Acute Oak Decline (AOD) is a serious threat facing native oak trees in Britain. AOD is widespread in southern and central England, with almost one third of woodlands affected. Symptoms of AOD include bleeding stems, necrotic lesions and larvae of the bark-boring beetle Agrilus biguttatus, and can result in tree death within 5 years of the first symptoms. Previous work on AOD has revealed that these lesions are caused by a bacterial “pathobiome”, a collection of bacteria that together cause damage to oak trees. Trees in warmer or drier regions are more likely to suffer from AOD, with extreme environmental conditions, such as drought, weakening trees to the point they cannot fight off these pathogens. To control or halt the further spread of AOD, we need to develop an understanding of forest health that combines knowledge of these biological and environmental elements.
As well as pathogenic bacteria, oak trees play host to a vast array of microorganisms, known as the oak microbiota, many of which have strongly beneficial effects on tree health. For example, mycorrhizal fungi on the roots of trees provide trees with nutrients required for growth, and some bacteria found on leaves may protect trees from infection by preventing the growth of pathogenic bacteria. This collection of microorganisms, along with the ways they interact with each other and the conditions in which they occur, is known as the oak microbiome, and is the context in which these health benefits occur. The aim of the FUTURE OAK project is to gain a better understanding of the identity of these microorganisms, what they do, and their role within the oak microbiome.
The key objectives of the project are as follows:
Characterise the oak microbiome in healthy and AOD affected trees at sites across Britain.
Identify AOD disease-suppressive microorganisms in the oak microbiome.
Using these naturally disease-suppressive microorganisms of the oak microbiome, design a biocontrol treatment that will suppress AOD lesion formation.
Engage with woodland managers and stakeholders to explore understandings and attitudes to the microbiome, engineered biocontrol treatments, and wider issues of oak health and management.
To achieve objectives 1 and 2, we will use state-of-the-art DNA sequencing technology to identify the microorganisms growing on oak trees across the UK. We will look at trees that are both infected with AOD and those that are not in order to understand how microbiomes change with infection, and identify micro-organisms that might protect from infection. We will characterise the microbiome across multiple parts of the tree, including the leaves, internal trunk tissue, and the roots, in order to build a full picture of the microbiome. We will use a technique called “single gene community profiling” to identify these microorganisms, which allows us to determine the species present on a tree, by examining and identifying the genetic material present. We will investigate how environmental factors, such as rainfall and temperature, affect the composition of microbiomes across the UK.
Using the results of this survey of oak microbiomes, we will use microbial culturing techniques in the lab to grow the microorganisms we identify as having potential the potential to suppress AOD (Objective 3). We will then trial these disease-suppressive microorganisms as potential biocontrol treatments, testing their ability to suppress or prevent the progression of AOD on oak logs and oak saplings which we infect with the AOD pathobiome. The results of these studies will build progress towards our long-term goal of engineering a biocontrol treatment that may be applied to oak trees, with the aim of preventing further spread of AOD and allowing trees to recover.
A key element of FUTURE OAK is also to engage with key stakeholders in oak woodlands, particularly woodland managers, in order to understand their attitudes towards and knowledge of microbiomes and their role in tree health (objective 4). By conducting a series of interviews with oak managers across Britain, we will explore the current knowledge of woodland managers with regard to oak health, microbiomes and AOD. We will combine this interview data with a large-scale survey produced in conjunction with the Sylva Foundation, which will provide a broader context for oak management and AOD within the UK. To help build understanding between the many communities involved in and affected by AOD, FUTURE OAK will also convene shared dialogue workshops between project scientists, forest managers, and other key stakeholders connected to tree health. By creating links between these different groups, we aim to foster understanding and knowledge-sharing among both practitioners and researchers.
While this project is focused on oaks and the spread of AOD, we aim to build an understanding of the role of the microbiome in tree health in all species. Trees across the globe are facing increasingly numerous threats to health, with escalating environmental stresses due to climate change, and the spread of new diseases through global trade becoming increasingly common. An understanding of tree health that includes these organisms may be integral to mitigating these problems, allowing us to expand control methods that contain the pathogen and prevent infection through the engineering of new biocontrol treatments.
In short, FUTURE OAK’s exploration of the oak microbiome and AOD, and how woodland managers understand and use this knowledge, may have deep and far-reaching impacts to how the tree health is understood across numerous species and landscapes.