RESEARCH ARTICLE u a

Monoterpenes represent a prominent group of volatile or-ganic compounds (VOC), with an estimated mean global emission of 117 Tg C yr-1 into the atmosphere [1] and a fast photochemical turnover [2]. Especially coniferous plants are considered to be main producers of monoter-penes, e.g. for thermotolerance or for communication between plants or the interaction between plants and insects [3-5]. Monoterpenes also enter the soil by the rhizosphere or by rotten leafs [6], where they inhibit growth of microorganisms as well as of seedlings [7-9], but also stimulate the bacterial activity detectable in higher biomass and CO2-production [5,10,11]. By defin-ition, monoterpenes possess a carbon skeleton based on two C5 units originating from isopentenyl pyrophos-phate (IPP), which is synthesized via the mevalonate * Correspondence