Tree leaves produce a variety of chemical compounds with the carbon they obtain from photosynthesis. Some of them evaporate very easily and are released into the air. Isoprene and Monoterpenes dominate the emissions of these so-called Biogenic Volatile Organic Compounds (BVOCs). Although invisible and sometimes even odorless, BVOCs play important roles. They help plants cope with stress, allow them to “communicate” with other organisms, and influence air quality and climate through chemical reactions in the atmosphere.
Tropical forests are especially important because they release more BVOCs than any other ecosystem on Earth. However, not every tree produces these compounds. We still don’t fully understand why some trees do and others do not, or why some release more than others. Such puzzling patterns greatly hinder the ability of models to predict emissions, especially from the extremely biodiverse Amazon rainforest.
Therefore, Michelle Robin and her colleagues wanted to find out whether emissions of isoprene and monoterpenes are linked to broader differences in how trees grow and use resources – known as “carbon economics strategies”. Some trees adopt a “fast” strategy. They invest all of their resources to produce leaves and stems that will allow them to grow quickly, but at the cost of being resistant. Others follow a “slow” strategy, growing more conservatively and investing in longer-lasting leaves and stems. Isoprene is a compound that needs little carbon and plants release it right after its production. So the team hypothesized that faster trees would favor its production. On the other hand, monoterpenes need a bit more carbon and plants can store it. So they hypothesized that slower trees would favor their production.
Robin and her colleagues studied trees distributed throughout three different environments in the ATTO site: upland terra firme forest, white sand campina forest, and non-flooded river terrace forest. They measured several characteristics of their leaves and stems to help determine which carbon economics strategies they followed. Then, they tested how their strategies varied with the presence and amount of isoprene and monoterpene emissions.
© Dr. Vinícius de Souza
They found that emissions were indeed linked to carbon economics strategies but opposite to how they expected. Plants that grew faster emitted higher amounts of monoterpenes. Plants with slower, more conservative strategies, on the other hand, were more likely to emit isoprene and tended to release it in greater amounts.
Their results indicate that the plants’ strategies can be used to help better predict which and how much of these BVOCs trees in the Amazon rainforest emit, and how this can impact local and regional air chemistry and climate. In addition to that, the study also gives insight into how trees may respond to stress depending on whether and what compounds they emit, and how much carbon they are releasing into the atmosphere via these emissions. This is especially important in tropical forests, where plant diversity is extremely high and current prediction models tend to oversimplify differences between trees and species.
Robin et al. published the study “Leaf isoprene and monoterpene emissions vary with fast-slow carbon economics strategies in central Amazon woody species” in the journal Plant Methods.
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