How a tree's chemical defense could spark future medical breakthroughs

Trees in tropical forests, which thrive in some of the most biologically rich ecosystems on Earth, are known for their staggering diversity. But a new study shows that the chemical diversity hidden within those trees may be just as impressive – and just as important.

Trees don’t just differ in size, shape, or leaf color. Each one brings its own chemical strategy to the forest floor, using unique compounds to fend off pests and diseases. Researchers from Washington University in St. Louis and the Missouri Botanical Garden set out to learn more about this chemical variation.

The findings shed light on the ecological forces that make tropical forests so rich in diversity. Furthermore, the research offers a reminder that these forests aren’t just beautiful – they may also hold the key to future medicines.

What trees reveal through their leaves

The research team analyzed leaves from 470 tree species, gathered as part of the Madidi Project – a large-scale survey in Bolivia’s Andes Mountains.

By focusing on trees from both low and high elevations, the team was able to compare how chemical compounds shift across climates. Using mass spectrometry, the experts identified over 20,000 unique chemical compounds in the leaf samples.

“It’s an amazing level of chemical diversity,” said Jonathan Myers, a professor of biology at Washington University.

Many of these compounds help plants survive in harsh conditions – especially in the warm, humid, and insect-rich tropics.

Over one-third of the compounds were terpenoids, chemicals that plants use to ward off threats like insects and pathogens. Terpenoids are already known for their medicinal uses. Some can fight cancer, reduce inflammation, and kill harmful bacteria and viruses.

Another quarter of the compounds were alkaloids, a class of chemicals found in many well-known medicines, including painkillers and antimalarial drugs.

Diversity as a defense strategy

As the researchers moved up in elevation, the diversity of both tree species and their chemical compounds decreased. In plots at 4,000 feet, they found nearly 140 species of trees per hectare. At 11,000 feet, there were fewer than 20 species.

This shift also impacted chemical diversity. Trees at higher elevations, even from different species, tended to rely on similar types of chemical compound defenses. But in the highly competitive lowland forests, chemical originality was the norm.

“If a tree has the same chemistry as a neighbor, it could be vulnerable to the same herbivores and pathogens,” said Myers.

In contrast, if each tree species uses different compounds for protection, it becomes harder for insects and diseases to adapt to all of them at once.

Building a global tree chemical library

The findings support efforts to study and protect tropical forests – not only for their biological value but also for their chemical potential.

The team contributed their data to a growing global database of tree and plant compounds. “With such a database, researchers could look for unique chemicals that could have real value for society,” said Myers.

The study also raises larger questions about how plant chemistry varies across regions. Myers is involved in a separate National Science Foundation project comparing tree communities from the Amazon, Canada, and the forests near Tyson Research Center in Missouri.

While the local forests can’t match tropical diversity, they are still richer in species and chemicals than the conifer-heavy forests of the north.

Global patterns of plant diversity

What drives this pattern of diversity? Climate might be a major factor. Warmer, wetter, and more stable environments allow more plant species to thrive – each with its own set of defenses.

This chemical arms race may help explain why tropical regions are rich in both species and compounds. According to Professor Myers, it could be another clue to understanding global patterns of plant diversity.

The take-home message is clear: Every tree in the forest is not only a life form but also a tiny chemistry lab. And the more species we protect, the more likely we are to preserve the invisible tools they use to survive – tools that could someday help us too.

The full study was published in the journal Ecology.

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