Similar to pinene, several monoterpenes can be found in alpha-pinene and alpha-pinene, which are mirror images of each other. Both of these volatile compounds can be released by plants either immediately after biosynthesis or from storage reservoirs in the leaves. In atmospheric modeling, these two chiral or enantiomeric forms are often not considered individually because they have identical physical and chemical properties.
However, a recent study from the Max Planck Institute has shown that these two mirror molecules are released by several processes in the plant and that they respond differently to stress, especially drought. Three months of drought stress in an artificial rainforest
The results come from experiments conducted in an enclosed artificial tropical rainforest within the Biosphere 2 complex in Arizona, which was originally built to create self-sustaining ecosystems. This device allowed a team of scientists from the Max Planck Institute for Chemistry, the University of Freiburg and the University of Arizona to precisely control the chemical and climatic conditions of the forest and measure its responses. The scientific team exposed the forest to moderate and then severe drought for three months.
Joseph Byron, a PhD student on the project from the Max Planck Graduate School, used gas chromatographs to determine the hourly emissions of alpha-pinene, camphene, limonene, terpinene and isoprene. To determine when plants emitted which chiral form, the researchers used isotopically labeled CO2 to track photosynthetic carbon and introduced “heavy” carbon dioxide (13CO2) into the air of the biosphere at specific times.
Using a mass spectrometer attached to the chromatograph, the team could then observe which monoterpenes contained heavy carbon atoms and which did not. This revealed which labeled compounds were produced and released immediately by the ecosystem and which unlabeled species came from storage pools.
Heavy carbon dioxide provides insight into plant metabolism.”To our surprise, many of the mirror molecules behaved differently under drought stress,” comments first author Joseph Byron “So (-) alpha-pinene was labeled, while ( ) alpha-pinene, which we measured at the same time, was not.” This means that the tropical rainforest ecosystem released (-) alpha-pinene directly after synthesis, while the mirror molecule comes from storage reservoirs in the plant.
More drought leads to a diurnal shift in monoterpene emissions
In addition, the researchers found that as the drought progressed, not only were more monoterpenes released, but the emission peak shifted to later in the afternoon and plants released more monoterpenes from storage pools. And there may be a reason for this, suspects project leader and atmospheric scientist Jonathan Williams: “We suspect that the later release of monoterpenes makes it more likely that clouds will form over the forest. The warmer it is during the day, the more vertical air mixing increases, which allows reactive volatiles to reach the upper layers of the air, where they have a better chance of becoming aerosol particles and possibly cloud condensation nuclei.”
Max Planck researcher Williams of Biosphere 2 studies concludes: “To accurately predict ecosystem responses to stress, we should measure and model emissions from chiral molecules separately in the future. This is particularly important for the Amazon rainforest, for which climate models predict more drought.” in the future.” The group leader from the Max Planck Institute for Chemistry in Mainz adds: “I am fascinated by the fact that we can decipher the internal, enzymatically controlled physiological processes of the forest by measuring the composition of the air. This will certainly help us elucidate the effects we have observed in the real rainforest.” Williams’ team also conducted research in the Brazilian rainforest at ATTO’s Amazon Tall Tower Observatory.
