Modelling the advection and diffusion of eggs and larvae of Greenland halibut (Reinhardtius hippoglossoides) in the north-east Arctic

Since the late 1980s there has been considerable uncertainty in recruitment levels of the north‐east Arctic stock of Greenland halibut (Reinhardtius hippoglossoides). The abundance of several year classes, originally considered very low at 0–3 yr age, appeared higher than expected at the age of 6+. This may be due to poor targeting of recruitment surveys of the younger year classes. The present work considers the transport and dispersion of eggs and larvae of Greenland halibut by numerical modelling in order to predict the locations of the initial recruitment grounds. Current fields from a 3D baroclinic hydrodynamic model are fed into a Lagrangian particle‐tracking model developed for the Barents Sea area. The particles are released into the current at the spawning field along the shelf slope from Lofoten to Bear Island (69–75°N). Vertically, the particles can follow a predefined depth‐by‐age curve or be kept at a fixed depth. This model system is used for different years to examine changes in the drift pattern. The results indicate that spawning location, transport depth and inflowing activity to the Barents Sea are important factors influencing the distribution of juveniles.     

In vivo receptor-mediated phosphorylation of a G protein in Dictyostelium

Extracellular adenosine 3',5'-monophosphate (cAMP) serves multiple roles in Dictyostelium development, acting as a chemoattractant, a cell-cell signaling molecule, and an inducer of differentiation. The Dictyostelium G-protein alpha subunit G alpha 2 appears to be the major transducer linking the surface cAMP receptor to these intracellular responses. On stimulation of cells with cAMP, G alpha 2 is phosphorylated on one or more serine residues, resulting in an alteration of its electrophoretic mobility. Phosphorylation of G alpha 2 is triggered by increased occupancy of the surface cAMP receptor and is rapid and transient, coinciding with the time course of activation of physiological responses.     

Effects of Soil Flooding on the Survival of Two Potato Pathogens, Sclerotinia sclerotiorum and Verticillium dahliae

Results of studies on survival of sclerotia of Sclerotinia and microsclerotia of Verticillium, demonstrated that soil flooding in western Washington is a possible alternative field rotation practice for S. sclerotiorum (white mold), but not for V. dahliae (Verticillium wilt). Cone-tainer experiments in the greenhouse showed that flooding at 16.5 °C caused S. sclerotiorium sclerotia to lose viability between 12 and 24 weeks while a growth chamber experiment revealed that flooding for 18 weeks at 11 °C or 20 °C was sufficient. V. dahliae microsclerotia appeared resistant to flooding under greenhouse and field settings; recovery ranged within 5 to 10 % of the initial soil population after 6 and 12 months. Potatoes planted into field microplots either flooded or fallowed the previous summer had similar Verticillium wilt ratings and potato yield. Lack of control of V. dahliae by flooding may be due partly to relatively low soil temperatures in a cool, marine climate.     

Effects of bioenergy extraction on visual preferences in boreal forests: a review of surveys from Finland,Sweden and Norway

Increased forest biomass production for bioenergy will have various consequences for landscape scenery, depending on both the landscape features present and the character and intensity of the silvicultural and harvesting methods used. We review forest preference research carried out in Finland, Sweden and Norway, and discuss these findings in relation to bioenergy production in boreal forest ecosystems. Some production methods and related operations incur negative reactions among the public, e.g. stump harvesting, dense plantation, soil preparation, road construction, the use of non-native species, and partly also harvest of current non-productive forests. Positive visual effects of bioenergy production tend to be linked to harvesting methods such as tending, thinning, selective logging and residue harvesting that enhance both stand and landscape openness, and visual and physical accessibility. Relatively large differences in findings between studies underline the importance of local contextual knowledge about landscape values and how people use the particular landscape where different forms of bioenergy production will occur. This scientific knowledge may be used to formulate guiding principles for visual management of boreal forest bioenergy landscapes.     

Do indicators of nitrogen retention and leaching differ between coniferous and broadleaved forests in Denmark?

The area of broadleaved forests is projected to increase in Denmark as well as in the rest of Europe. However, studies of the N leaching response to elevated N deposition have focused on coniferous stands and considerable uncertainty still remains on whether broadleaved and coniferous forests respond differently to elevated N. We studied N input–output relations for eight stands intensively monitored during 2002–2005 and literature data for 37 additional stands which together formed a comprehensive dataset on Danish forests including 26 broadleaved stands and 19 coniferous stands. Nitrate leaching was significantly higher in first generation stands on former arable land with mineral soil C/N ratios 10–15, but both low and high rates were observed independent of the N input. A net N loss was observed in some of these stands even though they are in the aggrading phase and accumulate N in the biomass. Broadleaved stands had significantly lower throughfall N deposition than coniferous stands and this seems to be the main process where forest type exerts an influence on the N cycle. Lower soil C/N ratios offset the effect of throughfall N deposition and thus N leaching did not differ between the two forest types. The best regression models for prediction of nitrate leaching included throughfall N deposition and C/N ratio, but only a minor part of the variability was explained. The C/N ratio of the upper mineral soil was more generally applicable than that of the organic layer. The N retention of the soil was reasonably well predicted above a C/N ratio of 25, but below this threshold the importance is not known. We suggest focusing future efforts on quantifying the relative retention functions (sink strength) of the vegetation and the soil organic matter to improve the predictions of N retention and N leaching.     

