Measured and Modeled Responses of Tropical Plant Carbon Balance at the TRACE Site to Long-Term Experimental Warming and Hurricane Disturbance Recovery
Authors
Molly A. Cavaleri1* (macavale@mtu.edu), Rob Tunison1, Sasha C. Reed2, Tana E. Wood3, Mingjie Shi4, Anthony P. Walker5, Xiaojuan Yang5
Institutions
1Michigan Technological University, Houghton, MI; 2U.S. Geological Survey, Southwest Biological Science Center, Moab, UT; 3USDA Forest Service International Institute of Tropical Forestry, Rio Piedras, PR; 4Pacific Northwest National Laboratory, Richland, WA; 5Oak Ridge National Laboratory, Oak Ridge, TN
Abstract
The team is using a unique understory warming experiment along with numerical modeling to determine how tropical forest plants respond to long-term warming and hurricane disturbance in Eastern Puerto Rico. The Tropical Responses to Altered Climate Experiment (TRACE), which uses infrared heaters to warm understory vegetation +4°C above ambient temperatures, was hit by two major hurricanes in September 2017. Researchers measured plant structure and physiological responses to changing post-hurricane canopy dynamics and experimental warming. They also used the nutrient-enabled Functionally Assembled Terrestrial Ecosystem Simulator (FATES-CNP) to determine how these changes reflect overall carbon exchange and nutrient fluxes in the system. Six years post-hurricane, in situ measurements showed warmed plots were half the height of control. Photosynthesis declined by ~60% in response to closing canopy conditions following the hurricanes and showed a ~30% decline in response to experimental warming. Neither photosynthesis nor plant respiration acclimated significantly to warming or hurricane disturbance; however, root biomass was reduced in warmed plots leading to ~50% reduction in overall ecosystem-level root respiration for warmed plots. Using site-specific data to parameterize the ELM-FATES model, researchers found that +4°C warming simulations had lower biomass, productivity, and respiration than ambient simulations when there was a hurricane disturbance every 10 years. These changes in biomass, productivity, and respiration, due to warming do not necessarily confer reduced net ecosystem productivity (NEP), which was not different between warmed and ambient simulations. Researchers found that NEP fell from ~2.5 g m-2 d-1 in base-FATES model runs to near zero in nutrient-enabled model runs (FATES-CNP), driven largely by heterotrophic respiration. This suggests that including more advanced soil processes into the FATES model has large effects on ecosystem processes. Overall, the team found that plant carbon exchange processes acclimated quickly to changes in post-hurricane canopy dynamics, but that warming induced limited physiological acclimation responses.