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University of Western Sydney (2018)

Effects of precipitation regimes on arbuscular mycorrhizal fungal communities

Deveautour, Coline A.

Titre : Effects of precipitation regimes on arbuscular mycorrhizal fungal communities

Auteur : Deveautour, Coline A.

Université de soutenance : University of Western Sydney

Grade : Doctor of Philosophy (PhD) 2018

Résumé partiel
Climate models predict an overall reduction in rainfall in mid-latitudes and subtropical dry regions. In southeast Australian grasslands, changes in rainfall may affect plant productivity and diversity because both are highly responsive to rainfall regimes. Associated soil microorganisms may help plants cope with these changes but also may respond themselves to altered rainfall patterns, directly or indirectly via responses of plants. Arbuscular mycorrhizal (AM) fungi are an important component of the soil microbial community in grasslands. They form symbiotic associations with the majority of plant species and are dependent on the carbon provided by their host. In return, they contribute to plant nutrition and tolerance of environmental stress, including drought. The overarching goal of this work was to study the response of AM fungal communities to altered rainfall regimes. In particular, I evaluated AM fungal responses to changes in rainfall in association with changes in root traits (chapter 2) and in the composition and richness of the plant community (chapter 4), using DNA sequencing techniques. I also used a trait-based approach to understand how precipitation regimes affect the AM fungal community (chapter 3). AM fungal communities may respond to altered rainfall regimes either directly or indirectly via changes in host traits. I studied the response of AM fungal communities associated with roots of four common plant species to experimentally altered rainfall patterns in replicated field plots established within an Australian mesic grassland. I found that altered rainfall affected the composition, but not the richness, of the AM fungal community. Specific root length was observed to correlate with AM fungal richness, while concentrations of phosphorus and calcium in root tissue and the proportion of root length allocated to fine roots were correlated with AM fungal community composition. However, I found no evidence that AM fungal response to rainfall resulted via changes in the host because none of the studied traits were affected by rainfall manipulations. However, the effect of altered rainfall patterns via root traits may occur in more responsive plant species or more water limited environments. In addition, I observed that variability among AM fungal communities was high even in communities from the same treatments, and a large proportion of the variation remained unexplained.

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