The variability of terpenes in conifers under developmental and environmental stimuli

•Differences in terpene amounts in Pinus, Picea and Abies.•Stress stimuli can affect terpene synthesis and emission in plants.•Terpene concentration in conifers can vary depending on many factors.•Terpene profile can be different within species. Plants produce a large variety of natural products. Terpenes seem to be the largest and the most important group of secondary metabolites in conifer trees. They protect the plant from invading pathogens and herbivores by representing constitutive or induced defense mechanisms. Moreover, antioxidant properties of some terpenes have also been shown, suggesting their role in overcoming oxidative stress provoked by internal and external stimuli. The abiotic and biotic stress factors such as drought, temperature fluctuations, air and soil pollution or pathogen attack rearrange the biosynthesis and emission of terpenes, however the response may depend on the stressor type and stress intensity. Although the general composition of terpenes is characteristic for each species, it has been shown that it can even differ between two individual trees. Reaching for the available literature data, the review is focused on systematizing the observed changes in terpene quantity and quality in the three most important forest-forming conifer genera of European temperate climate zone – pine (Pinus sp.), spruce (Picea sp.) and fir (Abies sp.). Moreover, in view of progressive climate change, the study emphasize a complex function of these interesting compounds in trees including interplant signaling in forest communities.