Digi-Nose Part 1: Characterization of volatile organic compounds (VOCs) emitted by European spruce trees under stress

In recent years, factors such as heat, drought, storms, and excessive rainfall, which can largely be attributed to man-made climate change, have weakened the European spruce population. Trees, especially during climate-related stress, communicate with each other by exchanging nutrients through their root system or by emitting volatile organic compounds (VOCs) via their needles, leaves, and bark. Some of these VOCs are attractive to pests, such as the bark beetle, as they indicate weakened defense mechanisms. Detection of these VOCs can be attained through gas chromatography-mass spectrometry analysis. Subsequently, a digital "nose" is planned to be developed, utilizing a combination of gas sensors, artificial intelligence, and image recognition to detect vulnerable trees early on. To achieve this, experimental trees were subjected to controlled conditions in a laboratory to simulate various stress situations, such as drought or waterlogging. Pre-filtered ambient air was drawn through ORBO32 sorbent tubes in the sampling set-up, eluted with petroleum ether, and then analyzed using gas chromatographymass spectrometry (GC-MS). Peak areas of volatile organic compounds were statistically evaluated and compared. The findings suggested that stressed spruce trees emitted higher quantities of volatile organic substances. Particularly noteworthy were alcohols, terpenes, alkanes and alkenes. This work is part of the development of a digital nose to detect tree stress funded by the Austrian Ministry for Agriculture, Forestry, Regions and Water Management.