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Amazon trees super-diverse in chemicals

Rainforest canopy in the Peruvian Amazon. Photo by Rhett A. Butler

In the Western Amazon—arguably the world’s most biodiverse region—scientists have found that not only is the forest super-rich in species, but also in chemicals. Climbing into the canopy of thousands of trees across 19 different forests in the region—from the lowland Amazon to high Andean cloud forests—the researchers sampled chemical signatures from canopy leaves and were surprised by the levels of diversity uncovered.

“We discovered that this incredible region is a patchwork mosaic of trees with chemical signatures organized into communities to maximize their growth potential given their local soils and elevation—two geological factors they must negotiate as living organisms,” said lead author Greg Asner with the Carnegie Institution for Science. “Within these communities, the trees have evolved chemical portfolios that are different from one another, maybe to help each species take a place in its community—what we call a niche.”

Trees use a wide swathe of chemicals to capture light, synthesize and store carbon, develop foliage, and even defend themselves. The study, published today in the Proceedings of the National Academy of Sciences (PNAS), found that the suite of chemicals used by canopy trees often depended on elevation, climate, and soil.

Carnegie botanist Felipe Sinca is high in an Amazonian tree canopy. Photo by Greg Asner.

Carnegie botanist Felipe Sinca is high in an Amazonian tree canopy. Photo by Greg Asner.

“Variation in this leaf chemical portfolio expresses multiple strategies evolved in plants to maximize fitness through growth and longevity in any given environment,” the scientists write.

Asner and his team took samples from an astounding 2,420 tree species, more than double the number of species found in the U.S. and Canada combined. In order to obtain these precious samples the team climbed into the canopy of 3,560 trees; the scientists than spent five years in lab work analyzing the chemicals found in the leaves. The massive study is the first foray of Carnegie’s Spectranomics project, which seeks to study the link between biological diversity and ecological function.

But the Amazon is currently facing a barrage of unprecedented threats, including clearing for agriculture, livestock, and logging; illegal mining and poaching; and worsening climate change. The scientists write that their finding may help uncover how tree species will fare in the future, especially in a warmer world.

“A clearer sense of the diversity and organization of canopy chemical traits may help us to forecast winners and losers
within specific communities in response to climate change. Predicted warmer temperatures may favor species that have evolved to invest more in light capture and growth chemicals.”

But the findings go beyond helping scientists to predict future survival, they also act as a warning of what’s at stake, according to Asner.

“I view the results as a wake-up call that we are shaking up a special tropical region full of chemically unique forest communities that have undergone millions of years of evolution and biogeographic construction.”


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