Effects of summer drought and winter freezing on stem hydraulic conductivity of Rhododendron species from contrasting climates

We studied the limits to maximum water transport in three diffuse-porous evergreen shrubs exposed to frequent winter freeze-thaw events (Rhododendron maximum L. and R. catawbiense Michaux from the Appalachian Mountains) and to a severe summer drought (R. macrophyllum G. Don. from the Oregon Cascades). Percent loss of hydraulic conductivity (PLC), vulnerability curves to xylem embolism and freezing point temperatures of stems were measured over 2 years. Controlled freeze-thaw experiments were also conducted to determine the effect of thaw rate on PLC. During both years, native PLC was significantly higher in winter than in summer for R. macrophyllum. Seasonal changes in PLC were variable in both R. catawbiense and R. maximum. Only R. maximum plants growing in gaps or clearings showed higher PLC than understory plants. A rapid (2-4 day) natural recovery of high native PLC during the winter was observed in both R. maximum and R. macrophyllum. Compared with the bench-dehydration method, vulnerability curves based on the air-injection method consistently had less negative slopes and greater variation. Fifty percent PLC (PLC(50)) obtained from vulnerability curves based on the dehydration method occurred at -1.75, -2.42 and -2.96 MPa for R. catawbiense, R. maximum and R. macrophyllum, respectively. Among the study species, R. macrophyllum, which commonly experiences a summer drought, had the most negative water potential at PLC(50). In all species, stem freezing point temperatures were not consistently lower in winter than in summer. A single fast freeze-thaw event significantly increased PLC, and R. catawbiense had the highest PLC in response to freezing treatments. Recovery to control PLC values occurred if a low positive hydraulic pressure was maintained during thawing. Rhododendron macrophyllum plants, which commonly experience few freeze-thaw events, had large stem diameters, whereas plants of R. catawbiense, which had small stem diameters, suffered high embolism in response to a single freeze-thaw event. Both drought-induced and winter-induced embolism caused a significant reduction in hydraulic conductivity in all species during periods when drought or freeze-thaw events occurred in their native habitats. However, rapid recovery of PLC following freezing or drought maintained the species above their relatively low margins of safety for complete xylem dysfunction.     

Spatiotemporal distribution of Atlantic cod (Gadus morhua L.) with intact and blocked olfactory sense during the spawning season in a Norwegian fjord with intensive salmon farming

In several areas along the Norwegian coast local fishermen claim that wild migrating Atlantic cod (Gadus morhua L.) have changed their spawning migratory behaviour following establishment of salmon farms, and no longer enter their natural spawning grounds in the fjords. This has created a heated debate in Norway and, in some areas, passed down a moratorium on establishing new salmon farms. Research has so far not been able to show a causal connection, but it has been suggested that water-soluble odorants from high density salmon stocks in commercial fish farms might be responsible for the avoidance of areas with fish farming and abandonment of nearby traditional spawning grounds. The aim of this study was to test this hypothesis by studying the spatiotemporal distribution of wild migrating cod tagged with acoustic transmitters using an array of automatic listening stations in Øksfjord, a Norwegian fjord with intensive fish farming and traditional spawning grounds for cod. The tagged cod were released either in the outer parts of Øksfjord, i.e. in the area they were caught, or in the inner part of the fjord close to their traditional spawning areas. The olfactory sense was physically blocked for 50% of the fish. Only one cod released in the outer part of the fjord visited the traditional spawning grounds. The majority of the cod that were released in the inner part of the fjord remained in this area for approximately three weeks before they left the fjord. There were no differences in spatiotemporal distribution between cod with intact and cod with blocked olfactory sense. Thus, the results provided no evidence that migrating wild cod avoid areas with fish farming as a response to odorants, but the results do not per se contradict the fishermen's observation that coastal cod have changed their migratory pattern in this fjord.     

Peptones from Atlantic Cod Stomach as Nitrogen Sources in Growth Media to Marine Bacteria

Peptones were obtained from cod stomachs as a by-product during enzyme production. Minced cod stomachs were autolyzed after acidification with either formic or phosphoric acid, and low molecular weight (< 10 kDa) peptones were recovered. When formic acid was used, an acid peptone was obtained, whereas phosphoric acid was removed from the peptone after calcium precipitation. The peptones were compared with Proteose Peptone (Difco, Detroit, MI, USA) as nitrogen sources in growth media for three marine bacteria. Two fish pathogens—Vibrio anguillarum and Aeromonas salmonicida—grew equally well or better on the cod stomach peptones, whereas a probiotic lactic acid bacteria (Carnobacterium divergens), isolated from salmon intestines, grew much better on the cod stomach peptones than on Proteose Peptone.     

