Der Einfluß einer variierten K-Ernährung auf die Inkorporierung von markiertem Stickstoff (15N) bei jungen Sonnenblumen (Helianthus annuus L.)

The effect of a varied K nutrition upon the incorporation of labelled nitrogen (¹⁵N) in young sun flower plants (Helianthus annuus L.) 1. The influence of the potassium nutritional status upon the incorporation of labelled nitrogen (¹⁵N) into the soluble amino fraction and into the protein fraction was studied with young sun flower plants (Helianthus annuus L.). The plants were cultivated in a solution culture with 3 different nitrogen and 2 different potassium levels. During the last 24 hours of this cultivation the nitrogen of the nutrient solution was labelled by ¹⁵N-nitrate in the various treatments. 2. The growth of the plants was affected considerably by the various nutritional treatments. The yield of the plant matter increased with increasing nitrogen supply. This nitrogen effect was enhanced by the better potassium nutrition. 3. The contents of soluble amino compounds in roots and upper plant parts increased with the increasing nitrogen application. This tendency was reduced by the higher potassium supply. The contents of protein nitrogen rose with the nitrogen nutrition. Potassium reduced the content of protein nitrogen in treatments with high growth rates. 4. Related on a single plant the incorporation rate of nitrate nitrogen into the organic matter was higher in plants with a good potassium nutritional status than in plants with a low potassium nutritional status. This effect was especially evident in the treatments with the highest nitrogen supply. Here the nitrate incorporation rate was 5–7 times higher with the higher potassium application. 5. This favorable effect of potassium upon the assimilation of nitrate nitrogen was also evident, if the incorporation rate was not related to a single plant, but on the unit of weight of plant material (fresh matter). Thus with high nitrogen supply the quantity of labelled nitrogen of the amino fraction was about 2 times higher in the plants with a high potassium nutritional status compared with plants of a low potassium nutritional status. In the protein fraction this potassium effect was still more evident. The influence of potassium upon the nitrate nitrogen assimilation was the better the better the plants were supplied with nitrate.     

Comparative studies on the distribution of foliar or root applied 15N-nitrogen in Beta vulgaris species

Recent anatomical studies on sugar beet suggest direct vascular connections between ontogenetically corresponding leaves and segments in the storage root (Stieber and Beringer, 1984). The objectives of two experiments were to test the use of these transport routes in the distribution of ¹⁵N. In adult Beta vulgaris L., spp. vulgaris plants (fodder beet cv Kyros and sugar beet cv Kawetina) ¹⁵NH₄ ¹⁵NO₃ was applied to leaf 10 (young) and 21 (old) respectively. Distribution of ¹⁵N within the plant was determined 2, 7 and 21 days later. In fodder beet ¹⁵N applied to leaf 21 was exported to 63% into the storage root, to 11% into younger leaves; the corresponding percentages in sugar beet were 51% and 31% respectively. ¹⁵N applied to leaf 10 was exported to only 37% into the storage root, 7% and 15% were translocated into the older leaves of fodder and sugar beet respectively. This pattern of ¹⁵N distribution does not fully contradict with the expected use of assumed vascular routes. It is suggested that N exported from an older leaf does not exclusively migrate into the ontogenetically corresponding tissues of the storage root, but part of the N is imported by the younger leaves and from there exported into the peripheral regions of the storage root. This view is supported by a short-term experiment on ¹⁵NO₃^- root-uptake by six week old fodder and sugar beet plants which gave the following sequence of specific ¹⁵N labeling: lateral roots ≧ young leaves > root crown > old leaves > storage root.     

The influence of tillage on the structure of rhizosphere and root-associated arbuscular mycorrhizal fungal communities

Soil environmental factors affect the structure of arbuscular mycorrhizal (AM) fungal communities present in soil. However, it is not understood to which degree management practices such as tillage lead to dissimilarities between intra- and extraradical AM fungal communities. This study aims to assess the influence of two different soil management practices (conventional tillage and no-till) on the diversity of AMF communities, both in rhizosphere soil and inside corn roots. We hypothesized that under no-till, roots are colonized as they grow through the undisturbed fungal mycelia left from the previous crop whereas under conventional tillage they are colonized by those propagules that survived disturbance and can re-establish in their new relocated and mixed environment. We predicted that the degree of similarity of AM fungal communities inside versus outside the roots would be greater under no-till than under tillage. Using terminal restriction fragment length polymorphism (T-RFLP) and denaturing gradient gel electrophoresis we observed a different AM fungal community present in roots under no-till than under conventional tillage. Moreover, the communities present in the rhizosphere soil were different than in the roots of the corn plants. These results suggest that soil management does alter the diversity of AM fungal communities associated with corn roots and that plants influence the structure of the AMF community colonizing their roots. Sequencing results indicated that the majority of AMF species found in this agricultural soil was Glomus spp. However, further work is required to determine the extent to which AM fungal genotypic alterations by soil management influences competitive relationships.     

