     

A Method for Studying Photosynthetic Capacities of Unicellular Algae Based on in vivo Chlorophyll Fluorescence

The correlation between photosynthesis and DCMU-induced fluorescence increase has been studied in four species of unicellular green algae from inoculation of the cultures to the stationary growth phase. The fluorescence increase induced by DCMU was high in exponentially growing cultures but decreased when the cultures approached the stationary phase of growth. Because of the good correlation between photosynthesis and DCMU-induced fluorescence increase, the fluorescence technique is a promising method for describing changes in photosynthetic capacities of algal populations in natural waters.     

Effects of Season and Low Temperature on Polypeptides from Thylakoids Isolated from Chloroplasts of Pinus silvestris

Thylakoids isolated from pine chloroplasts were solubilized by sodium dodecyl sulphate and the polypeptides were separated by polyacrylamide gel electrophoresis. The chlorophyll-protein complexes, P700-CPa₁ and LH-CPa/b, had apparent molecular weights of 92,000 and 25,000, respectively. When the chlorophyll of P700-CPa₁ was extracted or photobleached, the apoprotein of P700-CPa₁ appeared as a pronounced peak in the polypeptide scan profile. The molecular weight of the apoprotein was 70,000. During autumn and winter the complex P700-CPa₁ was destroyed. This was primarily caused by bleaching of chlorophyll, as the 70,000 apoprotein increased in the scan profile when the complex P700-CPa₁ decreased. The winter destruction of P700-CPa₁ was less pronounced in old needles than in young. Freezing of frost-hardened seedlings did not change the polypeptide scan profile, unless the temperature was lowered below the frost-killing point followed by thawing and post-treatment in light or darkness above 0°C. Again the main destruction occurred in the P700-CPa₁ complex, but in this case no significant increase of the apoprotein was observed. These alterations in the polypeptide scan profile of frost-killed needles were not caused by the low temperature treatment as such, but they occurred after thawing of the needles.     

Quantacorrected Spectrometer for Recording Different Types of Photobiological, Photochemical, and Spectrophotometric Measurements

An instrument is described which functions as a spectrophotometer, In addition it measures action spectra of photobiological processes, excitation and emission spectra of fluorescence, and gives data for calculation of action spectra of partial reactions of photosynthesis and photocontrolled enzymatic reactions. The instrument has a Bausch and Lomb 250 mm grating monochromator. Equal numbers of quanta at different wavelengths are adjusted electronically with control of the slit through a quantacorrected photocell and a servo motor which is programmed by a cam connected to the wavelength drive.     

Cernosvitoviella ampullax sp.n. (Oligochaeta, Enchytraeidae) from Hardangervidda, S Norway

Cernosvitoviella ampullax sp.n. is characterized by the long ampulla of the spermatheca (usually 5–7 times longer than the ectal duct), the funnel-shaped sperm funnel and the dorsal vessel which originates in segment XI. The species was found in peat soil on Hardangervidda (1 320 m a. s.l.) in an area where the soil remains frozen for about half the year.