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Title: The role of keystone species in driving microbial community diversity in U.K. lowland heaths
Author: Arnold, Paul
ISNI:       0000 0004 2741 5134
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2011
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Myrmica ruginodis ants and the gorse species U. europaeus have a national distribution in the U.K. and are considered important keystone species within British lowland heaths. These two species boost and maintain biodiversity by increasing habitat heterogeneity through ecosystem engineering of the soil physical and chemical environment, and are generally considered Keystone species in lowland heaths. Both species have been shown to increase limiting nutrients in the soil such as Nitrogen and Phosphorus. Here, for the first time in a single study, the extent to which these species augment soil chemistry and the resulting impacts on microbial communities is quantified. It was hypothesized that abiotic changes brought about by the action of keystone species directly and indirectly will lead to differences in both bacterial and fungal community diversity and composition, and such changes will be likely to modify ecosystem function. Analysis of soil cores taken from three U.K. lowland heath habitats representing a national distribution found that dissimilarities in microbial community structure (determined by T-RFLP) were largely attributable to differences in soil pH. However, pH was an imperfect predictor. To fully understand abiotic drivers and to identify the soil nutrients involved in augmenting microbial communities in heathlands, a data mining exercise was conducted using the large Countryside Survey 2007 bacterial data. The findings from this showed that as the soil pH gradient was shortened by focusing on low soil pH, and then by looking at a single type of vegetation cover (dwarf shrub heath), soil pH became less effective in explaining differences in the communities; other soil chemical properties then become more important, such as Carbon to Nitrogen (C:N) ratio and soil Phosphorus (P). The identification of these chemical attributes and the known impacts that the keystone species have on them led to the development of a controlled mesocosm experiment using Aberdeenshire lowland heath soil. In this experiment keystone species were isolated and found to impact upon soil chemistry and microbial diversity. Soil pH was identified as having an important defining role on communities, however soil P and C:N and Potassium (K) were also related to microbial community composition. Differences in respiration were also linked to the presence of the keystone species. A final field experiment was performed to test the mesocosm observations in the field site, but sampling specific soil regions (ant nest structures and rhizospheres). Less marked microbial community differentiation was found compared with the initial field experiment. Fungi had no responses to soil chemistry except for Dorset communities which responded to soil pH. Bacteria responded to all soil measures of chemistry for pooled region data and for Aberdeenshire. Cumbria communities responded P and Dorset to C:N. Soil chemistry and microbial communities were not affected by the same keystone species in the same way in any of the regions. Finally, community T-RFLP profiles for fungi and bacteria were directly compared for.any correlation; interaction was found to be limited, partly due to fundamental differences in the bacterial 16S rDNA and fungal ITS rDNA T-RFLP profiles and partly due to these microbes responding in different ways to their environment.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available