Sarah Addison

Candidature

PhD Candidate

Thesis title

Tree-root microbiome project: At the root of climate proofing forests

Research Project

Plant-microbe interactions have long been of significant scientific interest as they influence food supply and quality.  Interest in these interactions have recently expanded as new knowledge on the primacy of plant-microbe associations to primary productivity have become clear, to the stage that these can be viewed as a co-evolved ecological unit. Improving our knowledge of these relationships, and the benefits they can provide to plants, offers new opportunities to alter plant phenotypes, particularly in the Anthropocene – an era defined by rapidly changing climatic conditions. Realising these opportunities requires the development of model systems on which new ecological theory can be tested and validated.

Like other plants, trees exist in intimate association with a consortium of microorganisms on and in their tissues (the ‘holobiont’). This microbiome profoundly influences tree growth, fitness, physiology and health in a multitude of ways that are just becoming apparent. For individual trees, roots and leaves comprise the plant’s primary sensory network, assessing and triggering physiological responses to environmental conditions. Given the effects of climate change will be experienced most strongly by long-lived species such as trees, model systems appropriate to long life-history traits are also needed.  

The underground holobiont that is formed between the plant-root-soil-microbiome is often driven by the root itself and can provide the surrounding soil microbes with a continuum of gradients in environmental parameters in which to live. This provides multiple niches for microbes to thrive and grow in which exist in, on and around the plant root tissue and across very small spatial distances. This forms the basis for plant-root-soil-microbial interactions with the plant exuding various compounds to target specific microbes that can form beneficial relationships with the plant. These relationships are often complex, contain multiple microbial species and gaps in the literature remain exploring the true extent of these relationships for long-lived plant growth and survival.  


Pinus radiata D. Don is a widely grown conifer tree species.  It comprises an excellent model system to understand these questions due to a wide base of existing knowledge related to host genetics, physiology, production/growth, and health. There is also extant national and international series of research trials available that provide a current resource of trees of different ages and under a wide range of environmental, management, genetic, and other influences.  Furthermore, this species has survived millennia of significant climate events which makes it ideal to use to model the influence of the microbiome on tree adaptability. Information around understanding the microbiome will potentially provide a better understanding of the resilience of natural forests and ecosystems that depend on trees and how they can all be protected in our changing climate. To address these issues, my thesis will address the following key questions:

Key Questions:

1. What are the soil and root microbial associations that exist within the natural range of Pinus radiata?
2. How do associations with populations in their natural ranges compare with associations present in New Zealand, Australia and other ‘planted’ pine forests globally? Does the potential microbial diversity still exist? If not, where/why has it been lost?
3. Is there a ‘core microbiome’ associating with Pinus radiata, regardless of environmental conditions? This will determine those that are conditionally present during certain situations and those that are stochastically assembled.
4. Can global analysis be used to establish a tree-root-microbiome model system for P. radiata?

Supervisors

Distinguished Professor Brajesh Singh, Dr Steve Wakelin (Scion, NZ)