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How Herbivory Affects Nitrogen Fixation in Tropical Forests

By preferentially munching on nitrogen-fixing trees, could leaf eaters limit the ability of tropical forests to grow and store carbon?

Lead Scientist(s): Dr. Sarah Batterman

One promising tool in the quest to fix our planet’s climate is to reforest tropical lands that have been degraded, letting the trees soak up and store some of the atmosphere’s extra carbon. However, a tropical forest’s ability to grow back depends on nitrogen fixation — the process of pulling nitrogen out of the air and changing it into a form that trees can use to make chlorophyll, proteins, and other important materials for photosynthesis and carbon capture.

Our group works to understand the factors that constrain nitrogen fixation, and we think that herbivory may be a significant and overlooked factor.

Insect herbivory on the leaves of a tropical nitrogen-fixing Inga tree species. Credit: Sarah Batterman

Scientists have previously focused on how abiotic factors such as phosphorus scarcity or temperature limit nitrogen fixation. However, our findings indicate that animals may be very attracted to nitrogen-fixing trees, which have high nitrogen content in their leaf tissue. We found that nitrogen-fixing trees in the tropics undergo 26% more herbivory than non-fixers. This high herbivory may reduce the amount of new nitrogen coming into tropical forests and hinder tropical forests’ ability to serve as a carbon sink.

Understanding herbivory’s constraints on nitrogen fixation will be paramount to managing tropical forests and projecting the global carbon budget. However, many questions remain. To build on our previous work, we plan to explore the following:

  • How widespread are herbivory constraints on symbiotic nitrogen-fixing trees?
  • What are herbivory’s consequences for nitrogen fixation and ultimately for the tropical carbon sink?
  • How does herbivory affect nitrogen fixation under global change?

By resolving these dynamics, we can refine climate change projections and improve reforestation strategies — for example, by planting additional nitrogen-fixing trees to compensate for losses due to herbivory.


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