Effects of elevated CO2 and temperature on secondary compounds in the needles of Scots pine (Pinus sylvestris L.)

The aim of this study was to evaluate the long-term effects of elevated CO2 concentration (doubling of ambient CO2 concentration) and temperature (2–6°C elevation) on the concentration and content of secondary compounds in the needles of Scots pine (Pinus sylvestris L.) saplings grown in closed-top environmental chambers. The chamber treatments included (1) ambient temperature and CO2, (2) ambient temperature and elevated CO2, (3) elevated temperature and ambient CO2, and (4) elevated temperature and elevated CO2. The needle sampling and analyses of monoterpenes, HPLC-phenolics and condensed tannins in current- and 1-year-old needles were made in two consecutive years. The results showed that the effects of elevation of CO2 and temperature were greatest on the monoterpene concentration in the needles while the concentration of HPLC-phenolics remained almost unaffected by the changed growing conditions. Most of the observed decrease in monoterpene concentration was caused by the CO2 enrichment while the effect of elevated temperature alone was not as significant. The accumulation of condensed tannins tended to increase due to the elevation of CO2 alone compensating the reduced carbon allocation to monoterpenes. Overall, the responses of the concentrations of secondary compounds to the elevation of CO2 and temperature are variable and depend strongly on the properties and characteristics of each compound as well as on the interrelation between the production of these compounds and the primary production of trees.