Water fluxes within beech stands in complex terrain

We investigated the water balances of two beech stands (Fagus sylvatica L.) on opposite slopes (NE, SW) of a narrow valley near Tuttlingen in the southern Swabian Jura, a low mountain range in Southwest Germany. Our analysis combines results from continuous measurements of forest meteorological variables significant to the forest water balance, stand transpiration (ST) estimates from sap flow measurements, and model simulations of microclimate and water fluxes. Two different forest hydrological models (DNDC and BROOK90) were tested for their suitability to represent the particular sites. The investigation covers the years 2001–2007. Central aims were (1) to evaluate meteorological simulations of variables below the forest canopy, (2) to evaluate ST, (3) to quantify annual water fluxes for both beech stands using the evaluated hydrological models, and (4) to analyse the model simulations with regard to assumptions inherent in the respective model. Overall, both models were very well able to reproduce the observed dynamics of the soil water content in the uppermost 30 cm. However, the degree of fit depended on the year and season. The comparison of experimentally determined ST within the beech stand on the NE-slope during the growing season of 2007 with simulated transpiration did not yield a reliable statistical relationship. The simulation of water fluxes for the beech stand on the NE- and SW-slopes showed similar results for vegetation-related fluxes with both models, but different with respect to runoff and percolation flows. Overall, the higher evaporation demand on the warmer SW-slope did not lead to a significantly increased drought stress for the vegetation but was reflected mainly in decreased water loss from the system. This finding is discussed with regard to potential climate change and its impact on beech growth.     

Denitrification Potential, Root Biomass, and Organic Matter in Degraded and Restored Urban Riparian Zones

Hydrologic changes associated with urbanization often lead to lower water tables and drier, more aerobic soils in riparian zones. These changes reduce the potential for denitrification, an anaerobic microbial process that converts nitrate, a common water pollutant, into nitrogen gas. In addition to oxygen, denitrification is controlled by soil organic matter and nitrate. Geomorphic stream restorations are common in urban areas, but their effects on riparian soil conditions and denitrification have not been evaluated. We measured root biomass, soil organic matter, and denitrification potential (anaerobic slurry assay) at four depths in duplicate degraded, restored, and reference riparian zones in the Baltimore, Maryland, U.S.A., metropolitan area. There were three main findings in this study. First, although reference sites were wet and had high soil organic matter, they had low levels of nitrate relative to degraded and restored sites and therefore there were few differences in denitrification potential among sites. Evaluations of riparian restorations that have nitrate removal by denitrification as a goal should consider the complex controls of this process and how they vary between sites. Second, all variables declined markedly with depth in the soil. Restorations that increase riparian water tables will thus foster interaction of groundwater nitrate with near-surface soils with higher denitrification potential. Third, we observed strong positive relationships between root biomass and soil organic matter and between soil organic matter and denitrification potential, which suggest that establishment of deep-rooted vegetation may be particularly important for increasing the depth of the active denitrification zone in restored riparian zones.     

Disparate Geography of Consumption,Production, and Environmental Impacts

International trade transfers social and environmental impacts across national borders. The consumption of forest products often takes place far away from industrial production sites, and mills procure raw material from remote forests. Finland produces about 10% of forest products that are traded internationally, with the majority of its exports destined for other European countries. Here we report and analyze data that demonstrate that international leakage, in relative terms, increased faster than the production of commodities. The international consumption of products made in Finland increased, and an increase in wood imports from Russia provided the raw material for most of the incremental production. The international consumption‐production system translated the increasing global demand for Finnish products into increased harvests in Russia, until the Russian customs duties started to increase in 2007. We argue that national and regional policies for the promotion of sustainable consumption and production must be analyzed and assessed from an international, holistic perspective.     

Fluorescence-activated cell sorting for aptamer SELEX with cell mixtures

Aptamers that target a specific cell subpopulation within composite mixtures represent invaluable tools in biomedical research and in the development of cell-specific therapeutics. Here we describe a detailed protocol for a modular and generally applicable scheme to select aptamers that target the subpopulations of cells in which you are interested. A fluorescence-activated cell-sorting device is used to simultaneously differentiate and separate those subpopulations of cells having bound and unbound aptamers. There are fewer false positives when using this approach in comparison with other cell-selection approaches in which unspecific binding of nucleic acids to cells with reduced membrane integrity or their unselective uptake by dead cells occurs more often. The protocol provides a state-of-the-art approach for identifying aptamers that selectively target virtually any cell type under investigation. As an example, we provide the step-by-step protocol targeting CD19(+) Burkitt's lymphoma cells, starting from the pre-SELEX (systematic evolution of ligands by exponential amplification) measurements to establish suitable SELEX conditions and ending at completion of the SELEX procedure, which reveals the enriched single-stranded DNA library.     

