Subfossil Cladocera in relation to contemporary environmental variables in 54 Pan-European lakes

1. Changes in cladoceran subfossils in the surface sediments of 54 shallow lakes were studied along a European latitude gradient (36–68°N). Multivariate methods, such as regression trees and ordination, were applied to explore the relationships between cladoceran taxa distribution and contemporary environmental variables, with special focus on the impact of climate. 2. Multivariate regression tree analysis showed distinct differences in cladoceran community structure and lake characteristics along the latitude gradient, identifying three groups: (i) northern lakes characterised by low annual mean temperature, conductivity, nutrient concentrations and fish abundance, (ii) southern, macrophyte rich, warm water lakes with high conductivity and high fish abundance and (iii) Mid‐European lakes at intermediate latitudes with intermediate conductivities, trophic state and temperatures. 3. Large‐sized, pelagic species dominated a group of seven northern lakes with low conductivity, where acid‐tolerant species were also occasionally abundant. Small‐sized, benthic‐associated species dominated a group of five warm water lakes with high conductivity. Cladoceran communities generally showed low species‐specific preferences for habitat and environmental conditions in the Mid‐European group of lakes. Taxon richness was low in the southern‐most, high‐conductivity lakes as well as in the two northern‐most sub‐arctic lakes. 4. The proportion of cladoceran resting eggs relative to body shields was high in the northern lakes, and linearly (negatively) related to both temperature and Chl a, indicating that both cold climate (short growing season) and low food availability induce high ephippia production. 5. Latitude and, implicitly, temperature were strongly correlated with conductivity and nutrient concentrations, highlighting the difficulties of disentangling a direct climate signal from indirect effects of climate, such as changes in fish community structure and human‐related impacts, when a latitude gradient is used as a climate proxy. Future studies should focus on the interrelationships between latitude and gradients in nutrient concentration and conductivity.     

The role of light for fish–zooplankton–phytoplankton interactions during winter in shallow lakes – a climate change perspective

1. Variations in the light regime can affect the availability and quality of food for zooplankton grazers as well as their exposure to fish predation. In northern lakes light is particularly low in winter and, with increasing warming, the northern limit of some present-day plankton communities may move further north and the plankton will thus receive less winter light.
2. We followed the changes in the biomass and community structure of zooplankton and phytoplankton in a clear and a turbid shallow lake during winter (November–March) in enclosures both with and without fish and with four different light treatments (100%, 55%, 7% and <1% of incoming light).
3. In both lakes total zooplankton biomass and chlorophyll- a were influenced by light availability and the presence of fish. Presence of fish irrespective of the light level led to low crustacean biomass, high rotifer biomass and changes in the life history of copepods. The strength of the fish effect on zooplankton biomass diminished with declining light and the effect of light was strongest in the presence of fish.
4. When fish were present, reduced light led to a shift from rotifers to calanoid copepods in the clear lake and from rotifers to cyclopoid copepods in the turbid lake. Light affected the phytoplankton biomass and, to a lesser extent, the phytoplankton community composition and size. However, the fish effect on phytoplankton was overall weak.
5. Our results from typical Danish shallow eutrophic lakes suggest that major changes in winter light conditions are needed in order to have a significant effect on the plankton community. The change in light occurring when such plankton communities move northwards in response to global warming will mostly be of modest importance for this lake type, at least for the rest of this century in an IPCC A2 scenario, while stronger effects may be observed in deep lakes.     

Levels of Indol-3yl-acetic Acid and Acid Inhibitors in Green and Etiolated Bean Seedlings (Phaseolus vulgaris)

Indol-3yl-acetic acid (IAA) was identified in Phaseolus vulgaris L. Shoot tissue of seedlings, exposed to light for 5 days, had a higher level of IAA than etiolated seedlings of the same age. The content of IAA increased in green seedlings during light treatment for 5–12 days. No increase could be measured in dark-grown seedlings. Inhibitory substances appeared at different R_f-values. The main part was identical to the inhibitor-β complex and occurred in a higher amount in light-grown seedlings than in etiolated taller ones. One part of the inhibitor-complex appeared to be abscisic acid (ABA). It is suggested that both IAA and acid inhibitors may play an important role in the control of stem growth and differentiation, although light effects on other hormones and regulatory systems cannot be ignored.     

