Belowground drought response of European beech: fine root biomass and carbon partitioning in 14 mature stands across a precipitation gradient

How tree root systems will respond to increased drought stress, as predicted for parts of Central Europe, is not well understood. According to the optimal partitioning theory, plants should enhance root growth relative to aboveground growth in order to reduce water limitations. We tested this prediction in a transect study with 14 mature forest stands of European beech (Fagus sylvatica L.) by analysing the response of the fine root system to a large decrease in annual precipitation (970–520 mm yr⁻¹). In 3 years with contrasting precipitation regimes, we investigated leaf area and leaf biomass, fine root biomass and necromass (organic layer and mineral soil to 40 cm) and fine root productivity (ingrowth core approach), and analysed the dependence on precipitation, temperature, soil nutrient availability and stand structure. In contrast to the optimal partitioning theory, fine root biomass decreased by about a third from stands with >950 mm yr⁻¹ to those with <550 mm yr⁻¹, while leaf biomass remained constant, resulting in a significant decrease, and not an increase, in the fine root/leaf biomass ratio towards drier sites. Average fine root diameter decreased towards the drier stands, thereby partly compensating for the loss in root biomass and surface area. Both δ¹³C‐signature of fine root mass and the ingrowth core data indicated a higher fine root turnover in the drier stands. Principal components analyses (PCA) and regression analyses revealed a positive influence of precipitation on the profile total of fine root biomass in the 14 stands and a negative one of temperature and plant‐available soil phosphorus. We hypothesize that summer droughts lead to increased fine root mortality, thereby reducing root biomass, but they also stimulate compensatory fine root production in the drier stands. We conclude that the optimal partitioning theory fails to explain the observed decrease in the fine root/leaf biomass ratio, but is supported by the data if carbon allocation to roots is considered, which would account for enhanced root turnover in drier environments.     

Phylogenetic relationships and evolution of Orbiniidae (Annelida, Polychaeta) based on molecular data

The phylogenetic relationships of orbiniid taxa were reconstructed based on sequence data of the mitochondrial 16S rRNA and nuclear 18S rRNA genes. Both genes were analysed separately and in combination using maximum likelihood, Bayesian inference and maximum parsimony. Regardless of the method used, a clade consisting of the investigated Orbiniidae, Methanoaricia dendrobranchiata and Questa was strongly supported by the 18S dataset. The analysis of the combined dataset suggests inclusion of M. dendrobranchiata within the Orbiniidae with close relationships to species of Orbinia and Phylo, rather than as a sister taxon to all other orbiniids. Evidence is given for the paraphyletic status of Leitoscoloplos , Naineris , Orbinia , Phylo and Scoloplos , which represent the most species-rich genera of the Orbiniidae. It is thus reasoned that the morphological characters presently used for genus diagnosis are not informative for cladistic analysis. No support is found for the hypothesis that taxa of the Protoariciinae represent juveniles of Orbiniinae. Instead, in the case of Protoaricia oerstedi , strong support for a progenetic origin is found.  © 2005 The Linnean Society of London, Zoological Journal of the Linnean Society , 2005, 144 , 59−73.     

Tetcyclacis and Abscisic Acid-Sensitive Reduction of Extracellular Ferricyanide by Mesophyll Cells of Valerianella locusta and Lemna gibba

Electron transport across the plasma membrane of Valerianellalocusta mesophyll cells and intact fronds of Lemna gibba, inducedby 10^–3 M ferricyanide, was inhibited by tetcyclacis,an inhibitor regarded to be specific for cytochrome P-450 mono-oxygenases.The effect was dependent on the concentration of tetcyclacisand the duration of preincubation. The apparent rate of trans-membraneelectron transport increased in the presence of catalase, indicatingtetcyclacis-induced H₂O₂-production or additional tetcyclacis-independentH₂O₂ release. The findings suggest an interaction of cytochromeP-450 with the plasma membrane-located electron transport chain.This redox-chain could be involved in the degradation of abscisicacid, being located at the plasma membrane. This assumptionis supported by the finding that ABA inhibits extracellularferricyanide reduction. Key words: Abscisic acid, cytochrome P-450 mono-oxygenase, plasma membrane, tetcyclacis     

Association mapping for chilling tolerance in elite flint and dent maize inbred lines evaluated in growth chamber and field experiments

