Foliar limonene uptake scales positively with leaf lipid content: non-emitting species absorb and release monoterpenes

Monoterpenes synthesized and released by emitting vegetation can be taken up by neighboring non-emitting plants, but the uptake capacity of non-emitting species has not been studied extensively. We investigated the foliar uptake potential of the hydrophobic monoterpene limonene in 13 species of contrasting leaf structure and lipid content to determine the structural and chemical controls of monoterpene uptake. Leaf dry mass per unit area (M-A,M-D) varied 6.5-fold, dry to fresh mass ratio (D-F) 2.7-fold, lipid content per dry mass (L-M) 2.5-fold and per unit area (L-A) 4.6-fold across the studied species. Average foliar limonene uptake rate (U-A) from air at saturating limonene partial pressures varied from 0.9 to 6 nmol m(-2) s(-1), and limonene leaf to air partition coefficient (K-FA, ratio of limonene content per dry mass to limonene partial pressure) from 0.7 to 6.8 mu mol kg(-1) Pa-1. U-A and K-FA scaled positively with leaf lipid content, and were independent of D-F, indicating that variation in leaf lipid content was the primary determinant of species differences in monoterpene uptake rate and K-FA. Mass-based limonene uptake rates further suggested that thinner leaves with greater surface area per unit dry mass have higher uptake rates. In addition, limonene lipid to air partition coefficient (K-LA = K-FA/L-M) varied 19-fold, indicating large differences in limonene uptake capacity at common leaf lipid content. We suggest that the significant uptake of hydrophobic monoterpenes when monoterpene ambient air concentration is high and release when the concentration is low should be included in large-scale monoterpene emission models.