Managing with fire: effects of recurring prescribed fire on soil and root-associated fungal communities

Master of ScienceDepartment of BiologyAri JumpponenPrescribed fire is a necessary management tool used to reduce fuel loads and to maintain fire-adapted ecosystems over time. Although the effects of fire on vegetation and soil properties are well understood, the long-term impacts of different fire regimes on soil fungi, root-inhabiting and ectomycorrhizal (ECM) fungi remain largely unknown. Previous studies show that high intensity wildfires reduce soil fungal biomass and alter fungal communities, however the effects of repeated low intensity prescribed fires are less understood. Studies described in this thesis took advantage of a long-term (>25 years) fire management regime in southern yellow pine stands in the southeastern United States to analyze the effects of repeated prescribed fires on soil fungi, root-associated and ECM fungal communities. The fire management regimes included five fire treatments varying in season (winter and summer) and interval length (two-year, three-year, six-year, and unburned control) allowing us to address effects of burn season and fire frequency on these fungal communities. We used 454-pyrosequencing to analyze ECM roots to specifically focus on the root-associate fungi and ECM. After a pilot study comparing the use of non-proofreading and proofreading polymerases to generate deep high throughput sequence data on soil fungal communities using Illumina MiSeq technology, proofreading polymerase was chosen to create amplicon libraries to minimize overestimation of community richness and underestimation of community evenness. We found that season had no or only minimal effect on diversity and community composition on any of these fungal communities. However, both soil and root-associated fungi responded compositionally to frequent fire intervals. In contrast, we observed no effects of recurring fire on ECM communities. Indicator taxon analyses identified many taxa in each dataset (soil, root-associated, and ECM fungi) that represent potentially fire suppressed or fire adapted taxa. These findings indicate that frequent recurring prescribed fires result in distinct fire adapted/tolerant soil and root-associated fungal communities that are correlated with the desired fire-adapted plant communities. However, the ECM symbionts colonizing these hosts remain largely unaffected

Halo assembly bias and the tidal anisotropy of the local halo environment

We study the role of the local tidal environment in determining the assembly bias of dark matter haloes. Previous results suggest that the anisotropy of a halo's environment (i.e, whether it lies in a filament or in a more isotropic region) can play a significant role in determining the eventual mass and age of the halo. We statistically isolate this effect using correlations between the large-scale and small-scale environments of simulated haloes at $z=0$ with masses between $10^{11.6}\lesssim (m/h^{-1}M_{\odot})\lesssim10^{14.9}$. We probe the large-scale environment using a novel halo-by-halo estimator of linear bias. For the small-scale environment, we identify a variable $\alpha_R$ that captures the $\textit{tidal anisotropy}$ in a region of radius $R=4R_{\textrm{200b}}$ around the halo and correlates strongly with halo bias at fixed mass. Segregating haloes by $\alpha_R$ reveals two distinct populations. Haloes in highly isotropic local environments ($\alpha_R\lesssim0.2$) behave as expected from the simplest, spherically averaged analytical models of structure formation, showing a $\textit{negative}$ correlation between their concentration and large-scale bias at $\textit{all}$ masses. In contrast, haloes in anisotropic, filament-like environments ($\alpha_R\gtrsim0.5$) tend to show a $\textit{positive}$ correlation between bias and concentration at any mass. Our multi-scale analysis cleanly demonstrates how the overall assembly bias trend across halo mass emerges as an average over these different halo populations, and provides valuable insights towards building analytical models that correctly incorporate assembly bias. We also discuss potential implications for the nature and detectability of galaxy assembly bias.Comment: 19 pages, 15 figures; v2: revised in response to referee comments, added references and discussion, conclusions unchanged. Accepted in MNRA

Gene dynamics of toll-like receptor 4 through a population bottleneck in an insular population of water voles (Arvicola amphibius)

Acknowledgments We would like to thank all colleagues who have contributed to fieldwork and sampling during this study. We would especially like to thank Marius Wenzel and Sandra Telfer for collaboration with different aspects of the study, and Dave Jones and Nat Jones for Bartonella PCR assays. This work was supported by the BBSRC studentship to MKG (BB/J01446X/1) and a NERC studentship to MKO. The research was carried out under project license PPL 40/1813.Peer reviewedPublisher PD

Reduced, tame and exotic fusion systems

We define here two new classes of saturated fusion systems, reduced fusion systems and tame fusion systems. These are motivated by our attempts to better understand and search for exotic fusion systems: fusion systems which are not the fusion systems of any finite group. Our main theorems say that every saturated fusion system reduces to a reduced fusion system which is tame only if the original one is realizable, and that every reduced fusion system which is not tame is the reduction of some exotic (nonrealizable) fusion system

Student attitudes to entrepreneurship

This study on Student Attitudes to Entrepreneurship investigates the image which university students have of entrepreneurs and entrepreneurship. It is an initial exploratory/empirical study, which looks at the situation in Germany, Romania, Latvia, Italy and Austria. The study, based on questionnaires, shows that there are significant differences but also common features to the image of entrepreneurship and attitudes to it in the five countries. It is interesting to note that the students polled in connection with the study tended to have a neutral to positive/very positive image of entrepreneurs.attitude, attributes, entrepreneurs, entrepreneurship, opinion.