Tropical forest root systems key to understanding carbon stock change

International research led by Colorado State University suggests that studying root function in tropical forests could improve predictions of climate change.  

In a study published Feb. 28 in New Phytologist, an international group of scientists called TropiRoot, led by CSU Associate Professor Daniela Cusack, contributed to a better understanding of how carbon storage and belowground dynamics will respond to global change. TropiRoot has been working to provide much needed representation of tropical forests and root function in vegetation models. 

Vegetation models are important tools that help scientists study plant adaptation strategies to changing environmental conditions, including drying, warming and elevated carbon dioxide levels. Historically, these models have omitted one of the largest biomasses on Earth: tropical forests.  

TropiRoot studied root functions by synthesizing literature on the subject and measuring roots in tropical ecosystems in Costa Rica, Panama, Puerto Rico and Singapore.  

According to the study, tropical forests contain 30% of global soil carbon, most of which likely originates from root biomass, representing the second highest soil carbon storage rate after permafrost. By acting as carbon banks, tropical forests can help to prevent the most severe effects of climate change, but these banks are at risk as tropical forests experience warming, shifting rainfall patterns, deforestation and relative depletion of soil nutrients due to elevated levels of carbon dioxide in the atmosphere.  

“We are worried about how tropical carbon storage and carbon banks on land will respond to climate change, and to understand overall changes in carbon storage, we have to first understand how tropical roots will respond,” said Cusack, lead author and associate professor in the Department of Ecosystem Science and Sustainability.  

Compared to temperate forests, tropical forests have greater biodiversity, faster-acting processes and seasons based on rainfall rather than temperature. More than 50% of tropical forests are on old and strongly weathered soils, meaning their soils lack essential nutrients like phosphorus, so root systems have been forced to develop more efficient processes for recycling minerals.  

Additionally, tropical root systems have recently been described as growing differently from roots in other ecosystems, with unique combinations of physical traits and symbiosis with fungi and bacteria.  

These unique features, combined with a lack of funding to support tropical forest research, have made tropical forests difficult to study and underrepresented in vegetation and global land-climate models. Better understanding how these aspects are responding to global change could give insights into the future of land-climate feedbacks.    

“Our past work has shown that roots are the main way that carbon gets into the soil in tropical forests, so looking at how these roots function differently than roots in other ecosystems will help us understand how carbon gets transferred into long-term soil banks, which then helps us predict how these forests will respond to and affect climate change,” Cusack said.   

The study has 26 authors, 18 of whom are women, representing researchers from around the world and different tropical regions. Cusack credits the success of the study to the intentional inclusion of diverse perspectives.  

“What we have seen with this collaboration is that we can get so much more done and have a wealth of viewpoints when we cast a wider net across different career stages, countries, ethnicities, cultures, languages and genders,” she said. 

Cusack also is a research associate at the Smithsonian Tropical Research Institute and a research scientist in CSU's Natural Resource Ecology Laboratory.