Climate change impacts on ectomycorrhizal fungi associated with Australian eucalypts

Abstract

Ectomycorrhizal (ECM) fungi are an important component of soil fungal communities forming beneficial symbioses with their host plants. There is limited knowledge of how Australian ECM fungi respond to climate change. The aims of this study were (i) to collect, isolate into axenic culture and identify Australian Pisolithus sp., (ii) use this isolate collection to investigate the growth response of Pisolithus sp. to increasing C:N ratios in axenic culture, (iii) investigate the response of Pisolithus sp. in symbiosis with Eucalyptus globulus seedlings to ambient and elevated atmospheric [CO2] in laboratory microcosms, and (iv) to investigate the effects of elevated atmospheric CO2 concentrations and temperature on ectomycorrhizal fungal communities (including Pisolithus sp.) associated with E. globulus in a whole tree chamber experiment. These investigations were designed to gain information of ECM fungal responses to future projected climate change scenarios. This study was successful in generating a large collection of Pisolithus sp. isolates (46 isolates in total) from various locations on the east coast of NSW, Australia and identifying them by ITS sequencing and phylogenetic analysis with previous generated ITS sequences for Pisolithus sp. from the Genbank database. The final collection was shown to comprise three species: P. microcarpus, P. albus and another as yet unidentified Pisolithus species (denoted species 10). All Pisolithus isolates were incubated on liquid MMN plates with a gradient of C:N ratio of either 10:1, 20:1 or 40:1. There were inter- and intra-specific variations in the observed growth and nutrient uptake responses of the isolates representing the three Pisolithus sp. tested. Six isolates had highest growth rate at the lowest C:N ratio, a further six isolates increased growth rate with increasing carbon availability, while three isolates had highest growth rate, and a further three isolates had lowest growth rate, at 20:1 C:N ratio. To assess the effects of increased atmospheric CO2 concentration [CO2] on ECM symbioses, E. globulus seeds were surface sterilised and germinated under sterile conditions, colonised by 6 isolates of either P. albus or P. microcarpus mycelium plugs and grown in microcosms under ambient or elevated atmospheric [CO2] Mycorrhizal seedlings produced up to 500% more biomass than non-mycorrhizal seedlings in the ambient treatment and up to 300% more biomass in the elevated treatment. C was concentrated in the stem and leaves rather than the roots for both treatments. Pisolithus colonised seedlings and the rhizosphere soil, captured C in excess of the C lost to the system; up to 9 times more than non-mycorrhizal control microcosm in the ambient treatment and up to 7 times more in the elevated treatments. Overall this work showed that the combination of Pisolithus albus and E. globulus has high potential for C capture in both plant tissue and soil. Saplings of E. globulus were planted in the Hawkesbury Forest Experiment (HFE) whole tree chambers. These chambers were subjected to ambient and elevated (ambient + 3°C) temperature and atmospheric [CO2], (400 ppm and 640 ppm). Mesh bags filled with acid washed sand were inserted into soil underneath the saplings planted in the whole tree chambers and left in place for a period of 5 months. DNA was extracted from each of these bags and analysed using terminal restriction fragment length polymorphism (TRFLP) and Illumina MiSeq sequencing followed by multivariate statistical analysis. The I diversity (species richness) was found to be increased in the combined elevated [CO2] and temperature treatment (eTeCO2) and there was a difference in the I diversity (community composition) with individual species dominance altered. The major separation observed in the multivariate analysis was due to the combined effects of the elevated temperature and elevated [CO2] treatment. Overall, the results from the research presented in this thesis, support a key role for Pisolithus sp., which are important ectomycorrhizal fungal symbionts of Australian eucalypts in increasing C capture and C cycling in eucalypt dominated Australian ecosystems.

Date of Award	2015
Original language	English