Changes in soil ph over a 50-year period under different forest canopies in SW Sweden

Reinvestigation of soil profiles, down to 70 cm depth in mineral soil, sampled for measurements in 1927 revealed a general decrease in pH for spruce and hardwood stands with 0.3 to 0.9 units. The pH-changes in the top soil can partly be explained by biological acidification, increasing with stand age. Stand age and species composition have less influence in deeper soil horizons and much of the acidification there is ascribed to acid deposition.     

Behavior and the Crustacean Molt Cycle: Changes in Aggression of Homarus americanus

The phase of the molt cycle affects dominance status and the performance of agonistic acts in individual juvenile lobsters (Homarus americanus). Lobsters in the midphase of proecdysis are more aggressive than those in intermolt; the latter are more aggressive than lobsters in early or late proecdysis and those in postecdysis.     

Soil type, management history, and soil amendments influence the development of soil-borne (Rhizoctonia solani, Pythium ultimum) and air-borne (Phytophthora infestans, Hyaloperonospora parasitica) diseases

The impact of soil type, long-term soil management, and short-term fertility input strategies on the suppressiveness of soils against soil-borne (Ocimum basilicum – Rhizoctonia solani, Lepidium sativum – Pythium ultimum) as well as air-borne (Lycopersicon esculentum – Phytophthora infestans, Arabidopsis thaliana – Hyaloperonospora parasitica) diseases was studied. Soils from field trials established in five European sites with contrasting pedo-climatic conditions were examined. Sites included (i) a long-term management field trial comparing organic and conventional farming systems (DOK-trial, Therwil, Switzerland) (ii) a short-term fertility input field trial comparing mineral and organic matter fertilisation regimes (Bonn (BON), Germany) (iii) two short-term fertility input field trials (Stockbridge (STC) and Tadcaster (TAD), UK) comparing the impact of farmyard manure, composted farmyard manure, and chicken manure pellet amendements and (iv) soil from a site used as a reference (Reckenholz (REC), Switzerland). Soil type affected disease suppressiveness of the four pathosystems signficantly, indicating that soils can not only affect the development of soil-borne, but also the resistance of plants to air-borne diseases at relevant levels. Suppressiveness to soil- and air-borne diseases was shown to be affected by soil type, but also by long-term management as well as short-term fertility inputs.     

Announcements

The impact of acidifying substances on soils is examined and related to soil properties such as the amount of exchangeable cations in the soil and the proportion of those cations which are other than hydrogen ions. The importance and influence of differential soil horizons and the transport of water through the soil profile are also discussed. Differences between how agricultural and forest ecosystems affect nutrient cycling in soil systems are outlined.     

Critical point drying for scanning electron microscopic sthdy of ciliary motion

Scanning electron microscopic study of tile pattern of ciliary coordination and the form of the ciliary beat is now possible. Rapid fixation stops tile ciliary activity instantaneously, and critical point drying avoids distortion of the cilia by surface tension forces. Such stuidies have been made on the ciliate Opalina with this new technique.     

A field study of persistence of antibodies in California horses vaccinated against western, eastern, and Venezuelan equine encephalomyelitis.

As a result of the continuing threat of Venezuelan equine encephalomyelitis (VEE), a study was made to determine if revaccination against VEE (TC-83 vaccine) was feasible and if revaccination could be incorporated into other routine vaccination practices. Of the horses given annual vaccination with bivalent western equine encephalomyelitis (WEE) and eastern equine encephalomyelitis (EEE) vaccine, 57% retained detectable serum-neutralizing (SN) antiboyd titers for VEE 18 months after the initial VEE vaccination was given. Of horses with no record of WEE-EEE vacinnation, 100% retained detectable VEE SN antibody titers over the same period. The VEE geometric mean titer was 25 times greater for horses not previously vaccinated against WEE-EEE than for horses given annual WEE-EEE vaccination at the time of VEE vaccination. In horses vaccinated against VEE 18 months previously, the geometric mean titer increased from 4 to 70 at 48 days after the intitial WEE-EEE vaccination. This increase indicated that similar antigenic factors for VEE are possibly present in bivalent WEE-EEE vaccine. In horses previously vaccinated against WEE-EEE and VEE, the best SN antibody response to VEE revaccination occurred when VEE vaccine was given simultaneously with the bivalent WEE-EEE vaccine. Of 150 serum samples tested by both the SN and the hemagglutination-inhibiton tests, agreement between positive reactions at greater than or equal to 1:10 was 70% for VEE, 81% for EEE, and 87% for WEE.     

