Leaf traits and tree rings suggest different water-use and carbon assimilation strategies by two co-occurring Quercus species in a Mediterranean mixed-forest stand in Tuscany, Italy

We compared the water-use characteristics of co-occurring mature Quercus cerris L. and Quercus pubescens Willd. trees growing in resource-limited (mainly water) hilly habitats in Tuscany, Italy. The species differed in their distribution along soil water gradients and in their access to, and use of, water, even though the study year was wetter than average, though with a summer drought. Compared with Q. cerris, Q. pubescens had greater access to soil water (less negative predawn water potentials) and a more conservative water-use strategy based on its relatively low stomatal conductance, high instantaneous water-use efficiency, less negative midday water potential and high soil-to-leaf hydraulic conductance. Quercus cerris had less conservative water-use characteristics than Q. pubescens, exhibiting relatively high stomatal conductance, low instantaneous water-use efficiency, more negative midday water potentials and low soil-to-leaf hydraulic conductance; however, Q. cerris had higher photosynthetic rates than Q. pubescens. Photosynthesis and stomatal conductance were positively correlated in both species. Although a strong correlation between ring widths and precipitation patterns was not found, some dry periods influenced ring-width growth. Quercus pubescens has always grown faster than Q. cerris, probably because of more efficient water use, although stand dynamics (driven by exogenous disturbance factors, including coppicing, browsing and competition) cannot be excluded. Ring-width variability, as well as tree-ring growth in dry years, which should be unaffected by stand dynamics, were higher in Q. pubescens than in Q. cerris. Moreover, Q. pubescens recovered completely after the drought in the seventies, even showing higher tree-ring growth than in the recent past, whereas Q. cerris showed a minor growth decline followed by a recovery to values comparable with those observed before the 1970s drought. Beginning in the early eighties, tree-ring growth decreased in both species, though Q. pubescens showed consistently higher values than Q. cerris. These differences can be explained by differences in water-use efficiency. Despite differences between the species in water use and water status, the results are consistent with the interpretation that both are drought tolerant, but that Q. pubescens is at an advantage on xeric ridges because of its greater ability to access soil water and use it more conservatively compared with Q. cerris.     

Probability of freedom from disease after the first detection and eradication of PRRS in Sweden: Scenario-tree modelling of the surveillance system

In July 2007, PRRS was detected for the first time in Sweden. A total of eight positive herds were identified and various measures were taken to eradicate the disease, including restrictions and slaughter of infected herds. Subsequently, both active and passive surveillance activities were undertaken. This study describes stochastic scenario-tree modelling of all the various surveillance system components, to estimate the current probability that Sweden is free from PRRS. The model includes all actions taken after the first positive herd was detected. The surveillance system components included in the model were as follows: investigations undertaken in association with the outbreak, a serological study based on samples collected at slaughter, samples collected in the national PRRS surveillance programme and passive clinical surveillance. The probability of freedom was estimated in time steps of 1 month, from July to December 2007. After each time step, the calculated posterior probability of freedom from the previous month, combined with the probability of introduction, was used as a prior probability for the next month.The result from the model showed a 99.8% probability that Sweden was free from PRRS at the end of December 2007. The estimated total sensitivity of the surveillance system varied between 81.2% and 94.3% and was highest during the first months after the outbreak. For sensitivity analysis purposes, the model was also applied using higher risks of introduction. However, this did not make considerable difference to the final estimates.     

Emulating membrane protein evolution by rational design

How do integral membrane proteins evolve in size and complexity? Using the small multidrug-resistance protein EmrE from Escherichia coli as a model, we experimentally demonstrated that the evolution of membrane proteins composed of two homologous but oppositely oriented domains can occur in a small number of steps: An original dual-topology protein evolves, through a gene-duplication event, to a heterodimer formed by two oppositely oriented monomers. This simple evolutionary pathway can explain the frequent occurrence of membrane proteins with an internal pseudo-two-fold symmetry axis in the plane of the membrane.     

The Genome sequence of the SARS-associated coronavirus

We sequenced the 29,751-base genome of the severe acute respiratory syndrome (SARS)-associated coronavirus known as the Tor2 isolate. The genome sequence reveals that this coronavirus is only moderately related to other known coronaviruses, including two human coronaviruses, HCoV-OC43 and HCoV-229E. Phylogenetic analysis of the predicted viral proteins indicates that the virus does not closely resemble any of the three previously known groups of coronaviruses. The genome sequence will aid in the diagnosis of SARS virus infection in humans and potential animal hosts (using polymerase chain reaction and immunological tests), in the development of antivirals (including neutralizing antibodies), and in the identification of putative epitopes for vaccine development.     

Molecular basis of proton motive force generation: structure of formate dehydrogenase-N

The structure of the membrane protein formate dehydrogenase-N (Fdn-N), a major component of Escherichia coli nitrate respiration, has been determined at 1.6 angstroms. The structure demonstrates 11 redox centers, including molybdopterin-guanine dinucleotides, five [4Fe-4S] clusters, two heme b groups, and a menaquinone analog. These redox centers are aligned in a single chain, which extends almost 90 angstroms through the enzyme. The menaquinone reduction site associated with a possible proton pathway was also characterized. This structure provides critical insights into the proton motive force generation by redox loop, a common mechanism among a wide range of respiratory enzymes.     

Distribution of Arcellaceans (Testate Amoebae) in the Sediments of a Mine Water Impacted Bay of Lake Retunen, Finland

This study employs chemical fractionations of sedimentary metals and analyses of sediment arcellacean (thecamoebian) faunas to study the ecological effects of mining wastewaters in a boreal lake bay that receives metal-rich waters from a Cu mine. Sediment chemistry and arcellacean species compositions were analyzed from both surface sediment samples and a sediment profile to investigate spatial and temporal changes in mine water pollution and biota. Based on the results, geochemical gradients in the area are caused by dispersal and dilution of metal-rich, low-pH mine waters entering the lake; transport and focusing of fine grained metal precipitates and sulphate in the deep areas of the bay; increase in pH due to sulphate reduction and mobilization of redox-sensitive elements from deep water sites; and precipitation of the mobilized metals at shallower sites. Arcellacean species compositions change systematically with increasing distance from the source of pollution and species diversity as well as concentrations of tests in the samples increase as well. Fe:Mn ratio and adsorbed Al explained variation in surface sediment arcellaceans with statistical significance. Fe:Mn ratio is an indicator of the overall geochemical environment (Eh, pH), while the toxicity of Al in aquatic environments is well known. Changes in arcellacean species and geochemistry in the long core suggest that before the mine closure in 1983, mine waters differed in nature from the present acid drainage and metals such as Cu, Co, Zn and Ni may have affected arcellaceans at that time.