BVOC emissions across the seasons in the Amazon

If you ever walked through nature and have taken a deep breath, you already know BVOCs. Biogenic volatile organic compounds, short BVOCs, are emitted mainly by plants. BVOCs are incredibly diverse, but the most abundant ones are called isoprenoids. They are represented by isoprene (a short carbon chain), monoterpenes (a carbon chain twice as long) and sesquiterpenes (three times as long). Out of all plants, trees are the most important emitters. And tropical trees alone contribute around 80% to the global emissions of isoprenoids.

BVOCs, and isoprenoids, in particular, serve many functions, and they are responsible for the typical plant scents. But plants also use BVOCs to send messages to other plants or even insects like pollinators or predators of herbivores. In addition, plants utilize those compounds to protect plant cells, and they react with other chemicals in the atmosphere. Through this process of emitting reactive gases plants actively contribute to cloud formation. Put very simply, they make their own rain.

BVOC emissions in the Amazon have been studied for decades, and scientists have already learned a lot about them. But we still don’t fully understand when and under what conditions tree species or even individual trees emit more or fewer isoprenoids. Specifically, we lack detailed knowledge on the emission capacity of trees in response to their environment, such as weather and climate conditions, the characteristics of their environment, etc. In addition, most studies have focused on isoprene. To address this, Eliane Gomes Alves and her colleagues measured the emission capacities of isoprene, monoterpenes and sesquiterpenes on trees. Specifically, they looked at three tree species that are hyperdominant in the Amazon. They did this across seasons and environmental gradients in the vicinity of ATTO.

Eliane Gomes Alves measures tree emissions of isoprenoids in the forest canopy.
Eliane Gomes Alves measures tree emissions of isoprenoids in the forest canopy. © Tyeen Taylor

The team’s most important finding was that isoprene emissions declined during the shift from wet season to dry season. At the same time, emissions increased for those heavier monoterpenes and sesquiterpenes. In fact, one of the tree species the scientists looked at emitted sesquiterpenes only in the dry season, and increasingly so in the upland forests. Here, the groundwater table is much deeper than in the white-sand campina region. This means that is harder for the plants to access this water.

Variation in emission rates of the three isoprenoid classes between seasons (wet, dry) and habitats (WS = white sand, AR = ancient river terrace, Up = upland), grouped by plant species. Letters indicate significant differences in emission rates between habitats, within species and seasons. Stars indicate significant differences between seasons, within habitats and species. Figure from Gomes Alves et al. (2022).

Eliane Gomes-Alves and her team concluded that trees shift towards emitting more monoterpenes and sesquiterpenes in response to abiotic stress, such as heat and drought. This means that it is crucial for future studies to measure monoterpenes and sesquiterpenes in addition to isoprene. As climate shifts towards longer, hotter and drier dry seasons in the Amazon, these emissions will become even more relevant. Understanding what plants emit them under what conditions, and how those compounds affect cloud formation and precipitation will improve our understanding of how the Amazon rainforest reacts to climate change.

Eliane Gomes Alves et al. published the paper “Seasonal shifts in isoprenoid emission composition from three hyperdominant tree species in central Amazonia” Open Access in the journal Plant Biology.

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