Smithsonian Scientists Discover Tropical
Tree Microbiome in Panama
STRI Panama

More is known about the bacteria in human belly buttons than the bacteria on tropical tree leaves. A new study by STRI scientists and colleagues explored the leaf microbiome and discovered that even a tiny leaf sample can be home tom 400 different kinds of bacteria. Illustration by Jorge Alemán.

Human skin and gut microbes influence processes from digestion to disease resistance. Despite the fact that tropical forests are the most biodiverse terrestrial ecosystems on the planet, more is known about belly-button bacteria than bacteria on trees in the tropics. Smithsonian scientists and colleagues working on Panama’s Barro Colorado Island discovered that small leaf samples from a single tree were home to more than 400 different kinds of bacteria. The combined sample from 57 tree species contained more than 7,000 different kinds.

Bacteria in tropical forests may also play a vital role, protecting leaves against pathogens and even affecting the ability of forests to respond to climate change.

“Just as people are realizing that microbes carried by humans can have an influence on a person’s health —positive or negative— we hope to discover what bacteria on tree leaves can tell us about the health of a forest,” said S. Joseph Wright, a Smithsonian scientist and co-author of the new study published in Proceedings of the National Academy of Sciences.

In contrast to a previous study of bacteria on leaves in a temperate forest where different leaves had different bacteria, there was a core group of species of common bacteria present on leaves of nearly all of the species sampled in Panama. Just as on human skin, many of the bacteria on tropical tree leaves were Actinobacteria and Proteobacteria.

The researchers, from the Smithsonian Tropical Research Institute, University of Quebec, University of Arizona, University of Oregon, University of California—Los Angeles and Santa Fe Institute, also looked for relationships between the composition of bacterial communities on leaves and other plant characteristics.

Many bacteria were associated with certain functional traits such as leaf thickness, wood density or leaf nitrogen content, characteristics that directly impact tree growth, survival and reproduction.

The relationships between many of the bacteria and tree species were ancient, going back to the ancestors of both the bacteria and the trees as they evolved in tandem.

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