Counteractions Against Acidification in Forests Ecosystems. Effects on stream water quality after dolomite application to forest soil in Gjerstad,Norway

The deposition of strong acids is one of many threats to forest ecosystems and viable forestry. Several counteractions against acidification have been launched, e.g. changes in forestry management and the introduction of chemicals. The inter-institutional programme “Counteractions Against Acidification in Forest Ecosystems” was established in 1993 to evaluate existing knowledge and run experimental and fullscale field experiments. A total of 240 metric tons of coarse dolomite powder was spread by helicopter in September 1994 on 84 ha forest catchment dominated by pine (Pinus sylvestris) and Norway spruce (Picea abies). Potential desirable and undesirable effects after this carbonate application may be less pronounced than recorded at other sites due to the relatively moderate dose (3 tons ha^?1). Pre-liming stream water quality (mean values for May 1993-September 1994) was as follows: pH 4.8; Ca 1.13 mg L^?1; reactive Al (RAl) 248 μg L^?1; inorganic monomeric Al (Al) 72 μg L^?1. The reference station was slightly higher in Ca and slightly lower in both RAl and Al. Dolomite application resulted in a significant increase in pH to 5.7 as mean value for the post-liming period (September 1994-April 1995). Both Ca and Mg increased significantly after liming, and both RAl and Al, declined significantly. The rapid detoxification of stream-water may be explained by dissolution of dolomite particles in both streams and catchment, a resulting pH increase and change in Al species composition. Retention of Al in the catchment probably explains the reduction in RAl. No increase in NO₃, total N, total P or TOC was recorded the first seven months.     

Effects on stream water chemistry and forest vitality after whole-catchment application of dolomite to a forest ecosystem in southern Norway

An acidified, 0.8 km² coniferous-forested catchment was limed with 3 t ha⁻¹ of coarse-grained dolomite powder in September 1994. The liming resulted in an immediate change in runoff water chemistry relative to the stream of an adjacent reference catchment. pH, calcium, magnesium and acid neutralising capacity (ANC) increased and inorganic Al decreased after liming. Potential favourable water quality for sensitive organisms remained relatively constant over the post-liming period (7 years), and model simulations indicate that adequate water quality may last for an additional 40–50 years. NO₃ concentrations showed no significant change due to liming. A significant increasing trend in TOC was attributed to liming. Concentrations of Cd, Co, Fe, Mn, Ni and Zn were lower in the limed stream than in the reference stream during a period of 3 years after liming, whereas concentrations of As, Cu, and Pb were not significantly different. Steep slopes, thin soils, high amounts of precipitation and thus dominance of surface and subsurface flow in this catchment may explain the rapid response in runoff. During the first 6 years after liming there have been no significant effects on tree growth and vitality (crown density and crown colour). This experiment shows that liming of forested catchments may be a viable method to obtain long-term improvement in water quality and potential positive effects for acid-sensitive aquatic organisms.     

Survival of salmon lice, Lepeophtheirus salmonis Krøyer, on Arctic charr, Salvelinus alpinus (L.), in fresh water

The survival of salmon lice. Lepeophtheirus salmonis (Krøyer) on Arctic charr. Salvelinus alpinus (L.). in fresh water was studied. The results showed that salmon lice were able to survive for up to 3 weeks, in contrast with previous published information that the parasite is quickly shed when the fish enters fresh water.     

Characterization of nodavirus and viral encephalopathy and retinopathy in farmed turbot, Scophthalmus maximus (L.)

An outbreak of nodavirus infection in turbot larvae is described with respect to histopathology, immunohistochemistry, cell culture cultivation, RT-PCR amplification and sequence analysis of the capsid protein gene RNA2. Affected turbot developed classical signs of viral encephalopathy and retinopathy (VER) with abnormal swimming behaviour and high mortality levels. In the acute stage of infection, light microscopy revealed vacuolation of the central nervous system (CNS), with positive immunohistochemical staining for nodavirus. Later in the infection, CNS lesions appeared more chronic and contained clusters of cells immunopositive for nodavirus. Bacterial overgrowth in the intestines of the fish may have provoked or influenced the course of the nodavirus infection. We were unable to propagate the virus in cell culture. While RT-PCR using primers designed to detect Atlantic halibut nodavirus gave negative results, further testing with primers complementary to a more conserved region of RNA2 resulted in amplification of a product of the expected size. The entire RNA2 segment was cloned and sequenced. Sequence alignment showed that the turbot nodavirus (TNV) was different from previously described fish nodaviruses. In addition, phylogenetic analysis based on an 823 nt region of the sequence indicated that TNV clustered outside the four established fish nodavirus genotypes, suggesting a fifth genotype within the betanodaviruses.