Monoterpene emissions in relation to foliar photosynthetic and structural variables in Mediterranean evergreen Quercus species
Summary The relationships between foliar photosynthetic variables and monoterpene emission rates ( E ) are reported here for two sclerophylls, Quercus coccifera L. and Q. ilex L., which lack specialized foliar monoterpene‐storage structures. Photosynthesis rates and E were measured within a forest canopy, and in leaves of different exposure in a garrigue ecosystem. Leaf dry mass per unit area (LMA) was used as a proxy of long‐term leaf light availability. Maximum photosynthetic electron transport rate ( J max ), Rubisco carboxylase activity ( V cmax ) and light‐saturated E ( E max ) per unit area increased strongly with increasing LMA. The positive effect of LMA on area‐based E max resulted from an accumulation of enzymes responsible for monoterpenoid synthesis per unit area. Positive relationships were observed between both area‐ and mass‐based E max and J max , but not with photosynthesis rates, suggesting a possible control of terpene synthesis by foliar electron transport rates. Results suggested that monoterpene volatility limitations at low temperatures might also constrain E . Nonspecific storage may explain bursts of monoterpene emission on warm days following cold days, and monoterpene emission in low quantities during night. Although the correlations between E max and J max do not necessarily give mechanistic insight into the physiology of monoterpene emission, they provide a basis for scaling up leaf emissions to a canopy level. However, both the leaf‐to‐leaf differences in monoterpene synthase activities, and monoterpene storage may perplex the relations between the electron transport rates and E .