A workflow for metabolomics of forest tree biotic stress response and applications for management

Abstract

Trees are exposed to a variety of stressors over their lifetimes. To survive and thrive under diverse conditions, they have evolved a suite of defenses, which confer resistance or tolerance to most biotic and abiotic stressors. Even though disease (or insect pest infestation) is the exception and not the rule, pests and pathogens have had and continue to have a profound impact on the health of forests globally. This is especially true for invasive and/or non-native pests and pathogens and, more recently, for native pests and pathogens whose range or virulence has changed because of climate change (1–3). Any estimate of the impact of pests and pathogens on forests is likely conservative and an underestimate of the actual impact on forests and the communities that rely on them. The incidence of non-native insects (and pathogens) continues to increase every year (4), and increased tree mortality within just the United States is predicted in 63% of forestland due to non-native insect pests and pathogens (5). Over the last 100 years, invasive pests and pathogens have functionally eradicated or decimated multiple forest tree species in local populations or across species ranges. Examples of impacted forest tree species include, but are not limited to, chestnut (chestnut blight), pines (white pine blister rust and mountain pine beetle), ash (emerald ash borer and ash dieback), and tanoak, oaks, and larch (sudden oak death and Ramorum blight).

The impacts of pests and pathogens are widespread, from economic losses to loss of forest ecosystem services and negative outcomes for human health. For example, emerald ash borer, which was first identified in the early 2000s, is estimated to have killed tens of millions of ash trees in the eastern United States (6). In areas of emerald ash borer infestation, increased human mortality from cardiovascular illness has been reported (7). Impacts have also been felt in the housing industry, where emerald ash borer infection negatively impacted home values in one Midwestern United States city (8). These studies do not even include more direct impacts, such as costs of forest management for the treatment, removal, or replacement of susceptible ash trees (9). Wide-reaching impacts are not exclusive to the emerald ash borer. Similar impacts have been observed or estimated for other pathogens and pests of trees across wildlands and urban landscapes (10, 11).

To counter biotic threats, trees possess a suite of defenses that act directly and/or indirectly on the attacking pest or pathogen, and range from physical defenses, including bark and lignin, to chemical defenses, such as phenolics and terpenoids. These defenses can be general or specific for a given organism and can be produced constitutively (pre-infection) or induced following infection. The reason why invasive and non-native pests and pathogens have been particularly problematic is because affected tree species lack a co-evolutionary history with them, so the pests and pathogens have no co-evolved natural enemies. Thus, the suite of defenses that the novel host possesses is unable to prevent infection or minimize adverse impacts to tree health, ultimately, resulting in higher-than-normal levels of mortality of impacted host tree species, often across larger spatial scales.

In this chapter, we focus on the role of metabolite defenses in forest tree responses to biotic stress. Within this context, we describe a workflow (Figure 5.1) for use in metabolomics studies of forest tree-pest/pathogen interactions. Applications for the workflow as well as considerations for applying it across scales, from individual trees to landscapes, are also discussed. Finally, case studies from multiple tree-pathogen and pest systems are presented, including oak (sudden oak death and European oak leafroller), ash (emerald ash borer and ash dieback), and pine (Diplodia tip blight and mountain pine beetle).

Citation

​Conrad, Anna O.; Villari, Caterina; Bonello, Pierluigi. 2024. A workflow for metabolomics of forest tree biotic stress response and applications for management. In: António, Carla, ed. Monitoring forest damage with mass spectrometry-based metabolomics methods, first edition. Hoboken, New Jersey: John Wiley & Sons, Inc: 109-126. Chapter 5.