The structural and functional diversity of arbuscular mycorrhiza in Australia

Abstract

Both land degradation of natural systems and the use of finite fertilisers in crop production highlight the need to more efficiently utilise limited nutritional resources in soils. Furthermore, greater protection against plant pathogens is required to lessen the effects of diseases that severely limit productivity in both natural and managed systems. The symbiotic association known as arbuscular mycorrhiza, which forms between most plants and arbuscular mycorrhizal (AM) fungi, is a promising potential solution to these issues facing plant productivity. These multifunctional associations have been observed to improve host nutrient-uptake as well as offer a degree of pathogen protection to host plants. However, AM fungal taxa vary in how capably they perform these functions. These taxa can also respond differently to changes in their environment. Therefore, there is a need to better understand how particular environmental variables might alter the structure and function of AM fungal communities. Current models of partner promotion in AM associations suggest AM fungi are promoted for their nutrient trade capabilities. However, it remains unclear how the availability of these soil nutrients influence the structure and function of AM fungal communities. Furthermore, these partner promotion models do not account for the promotion of AM fungi that specialise in secondary functions, such as pathogen protection. This thesis aimed to address two primary objectives. The first was to study the role of soil fertility as a driver of functional diversity in AM fungal communities. The second was to investigate the significance and taxonomic distribution of capable pathogen protection among AM fungi in natural systems. This work suggests that AM fungi most beneficial in alleviating nutrient limitation in hosts, such as the Gigasporaceae, are more frequently observed as soil fertility declines. This is consistent with current models of partner promotion in AM associations, but fails to explain why the populations of AM fungal taxa that do not specialise in nutrient trade are maintained in natural systems. A common hypothesis is that taxa such as the Glomeraceae might instead be promoted for more capable pathogen protection. However, I found no evidence to suggest that the Glomeraceae are proportionally more capable than other AM fungal families at altering the distribution of fungal plant pathogens in natural systems. These findings contribute to our ability in predicting the responses of AM fungal communities to environmental conditions and developing optimal AM fungal inoculum for targeted applications.

Date of Award	2021
Original language	English