Reliability of the Indolo-α-Pyrone Fluorescence Method for Indole-3-acetic Acid Determination in Crude Plant Extracts

Indole-3-acetic acid (IAA) contents in plant extracts were determined spectrofluorometrically after conversion of the compound into indolo-α-pyrone. The method is sensitive and accurate and showed good reproducibility. The values obtained by this method corresponded well with those obtained with the Avena coleoptile straight-growth assay. Impurities in extracts often cause various difficulties. Colored compounds influence the readings and may even make indole-3-acetic acid determination impossible by strong quenching of the fluorescence light. Insoluble compounds can be formed in the reaction and cause increased opalescence and light scattering which interferes with the fluorescence measurements. The necessities for the method to be reliable are that the insoluble compounds are removed or brought into solution and that the exciting light is sufficiently monochromatic. Indolo-α-pyrone is fairly stable in the dark but is rapidly broken down by UV radiation. This decay may be used as a check to see if the measured light represents fluorescence of indolo-α-pyrone.     

Glycolate and glyoxylate stimulation of growth in Lemna gibba

A 10 to 20% stimulation of growth in Lemna gibba L. G3 occurred following the addition of 0.5 to 3 mM glycolate or glyoxylate, although concentrations of 5 mM or higher were inhibitory. Glyoxylate gave a higher stimulation than glycolate. The stimulating effect on growth was obtained in media with or without 2% added sucrose. A higher stimulation was obtained when the plants were cultivated in open flasks in comparison to cultivation in flasks plugged with cellulose stoppers, which presumably retarded gas exchange.     

A SIMPLE PROCEDURE TO DETECT NISIN IN CHEESE

SUMMARY: A suitable amount of agar medium inoculated with a test organism sensitive to nisin ( Lactobacillus lactis or Streptococcus cremoris ) is poured on a cheese cylinder placed in a Petri dish. After a convenient incubation time the presence of a clear zone around the cheese cylinder will indicate the presence of nisin.
The method is applicable both to natural and processed cheese and can also be used for other antibiotics that may be present in cheese.     

Effects of contrasting omnivorous fish on submerged macrophyte biomass in temperate lakes: a mesocosm experiment

1. Freshwater fish can affect aquatic vegetation directly by consuming macrophytes or indirectly by changing water quality. However, most fish in the temperate climate zone have an omnivorous diet. The impact of fish as aquatic herbivores in temperate climates therefore remains unclear and depends on their dietary flexibility. 2. We tested the effects of a flexible omnivore and an herbivore on aquatic vegetation by comparing the effects of rudd (Scardinius erythrophthalmus, the most herbivorous fish in temperate climates) with grass carp (Ctenopharyngodon idella) in a mesocosm pond study. Exclosures distinguished herbivorous effects of fish on submerged macrophytes from indirect effects through changes in water quality, whereas stable isotope food‐web analysis provided information on fish diets. 3. We hypothesised that rudd, with its flexible diet and preference for animal food items, would only indirectly affect macrophytes, whereas grass carp, with its inflexible herbivorous diet, would directly affect macrophyte biomass. 4. Only grass carp significantly reduced macrophyte biomass through consumption. Rudd had no effect. Food‐web analysis indicated that rudd predominantly consumed animal prey, whereas grass carp included more plants in their diet, although they also consumed animal prey. Grass carp significantly affected water quality, resulting in lowered pH and increased N‐NH₄ concentrations, whereas more periphyton growth was observed in the presence of rudd. However, the indirect non‐herbivorous effects of both fish species had no effect on macrophyte biomass. 5. Both fish species should be considered as omnivores. Despite the fact that rudd is the most herbivorous fish in the western European climate zone, its effect on submerged macrophyte biomass is not substantial at natural densities and current temperatures.