The Exotic Eclipsing Nucleus of the Ring Planetary Nebula SuWt 2

SuWt 2 is a planetary nebula (PN) consisting of a bright ionized thin ring seen nearly edge-on, with much fainter bipolar lobes extending perpendicularly to the ring. It has a bright (12th magnitude) central star, too cool to ionize the PN, which we discovered in the early 1990s to be an eclipsing binary. Although it was anticipated that there would also be an optically faint, hot, ionizing star in the system, a spectrum from the International Ultraviolet Explorer (IUE) did not reveal a UV source. We present extensive ground-based photometry and spectroscopy of the central binary collected over the ensuing two decades, resulting in the determination that the orbital period of the eclipsing pair is 4.9 days, and that it consists of two nearly identical A1 V stars, each of mass ~2.7 M sun. The physical parameters of the A stars, combined with evolutionary tracks, show that both are in the short-lived "blue-hook" evolutionary phase that occurs between the main sequence and the Hertzsprung gap, and that the age of the system is about 520 Myr. One puzzle is that the stars' rotational velocities are different from each other, and considerably slower than synchronous with the orbital period. It is possible that the center-of-mass velocity of the eclipsing pair is varying with time, suggesting that there is an unseen third orbiting body in the system. We propose a scenario in which the system began as a hierarchical triple, consisting of a ~2.9 M sun star orbiting the close pair of A stars. Upon reaching the asymptotic giant branch stage, the primary engulfed the pair into a common envelope, leading to a rapid contraction of the orbit and catastrophic ejection of the envelope into the orbital plane. In this picture, the exposed core of the initial primary is now a white dwarf of ~0.7 M sun, orbiting the eclipsing pair, which has already cooled below the detectability possible by IUE at our derived distance of 2.3 kpc and a reddening of E(B - V) = 0.40. The SuWt 2 system may be destined to perish as a Type Ia supernova.

Agricultural intensification and biodiversity partitioning in European landscapes comparing plants, carabids, and birds

Effects of agricultural intensification (AI) on biodiversity are often assessed on the plot scale, although processes determining diversity also operate on larger spatial scales. Here, we analyzed the diversity of vascular plants, carabid beetles, and birds in agricultural landscapes in cereal crop fields at the field (n = 1350), farm (n = 270), and European-region (n = 9) scale. We partitioned diversity into its additive components alpha, beta, and gamma, and assessed the relative contribution of beta diversity to total species richness at each spatial scale. AI was determined using pesticide and fertilizer inputs, as well as tillage operations and categorized into low, medium, and high levels. As AI was not significantly related to landscape complexity, we could disentangle potential AI effects on local vs. landscape community homogenization. AI negatively affected the species richness of plants and birds, but not carabid beetles, at all spatial scales. Hence, local AI was closely correlated to beta diversity on larger scales up to the farm and region level, and thereby was an indicator of farm-and region-wide biodiversity losses. At the scale of farms (12.83-20.52%) and regions (68.34-80.18%), beta diversity accounted for the major part of the total species richness for all three taxa, indicating great dissimilarity in environmental conditions on larger spatial scales. For plants, relative importance of alpha diversity decreased with AI, while relative importance of beta diversity on the farm scale increased with AI for carabids and birds. Hence, and in contrast to our expectations, AI does not necessarily homogenize local communities, presumably due to the heterogeneity of farming practices. In conclusion, a more detailed understanding of AI effects on diversity patterns of various taxa and at multiple spatial scales would contribute to more efficient agri-environmental schemes in agroecosystems.