The impact of nitrogen deposition on carbon sequestration by European forests and heathlands

In this study, we present estimated ranges in carbon (C) sequestration per kg nitrogen (N) addition in above-ground biomass and in soil organic matter for forests and heathlands, based on: (i) empirical relations between spatial patterns of carbon uptake and influencing environmental factors including nitrogen deposition (forests only), (ii) ¹⁵N field experiments, (iii) long-term low-dose N fertilizer experiments and (iv) results from ecosystem models. The results of the various studies are in close agreement and show that above-ground accumulation of carbon in forests is generally within the range 15–40 kg C/kg N. For heathlands, a range of 5–15 kg C/kg N has been observed based on low-dose N fertilizer experiments. The uncertainty in C sequestration per kg N addition in soils is larger than for above-ground biomass and varies on average between 5 and 35 kg C/kg N for both forests and heathlands. All together these data indicate a total carbon sequestration range of 5–75 kg C/kg N deposition for forest and heathlands, with a most common range of 20–40 kg C/kg N. Results cannot be extrapolated to systems with very high N inputs, nor to other ecosystems, such as peatlands, where the impact of N is much more variable, and may range from C sequestration to C losses.     

When to count your eggs: Is fecundity in Greenland halibut (Reinhardtius hippoglossoides W.) down-regulated?

Fecundity in several fish species is subjected to down-regulation by atresia so if fecundity is estimated many months before spawning, this will be an overestimation of the realised fecundity (actual number of eggs spawned). In order to get accurate measurements of fecundity it is important to have knowledge on when potential fecundity (estimated fecundity at time of sampling) closely resembles the realised fecundity. Down-regulation of fecundity for Greenland halibut (Reinhardtius hippoglossoides W.) was assessed using fish caught off East Greenland in 1998, 1999 and 2000. The fish caught in 1998 and 1999 were in early and late stages of vitellogenesis, respectively of the same maturation cycle. The fish caught in 2000 were also in an early stage of vitellogenesis. Fecundity decreased by 43% between early and late vitellogenesis. Fecundity in 1999 appeared to be the second lowest recorded for Greenland halibut but it is believed to be due to developmental stage rather than low productivity. There was no difference in fecundity between 1997 and 1998. It is believed that differences in fecundity between years only become apparent in late maturation as size during oocyte recruitment has a very large influence on fecundity. Neither Fulton's condition nor hepatosomatic index had any significant influence on fecundity.     

Single reconstituted neuronal SNARE complexes zipper in three distinct stages

Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins drive membrane fusion by assembling into a four-helix bundle in a zippering process. Here, we used optical tweezers to observe in a cell-free reconstitution experiment in real time a long-sought SNARE assembly intermediate in which only the membrane-distal amino-terminal half of the bundle is assembled. Our findings support the zippering hypothesis, but suggest that zippering proceeds through three sequential binary switches, not continuously, in the amino- and carboxyl-terminal halves of the bundle and the linker domain. The half-zippered intermediate was stabilized by externally applied force that mimicked the repulsion between apposed membranes being forced to fuse. This intermediate then rapidly and forcefully zippered, delivering free energy of 36 k(B)T (where k(B) is Boltzmann's constant and T is temperature) to mediate fusion.     

Nitrex: The timing of response of coniferous forest ecosystems to experimentally-changed nitrogen deposition

In large regions of Europe and eastern North America atmospheric deposition of inorganic nitrogen (N) compounds has greatly increased the natural external supply to forest ecosystems. This leads to N saturation, in which availability of inorganic N is in excess of biological demand and the ecosystem is unable to retain all incoming N. The large-scale experiments of the NITREX project (NITRogen saturation EXperiments) are designed to provide information regarding the patterns and rates of responses of coniferous forest ecosystems to increases in N deposition and the reversibility and recovery of impacted ecosystems following reductions in N deposition.The timing of ecosystem response generally followed a hypothesized cascade of response. In all sites N outputs have responded markedly but to very different degrees within the first three years of treatment. Within this time significant effects on soil processes and on vegetation have only been detected at two sites. This delayed response is explained by the large capacity of the soil system to buffer the increased N supply by microbial immobilization and adsorption. We believe that this concept provides a framework for the evaluation and prediction of the ecosystem response to environmental change.