Probing carbon flux patterns through soil microbial metabolic networks using parallel position-specific tracer labeling

In order to study controls on metabolic processes in soils, we determined the dynamics of ¹³CO₂ production from two position-specific ¹³C-labeled pyruvate isotopologues in the presence and absence of glucose, succinate, pine, and legume leaf litter, and under anaerobic conditions. We also compared ¹³CO₂ production in soils along a semiarid substrate age gradient in Arizona. We observed that the C from the carboxyl group (C₁) of pyruvate was lost as CO₂ much faster than its other C atoms (C_2,3). Addition of glucose, pine and legume leaf litter reduced the ratio between ¹³CO₂ production from 1-¹³C pyruvate and 2,3-¹³C pyruvate (C₁/C_2,3 ratio), whereas anaerobic conditions increased this ratio. Young volcanic soils exhibited a lower C₁/C_2,3 ratio than older volcanic soils. We interpret a low C₁/C_2,3 ratio as an indication of increased Krebs cycle activity in response to carbon inputs, while the higher ratio implies a reduced Krebs cycle activity in response to anaerobic conditions. Succinate, a gluconeogenic substrate, reduced ¹³CO₂ production from pyruvate to near zero, likely reflecting increased carbohydrate biosynthesis from Krebs cycle intermediates. The difference in ¹³CO₂ production rate from pyruvate isotopologues disappeared 4-5 days after pyruvate addition, indicating that C positions were scrambled by ongoing soil microbial transformations. This work demonstrates that metabolic tracers such as pyruvate can be used to determine qualitative aspects of C flux patterns through metabolic pathways of soil microbial communities. Understanding the controls over metabolic processes in soil may improve our understanding of soil C cycling processes.     

Intrathoracic esophageal perforation of unknown cause in four horses

Three horses (age 17 - 23 years) were referred to the equine clinic of the University of Berne due to colic, fever, tachycardia and tachypnea. All horses showed pleural effusion. Clinical findings in 2 of the horses were highly suggestive of an intra-thoracic esophageal perforation. Severe septic pleuropneumonia without suspicion of an esophageal lesion was diagnosed in the 3rd horse. In addition, an 11 year old stallion was referred to the equine clinic for treatment of a presumptive large colon impaction. The horse was given laxatives after nasogastric intubation. Subsequent dramatic clinical deterioration and signs consistent with severe pleuropneumonia suggest that esophageal perforation had occurred when passing the nasogastric tube. All 4?horses were euthanized due to a poor prognosis. Esophageal perforation was diagnosed or confirmed post mortem in all cases. A hypertrophy of the tunica muscularis of the intra-thoracic esophagus was found in 3 of 4?horses.     

Developing an online professional network for veterinary education: the NOVICE project

An online professional network for veterinarians, veterinary students, veterinary educationalists, and ICT (Information and Communication Technology) educationalists is being developed under the EU (European Union) Lifelong Learning Programme. The network uses Web 2.0, a term used to describe the new, more interactive version of the Internet, and includes tools such as wikis, blogs, and discussion boards. Focus groups conducted with qualified and student veterinarians within the project's five founding countries (The Netherlands, Germany, United Kingdom, Hungary, Romania) demonstrated that online professional communities can be valuable for accessing information and establishing contacts. Online networks have the potential to overcome common challenges to face-to-face communities-such as distance, cost, and timing-but they have their own drawbacks, such as security and professionalism issues. The Network Of Veterinary ICt in Education (NOVICE) was developed using Elgg, an open-source, free social networking platform, after several software options had been considered. NOVICE aims to promote the understanding of Web 2.0, confidence to use social software tools, and participation in an online community. Therefore, the Web site contains help sections, Frequently Asked Questions, and access to support from ICT experts. Five months after the network's launch (and just over one year into the project) 515 members from 28 countries had registered. Further research will include analysis of a core group's activities, which will inform ongoing support for and development of informal, lifelong learning in a veterinary context.     

Virulence of newcastle disease virus: what is known so far?

ABSTRACT: In the last decade many studies have been performed on the virulence of Newcastle disease virus (NDV). This is mainly due to the development of reverse genetics systems which made it possible to genetically modify NDV and to investigate the contribution of individual genes and genome regions to its virulence. However, the available information is scattered and a comprehensive overview of the factors and conditions determining NDV virulence is lacking. This review summarises, compares and discusses the available literature and shows that virulence of NDV is a complex trait determined by multiple genetic factors.     

Contrasting physiological responses of two co-occurring eucalypts to seasonal drought at restored bauxite mine sites

This study describes the physiological response of two co-occurring tree species (Eucalyptus marginata and Corymbia calophylla) to seasonal drought at low- and high-quality restored bauxite mine sites in south-western Australia. Seasonal changes in photosynthesis (A), stomatal conductance (g(s)), leaf water potential (ψ), leaf osmotic potential (ψ), leaf relative water content (RWC) and pressure-volume analysis were captured over an 18-month field study to (i) determine the nature and severity of physiological stress in relation to site quality and (ii) identify any physiological differences between the two species. Root system restriction at the low-quality site reduced maximum rates of gas exchange (g(s) and A) and increased water stress (midday ψ and daily RWC) in both species during drought. Both species showed high stomatal sensitivity during drought; however, E. marginata demonstrated a higher dehydration tolerance where ψ and RWC fell to -3.2 MPa and 73% compared with -2.4 MPa and 80% for C. calophylla. Corymbia calophylla showed lower g(s) and higher ψ and RWC during drought, indicating higher drought tolerance. Pressure-volume curves showed that cell-wall elasticity of E. marginata leaves increased in response to drought, while C. calophylla leaves showed lower osmotic potential at zero turgor in summer than in winter, indicating osmotic adjustment. Both species are clearly able to tolerate seasonal drought at hostile sites; however, by C. calophylla closing stomata earlier in the drought cycle, maintaining a higher water status during drought and having the additional mechanism of osmotic adjustment, it may have a greater capacity to survive extended periods of drought.