Terpenoid Emissions of Two Mediterranean Woody Species in Response to Drought Stress

Abstract

Drought is a major environmental constrain affecting plant performance and survival, particularly in Mediterranean ecosystems. Terpenoids may play a protective role under these conditions, however, observations of drought effects on plant terpenoid emissions are controversial ranging from decreased emissions to unaffected or increased release of terpenoids. In the present study we investigated terpenoid emissions of cork oak (Quercus suber) and gum rockrose (Cistus ladanifer) in response to summer drought stress in 2017. Pre-dawn leaf water potential (ΨPD) decreased from -0.64 to -1.72 MPa in Q. suber and from -1.69 to -4.05 MPa in C. ladanifer, indicating a transition from mild to severe drought along summer. Total terpenoid emissions decreased with drought, but differed significantly between species (p < 0.001) and in response to ΨPD, air temperature and assimilation rates. C. ladanifer emitted a large variety of >75 compounds comprising monoterpenes, sesquiterpenes and even diterpenes, which strongly decreased from 1.37 ± 0.23 μg g-1h-1 to 0.40 ± 0.08 μg g-1h-1 (p < 0.001) in response to drought. Total emission rates were positively correlated to air temperature (p < 0.001). C. ladanifer behavior points toward terpenoid leaf storage depletion and reduced substrate availability for terpenoid synthesis with increasing drought, most likely accelerated by high air temperatures. Q. suber emitted mainly monoterpenes and emissions declined significantly from June (0.50 ± 0.08 μg g-1h-1) to August (0.29 ± 0.02 μg g-1h-1) (p < 0.01). Emission rates were weakly correlated with net assimilation rates (R2 = 0.19, p < 0.001), but did not respond strongly to ΨPD and air temperature. Early onset of drought in 2017 most likely reduced plant metabolism in Q. suber, resulting in diminished, but stable terpenoid fluxes. Calculation of standard emission factors (at 30°C) revealed contrasting emission patterns of decreasing, unaffected, or increasing fluxes of single terpenoid compounds. Unaffected or drought-enhanced emissions of compounds such as α-pinene, camphene or manoyl oxide may point toward a specific role of these terpenoids in abiotic stress adaptation. In conclusion, these results suggest a strong negative, but species- and compound-specific effect of severe drought on terpenoid fluxes in Mediterranean ecosystems.

Biogenic isoprenoid emissions under drought stress: Different responses for isoprene and terpenes

“…The emission of the monoterpene -pinene is declining for Cistus albidus (S3), stays put for Rosmarinus officialis (S6) and enhances for Pinus halepensis and Quercus coccifera. Similar observations can be made for SQT emissions with SM values near the PWP: -cadinene emissions increase with decreasing SM, while -zingiberene emission decline for Rosmarinus officialis Haberstroh et al (2018). monitored decreasing emission fluxes for all the individual chemical SQT structures for Cistus ladanifer and Quercus robur in a very narrow SM range (SWA% = ca.…”

“…Depending on the specific tree species some molecular structures of terpenes e.g. the more reactive ones like -pinene and -myrcene (Haberstroh et al, 2018;Ormeno et al, 2007) and farnesene (Duhl et al, 2008;Haberstroh et al,2018) display an elevated relative terpene flux contribution at lower soil moisture (Figs. S3-S8), indicating a defensive strategy of plants against oxidative stress at lower soil water concentrations, thus warmer conditions and in total critical for the plants survival.…”

“…CC BY 4.0 License. method described by Haberstroh et al (2018). For this purpose, BVOCs emitted from beech leaves were collected during daytime using air-sampling tubes filled with Tenax (Gerstel).…”

“…CC BY 4.0 License.Cistus ladanifer(Haberstroh et al, 2018) and Rosmarinus officialis(Ormeno et al, 2007)) display a second maximum close to PWP not only for some of the MT (Cistus ladanifer: d-limonene, myrcene and trans--ocimene(Haberstroh et al, 2018); Rosmarinus off. : -pinene and -myrcene(Ormeno et al, 2007)) but also for some of the SQT (Cistus ladanifer: -cubebene, -farnesene, ent-16-kaurene and -chamigrene(Haberstroh et al, 2018); Rosmarinus off. : -cardinene and -zingiberene(Ormeno et al, 2007),Fig.…”

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

“…We tested these hypotheses in two different species, Quercus suber L. and Cistus ladanifer L., known to emit a blend of different BVOCs (Haberstroh et al, 2018). Q. suber is an evergreen Mediterranean oak species well adapted to the naturally occurring summer drought by accessing deep-water resources, hydraulic lift and stomatal control to avoid water losses (David et al, 2007;Grant et al, 2010).…”