Effects of ultraviolet-B radiation on growth, mycorrhizas and mineral nutrition of silver birch (Betula pendula Roth) seedlings grown in low-nutrient conditions

The effects of increased ultraviolet‐B (UV‐B) radiation on the growth, mycorrhizas and mineral nutrition of silver birch (Betula pendula Roth) seedlings were studied in greenhouse conditions. Seedlings—planted in a birch‐forest top soil and sand substrate—were grown without additional nutrient supply. Ultraviolet treatment started immediately after the seedlings emerged and the daily integrated biologically effective UV‐B irradiance on the UV‐B‐treated plants was equivalent to a 25% depletion of stratospheric ozone under clear sky conditions. Visible symptoms of UV‐B damage or nutrient deficiency were not observed throughout the experiment. Seedling height and dry weight (DW) (measured after 58 days and 76 days of treatment) were not affected by increased UV‐B. However, a significant shift in DW allocation toward roots resulted in a lower shoot/root ratio and leaf area ratio in UV‐B‐treated plants compared to control plants. At the first harvest (after 58 days of treatment), the percentage of various mycorrhizal morphotypes and the number of short roots per unit of root length or weight were not affected by increased UV‐B despite significantly increased DW allocation toward roots. Subtle reduction in the allocation of nitrogen (N) to leaves and increased allocation of phosphorus (P) to roots may suggest cumulative effects that could affect the plant performance over the long‐term.     

Development of Acartia bifilosa (Copepoda: Calanoida) eggs in the northern Baltic Sea with specialreference to dormancy

Development of eggs produced by Acartia bifilosa in summer andautumn was studied in the northern Baltic Sea. Resting eggsof the species have previously been found in sediments, andthe aim of this study was to reveal the type of dormancy inthe eggs. Eggs were incubated at temperatures ranging from 1.5to 18°C. The effect of continuous darkness on hatching wasalso tested. Hatching success in the experiments varied between56 and 97%. Egg development was similar in summer and autumn,indicating that A. bifilosa does not produce diapause eggs inthe area. Furthermore, dormancy was not induced at any of thetemperatures tested, nor by darkness. Results are compared withthose of Castro-Longoria and Williams (Castro-Longoria and Williams,1999b, J. Plankton Res., 21, 65–84) who studied A. bifilosain the English Channel, where both production of diapause eggsand arrest of development in the subitaneous eggs at low temperaturesoccurred. The possible causes of the difference in dormancystrategies in the two areas are discussed.     

Effects of liming and boron fertilization on boron uptake of Picea abies

The effects of liming on concentrations of boron and other elements in Norway spruce [Picea abies (L) Karst.] needles and in the mor humus layer were studied in long-term field experiments with and without B fertilizer on podzolic soils in Finland. Liming (2000+4000 kg ha^-1 last applied 12 years before sampling) decreased needle B concentrations in the four youngest needle age classes from 6–10 mg kg^-1 to 5 mg kg^-1. In boron fertilized plots the corresponding concentrations were 23–35 mg kg^-1 in control plots and 21–29 mg kg^-1 in limed plots. Both liming and B fertilizer decreased the Mn concentrations of needles. In the humus layer, total B concentration was increased by both lime and B fertilizer, and Ca and Mg concentrations and pH were still considerably higher in the limed plots than controls. Liming decreased the organic matter concentration in humus layer, whilst B fertilizer increased it.The results about B uptake were confirmed in a pot experiment, in which additionally the roles of increased soil pH and increased soil Ca concentration were separated by means of comparing the effects of CaCO₃ and CaSO₄. Two-year-old bare-rooted Norway spruce seedlings were grown in mor humus during the extension growth of the new shoot. The two doses of lime increased the pH of soil from 4.1 to 5.6 to 6.1, and correspondingly decreased the B concentrations in new needles from 22 to 12 to 9 mg kg^-1. However, CaSO₄ did not affect the pH of the soil or needle B concentrations. Hence the liming effect on boron availability in these soils appeared to be caused by the increased pH rather than increased calcium concentration.     

Phylogenetic evidence for the distinction of Saaremaa and Dobrava hantaviruses

Background

Simian virus 40 (SV40) enters cells via an atypical caveolae-mediated endocytic pathway, which delivers the virus to a new intermediary compartment, the caveosome. The virus then is believed to go directly from the caveosome to the endoplasmic reticulum. Cholera toxin likewise enters via caveolae and traffics to caveosomes. But, in contrast to SV40, cholera toxin is transported from caveosomes to the endoplasmic reticulum via the Golgi. For that reason, and because the caveosome and Golgi may have some common markers, we revisited the issue of whether SV40 might access the endoplasmic reticulum via the Golgi.

Results

We confirmed our earlier finding that SV40 co localizes with the Golgi marker β-COP. However, we show that the virus does not co localize with the more discriminating Golgi markers, golgin 97 and BODIPY-ceramide.