THE IMPACT OF BURNING AND GRAZING OF HEATHLAND PLANTS AND INVERTEBRATES IN COUNTRY ANTRIM

The impact of burning and grazing on plant, ground beetle and spider species was investigated experimentally in stands of varying ages (burnt in 1982 and 1988 and unburnt plots) on an area of heather moorland in County Antrim, north-east Ireland. Burning initiated complex succession pathways which appear to have characteristic plant and invertebrate species associations. Removal of Calluna dominance initiated a period of high plant species diversity. Investigation of initial post-fire regeneration suggested that the frequency of occurrence of plant species changed over time and was affected by grazing. Grouping of species by the position of their renewal bud, i.e. their life-form, did not account for all observed interspecific variation. The dominant species after burning were Eriophorum vaginatum, E. angustifolium and Vaccinium myrtillus. Studies of vegetation canopy structure showed that, even with the exclusion of the main grazing herbivores, Calluna will not re-establish itself as the dominant species until several years after burning. The ground beetle Nebria salina was trapped more often on plots burnt in 1988 than on unburnt plots or those burnt in 1982. In comparison, Pterostichus niger and Carabus granulatus were trapped in greater numbers on plots burnt in 1982 than on unburnt plots and plots burnt in 1988. The large species Carabus problematicus and Carabus glabratus were trapped in greater numbers on unburnt plots. Similarly, more of the spiders Ceratinella brevipes and Centromerita concinna were trapped on the plots burnt in 1982. In comparison, Lepthyphantes zimmermanni and Robertus lividus were trapped more often on unburnt plots than on plots burnt in 1982 and 1988. Results are discussed with respect to the importance of the continuation of traditional heathland management practices.

Four new exotic red seaweeds on European shores

We report the occurrence of four red macroalgae new to Europe. Two species were unambiguously determined to the species level with a DNA barcoding approach, while the remaining two species could only be assigned to a genus. Gelidium vagum was found in the Oosterschelde estuary (the Netherlands). Gracilariopsis chorda, Chondracanthus sp. and Solieria sp. were found in the Gulf of Morbihan in Brittany (France); Solieria sp. was also subsequently observed in the Thau Lagoon (France). Gelidium vagum and Gracilariopsis chorda are species originating from the north-western Pacific, around the Japanese archipelago. Phylogenetic analyses also show a likely Pacific origin for Chondracanthus sp. and Solieria sp. Three of these species are likely to have been introduced after 2008, indicating some active transport pathways between the Pacific and the north-eastern Atlantic. These findings also underline the importance of consistent and continuous local expertise (versus rapid assessment) in early warning systems.

Uptake and translocation of inorganic and methylated arsenic species by plants

The uptake and translocation into shoots of arsenate, methylarsonate (MA), and dimethylarsinate (DMA) by 46 different plant species were studied. The plants (n = 3 per As species) were exposed for 24 h to 1 mg of As per litre under identical conditions. Total arsenic was measured in the roots and the shoots by acid digestion and inductively coupled plasma mass spectrometry from which, besides total As values, root absorption factors and shoot-to-root transfer factors were calculated. As uptake into the root for the different plant species ranged from 1.2 to 95 (mu g of As per g of dry weight) for As-V, from 0.9 to 44 for MA(V) and from 0.8 to 13 for DMA(V), whereas in shoots the As concentration ranged from 0.10 to 17 for As-V, 0.1 to 13 for MA(V), and 0.2 to 17 for DMA(V). The mean root absorption factor for As-V (1.2 to 95%) was five times higher than for DMA(V) (0.8 to 13%) and 2.5 times higher than for MA(V) (0.9 to 44%). Although the uptake of arsenic in the form of As-V was significantly higher than that of MA(V) and DMA(V), the translocation of the methylated species was more efficient in most plant species studied. Thus, an exposure of plants to DMA(V) or MA(V) can result in higher arsenic concentrations in the shoots than when exposed to As-V. Shoot-to-root transfer factors (TFs) for all plants varied with plant and arsenic species. While As-V had a median TF of 0.09, the TF of DMA(V) was nearly a factor of 10 higher (0.81). The median TF for MA(V) was in between (0.30). Although the TF for MA(V) correlates well with the TF for DMA(V), the plants can be separated into two groups according to their TF of DMA(V) in relation to their TF of As-V. One group can immobilise DMA(V) in the roots, while the other group translocates DMA(V) very efficiently into the shoot. The reason for this is as yet unknown.