Soil “Breathes Out” More CO2 During Warmer Temperatures When Near Large Trees

Tree presence impacts how soils respond to temperature change in coastal forest.

The Science

Soil respiration—the flow of carbon dioxide (CO2) from the soil surface to the atmosphere—is one of the largest carbon fluxes in the terrestrial biosphere. A recent U.S. Department of Energy (DOE)–funded study, conducted in a coastal deciduous forest, investigated the role of tree presence and temperature on soil respiration. Results found soils closer to trees were more sensitive to temperature changes and had higher CO2 emissions. These findings suggest that heterotrophs, such as trees, are more sensitive to temperature changes than autotrophs, like microbes.

The Impact

Monitoring greenhouse gas exchange between trees and soil sheds light on the resilience of coastal soil systems during changing environmental conditions. Soil respiration is influenced by soil temperature, moisture, and the presence of plant roots. Disturbances such as sea level rise, increased extreme weather events, and climate change can have lasting impacts on the global carbon cycle and coastal forest ecosystems. Specifically, these findings could have implications on soil functions and interactions at the ecosystem -scale, helping inform large-scale climate models.

Summary

Led by Stephanie Pennington and Ben Bond-Lamberty of Pacific Northwest National Laboratory, the research team examined soil respiration in a Maryland coastal forest ecosystem over one year. The goal was to determine if and how soil CO2 emissions varied based on proximity to trees, during different seasons and during drier conditions. Soil respiration increased under a number of conditions, including in the presence of trees, during the growing season versus the dormant season, and with greater moisture. The team measured CO2 soil respiration, along with size and species of each tree within a 15-meter radius at nine sites. Researchers found that soils closer to large numbers of larger trees were more sensitive to temperature changes—and had higher CO2 emissions—than soils farther from tree trunks. In their recently published paper in Biogeosciences, the researchers discuss the variable nature of soil respiration, particularly in relation to carbon exchange in coastal forests that are vulnerable to sea level rise and extreme weather events.

The team measured CO2 soil respiration, along with size, and species of each tree within a 15-meter radius at nine sites. They found that soils closer to large numbers of larger trees were more sensitive to temperature changes—and had higher CO2 emissions—than soils farther from tree trunks.

In their recently published paper in Biogeosciences, the researchers discuss the variable nature of soil respiration, particularly in relation to carbon exchange in coastal forests that are vulnerable to sea level rise and extreme weather events.

Principal Investigator

Stephanie Pennington
Pacific Northwest National Laboratory
stephanie.pennington@pnnl.gov

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

Funding

This research is part of the ongoing initiative called Predicting Ecosystem Resilience through Multiscale and Integrative Science (PREMIS) at Pacific Northwest National Laboratory (PNNL), a multiprogram national laboratory operated by Battelle for the U.S. Department of Energy (DOE) under Contract No. DE-AC05-76RL01830. PREMIS is supported by the Office of Biological and Environmental Research (BER), within the DOE Office of Science. This project was conducted under PNNL’s Laboratory Directed Research and Development Program. The research was also supported by the Smithsonian Environmental Research Center in Maryland.

Related Links

References

Pennington, S. C., N. G. McDowell, J. P. Megonigal, and J. C. Stegen, et al. "Localized basal area affects soil respiration temperature sensitivity in a coastal deciduous forest". Biogeosciences 17 (3), 771–780  (2020). https://doi.org/10.5194/bg-17-771-2020.