Conclusion

The caveolae-mediated SV40 entry pathway does not intersect the Golgi. SV40 is seen to co localize with β-COP because that protein is a marker for caveosomes as well as the Golgi. Moreover, these results are consistent with the likelihood that the caveosome is a sorting organelle. In addition, there are at least two distinct but related routes by which a ligand might traffic from the caveosome to the ER; one route involving transport through the Golgi, and another pathway that does not involve the Golgi.     

Enhanced leptin sensitivity and attenuation of diet-induced obesity in mice with haploinsufficiency of Socs3

Leptin is an adipocyte-derived hormone that regulates energy balance and neuroendocrine function primarily by acting on specific hypothalamic pathways. Resistance to the weight reducing effects of leptin is a feature of most cases of human and rodent obesity, yet the molecular basis of leptin resistance is poorly understood. We have previously identified suppressor of cytokine signaling-3 (Socs3) as a leptin-induced negative regulator of leptin receptor signaling and potential mediator of leptin resistance. However, due to the non-viability of mice with targeted disruption of Socs3 (ref. 6), the importance of Socs3 in leptin action in vivo was unclear. To determine the functional significance of Socs3 in energy balance in vivo we undertook studies in mice with heterozygous Socs3 deficiency (Socs3(+/-)). We report here that Socs3(+/-) mice display greater leptin sensitivity than wild-type control mice: Socs3(+/-) mice show both enhanced weight loss and increased hypothalamic leptin receptor signaling in response to exogenous leptin administration. Furthermore, Socs3(+/-) mice are significantly protected against the development of diet-induced obesity and associated metabolic complications. The level of Socs3 expression is thus a critical determinant of leptin sensitivity and obesity susceptibility in vivo and this molecule is a potential target for therapeutic intervention.     

The Logic and Realism of the Hypothesis of Exploitation Ecosystems

Hypotheses on trophic dynamics in terrestrial ecosystems fall into two major categories: those in which plants are assumed to be invulnerable to their consumers and those in which the build-up of plant biomass is assumed to require top-down control of folivores. The hypothesis of exploitation ecosystems (EEH) belongs to the latter category and focuses particularly on the consequences of the high energetic costs of maintenance of endotherms. Carnivorous endotherms require relatively high prey densities in order to break even. Moreover, they are dependent on folivorous prey during the limiting season, at least at high latitudes. The endotherm branch of the grazing web is thus predicted to collapse from three-link trophic dynamics (carnivores --> folivores --> plants --> inorganic resources) to two-link dynamics (folivores --> plants --> inorganic resources) along gradients of decreasing primary productivity. Consequently, the vegetation of cold and unproductive areas is predicted to be under intense winter grazing pressure, which prevents the accumulation of aboveground plant biomass and excludes erect woody plants. In the most extreme habitats (e.g., polar deserts and their high alpine counterparts), even folivorous endotherms are predicted to be absent, and the scanty vegetation is predicted to be structured by preemptive competition. Within temperature-determined productivity gradients, EEH is corroborated by biomass patterns, by patterns in the structure and dynamics of carnivore, folivore, and plant communities, and by experimental results. The general idea of top-down trophic dynamics is supported for other autotroph-based systems, too, but the relevance and sufficiency of the energy constraint in explaining patterns in trophic dynamics appears to be variable. Moreover, critical empirical evidence for or against the capacity of folivorous insects to regulate plant biomass has not yet been obtained. Another open question is the ability of boreal and temperate browsers, evolved in productive environments with intense predation pressure and abundance of forage, to prevent the regeneration of the least palatable tree species. There are, thus, many open questions waiting to be answered and many exciting experiments waiting to be conducted.     

Genotype × Herbivore Effect on Leaf Litter Decomposition in Betula Pendula Saplings: Ecological and Evolutionary Consequences and the Role of Secondary Metabolites

Plant genetic variation and herbivores can both influence ecosystem functioning by affecting the quantity and quality of leaf litter. Few studies have, however, investigated the effects of herbivore load on litter decomposition at plant genotype level. We reduced insect herbivory using an insecticide on one half of field-grown Betula Pendula saplings of 17 genotypes, representing random intrapopulation genetic variation, and allowed insects to naturally colonize the other half. We hypothesized that due to induced herbivore defence, saplings under natural herbivory produce litter of higher concentrations of secondary metabolites (terpenes and soluble phenolics) and have slower litter decomposition rate than saplings under reduced herbivory. We found that leaf damage was 89 and 53% lower in the insecticide treated saplings in the summer and autumn surveys, respectively, which led to 73% higher litter production. Litter decomposition rate was also affected by herbivore load, but the effect varied from positive to negative among genotypes and added up to an insignificant net effect at the population level. In contrast to our hypothesis, concentrations of terpenes and soluble phenolics were higher under reduced than natural herbivory. Those genotypes, whose leaves were most injured by herbivores, produced litter of lowest mass loss, but unlike we expected, the concentrations of terpenes and soluble phenolics were not linked to either leaf damage or litter decomposition. Our results show that (1) the genetic and herbivore effects on B. pendula litter decomposition are not mediated through variation in terpene or soluble phenolic concentrations and suggest that (2) the presumably higher insect herbivore pressure in the future warmer climate will not, at the ecological time scale, affect the mean decomposition rate in genetically diverse B. pendula populations. However, (3) due to the significant genetic variation in the response of decomposition to herbivory, evolutionary changes in mean decomposition rate are possible.     

