Eucalypt decline and ectomycorrhizal fungal community ecology of Eucalyptus delegatensis forest, Tasmania, Australia
Horton, BM (2011) Eucalypt decline and ectomycorrhizal fungal community ecology of Eucalyptus delegatensis forest, Tasmania, Australia. PhD thesis, University of Tasmania.
Ectomycorrhizal fungi underpin critical ecosystem processes which affect tree health.
Eucalypt decline is widespread throughout Australia, and its cause has been attributed to a
variety of factors, including forest management. In Tasmania, dieback in Eucalyptus
delegatensis R.T. Baker has been linked to altered fire regimes and associated changes in
mycorrhizal communities. This thesis presents a study that explores ectomycorrhizal
species richness and community composition in relation to eucalypt health, understorey
vegetation and soil chemistry in the context of fire history. The results further our
understanding of ectomycorrhizal ecology and elucidate factors important to the
maintenance of a healthy forest ecosystem.
Study sites were established in E. delegatensis forest with either sclerophyll understorey
(six plots) or rainforest understorey (six plots). Eight of the plots, located in north-east
Tasmania, had been established for a study of fire ecology and had known fire histories
ranging from 42 years since the last fire to long unburnt (>120 years). Four plots located in
north-western Tasmania were long unburnt but had been disturbed by logging 22-25 years
previously. Ectomycorrhizal fungal sporocarps, root tips and soil samples were collected
during a three-year period from all 12 plots. Samples from soil, root tips and sporocarps
gave rise to different but complementary information about ectomycorrhizal communities.
Fungal operational taxonomic units were identified through DNA sequencing and
phylogenetic analysis. At each site, understorey vegetation was characterised, soil and
eucalypt foliage chemistry was analysed, and eucalypt crown condition was assessed.
Primary crown dieback was identified as the most effective method for the measurement
of eucalypt health. Multivariate statistical analyses were used to explore the relationships
among ectomycorrhizal communities, eucalypt health, vegetation and abiotic variables.
E. delegatensis forest with rainforest understorey was more than likely to be affected by
severe eucalypt decline, had higher concentrations of soil inorganic nitrogen (nitrate and
ammonium) and eucalypt foliar nitrogen, and had lower concentrations of soil and eucalypt
foliar phosphorus, than forest with sclerophyll understorey. As forest declined in health the
ecosystem moved from being nitrogen limiting to phosphorus limiting due to reduced
phosphorus availability and plant uptake, potentially due to altered mycorrhizal activity.
Ectomycorrhizal communities differed between moderately and severely declining forest
and were correlated to crown health and altered soil chemistry associated with the two levels of decline. The Cortinariaceae had high species richness in healthiest sites while the
Russulaceae and Thelephoraceae were rich in forest affected by severe decline. In northwestern
and north-eastern Tasmania unique and distinctly different ectomycorrhizal fungal
communities were found to occur in E. delegatensis forest with rainforest understorey
versus those with sclerophyll understorey.
Irrespective of understorey type and health status, the Cortinariaceae were highly diverse,
and were the most species-rich family within the ectomycorrhizal community of
E. delegatensis forest. The Cortinariaceae also was the most abundant family in the root tip
community. The Helotiales, Russulaceae and Thelephoraceae also were important
components. The importance of the Cortinariaceae in E. delegatensis forest is similar to
other Australian eucalypt forests but distinctly different from northern hemisphere forests,
which tend to be dominated by the Russulaceae, Thelephoraceae and Corticeaceae.
Distance-based multiple linear regression models using only significant predictor variables
based on soil and foliage nutrient concentrations and crown health were able to explain
52% of the variation in fungal community composition, and 44% of the variation in
ectomycorrhizal community proportional composition at the family level. Soil pH, total soil
nitrate, soil organic carbon and soil phosphorus were significant in predicting
ectomycorrhizal species composition and proportional composition in the final models. A
multiple linear regression model showed that available soil nitrate and phosphorus were
significant in predicting ectomycorrhizal community richness. High richness was associated
with low available soil nitrate or phosphorus.
Northern hemisphere studies which show that changes in soil chemistry, especially mineral
nitrogen, can strongly influence mycorrhizal species richness, species composition and
community structure corroborate the likely influence of soil nitrogen on the
ectomycorrhizal communities of E. delegatensis forest. This is the first study to find a strong
correlation between ectomycorrhizal fungal communities and the status of eucalypt forest
health. The results support the currently proposed model that, in the absence of fire,
premature decline of temperate Australian eucalypt forests is closely linked to changes in
soil chemistry, understorey vegetation and mycorrhizal communities.
|Item Type:||Thesis (PhD)|
|Additional Information:||Copyright the Author. The published article which forms Ch. 2 is -- Horton, B. M., D. C. Close, T. J. Wardlaw & N. J. Davidson (2011) Crown condition assessment: An accurate, precise and efficient method with broad applicability to Eucalyptus. Austral Ecology, 36(6), 709-721.|
|Keywords:||dieback, sclerophyll, rainforest, molecular DNA, crown, health, cortinaraceae|
|Deposited By:||ePrints Officer|
|Deposited On:||08 Dec 2011 12:23|
|Last Modified:||19 Apr 2012 13:39|
|ePrint Statistics:||View statistics for this ePrint|
Repository Staff Only: item control page