Abstract
Climate changes, exemplified by increased temperatures and CO2 concentration, pose a global threat to forest health. Of particular concern are pests and pathogens, with a warming climate altering their distributions and evolutionary capacity, while impairing the ability of some plants to respond to infections. Progress in understanding and mitigating such effects is currently hindered by a lack of empirical research. Norway spruce (Picea abies) is one of the most economically important tree species in northern Europe, and is considered highly vulnerable to changes in climate. It is commonly infected by the fungus Endoconidiophora polonica, and we hypothesized that damage caused to trees will increase under future climate change predictions. To test this hypothesis an in vivo greenhouse experiment was conducted to evaluate the effects of a changed growing environment on E. polonica infected Norway spruce seedlings, comparing ambient conditions to predicted temperatures and CO2 levels in Finland for the years 2030 and 2100. In total, 450 seedlings were randomized amongst the three treatments, with 25 seedlings from each allocated to inoculation with one of five different fungal strains or mock-inoculation. Seedlings were monitored throughout the thermal growing season for mortality, and lesion length and depth indices were measured at the experiment conclusion. Disease severity (mortality and lesions) was consistently greater in fungal-inoculated than mock-inoculated seedlings. However, substantial differences were observed among fungal strains in response to climate scenarios. For example, although overall seedling mortality was highest under the most distant (and severe) climate change expectations, of the two fungal strains with the highest mortality counts (referred to as F4 and F5), one produced greater mortality under the 2030 and 2100 scenarios than ambient conditions, whereas climate scenario had no effect on the other. This study contributes to a limited body of empirical research on the effects of projected climate changes on forestry pathosystems, and is the first to investigate interactions between Norway spruce and E. polonica. The results indicate the potential for future climate changes to alter the impact of forest pathogens with implications for productivity, while highlighting the need for a strain-specific level of understanding of the disease agents.
Highlights
Human-related disturbances including climate change and globalization pose novel threats to global forest health (Gauthier et al, 2015; Trumbore et al, 2015; Wingfield et al, 2015; Ghelardini et al, 2016)
More seedling deaths occurred under the 2100 climate change scenario than under ambient conditions (26 versus 9 deaths; χ2 value = 9.35, P = 0.002; Figure 2A)
For seedlings inoculated with fungal strain F5, mortality varied based on the climate change scenario (Table 1 and Figure 2B)
Summary
Human-related disturbances including climate change and globalization pose novel threats to global forest health (Gauthier et al, 2015; Trumbore et al, 2015; Wingfield et al, 2015; Ghelardini et al, 2016). Pathogens and pests represent some of the most important threats to forest health where climate change is occurring (Ayres and Lombardero, 2000; Allen et al, 2010; Wingfield et al, 2015; Ghelardini et al, 2016). Other studies have identified reduced or no effect of climate change on plant diseases (Chakraborty et al, 1998; Coakley et al, 1999; Roy et al, 2004) These effects vary geographically and are often species and strain specific (Coakley et al, 1999; Sallé et al, 2005; Garret et al, 2006), highlighting the need for systems-based research
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