Sex, bugs and Haldane's rule: the nematode genus Pristionchus in the United States

The haplodiploid sex determining mechanism in Hymenoptera (males are haploid, females are diploid) has played an important role in the evolution of this insect order. In Hymenoptera sex is usually determined by a single locus, heterozygotes are female and hemizygotes are male. Under inbreeding, homozygous diploid and sterile males occur which form a genetic burden for a population. We review life history and genetical traits that may overcome the disadvantages of single locus complementary sex determination (sl-CSD). Behavioural adaptations to avoid matings between relatives include active dispersal from natal patches and mating preferences for non-relatives. In non-social species, temporal and spatial segregation of male and female offspring reduces the burden of sl-CSD. In social species, diploid males are produced at the expense of workers and female reproductives. In some social species, diploid males and diploid male producing queens are killed by workers. Diploid male production may have played a role in the evolution or maintenance of polygyny (multiple queens) and polyandry (multiple mating). Some forms of thelytoky (parthenogenetic female production) increase homozygosity and are therefore incompatible with sl-CSD. We discuss a number of hypothetical adaptations to sl-CSD which should be considered in future studies of this insect order.     

A multimeric membrane protein reveals 14-3-3 isoform specificity in forward transport in yeast

Arginine (Arg)-based endoplasmic reticulum (ER) localization signals are sorting motifs involved in the quality control of multimeric membrane proteins. They are distinct from other ER localization signals like the C-terminal di-lysine [-K(X)KXX] signal. The Pmp2p isoproteolipid, a type I yeast membrane protein, reports faithfully on the activity of sorting signals when fused to a tail containing either an Arg-based motif or a -KKXX signal. This reporter reveals that the Arg-based ER localization signals from mammalian Kir6.2 and GB1 proteins are functional in yeast. Thus, the machinery involved in recognition of Arg-based signals is evolutionarily conserved. Multimeric presentation of the Arg-based signal from Kir6.2 on Pmp2p results in forward transport, which requires 14-3-3 proteins encoded in yeast by BMH1 and BMH2 in two isoforms. Comparison of a strain without any 14-3-3 proteins (Deltabmh2) and the individual Deltabmh1 or Deltabmh2 shows that the role of 14-3-3 in the trafficking of this multimeric Pmp2p reporter is isoform-specific. Efficient forward transport requires the presence of Bmh1p. The specific role of Bmh1p is not due to differences in abundance or affinity between the isoforms. Our results imply that 14-3-3 proteins mediate forward transport by a mechanism distinct from simple masking of the Arg-based signal.     

Alteration of Ecosystem Function by Zebra Mussels in Oneida Lake: Impacts on Submerged Macrophytes

Dreissenid mussels (the zebra mussel Dreissena polymorpha and the quagga mussel D. bugensis) are ecosystem engineers that modify the physical environment by increasing light penetration. Such a change is likely to affect the distribution and diversity of submerged macrophytes. Filter-feeding by these mussels has been associated with increased water clarity in many North American and European lakes. In this study, we report the increase in water clarity of Oneida Lake, New York, USA, for 1975–2002 and argue that the increase was caused by zebra mussel invasion rather than declines in nutrients. Over the study period, although mean total phosphorus decreased significantly, the main increase in water clarity occurred after the zebra mussel invasion in 1991. The average depth receiving 1% surface light increased from 6.7 m to 7.8 m after the invasion of zebra mussels, representing a 23% areal expansion. The maximum depth of macrophyte colonization, as measured by diver and hydroacoustic surveys, increased from 3.0 m before the invasion of zebra mussels to 5.1 m after their establishment. In addition, macrophyte species richness increased, the frequency of occurrence increased for most species, and the composition of the macrophyte community changed from low-light–tolerant species to those tolerating a wide range of light conditions. Comparisons with observations reported in the literature indicate that increased light penetration alone could explain these changes in macrophyte distribution and diversity. Such changes will increase the importance of benthic primary production over pelagic production in the food web, thereby representing an overall alteration of ecosystem function, a process we refer to as “benthification”.     

Structure and development of onychophoran eyes: what is the ancestral visual organ in arthropods?

Scarce and controversial information on visual organs and their innervation in Onychophora currently do not allow a thorough comparison with Euarthropoda. Therefore, this study sets out to provide additional data on the architecture and morphogenesis of the onychophoran visual system and to explore similarities and differences between the visual organs of onychophorans and other arthropods. Based on the new data for Epiperipatus biolleyi (Peripatidae) and Metaperipatus blainvillei (Peripatopsidae), it is suggested that the compound eyes represent an autapomorphy of Euarthropoda since similarities with the onychophoran eyes are weak or absent. Instead, the innervation from a central rather than lateral part of the brain, the presence of only one (paired or unpaired) visual center, and a similar ontogenetic origin from an ectodermal groove rather than a proliferation zone suggest homology between the onychophoran eyes and the median ocelli of euarthropods. In conclusion, I suggest that the last common ancestor of arthropods bore only one pair of ocellus-like visual organs that were modified in several arthropod lineages. This hypothesis is supported by recent paleontological data.