“More carbon dioxide is good for plants” is a common statement used to justify rising carbon dioxide levels as a Good Thing. But plants are not simple growing machines, and balance complex chemistry in the form of secondary metabolites. These are the chemicals plants create to fight off infections, attract pollinators, or signal to mycorrhizal fungi. New research by Tao Li and colleagues shows that, due to these secondary metabolites, increasing carbon dioxide concentration has a bit more of a complex relationship with plants than some people think.
The study covers the chemicals plants make that aren’t just new bits of plant. These chemicals regulate how a plant interacts with other organisms in its environment. Scents for flowers are a secondary metabolite. Losing the ability to make them isn’t going to immediately kill a plant. However, even if more carbon dioxide makes a plant bigger, this is doesn’t help in the long-term if its ability to attract pollinators is compromised.
Li and colleagues looked at Calluna vulgaris, common heather. “We measured VOC [volatile organic compound] emissions of C. vulgaris branches in a temperate heathland and quantified the accumulation of phenolics and condensed tannins in different plant organs (leaves, stems and flowers) over two growing seasons after 6 years of exposure to realistic climatic manipulations,” write the authors.
“We hypothesized that when acting independently, both elevated CO2 and temperature will enhance phenolic production and VOC emissions, probably by stimulating carbon assimilation and growth, and boosting activities of enzymes associated with compound synthesis. We expected drought stress to reduce phenolic production and VOC emission, via suppression of plant photosynthesis. When acting in concert, elevated CO2 and temperature are expected to show synergistic responses except with drought. While CO2 would be likely to, at least partially, mitigate drought effects, warming could aggravate these due to enhanced soil evaporation and plant transpiration.”
