Fig. 3: Emissions of α-pinene enantiomers are not equally enriched in ¹³C.

Carbon sources (de novo or storage) for monoterpene emissions were clearly separated by ε¹³C values of monoterpenes and their enantiomers after ¹³C-enriched CO₂ was added during one morning in pre-drought (1st ¹³CO₂) and severe drought (2nd ¹³CO₂) phases. ¹³CO₂ gas was introduced into the atmosphere so that plants taking up CO₂ and directly producing immediate monoterpene emissions (de novo) would produce emissions enriched in ¹³C. Therefore, emissions that did not become enriched in ¹³C came from storage pools. a, Enrichment of chiral monoterpenes. b, Enrichment of non-chiral monoterpenes. Grey shading represents the standard deviation of the ε¹³C values of the compounds in ambient air when there is no ¹³CO₂ pulse. The black line through the grey boxes represents the mean. The box plots present the median and 25th and 75th percentiles. The small squares represent the mean and the whiskers represent the maximum and minimum acquired data points that are not as considered outliers. Significantly ¹³C-enriched values are indicated by the asterisk (*) above the box (that is, results are significant if P ≤ 0.05). n values are given in Extended Data Table 3.