Canopy Uptake of 15NH3 by Four Temperate Tree Species and the Interaction with Leaf Properties

Tree canopies are believed to act as a sink of atmospheric ammonia (NH₃). However, few studies have compared the uptake efficiency of different tree species. This study assessed the uptake of ¹⁵N-labelled NH₃ at 5, 20, 50 and 100?ppb_v by leaves and twigs of potted silver birch, European beech, pedunculate oak and Scots pine saplings in June, August and September 2008. Additionally, foliar uptake of ¹³C-labelled carbon dioxide (¹³CO₂) and leaf stomatal characteristics were determined per species and treatment date and the relation with ¹⁵NH₃ uptake and estimated stomatal ¹⁵NH₃ uptake were assessed. Both ¹⁵NH₃ and ¹³CO₂ uptake were affected by tree species and treatment date, but only ¹⁵NH₃ uptake was influenced by the applied NH₃ concentration. Depending on the treatment date, ¹⁵NH₃ uptake by leaves and twigs was highest at 5 (September), 20 (June) or 50 (August) ppb_v. Birch, beech and oak leaves showed the highest uptake in August, while for pine needles this was in June and, except at 5?ppb_v in June, the ¹⁵NH₃ uptake was always higher for the deciduous species than for pine. For all species except beech ¹³CO₂ uptake was highest in August and on every treatment date the ¹³CO₂ uptake by leaves of deciduous species was significantly higher than by pine needles. Leaf characteristics and ¹³CO₂ uptake did not provide a strong explanation for the observed differences in ¹⁵NH₃ uptake. This study shows that on the short-term a high interspecific variability exists in NH₃ uptake, which depends on the time in the growing season.     

Competition between the invasive macrophyte <Emphasis Type="Italic">Caulerpa taxifolia</Emphasis> and the seagrass <Emphasis Type="Italic">Posidonia oceanica</Emphasis>: contrasting strategies

Background  

Plant defense strategy is usually a result of trade-offs between growth and differentiation (i.e. Optimal Defense Theory – ODT, Growth Differentiation Balance hypothesis – GDB, Plant Apparency Theory – PAT). Interaction between the introduced green alga Caulerpa taxifolia and the endemic seagrass Posidonia oceanica in the Mediterranean Sea offers the opportunity to investigate the plausibility of these theories. We have accordingly investigated defense metabolite content and growth year-round, on the basis of an interaction gradient.     

Factors affecting the serological response of dogs and cats to rabies vaccination

After being vaccinated against rabies some cats and dogs fail to show an antibody titre adequate to meet the requirements of the UK Pet Travel Scheme. To investigate this problem, the data derived from 16,073 serum samples submitted to the Veterinary Laboratories Agency for serological testing between 1999 and 2002, 1002 samples submitted to BioBest during March and April 2001, and 1264 samples associated with one make of vaccine submitted to BioBest between June 2001 and January 2003, were analysed. The probability of antibody titre failing to reach at least 0.5 iu/ml was analysed by logistic regression as a function of the choice of vaccine, the interval between vaccination and sampling, the sex and age of the animal, and its country of origin. In dogs, all these factors, except sex, had highly significant (P < 0.001) effects on the test failure rate, and in cats all the factors had a significant effect (P < 0.05).     

Spatial correlates of amphibian use of constructed wetlands in an urban landscape

Many amphibian species rely on both aquatic and terrestrial habitats to complete their life cycles. Therefore, processes operating both within the aquatic breeding habitat, and in the surrounding uplands may influence species distributions and community composition. Moreover, changes in land use adjacent to breeding site may degrade aquatic habitats. To assess land use effects on pond-breeding amphibian assemblages, we investigated relationships between land use, breeding habitat conditions, and breeding amphibian use of constructed wetlands in urban environments of the Baltimore metropolitan area, USA. Forest and impervious surface associations with species richness and occurrence occurred at spatial scales ranging from 50 to 1,000 m, with strongest relationships at 500 m. Forest and impervious surface cover within 1,000 m of ponds were also related to water and sediment quality, which in turn were capable of explaining a proportion of the observed variation in species richness and occurrence. Taken together, our results suggest that forest and other land covers within relatively proximal distances to ponds (i.e., within 50–1,000 m) may be influencing species richness directly via the provisioning of upland habitat, and indirectly via influences on within pond habitat quality. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Particle size reduction leading to cell wall rupture is more important for the β-carotene bioaccessibility of raw compared to thermally processed carrots

The amount of nutrients that can be released from food products (i.e., nutrient in vitro bioaccessibility) is often studied as it is a starting point for investigating nutrient bioavailability, an indicator for the nutritional value of food products. However, the importance of mastication as a particle size reduction technique is poorly understood and is often neglected during in vitro procedures determining bioaccessibility. Therefore, the aim of the present work was to study the effect of mechanical breakdown on the β-carotene bioaccessibility of carrot samples, having different textural/structural characteristics (as a result of thermal processing). In the first part of this study, the all-E-β-carotene bioaccessibility of carrot particles of different sizes (ranging from cell fragments up to large cell clusters), generated from raw as well as from gently and intensely cooked carrot samples, was determined. In the second part of the study, the effect of human mastication on the particle size reduction of raw as well as of gently and intensely cooked carrot samples was investigated in order to allow identification and validation of a technique that could mimic mastication during in vitro procedures. Results showed a strong dependency of the all-E-β-carotene bioaccessibility on the particle size for raw and gently cooked carrots. After intense cooking, on the other hand, a considerable amount of all-E-β-carotene could be released from cell fragments (smaller than a cell) as well as from small and large cell clusters. Hence, the importance of mechanical breakdown, and thus also of (in vitro) mastication, is dependent on the carrot sample that is considered (i.e., the extent to which the carrot sample has been thermally processed prior to the particle size reduction). Structural changes occurring during mechanical and thermal processing are hereby key factors determining the all-E-β-carotene bioaccessibility. The average particle size distribution curves of raw and cooked carrots, which were chewed by 15 persons, could be mimicked by mixing 50 g of carrots using a Grindomix (Retsch) at 2500 rpm during 5 s. Based on this scientific knowledge, the identified in vitro mastication technique was successfully integrated in the in vitro digestion procedure determining the all-E-β-carotene bioaccessibility of carrot samples.