Daber, L. E. | Search bioRxiv

bioRxiv2025

Chiral monoterpene dynamics of shoots and roots of Norway spruce in response to drought

Although chiral monoterpenes emitted by plants above- and belowground shape the chemical landscape of many ecosystems, their biosynthesis and emissions, especially in response to drought, are poorly understood. We imposed a 6-week drought on two-year old, potted saplings of Norway spruce and analysed chiral monoterpene emissions and tissue concentrations from needles and roots. Isotopically labelled pyruvate was used to compare tissue-specific contributions of de novo synthesis to chiral monoterpene concentrations. While de novo synthesis of (-)--pinene and both enantiomers of limonene was apparent in needle emissions, no label was incorporated in roots. Drought reduced chiral monoterpene emissions to 30% of control levels, but increased needle and root tissue concentrations by 150 and 230%, respectively. Aboveground monoterpene concentrations were dominated by (-)-limonene, whereas belowground concentrations mainly consisted of the (-)-enantiomers of -pinene, {beta}-pinene, {beta}-phellandrene and camphene. Chiral composition in needles shifted in response to drought but remained stable in roots. We conclude that chiral monoterpene composition is tissue-specific and likely related to tissue-specific functioning. Instead of being passively emitted from storage pools, our results suggest active control mechanisms regulating chiral monoterpene emissions under drought conditions. Our findings imply important ramifications for understanding the regulation of emissions in relation to storage pools and plant-environmental interactions. Summary StatementEmissions of chiral monoterpenes and their composition is tissue-specific and regulated independent from storage pools in Picea abies. Chiral monoterpene ratios shift aboveground in response to drought, but are not affected belowground.

plant biology↗

bioRxiv2022

Leaf-level metabolic changes in response to drought affect daytime CO2 emission and isoprenoid synthesis

In the near future, climate change will cause enhanced frequency and/or severity in terrestrial ecosystems, including tropical forests. Drought responses by tropical trees may affect their carbon use, including production of volatile organic compounds (VOCs), with unpredictable implications for carbon cycling and atmospheric chemistry. It remains unclear how metabolic adjustments by mature tropical trees in response to drought will affect their carbon fluxes associated with daytime CO2 production and VOC emission. To address this gap, we used position-specific 13C-pyruvate labeling to investigate leaf CO2 and VOC fluxes from four tropical species before and during a controlled drought in the enclosed rainforest of Biosphere 2. Overall, plants that were more sensitive to drought had greater reductions in daytime CO2 production. Although daytime CO2 production was always dominated by non-mitochondrial processes, the relative contribution of CO2 from the tricarboxylic acid cycle tended to increase under drought. A notable exception was the legume tree Clitoria fairchildiana, which had less anabolic CO2 production than the other species even under pre-drought conditions, perhaps due to more efficient refixation of CO2 and anaplerotic use for amino acid synthesis. C. fairchildiana was also the only species to allocate detectable amounts of 13C label to VOCs, and was a major source of VOCs in the Biosphere 2 forest. In C. fairchildiana leaves, our data indicate that intermediates from the mevalonic acid pathway are used to produce the volatile monoterpene trans-{beta}-ocimene, but not isoprene. This apparent crosstalk between the mevalonic acid and methylerythritol phosphate pathways for monoterpene synthesis declined with drought. Finally, although trans-{beta}-ocimene emissions increased under drought, it was increasingly sourced from stored intermediates and not de novo synthesis. Unique metabolic responses of legumes may play a disproportionate role in the overall changes in daytime CO2 and VOC fluxes in tropical forests experiencing drought.

plant biology↗