Microbial influences on the conservation and recovery of Wollemi pine

  • Jessica L. Rigg

Western Sydney University thesis: Doctoral thesis

Abstract

The iconic and critically endangered Wollemi pine (Wollemia nobilis W. Jones, K. Hill & J. Allen) is known from fewer than 100 trees within Wollemi National Park in New South Wales, Australia. Hundreds of seedlings germinate in the wild but few reach maturity, suggesting there is a potential environmental or competition-driven bottleneck preventing seedlings from establishing. Understanding what limits seedling survival in the wild and establishment in novel environments (i.e. translocation) is critical for effective conservation of this critically endangered conifer. Wollemi pine grows on highly acidic, shallow soil of poor nutrient status and therefore is likely to be highly dependent on microorganisms such as mycorrhizal fungi and others that contribute to nutrient cycling. Pathogens are also likely to be important. The overarching goal of this project was to characterise variation in microbial communities associated with Wollemi pine in a variety of contexts. In particular, microbial communities associated with adult Wollemi pine in the wild (Chapter 2), in the roots of inoculated seedlings (Chapter 2 & 3), in translocated Wollemi pine (Chapter 4) and in soils surrounding the wild Wollemi pine site drenched with fungicide (Chapter 5). Community variation was then linked to potential functional impacts on seedling recruitment (Chapter 3), translocation outcomes (Chapter 4) and practical management of pathogens within the wild Wollemi pine site (Chapter 5), all critical aspects of the conservation of Wollemi pine. Competition between Wollemi pine and its immediate neighbours may limit Wollemi expansion in the wild. I investigated whether wild Wollemi pine gathered a specific soil microbial community compared to a dominant neighbour, coachwood (Chapter 2). I found that, to a certain extent, Wollemi pine tended to be associated with a fungal and bacterial community that differed from under a neighbouring species. However, there was substantial additional variation in these soil microbial communities that was linked to edaphic gradients within a host species range (Chapter 2). The plant species-specific differences in soil communities observed in the wild went on to influence the fungal community composition that assembled in seedlings grown under glasshouse conditions when inoculated with field soil in a 'plant-soil feedback' (PSF) experiment (Chapter 2). Root bacterial communities were influenced only by the seedling species identity (Chapter 2). There was no evidence that seedling growth was affected by the tree species associated with field-soil inocula, suggesting that species-specific pathogens are not likely to be limiting recruitment of Wollemi pine in the natural population (Chapter 3). Nonetheless, there was evidence of fungal, but not bacterial, community variation impacting seedling growth independently of PSFs (Chapter 3). During a translocation event, where Wollemi pine were planted into a new location in the wild, I considered whether variation in microbial communities present at planting and subsequently associated with Wollemi pine in this new location impacted translocation success (Chapter 4). Translocated Wollemi pine assembled distinct microbial communities over time: in the first year after translocation for fungi and between the first and second year after translocation for bacteria. Variation in the microbial communities that were already present at the site did not impact the early growth responses of Wollemi pine; instead physical and chemical edaphic properties were better predictors of initial translocation success. Translocated Wollemi pine that did not assemble species-specific fungal communities distinct from the surrounding environment had reduced growth and low establishment success. The deadly root-rot pathogen Phytophthora cinnamomi has infected a number of Wollemi pine in the wild. To understand how management strategies being used to control this pathogen, that is widespread drenching with the fungicide metalaxyl, had influenced the composition of native soil communities in the wild, I performed 454-pyrosequencing of soil collected from treated and untreated locations (Chapter 5). Overall, long-term fungicide drenching only influenced a few fungal and bacterial taxa. The effect of fungicide was small compared to the natural variation in soil communities within the wild Wollemi pine site suggesting that negative impacts of drenching with this fungicide have been small. This work is the first to consider soil microbial communities during the conservation of a critically endangered conifer species. Wollemi pine assembles species-specific microbial communities in the wild and in novel environments. Variation in the fungal, but not bacterial, communities associated with Wollemi pine was observed to have functional consequences for Wollemi pine growth; therefore potential manipulation of microbial communities during conservation should focus on fungi. Future work could consider the use of fungal inoculants or management techniques to promote beneficial fungal communities to improve conservation outcomes. In addition, the empirical approaches developed here may be valuable for considering the role of soil microbial communities in the conservation of other rare plants.
Date of Award2016
Original languageEnglish

Keywords

  • Wollemi National Park (N.S.W.)
  • Wollemia nobilis
  • conifers
  • pine
  • plant translocation
  • soil microbiology
  • endangered plants
  • Sydney (N.S.W.)

Cite this

'