Chiral monoterpenes reveal forest emission mechanisms and drought responses

Monoterpenes exist in mirror image forms called enantiomers, but their individual formation pathways in plants and ecological functions are poorly understood, as enantiomers are usually measured and modelled together. Here we present enantiomerically separated atmospheric monoterpene and isoprene data from an enclosed tropical rainforest ecosystem without photo-chemistry during a four-month controlled drought and rewetting experiment. Surprisingly, the enantiomers showed distinct diel emission peaks, which responded differently to progressive drying. Isotopic labelling established that vegetation emitted (-)-α-pinene mainly de novo while (+)-α-pinene was emitted from storage pools. As drought stress increased, (-)-α-pinene emis-sions shifted to storage pools, which are released later in the day, favouring cloud formation. The α-pinene enantiomers each correlated better with other monoterpenes than with each other, indicating different enzymatic controls. These results show that enantiomeric distribution is key to understanding the processes driving monoterpene emission from ecosystems and to predict-ing atmospheric feedbacks in response to climate change.

Leaf Monoterpene Emission Limits Photosynthetic Downregulation under Heat Stress in Field-Grown Grapevine

Rising temperature is among the most remarkably stressful phenomena induced by global climate changes with negative impacts on crop productivity and quality. It has been previously shown that volatiles belonging to the isoprenoid family can confer protection against abiotic stresses. In this work, two Vitis vinifera cv. ‘Chardonnay’ clones (SMA130 and INRA809) differing due to a mutation (S272P) of the DXS gene encoding for 1-deoxy-D-xylulose-5-phosphate (the first dedicated enzyme of the 2C-methyl-D-erythritol-4-phosphate (MEP) pathway) and involved in the regulation of isoprenoids biosynthesis were investigated in field trials and laboratory experiments. Leaf monoterpene emission, chlorophyll fluorescence and gas-exchange measurements were assessed over three seasons at different phenological stages and either carried out in in vivo or controlled conditions under contrasting temperatures. A significant (p < 0.001) increase in leaf monoterpene emission was observed in INRA809 when plants were experiencing high temperatures and over two experiments, while no differences were recorded for SMA130. Significant variation was observed for the rate of leaf CO2 assimilation under heat stress, with INRA809 maintaining higher photosynthetic rates and stomatal conductance values than SMA130 (p = 0.003) when leaf temperature increased above 30 °C. At the same time, the maximum photochemical quantum yield of PSII (Fv/Fm) was affected by heat stress in the non-emitting clone (SMA130), while the INRA809 showed a significant resilience of PSII under elevated temperature conditions. Consistent data were recorded between field seasons and temperature treatments in controlled environment conditions, suggesting a strong influence of monoterpene emission on heat tolerance under high temperatures. This work provides further insights on the photoprotective role of isoprenoids in heat-stressed Vitis vinifera, and additional studies should focus on unraveling the mechanisms underlying heat tolerance on the monoterpene-emitter grapevine clone.

Emissions of monoterpenes from new Scots pine foliage: dependency on season, stand age and location and importance for models

Models to predict the emissions of biogenic volatile organic compounds (BVOCs) from terrestrial vegetation largely use standardised emission potentials derived from shoot enclosure measurements of mature foliage and usually assume that the contribution of BVOCs from new conifer needles is minor to negligible. Extensive observations have, however, recently demonstrated that the potential of new Scots pine needles to emit several different BVOCs can be up to about 500 times higher than that of the corresponding mature foliage. Thus, we build on these discoveries and investigate the impact of previously neglecting enhanced emissions from new Scots pine foliage on estimates of monoterpene emissions and new atmospheric aerosol particle formation and their subsequent growth. We show that the importance of considering the enhanced monoterpene emission potential of new Scots pine foliage decreases as a function of season, tree age and latitude, and that new foliage is responsible for the majority of the whole tree's foliage emissions of monoterpenes during spring time, independently of tree age and location. Our results suggest that annual monoterpene emission estimates from Finland would increase with up to ~ 25 % if the emissions from new Scots pine foliage were explicitly considered, with the majority being emitted during spring time where also new particle formation has been observed to occur most frequently. We estimate that our findings can lead to increases in predictions of the formation rates of 2 nm particles during spring time by ~ 75–275 % in northern Finland and by ~ 125–865 % in southern Finland. Likewise, simulated growth rates of 2–3 nm particles would increase by ~ 65–175 % in northern Finland and by ~ 110–520 % in southern Finland if the enhanced emissions of monoterpenes from new Scots pine foliage were explicitly considered. Our findings imply that we need to introduce a more comprehensive treatment of the emissions of BVOCs from new coniferous foliage in biogenic emission models.

Seasonal Changes in Interclone Variation Following Ozone Exposure on Three Major Gene Pools: An Analysis of Cryptomeria Japonica Clones

Recently, there has been a continuous increase in the concentration of tropospheric ozone in urban forests in Japan. Since monoterpenes are precursors to ozone, we need to evaluate the effects of ozone exposure on all tree species that are considered to be sources of monoterpenes. Cryptomeria japonica, which is the most widely planted afforestation tree, is classified into three different gene pools. However, the interclone variation for seasonal changes in the ozone exposure effect has not been evaluated. Thus, free-air ozone enhancement experiments were conducted using three representative clones of C. japonica in the summer and winter. After exposure to twice the ozone concentration in the ambient atmosphere, the effect on the monoterpene emission rate was found to be considerably different among the clones and for the different seasons. The monoterpene emission rate after ozone exposure increased in winter and summer in the native clones (Donden and Yakushima) in the snow area and heavy rain area, respectively. Since monoterpenes are antibacterial substances, each clone adapted sensitivity to stress during each season upon considerable damage. These results suggest that not only differences between tree species but also differences between clones are important for evaluating seasonal variation characteristics after ozone exposure.