A Novel Tool to Mitigate By-Catch Mortality of Baltic Seals in Coastal Fyke Net Fishery

Developing methods to reduce the incidental catch of non-target species is important, as by-catch mortality poses threats especially to large aquatic predators. We examined the effectiveness of a novel device, a “seal sock”, in mitigating the by-catch mortality of seals in coastal fyke net fisheries in the Baltic Sea. The seal sock developed and tested in this study was a cylindrical net attached to the fyke net, allowing the seals access to the surface to breathe while trapped inside fishing gear. The number of dead and live seals caught in fyke nets without a seal sock (years 2008–2010) and with a sock (years 2011–2013) was recorded. The seals caught in fyke nets were mainly juveniles. Of ringed seals (Phoca hispida botnica) both sexes were equally represented, while of grey seals (Halichoerus grypus) the ratio was biased (71%) towards males. All the by-caught seals were dead in the fyke nets without a seal sock, whereas 70% of ringed seals and 11% of grey seals survived when the seal sock was used. The seal sock proved to be effective in reducing the by-catch mortality of ringed seals, but did not perform as well with grey seals.     

Coping with fast climate change in northern ecosystems: mechanisms underlying the population‐level response of a specialist avian predator

Northern ecosystems are facing unprecedented climate modifications, which pose a major threat for arctic species, especially the specialist predator guild. However, the mechanisms underlying responses of predators to climate change remain poorly understood. Climate can influence fitness parameters of predators either through reduced reproduction or survival following adverse weather conditions, or via changes in the population dynamics of their main prey. Here, we combined three overlapping long‐term datasets on the breeding density and parameters of a rodent‐specialist predator, the rough‐legged buzzard Buteo lagopus, its main prey population dynamics and climate variables, collected in subarctic areas of Finland and Norway, to assess the impact of changing climate on the predator reproductive response. Rough‐legged buzzards responded to ongoing climate change by advancing their laying date (0.1 d yr^?1 over the 21 yr of the study period), as a consequence of earlier snowmelt. However, we documented for the same period a decrease in breeding success, which principally resulted from an indirect effect of changes in the dynamics of their main prey, i.e. grey‐sided voles Microtus oeconomus, and not from the expected negative effect of unfavorable weather conditions during the brood‐rearing period on nestling survival. Additionally, we showed the striking impact of autumn and winter weather conditions on vole population growth rates in subarctic ecosystems, with a strong positive correlation between mean snow depth in autumn and winter and both winter and summer population growth rates. Our results highlighted that, in northern ecosystems, ongoing climate change has the potential to impact specialist predator species through two mechanistic linkages, which may in the long‐run, threaten the viability of their populations, and lead to potential severe cascading trophic effects at the ecosystem level.     

Identification and characterization of SNJ2, the first temperate pleolipovirus integrating into the genome of the SNJ1‐lysogenic archaeal strain

Proviral regions have been identified in the genomes of many haloarchaea, but only a few archaeal halophilic temperate viruses have been studied. Here, we report a new virus, SNJ2, originating from archaeal strain Natrinema sp. J7‐1. We demonstrate that this temperate virus coexists with SNJ1 virus and is dependent on SNJ1 for efficient production. Here, we show that SNJ1 is an icosahedral membrane‐containing virus, whereas SNJ2 is a pleomorphic one. Instead of producing progeny virions and forming plaques, SNJ2 integrates into the host tRNA^Met gene. The virion contains a discontinuous, circular, double‐stranded DNA genome of 16 992 bp, in which both nicks and single‐stranded regions are present preceded by a ‘GCCCA’ motif. Among 25 putative SNJ2 open reading frames (ORFs), five of them form a cluster of conserved ORFs homologous to archaeal pleolipoviruses isolated from hypersaline environments. Two structural protein encoding genes in the conserved cluster were verified in SNJ2. Furthermore, SNJ2‐like proviruses containing the conserved gene cluster were identified in the chromosomes of archaea belonging to 10 different genera. Comparison of SNJ2 and these proviruses suggests that they employ a similar integration strategy into a tRNA gene.