Tree defense in a changing world

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Carbon (C) is the central element of life because it can bind with other elements to form complex molecules that are important for plant and animal metabolism. C assimilated via photosynthesis plays a fundamental role in growth, survival and reproduction of plants, as they cannot escape stressful situations like drought by migration but only via strategically allocating resources to life-sustaining functions and biosynthesis of compounds required for metabolism. Compounds that are directly involved in growth, development, and reproduction are called primary metabolites while secondary metabolites (SM) are important for species interactions, detoxification and defense.Allocation of C plays also a critical role for life on Earth as it channels solar energy through the terrestrial vegetation and drives global biogeochemical cycles (e.g., energy, water, nutrients) and mediates provision of ecosystem services such commodity production, climate regulation or biodiversity conservation. Yet, rapidly changing climate is posing an increasing threat to the global vegetation and climate change-induced vegetation mortality has been documented across all vegetated continents. Such mortality is most often driven by an interaction between climate, plant physiology and plant antagonists (e.g., herbivores) and can lead to large-scale vegetation mortality like forest die off from epidemic bark beetle outbreaks.However, investigations of climate changed-induced vegetation mortality often neglect the role of biotic agents and tree defense, i.e. secondary metabolism, and thus cannot provide mechanistic relationships for predictive tools like vegetation simulation models. Theories on the linkages between environmental cues and the plants’ primary and secondary metabolism have been developed decades ago but still lack empirical support, and likely do not hold under rapid environmental change. Such gaps lead to substantial incertitude about the fate of the Earth’s future vegetation.The suggested project targets three important knowledge gaps of plant defense responses to ongoing environmental change: 1) how does climate change influence patterns of tree defense globally, in particular during drought and across different species; 2) how do different levels of defense influence the development and the life cycle of an important forest pest, the European spruce bark beetle as well as its associated fungus and 3) use information derived from 2 to improve predictions of bark beetle disturbance in central European forests. This project is challenging but highly promising as it builds not only on integrative transdisciplinary research that combines ecological field manipulations, physiological analysis and biochemical assays, but also capitalizes on transcontinental collaborations spanning a large variety of species and several biomes.