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Summary The prevalence of storage mite allergy was investigated in an epidemiological study of respiratory symptoms in farmers on Gotland, an island in the Baltic Sea. A questionnaire concerning work‐related and chronic symptoms from the airways and eyes was completed by 2578 farmers. A sample of 440 farmers subsequently underwent examination comprising skin‐prick tests (animal danders, pollens, moulds and house dust mite), blood sampling for RAST against four storage mites (Acarus siro, Lepidoglyphus destructor. Tyrophagus putrescentiae and Glycyphagus domesticus) and total IgE analyses. Immediate onset hypersensitivity reactions in the airways and eyes were very common among active farmers on Gotland, the prevalence being as high as 40.0%. The prevalence of atopic allergy was 15.6%. Allergy to storage mites was diagnosed, from the case history and a positive RAST to at least one of the four storage mites, in fifty‐two of 440 studied farmers (12%), corresponding to a calculated prevalence of storage mite allergy in the whole farming population of Gotland of 6.2%. The corresponding prevalence among farmers with hypersensitivity symptoms was 15.4%and among those with possibly IgE‐mediated symptoms it was as high as 37.8%. The present study clearly demonstrates a high prevalence of allergy to storage mites among farmers with respiratory symptoms.

Leaf chemistry of a willow clone (Salix aquatica Smith) differed significantly when grown at constant relative growth rates depending upon the relative availability of nutrients and light. Concentration of amino acids and nitrate were high in plants grown with a relative surplus of nutrients. Concentrations of starch, tannin, and lignin, on the other hand, were high in plants grown with a relative surplus of carbon. Photosynthetic rates, expressed per unit leaf area, were similar when plants were grown under high light conditions, regardless of nutrient availability. Dark respiration was much higher in plants supplied with abundant nutrients than in those with a more limited supply, reflecting differences in nitrogen concentration of the tissue. The experimental approach allows plants to be grown to a standard size with differing, but highly uniform chemistry. Plants grown in such a manner may provide good experimental material to evaluate interactions between herbivores or pathogens and their hosts.

Soil samples were collected from the litter, humus and five mineral soil layers to a depth of 50 cm in acid, but highly productive, Norway spruce forests in S Sweden and E Denmark for determination of net N mineralization and potential nitrification. The samples were sieved while still fresh and incubated at a constant temperature (15°C) and soil moisture for 74-117 days with periodic subsamplings. Net N mineralization rates, expressed per g organic matter or per g of total N, decreased with increasing depth. Net N mineralization in the ten soils studied ranged from 35 to 105 kg N ha -1 yr -1, of which the organic horizons contributed 32-74%. Nitrate formation patterns were variable. Almost no nitrification could be detected at pH (H20) values lower than 4.0. Nitrate was formed in humus layers with pH values of 4.0-4.5, but the nitrification was never complete. By contrast, the nitrification was almost complete at a depth of 10-50 cm, where the pH (H20) was 4.1-4.5. Addition of CaCO3 stimulated nitrification in the humus layer, indicating the presence of acid-sensitive nitrifiers, while nitrification in the mineral soil was sometimes stimulated and sometimes inhibited by the addition of CaCO3. Tests with the acetylene block method showed that nitrification, when it occurred, was autotrophic in the humus layer but less easy to characterize in the mineral soil. Thus, further studies are needed to characterize the nitrifier organisms and identify the factors regulating the activity of these organisms. Actual nitrification rates in the field could not be determined, but our findings showed that the B horizon in acid forest soils has a great potential for nitrification. Because N deposition does not appear to decrease in Scandinavian forests, we conclude that an ammonium surplus in the forest floor followed by a downward transport of ammonium to the nitrifying subsoil can increase the risk of nitrate leaching in the future.

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