Tritrophic interactions among plants, mycorrhizal fungi and soil fauna in contrasting forest biomes

Supervisors: David Burslem, David Johnson, Uffe Nielsen, Ian Anderson

Recent studies have shown that the outcome of mutualistic interactions is highly context dependent, varying through space and time in response to abiotic and biotic factors. The mutualisms between plants and mycorrhizal fungi contribute to plant nutrient acquisition and regulation of carbon and nutrient fluxes through ecosystems. However, the balance of benefits and thus the fitness consequences of these mutualisms may differ depending on nutrient availability, light environment and interactions with the soil fauna. In particular, grazing of mycorrhizal fungal hyphae by soil fauna may influence nutrient uptake by plants and thus their growth and survival, particularly in soils that are inherently nutrient-poor. Nematodes that graze on mycorrhizal hyphae disrupt nutrient acquisition by the fungal symbiont and create a sink for plant-derived carbohydrate that is directed away from the fungus and into nematode biomass. Hence nematode grazing on mycorrhizal fungi has the potential to influence the outcome of competition between plants growing on nutrient-poor soils, although it is currently unknown how these outcomes are affected by mycorrhizal type (ecto- vs arbuscular), and interactions with the abiotic environment (nutrient and light availability). The aim of this project is to compare the impact of fungal-feeding nematodes on growth and nutrient uptake of plants associated with ecto- (EM) vs arbuscular mycorrhizas (AM) in natural forest communities growing in N-limited temperate forests in Scotland (e.g. dominated by Pinus) and P-limited sub-tropical forests in Australia (e.g. sclerophyllous woodland dominated by Eucalypts). In both settings the dominant woody plants are EM, but there are numerous species adopting other mycorrhizal strategies (AM, ericaceous) available for comparison. We will focus on the role of nematodes in these interactions because they are known to play major roles as root herbivores and fungivores and species adopting these feeding strategies can be recognised by morphological examination under a light microscope.