Volatile diterpene emission by two Mediterranean Cistaceae shrubs

Abstract

Mediterranean vegetation emits a wide range of biogenic volatile organic compounds (BVOCs) among which isoprenoids present quantitatively the most important compound class. Here, we investigated the isoprenoid emission from two Mediterranean Cistaceae shrubs, Halimium halimifolium and Cistus ladanifer, under controlled and natural conditions, respectively. For the first time, diurnal emission patterns of the diterpene kaurene were detected in real-time by Proton-Transfer-Reaction-Time-of-Flight-Mass-Spectrometer. Kaurene emissions were strongly variable among H. halimifolium plants, ranging from 0.01 ± 0.003 to 0.06 ± 0.01 nmol m−2 s−1 in low and high emitting individuals, respectively. They were in the same order of magnitude as monoterpene (0.01 ± 0.01 to 0.11 ± 0.04 nmol m−2 s−1) and sesquiterpene (0.01 ± 0.01 to 0.52 nmol m−2 s−1) emission rates. Comparable range and variability was found for C. ladanifer under natural conditions. Labelling with 13C-pyruvate suggested that emitted kaurene was not derived from de novo biosynthesis. The high kaurene content in leaves, the weak relationship with ecophysiological parameters and the tendency of higher emissions with increasing temperatures in the field indicate an emission from storage pools. This study highlights significant emissions of kaurene from two Mediterranean shrub species, indicating that the release of diterpenes into the atmosphere should probably deserve more attention in the future.

Natural Carbon Isotope Composition Distinguishes Compound Groups of Biogenic Volatile Organic Compounds (BVOC) in Two Mediterranean Woody Species

“…Q. suber does not possess specialized storage structures for BVOCs (Loreto et al, 1996) and can, per se, only emit de novo produced BVOCs. Several studies also indicate that BVOC storing plants, such as C. ladanifer, are also able to emit substantial amounts of BVOCs from de novo production (Lluisà et al, 2010;Yáñez-Serrano et al, 2018). Hence, the changes of the δ 13 C-values of BVOCs over time support our first hypothesis that changing environmental conditions evoke changes in the FIGURE 5 | Suggested scheme for different metabolic pathways for selected terpenoids and aromatics.…”

“…In addition, we investigated two species, which are known to possess dissimilar emission patterns (Haberstroh et al, 2018) and different reactions to changing environmental conditions (Caldeira et al, 2015). Moreover, single plant individuals of the same species can have a very distinct fingerprint regarding the composition and amplitude of their emissions, even at controlled environmental conditions (Loreto et al, 2009;Yáñez-Serrano et al, 2018). Nevertheless, both species and all individuals reacted similar in their photosynthetic discrimination to decreasing water availability, which reflected synonymously the carbon isotope ratio of emitted BVOCs.…”

“…C. ladanifer, on the other hand, stores substantial amounts of BVOCs in secretory trichomes (Gülz et al, 1996). Emissions include monoterpenoids, sesquiterpenoids and even diterpenoids in measurable amounts (Pio et al, 1993;Haberstroh et al, 2018;Yáñez-Serrano et al, 2018).…”

Real-time carbon allocation into biogenic volatile organic compounds (BVOCs) and respiratory carbon dioxide (CO2) traced by PTR-TOF-MS, 13CO2 laser spectroscopy and 13C-pyruvate labelling

“…Moreover, specific compounds such as methyl acetate or kaurene emissions by our H . halimifolium plants were validated in previous studies by TD-GC-MS measurements and calibration standards [ 22 , 30 ].…”

“…We aimed at analyzing the trace gas emissions of a Mediterranean shrub Halimium halimifolium under standardized environmental conditions. On the one hand, Mediterranean shrubs from the Cistaceae family possess a very active secondary metabolism resulting in the biosynthesis of a plethora of plant secondary metabolites including many BVOC [ 21 , 22 ]. On the other hand, H .…”