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Mr Donald A'Bear 

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I am a soil ecologist, interested in climate change, interactions between decomposer fungi and soil invertebrates, and the role of these interactions in ecosystem regulation. I am funded by a Natural Environment Research Council (NERC) PhD studentship, and supervise Dr Hefin Jones and Prof. Lynne Boddy.

PhD project: Impacts of climate change on decomposer fungus–invertebrate interactions and ecosystem processes

The role of soil biota (fauna and microbes) in ecosystem regulation is well recognised, but detailed understanding of the impacts of climate change on these organisms is lacking. Climate change has potential to influence the biological mechanisms regulating ecosystem–atmosphere carbon exchange. The relationship between warming and heterotrophic microbial respiration remains poorly understood, not least in terms of the differential sensitivity of microbial groups to temperature, and the complexity of interactions with other biota.

Cord-forming basidiomycete fungi are the dominant primary decomposers in temperate woodland, where a considerable proportion of terrestrial carbon is stored. These fungi grow out from colonised resources to forage for new ones forming large, dynamic networks of mycelium. Decomposition rates are determined by decomposer community composition, ecophysiological relationships between fungi and abiotic factors, and interactions with other soil organisms. Amongst the latter, a major determinant is the balance between mycelial growth and removal by invertebrate (e.g. collembola) grazers, which can themselves be affected by climate change.

The first empirical study of my PhD used compressed soil microcosms to investigate whether increased fungal growth and activity, or increased abundance of invertebrate grazers (potentially reducing fungal growth and activity), is the dominant factor in the control of primary decomposition rates under elevated temperature. The key findings were: (i) grazing collembola can counteract warming-induced stimulation of fungal growth, potentially preventing increased colonisation rates of new resources; and (ii) high grazing pressure did not prevent increased fungal-mediated decomposition of colonised wood at elevated temperature.

Future work will consider the impacts of combinations of climatic factors (e.g. elevated temperature and drought or increased precipitation) on these interactions and ecosystem processes. Forest soil mesocosms will be used to provide more realistic structural complexity and composition of the faunal and microbial communities, in an effort to bridge the gap between laboratory studies and the field.

Other Research

As a Final Year undergraduate I investigated the influence of oribatid mites on the growth of decomposer basidiomycete fungi. While grazing impacts of other ubiquitous soil fauna, particularly collembola, on fungal mycelia were already relatively well-studied, it was not know whether oribatid mites would affect fungal growth and morphology. This study provided the first evidence for non-grazing effects of these mites on mycelial foraging, potentially mediated by the chemical cornucopia (containing numerous compounds with anti-fungal properties) secreted from the opisthonotal and compact dermal glands of many oribatid species (A’Bear et al. 2010).

Alongside my PhD, I am involved in collaborative projects with Tom Crowther:

  1. Impacts of grazing soil invertebrates (ranging from microfauna [e.g. nematodes] to macrofauna [e.g. woodlice, millipedes]) on mycelial growth and functioning are known to be species-specific. It has been argued, however, that considering the high degree of functional redundancy assumed among soil invertebrate taxa, grazer density rather than identity could more important in affecting fungal growth. By comparing the impacts of a range of soil invertebrate taxa grazing at low, medium and high representations of field density, we found that species-specific impacts were not masked by density-dependence (Crowther and A’Bear 2012).
  2. Woodlice have been shown to reverse the outcome of competitive interactions between two fungal mycelia in compressed soil microcosms (Crowther et al. 2011, Ecol. Lett. 14, 1134-1142). By feeding on the dominant fungus, woodlice can prevent the competitive exclusion of the weaker species. To test the implications of this for fungal species diversity, woodlice were added to forest soil mesocosms (containing the full faunal and microbial communities) inoculated with two competing decomposer basidiomycete fungi growing from beech (Fagus sylvatica) wood blocks. Removal of mycelia by grazing woodlice enabled a greater diversity of soil microfungi (top-down regulation of microbial community composition), which in turn increased collembola abundance (bottom-up effect on other fungal-feeding invertebrate taxa). Activity of some extracellular enzymes produced by basidiomycete mycelia was reduced by woodlice grazing, further highlighting the important role of these fauna in regulating fungal-mediated ecosystem processes.

I am also involved in a study examining the potential effects of elevated CO2-driven changes in leaf chemistry on subsequent processing by a range of terrestrial and aquatic invertebrate detritivores. This project is collaborative with Matthew Dray, Tom Crowther and Stephen Thomas (PhD students in Cardiff School of Biosciences).

External collaborators

Tom Crowther (Yale University, USA) - Decomposer fungus–invertebrate interactions and ecosystem functioning.

Guenther Raspotnig (Karl-Franzens University, Graz, Austria) - Chemical effects of oribatid mites on basidiomycete fungus mycelial foraging.

Ellen Kandeler (University of Hohenheim, Germany) - Climate change impacts on microbial community composition and extracellular enzyme activity.