How does European beech smell under drought stress? Volatile responses across genetically diverse backgrounds

European beech (Fagus sylvatica) is widespread and dominant in many central European forests. Increasing drought stress due to climate change has caused severe damage in beech stands across the continent (Geßler et al., 2007; Leuschner, 2020). Volatile organic compounds (VOCs) are key ecological signals during drought, mediating within-plant responses and interactions with other plants and trophic levels (Baldwin, 2010). Understanding VOC responses in European beech is therefore important for future forest management under climate change. However, the volatile profiles of European beech under drought stress remain poorly studied.

In this study, we used 72 four-year-old European beech trees from seven provenances and 12 seed families (same maternal trees), assigning them to drought and control groups in a common garden located in Zurich, Switzerland. Drought-treated trees received no water for a total of 14 days, while the control group remained well watered throughout the experiment. VOCs were sampled at three time points for both groups: before drought, after 7 days of drought treatment, and after 14 days of re-watering. A “push–pull” system was used to actively collect headspace volatiles around each whole tree into Tenax tubes, and samples were analyzed using gas chromatography–mass spectrometry (GC–MS). Features were detected and aligned among samples using MZmine (Heuckeroth et al., 2024), and peak heights were analyzed with linear models and variance partitioning to identify VOC signals related to genetic background and drought stress.

We found that several monoterpenes displayed genetically specific emission patterns under well-watered conditions, reflecting underlying genetic differentiation in VOC physiology. During drought, a large proportion of the variation in VOCs was explained by drought treatment, while the variation attributed to seed family decreased substantially. In particular, monoterpenes and green leaf volatiles indicated strong activation of stress-response pathways. Notably, a subset of drought-induced VOCs remained elevated even after re-watering, suggesting a legacy effect of drought stress. Our results show that drought-related VOC signals can serve as valuable biomarkers for assessing drought stress in European beech, thereby improving our ability to monitor tree health under climate change.