Genetic structure and pathogenicity of populations of Phytophthora infestans from organic potato crops in France, Norway, Switzerland and the United Kingdom

Genetic variation and pathogenicity of Phytophthora infestans isolates collected from organic potato crops of the susceptible cv. Bintje and the moderately resistant cv. Santé were assessed in France, Norway, and the United Kingdom in 2001 and in Switzerland in 2001 and 2002. Population structures differed considerably between the four P. infestans populations. Those from France, Switzerland and the UK were mainly clonal populations showing restricted levels of genetic diversity, whilst those from Norway were mixed A1 and A2 mating type populations with high levels of genetic diversity, suggesting periodical sexual reproduction. Isolates collected from cv. Bintje were on average more aggressive than or comparable to isolates from cv. Santé. Race complexity varied considerably between the regional P. infestans populations, with isolates from France and Switzerland showing the highest number of virulence factors. In all pathogen samples but the French, isolates collected from cv. Santé were more complex than isolates collected from cv. Bintje. No directional selection towards increased aggressiveness towards the more resistant cultivar Santé was observed. This suggests that there is no shift towards increased levels of pathogenicity in P. infestans populations following the large-scale introduction of more resistant potato varieties in organic production systems in Europe.     

Species differences in timing of leaf fall and foliage chemistry modify nutrient resorption efficiency in deciduous temperate forest stands

Extensive variation in fractional resorption of mineral elements from plant leaves is still not fully understood. In multi-species forest stands, species leaf fall phenology and leaf constitution may significantly modify the timing of nutrient return to the soil and overall plant nutrient loss. We studied leaf fall and nutrient loss kinetics, and leaf composition in three natural, temperate, deciduous broadleaf forest stands to determine the role of timing of leaf abscission and nutrient immobilization in cell walls on nutrient resorption efficiency of senescing leaves. Nitrogen (N), phosphorus and potassium contents decreased continuously in attached leaves after peak physiological activity during mid-season. Changes in nutrient contents of attached leaves were paralleled by decreases in nutrient contents in freshly fallen leaf litter. In different species and for different nutrients, resorption of nutrients from senescing leaves proceeded with different kinetics. The maximum nutrient resorption efficiency (the fraction of specific nutrient resorbed from the leaves at the end of leaf fall) did not depend on the mid-seasonal nutrient concentration. Species with earlier leaf fall resorbed leaf nutrients at a faster rate, partly compensating for the earlier leaf fall. Nevertheless, the litter-mass weighted mean nutrient contents in leaf litter were still larger in species with earlier leaf fall, demonstrating an inherent trade-off between early leaf fall and efficient nutrient resorption. This trade-off was most important for N. Losses of the non-mobile nutrients calcium and magnesium were unaffected by the timing of leaf fall. There was large variation in the maximum N resorption efficiency among species. Correlations among leaf chemical variables suggested that the maximum N resorption efficiency decreased with the increasing fraction of cell walls in the leaves, possibly due to a greater fraction of N occluded in cell wall matrix. We conclude that species leaf fall phenology and leaf chemistry modify the timing and quantities of plant nutrient losses, and that more diverse forest stands supporting a spectrum of species with different phenologies and leaf types produce litter with more variable chemical characteristics than monotypic stands.     

Nitrogen saturation in a long-term forest experiment with annual additions of nitrogen

A fertilizer experiment laid out 1971 in a pine (Pinus sylvestris) in N. Sweden is described. The aim was to study the behaviour of a forest ecosystem under controlled nutrient regimes. A primary objective was to study tree production and vitality at different internal nitrogen levels, checked by annual foliar analysis. Tree growth was nitrogen-limited on the site, and the nitrogen regimes ranged from no nitrogen added over near-optimum to excess nitrogen. Interaction with PK addition was studied in a factorial design. Since the question of ecological effects of increasing atmospheric deposition of nitrogen and sulphur was raised by Odén in 1968, this problem became one of the main objectives of this experiment and other experiments in the project The Swedish Optimum Nutrition Experiments in Forest Stands. The experiment started in a young stand which has now been under treatment for more than 20 years. In the beginning nitrogen addition increased tree biomass at all nitrogen levels, but with time the growth increase was reduced at the highest nitrogen regime, partly also at the middle level. Retention of added nitrogen in stand and soil has been high at the lowest level of nitrogen addition, while considerable losses from the sites have occurred at higher levels, indicating nitrogen saturation. Some of the treatment effects on ecosystem properties are described, such as distribution of bioelements between stand and soil and apparent efficiency of needles in stem formation.