Mapping nutrient transport in fungal networks

Background:

A feature of virtually all of the world’s terrestrial ecosystems is the dependence of their plant communities on the development and functioning of symbiotic mycorrhizal fungal networks. Mycorrhizae are the main pathway through which mineral nutrients are acquired from soil, and are also a large sink for photosynthate produced by host plants. Most plants are colonised by several fungi, and this observation raises many intriguing questions about the regulation of resources between a plant and its fungal partners. Likewise, the ability to grow many metres beyond roots also leads to the development of so-called ‘common mycelial networks’, which connect the roots of two or more individuals of the same or different species. The formation of such complex networks, where many individual plants and fungi are interconnected over relatively large areas, suggests the need for a sophisticated series of genetic and physiological controls of resource transfer between plant and fungus. The Oxford group has developed a range of novel techniques to image nutrient transport and network analysis in saprotrophic fungi, whilst the Aberdeen group has worked extensively with mycorrhizal systems in microcosm experiments and in the field. Nevertheless, at present, we have remarkably little knowledge of long-distance nutrient transport in mycorrhizal networks, how resource exchange is controlled, and how competition or co-operation is resolved in multi-species consortia.

Enabling technology from saprotrophic mycelial networks:

Saprotrophic fungal networks are the primary route to decomposition of woody plant remains in terrestrial ecosystems, whilst also mobilising nutrient resources in soil, and have provided a simpler experimental system to characterise network formation and function. The Oxford group have made three significant breakthroughs in analysis of saprotrophic fungal networks:
(1) automated image analysis using intensity-independent contrast enhancement with phase-congruency tensors, followed by watershed segmentation and cost-based pruning to characterize fungal networks rapidly and at high resolution (Obara et al., 2012, Bioinformatics 28, 2374-2381).
(2) Linking network architecture to predicted nutrient transport, based on mathematical models of fluid flow advection and diffusion dynamics (Bebber et al., 2007, Proc. Roy. Soc. 274, 2307-2315; Tero et al., 2010, Science 327, 439–442; Heaton et al., 2010, Proc. Roy. Soc. 277 3265-3274; Heaton et al., 2012 Phys. Rev. E 86, 021905).
(3) Experimental determination of nutrient flows by continuous imaging of radiolabelled nutrient transport in mycelial networks using photon-counting scintillation imaging (Tlalka et al., 2002, New Phytol.153 173-184; Tlalka et al., 2003, New Phytol. 158 325-335; Tlalka et al., 2007, FGB 44 1085-1095; Fricker et al., 2007, FGB 44, 1085-1095; Tlalka et al., 2008, J. Microsc. 231, 317-331; Tlalka et al., FGB 45, 1111-1121; Simonin et al., 2012, Eukaryotic Cell 11, 1345-1352).

This D.Phil proposal is to transfer application of these interdisciplinary approaches from saprotrophic systems to mycorrhizal network formation and function, combining the expertise of the Oxford and Aberdeen groups. The project will increase the complexity of the number of interacting partners in microcosm experiments to determine:

(i) the mechanisms by which an individual fungus transports specific mineral nutrients to a particular host plant root;
(ii) the mechanisms enabling a fungus to direct resource to a particular plant if it is colonising two or more plants;
(iii) the mechanisms by which a host plant directs carbon to a particular fungus when it is colonised by several fungi

STUDENT PROFILE:

This project would suit a candidate with a strong background in fungal biology, with an interest in image processing and network analysis.