Total N difference method and 15N isotope dilution methode - A comparative study on N-fixation

In the study, the 15N fixation of a number of green manure crops were studied using either the 15N dilution technique, or the simple total N difference method. The results of the two methods were not very different, and the total N difference method seemed to give as good results as the more complicated and expencive 15N dillution method

Catch Crops in Organic Farming Systems without Livestock Husbandry - Simulations with the DAISY model

This paper presents simulations of the soil-plant-atmosphere model DAISY based on an organic crop rotation with incorporation of different catch crops following pea as a leguminous cash crop. Special emphasise was put on the simulation of N-mineralisation/-immobilisation and of soil microbial biomass N. The DAISY model was able to simulate soil mineral N and soil microbial biomass N after soil incorporation of catch crop plant residues to some extend. Several processes need further attention and may be integrated into the DAISY model: (1) soil tillage induced mobilisation of organic material including considerable amounts of organic N, (2) winter killing of sensitive plant species and varieties, (3) decomposition of plant residues at the soil surface as occurring after winter killing, (4) decomposition of easily decomposable plant residues at low temperatures, (5) soil microbial residues as an organic pool temporarily protected against turnover. Furthermore, reliable criteria for the subdivision of green plant residues into an easily decomposable pool and a more recalcitrant pool have to be developed

Storytelling in Focus Group Discussions: A Narrative Approach to Phenomena With Temporal Dimensions in Medical Education Research

People can express experiences, opinions, and perspectives in stories. In a story, the experiences can be relived and discovered independently of time and place. In medical education, it is a fundamental premise that time progresses, and it is within this temporal space that students learn, acquire competencies, and form identity. It is also within this space that much qualitative research is conducted. However, qualitative examinations at one point in time will result in only a snapshot of a dynamic phenomenon that evolves over time. Existing approaches to qualitative research are often inadequate to accommodate this dynamic development without applying a time- and cost-consuming design such as longitudinal investigations. The purpose of this paper is to present storytelling as a useful research approach to include temporal dimensions in cross-sectional qualitative data collection. We describe the background for the approach, argue for its use, and provide a practical example of storytelling with the use of a fictional character in online focus group discussions to explore a dynamic phenomenon in medical education research. Overall, storytelling offers a narrative approach to qualitative research that allows the researcher to explore phenomena across time and space. The approach has the advantage that it can be used in different formats both oral and written, digital or physical.</p

Sustained positive consequences of genetic rescue of fitness and behavioural traits in inbred populations of <i>Drosophila melanogaster</i>

One solution to alleviate the detrimental genetic effects associated with reductions in population size and fragmentation is to introduce immigrants from other populations. While the effects of this genetic rescue on fitness traits are fairly well known, it is less clear to what extent inbreeding depression and subsequent genetic rescue affect behavioural traits. In this study, replicated crosses between inbred lines of Drosophila melanogaster were performed in order to investigate the effects of inbreeding and genetic rescue on egg‐to‐adult viability and negative geotaxis behaviour—a locomotor response used to measure, e.g. the effects of physiological ageing. Transgenerational effects of outcrossing were investigated by examining the fitness consequences in both the F(1) and F(4) generation. The majority of inbred lines showed evidence for inbreeding depression for both egg‐to‐adult viability and behavioural performance (95% and 66% of lines, respectively), with inbreeding depression being more pronounced for viability compared with the locomotor response. Subsequent outcrossing with immigrants led to an alleviation of the negative effects for both viability and geotaxis response resulting in inbred lines being similar to the outbred controls, with beneficial effects persisting from F(1) to F(4). Overall, the results clearly show that genetic rescue can provide transgenerational rescue of small, inbred populations by rapidly improving population fitness components. Thus, we show that even the negative effects of inbreeding on behaviour, similar to that of neurodegeneration associated with physiological ageing, can be reversed by genetic rescue

Biotic and abiotic factors investigated in two <i>Drosophila </i>species – evidence of both negative and positive effects of interactions on performance

Multiple environmental factors acting in concert can interact and strongly influence population fitness and ecosystem composition. Studies investigating interactions usually involve only two environmental factors; most frequently a chemical and another abiotic factor such as a stressful temperature. Here we investigate the effects of three environmental factors: temperature, an insecticide (dimethoate) and interspecific co-occurrence. We expose two naturally co-occurring species of Drosophila (D. hydei and D. melanogaster) to the different environments during development and examine the consequences on several performance measures. Results are highly species and trait specific with evidence of two- and three-way interactions in approximately 30% of all cases, suggesting that additive effects of combined environmental factors are most common, and that interactions are not universal. To provide more informative descriptions of complex interactions we implemented re-conceptualised definitions of synergism and antagonism. We found approximately equal proportions of synergistic and antagonistic interactions in both species, however the effects of interactions on performance differed between the two. Furthermore, we found negative impacts on performance in only 60% of interactions, thus our study also reveals a high proportion of cases with positive effects of interactions

Population bottlenecks constrain host microbiome diversity and genetic variation impeding fitness

It is becoming increasingly clear that microbial symbionts influence key aspects of their host's fitness, and vice versa. This may fundamentally change our thinking about how microbes and hosts interact in influencing fitness and adaptation to changing environments. Here we explore how reductions in population size commonly experienced by threatened species influence microbiome diversity. Consequences of such reductions are normally interpreted in terms of a loss of genetic variation, increased inbreeding and associated inbreeding depression. However, fitness effects of population bottlenecks might also be mediated through microbiome diversity, such as through loss of functionally important microbes. Here we utilise 50 Drosophila melanogaster lines with different histories of population bottlenecks to explore these questions. The lines were phenotyped for egg-to-adult viability and their genomes sequenced to estimate genetic variation. The bacterial 16S rRNA gene was amplified in these lines to investigate microbial diversity. We found that 1) host population bottlenecks constrained microbiome richness and diversity, 2) core microbiomes of hosts with low genetic variation were constituted from subsets of microbiomes found in flies with higher genetic variation, 3) both microbiome diversity and host genetic variation contributed to host population fitness, 4) connectivity and robustness of bacterial networks was low in the inbred lines regardless of host genetic variation, 5) reduced microbial diversity was associated with weaker evolutionary responses of hosts in stressful environments, and 6) these effects were unrelated to Wolbachia density. These findings suggest that population bottlenecks reduce hologenomic variation (combined host and microbial genetic variation). Thus, while the current biodiversity crisis focuses on population sizes and genetic variation of eukaryotes, an additional focal point should be the microbial diversity carried by the eukaryotes, which in turn may influence host fitness and adaptability with consequences for the persistence of populations