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 chromatography-mass
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.