Chilling sensitivity of maize is a strong limitation for its cultivation in the cooler areas of the northern and southern hemisphere because reduced growth in early stages impairs on later biomass accumulation. Efficient breeding for chilling tolerance is hampered by both the complex physiological response of maize to chilling temperatures and the difficulty to accurately measure chilling tolerance in the field under fluctuating climatic conditions. For this research, we used genome‐wide association (GWA) mapping to identify genes underlying chilling tolerance under both controlled and field conditions in a broad germplasm collection of 375 maize inbred lines genotyped with 56 110 single nucleotide polymorphism (SNP). We identified 19 highly significant association signals explaining between 5.7 and 52.5% of the phenotypic variance observed for early growth and chlorophyll fluorescence parameters. The allelic effect of several SNPs identified for early growth was associated with temperature and incident radiation. Candidate genes involved in ethylene signalling, brassinolide, and lignin biosynthesis were found in their vicinity. The frequent involvement of candidate genes into signalling or gene expression regulation underlines the complex response of photosynthetic performance and early growth to climatic conditions, and supports pleiotropism as a major cause of co‐locations of quantitative trait loci for these highly polygenic traits.     

A revision of the Afrotropical taxa of the genus Amerila Walker (Lepidoptera: Arctiidae)

This paper comprises a complete revision of the Afrotropical species of the genus Amerila ( Rhodogastria auct.), based on adult morphology. Examination of type material for most described taxa has resulted in numerous taxonomic changes. From a total of forty-seven previously described African taxa, thirty-five species including five newly described species and two new subspecies are recognized. For ten taxa, lectotypes have been selected, and for one species a neotype had to be designated. For each species, in addition to synonymy, a brief diagnosis based on external characters and genitalia is given, and the known distribution summarized. All species are illustrated by photographs and illustrations of male genitalia (except A.rufifemur , the male of which is unknown), and a key for determination of males by external characters is provided.     

Subsidy‐stress and multiple‐stressor effects along gradients of deposited fine sediment and dissolved nutrients in a regional set of streams and rivers

1. Stream managers need to understand relationships between multiple stressors and ecological responses. We examined responses of benthic invertebrates and algae along two land‐use‐related stressor gradients of concern in running waters. Our correlative study of the consequences of augmented deposited fine sediment and nutrient concentrations was conducted in a regional set of streams and rivers monitored by a water management authority in New Zealand and incorporated a wide range of catchment geologies and stream orders. 2. We used multiple linear regression analysis and an information‐theoretic approach to select the best predictive models for our biological response variables by testing multiple competing hypotheses that include nonlinear subsidy‐stress relationships and interactive effects between the two stressors. 3. Patterns consistent with a subsidy‐stress response to increasing dissolved inorganic nitrogen concentration were found for the relative abundances of the common invertebrate genera Pycnocentrodes and Deleatidium and for the relative abundance of total individuals in the EPT orders (Ephemeroptera, Plecoptera, Trichoptera). 4. Fine sediment seemed the more pervasive stressor, apparently counteracting and overwhelming any initial subsidy effect of increased nutrients, and accounting for more of the variance in biological response variables. Relationships with high nutrient concentrations were weaker and modelled with less certainty, probably reflecting the indirect modes of action of nutrients compared to those underlying sediment effects. Nevertheless, in several cases, the models indicated that nutrients interacted synergistically with fine sediment, lending further weight to the conclusion that managers need to address both stressors to achieve the best outcomes.     

AUTONOMY AND AUTHENTICITY OF ENHANCED PERSONALITY TRAITS

There is concern that the use of neuroenhancements to alter character traits undermines consumer's authenticity. But the meaning, scope and value of authenticity remain vague. However, the majority of contemporary autonomy accounts ground individual autonomy on a notion of authenticity. So if neuroenhancements diminish an agent's authenticity, they may undermine his autonomy. This paper clarifies the relation between autonomy, authenticity and possible threats by neuroenhancements. We present six neuroenhancement scenarios and analyse how autonomy accounts evaluate them. Some cases are considered differently by criminal courts; we demonstrate where academic autonomy theories and legal reasoning diverge and ascertain whether courts should reconsider their concept of autonomy. We argue that authenticity is not an appropriate condition for autonomy and that new enhancement technologies pose no unique threats to personal autonomy.