Acclimation of Photosynthesis and Respiration in Tropical Plants at the TRACE Site Under Long-Term Experimental Warming and Hurricane Disturbance Recovery

Authors

Rob Tunison¹* (rptuniso@mtu.edu), Molly A. Cavaleri¹, Sasha C. Reed², Tana E. Wood³, Anthony P. Walker⁴, Xiaojuan Yang⁴

Institutions

¹Michigan Technological University, Houghton, MI; ²Southwest Biological Science Center, U.S. Geological Survey, Moab, UT; ³USDA Forest Service International Institute of Tropical Forestry, Rio Piedras, PR; ⁴Oak Ridge National Laboratory, Oak Ridge, TN

URLs

• https://www.forestwarming.org/

Abstract

Background and Methods. Climate change projections over the next 80 years predict increased global temperatures and more frequent and intense hurricane disturbances. How plants respond to these changes could have huge implications for how carbon is cycled between ecosystems and the atmosphere. Thermal acclimation, or the ability of individuals to change metabolic processes to work more efficiently at different temperatures, could help plants perform better at higher temperatures or mitigate the effects of temperature damage. While thermal acclimation has been observed in temperate systems, it could be minimal to nonexistent in tropical systems that experience narrower temperature ranges than temperate systems. The team assessed the acclimation potential of plant physiological processes to experimental warming and tracked their changes during post-hurricane recovery at the Tropical Responses to Altered Climate Experiment (TRACE), a long-term in situ experimental warming project in eastern Puerto Rico where the forest understory is warmed +4°C above ambient temperature using infrared heaters. Researchers measured temperature response curves on root respiration, leaf photosynthesis and respiration, and leaf thermotolerance for experimentally warmed and ambient temperature plants; these data were collected after two major hurricanes impacted the study site in 2017.

Results and Conclusions. Tropical root respiration did not acclimate through changes in root specific respiration rates, but ecosystem root respiration declined under warming due to lower root biomass. Hurricane disturbance increased variability in root respiration, but the effects are likely short term. Researchers observed photosynthetic thermal acclimation through wider thermal niche breadth but at the cost of overall lower photosynthesis for warmed plants. Additionally, photosynthesis was highest after the hurricanes and decreased as the canopy closed. The temperature optimum for photosynthesis, which did not show signs of acclimation, was near the temperature of warmed plots. Leaf respiration was not affected by experimental warming but decreased with canopy closure after the hurricanes. Leaf thermotolerance did not acclimate to warming and was lowest when the canopy was open and increased as the canopy closed. Together, these results suggest that there is a brief boost to understory carbon assimilation after hurricane disturbance independent of warming effects but at the potential cost of higher respiration. Scaling these responses to an ecosystem is dependent on overall biomass of the system and environmental forcings. Future goals are to estimate the biomass at the site and model the carbon flux responses to experimental warming using the E3SM Land Model–FATES model.