Indications for the tracking of elevated nitrogen levels through the fungal route in a soil food web.

The objective of the present study was to determine the effects of elevated N in dead organic matter on the growth of fungi and to establish the consequences for the development of microbivores. Therefore, three fungal species were cultured on Scots pine litter differing in N content. The growth of the soil fungal species Trichoderma koningii, Penicillium glabrum and Cladosporium cladosporioides was directly influenced by the N content (ranging from 1.25 to 2.19% N) of the substrate. For all three fungal species maximum growth was highest at intermediate N content (1.55%) of the substrate. The fungivorous collembolan Orchesella cincta reached highest asymptotic body mass when fed with C. cladosporioides, grown on litter medium with intermediate N content (1.55%). The growth of O. cincta was lower when fed with C. cladosporioides from litter medium with the highest N content (2.19%). Similar results were obtained in mesocosm experiments in which pine litter with three levels of N (1.11, 1.78, 2.03% N) was used as substrate for the fungi. On litter with the highest N content (2.03%) hyphal length and asymptotic body mass of O. cincta were reduced. The results show that the N content of the substrate determines the growth of both fungi and fungivores, and suggest that elevated levels of N in soil track through the fungal part of the soil food web.

Metal accumulation in soil arthropods in relation to micro-nutrients.

Nine species of soil arthropod collected at two sites of different pollution levels were compared for concentrations of seven different elements (Ca, Cd, Cu, Fe, Mn, Pb, Zn) and correlations between the different elements were calculated. Significant effects of site on element concentrations of the animals were found for cadmium, iron, manganese and zinc, whereas calcium, copper and lead concentrations showed no significant difference between the sites. Significant differences between the species were found for all metal. The pattern of accumulation was comparable for some of the metals. Correlations were found between calcium, iron, manganese and lead concentrations and between zinc and cadmium concentrations of the species. No significant correlations were found for copper. The study showed that species can not be easily categorised as accumulators or non-accumulators; the pattern depends on the metal.

Adaptation to soil pollution by cadmium excretion in natural populations of Orchesella cincta (L.) (Collembola).

Population differentiation in Orchesella cincta (L.) (Collembola) populations, from various heavy metal contaminated sites, was studied by comparing cadmium excretion efficiency in first generation (F1) laboratory individuals. Animals from sites with high metal concentrations in the litter and with a long history of contamination showed significantly higher excretion efficiencies than animals from low pollution, or reference sites. Differences found in the F1 laboratory animals suggest evidence for genetic differences between the populations. Beneficial and detrimental effects of cadmium excretion were studied in relation to body growth and cadmium concentrations. In chronically exposed animals from an unpolluted site, no physiological acclimation was observed. Excretion efficiency was negatively correlated with body concentrations of cadmium. No detrimental effects were found. Whole-body equilibrium concentrations of cadmium and lead were similar in F1 animals from the reference site and polluted sites. Significant differences in excretion efficiencies imply that the distribution of toxic metals over body compartments differs, tolerant populations having a higher proportion deposited in the gut. Body concentrations of zinc were consistently higher in animals from the polluted site, during both cadmium and zinc exposure. No detrimental effects of increased cadmium excretion on body concentrations of zinc were observed. Population comparisons of cadmium excretion efficiency data and growth reduction in F1 laboratory animals showed that both parameters were inversely related. Cadmium and lead contamination were not the sole factors determining tolerance differentiation.

Discrete eye-position recording for alternative communication.

A feasibility study for using Electro-Oculo-Graphy in a two-step direct-selection type of communication is carried out. The magnitude of any saccade at a certain adjustable time Ts after the start of the saccade is measured and compared to a number of previously adjusted set reference potentials by a multicomparator. Any E.O.G. signal within a certain range is classified to have the central reference-potential of a band. Once the corresponding potential band is determined, a light source will light up, serving as a visual feed-back. The automatic reset circuit will keep the potential of the E.O.G. signal at the central reference potential as long as the eye stays 'fixed' on the same light source in the column of light sources. Slow pursuit movement of the eye and/or the head are possible however below the trigger-velocity on any saccade before the selection of another light source, giving the user a certain degree of freedom. It is concluded, that the construction of a two-step E.O.G. controlled communicator by direct selection with discrete vertical eye-positions is a possible approach. Application of the saccade-discretisator to the field of rehabilitation is discussed.