19 research outputs found
Impacts of organic and conventional crop management on diversity and activity of free-living nitrogen fixing bacteria and total bacteria are subsidiary to temporal effects
A three year field study (2007-2009) of the diversity and numbers of the total and metabolically active free-living diazotophic bacteria and total bacterial communities in organic and conventionally managed agricultural soil was conducted at the Nafferton Factorial Systems Comparison (NFSC) study, in northeast England. The result demonstrated that there was no consistent effect of either organic or conventional soil management across the three years on the diversity or quantity of either diazotrophic or total bacterial communities. However, ordination analyses carried out on data from each individual year showed that factors associated with the different fertility management measures including availability of nitrogen species, organic carbon and pH, did exert significant effects on the structure of both diazotrophic and total bacterial communities. It appeared that the dominant drivers of qualitative and quantitative changes in both communities were annual and seasonal effects. Moreover, regression analyses showed activity of both communities was significantly affected by soil temperature and climatic conditions. The diazotrophic community showed no significant change in diversity across the three years, however, the total bacterial community significantly increased in diversity year on year. Diversity was always greatest during March for both diazotrophic and total bacterial communities. Quantitative analyses using qPCR of each community indicated that metabolically active diazotrophs were highest in year 1 but the population significantly declined in year 2 before recovering somewhat in the final year. The total bacterial population in contrast increased significantly each year. Seasonal effects were less consistent in this quantitative study
Patterns and dynamics of neutral lipid fatty acids in ants – implications for ecological studies
Background: Trophic interactions are a fundamental aspect of ecosystem functioning, but often difficult to observe
directly. Several indirect techniques, such as fatty acid analysis, were developed to assess these interactions. Fatty
acid profiles may indicate dietary differences, while individual fatty acids can be used as biomarkers. Ants
are among the most important terrestrial animal groups, but little is known about their lipid metabolism,
and no study so far used fatty acids to study their trophic ecology. We set up a feeding experiment with
high- and low-fat food to elucidate patterns and dynamics of neutral lipid fatty acids (NLFAs) assimilation
in ants. We asked whether dietary fatty acids are assimilated through direct trophic transfer, how diet
influences NLFA total amounts and patterns over time, and whether these assimilation processes are similar
across species and life stages.
Results: Ants fed with high-fat food quickly accumulated specific dietary fatty acids (C18:2n6, C18:3n3 and
C18:3n6), compared to ants fed with low-fat food. Dietary fat content did not affect total body fat of workers or amounts
of fatty acids extensively biosynthesized by animals (C16:0, C18:0, C18:1n9). Larval development had a strong effect on the
composition and amounts of C16:0, C18:0 and C18:1n9. NLFA compositions reflected dietary differences, which became
more pronounced over time. Assimilation of specific dietary NLFAs was similar regardless of species or life stage, but
these factors affected dynamics of other NLFAs, composition and total fat.
Conclusions: We showed that ants accumulated certain dietary fatty acids via direct trophic transfer. Fat content of the
diet had no effect on lipids stored by ants, which were able to synthesize high amounts of NLFAs from a sugar-based
diet. Nevertheless, dietary NLFAs had a strong effect on metabolic dynamics and profiles. Fatty acids are a useful tool to
study trophic biology of ants, and could be applied in an ecological context, although factors that affect NLFA patterns
should be taken into account. Further studies should address which NLFAs can be used as biomarkers in natural ant
communities, and how factors other than diet affect fatty acid dynamics and composition of species with
distinct life histories