Wednesday, August 8, 2018: 2:10 PM
348-349, New Orleans Ernest N. Morial Convention Center
Sean Michaletz1,2,3, Gregory P. Asner4, Lisa Patrick Bentley5, James H. Brown6, Vanessa R. Buzzard7, Sandra M. Duran8, William Farfan-Rios9, Megan Gaitan5, Aud H. Halbritter10, Jonathan J. Henn11, Manuel Hernandez5, J. Aaron Hogan12, Michael Kaspari13, Kari Klanderud14, Hanna Lee15, Brian S. Maitner16, Nathan McDowell17, Jeanine McGann18, Angelo Moerland19, Imma Oliveras20, Lorah Patterson21, Fei Ran22, Van M. Savage23, Miles R. Silman24, Richard Telford10, Vigdis Vandvik10, Robert B. Waide25, Michael Weiser13, Daniel J. Wieczynski26, Yan Yang22, Jizhong Zhou27 and Brian Enquist16, (1)Department of Botany and Biodiversity Research Centre, University of British Columbia, Vancouver, BC, Canada, (2)Biosphere 2 and Ecology & Evolutionary Biology, University of Arizona, Tucson, AZ, (3)Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM, (4)Department of Global Ecology, Carnegie Institution for Science, Stanford, CA, (5)Department of Biology, Sonoma State University, Rohnert Park, CA, (6)Department of Biology, University of New Mexico, Albuquerque, NM, (7)University of Arizona, Tucson, AZ, (8)Ecology & Evolutionary Biology, University of Arizona, (9)Biology, Living Earth Collaborative, Washington University in Saint Louis, St. Louis, MO, (10)Department of Biological Sciences, University of Bergen, Bergen, Norway, (11)Integrative Biology, University of Wisconsin - Madison, Madison, WI, (12)Department of Environmental Science, University of Puerto Rico - Rio Piedras, San Juan, PR, (13)Department of Biology, University of Oklahoma, Norman, OK, (14)Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, Norway, (15)University of Bergen, (16)Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, (17)Atmospheric Sciences & Global Change, Pacific Northwest National Laboratory, Richland, WA, (18)Dept. of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, (19)Kew and Reading University, (20)Environmental Change Institute School of Geography and the Environment, University of Oxford, Oxford, United Kingdom, (21)Ecology & Evolutionary Biology, University of Arizona, Tucson, AZ, (22)Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, China, (23)Department of Biomathematics, UCLA, Los Angeles, CA, (24)Biology, Wake Forest University, Winston-Salem, NC, (25)Biology, University of New Mexico, Albuquerque, NM, (26)Ecology & Evolutionary Biology, University of California, Los Angeles, Los Angeles, CA, (27)Institute for Environmental Genomics, Consolidated Core Laboratory, Department of Microbiology and Plant Biology, and School of Civil Engineering and Environmental Sciences, University of Oklahoma, Norman, OK
Background/Question/Methods The metabolic theory of ecology (MTE) hypothesizes that the kinetics of plant metabolism, from cells to ecosystems, are characterized by a Boltzmann-Arrhenius relationship following an activation energy E = 0.32 eV corresponding to net photosynthesis. This prediction was estimated using the Farquhar approach for Rubiscio-limited C3 photosynthesis, parameterized for a single species of Nicotiana. While this numeric value has become canon, it has surprisingly never been tested for photosynthesis in diverse taxa. Additionally, most studies quantifying E at higher levels (individuals, communities, and ecosystems) have reported values significantly lower than hypothesized. Here we evaluate these predictions for kinetics of plant growth at three levels of organization: leaves, individuals, and communities. First, we use a new compilation of Rubisco kinetics data for diverse taxa to give a new MTE prediction of E. Next, we evaluate the MTE hypothesis using leaf-level data for the temperature response of net photosynthesis obtained at sites spanning elevation and latitude in China, Costa Rica, Peru, and USA. Finally, we evaluate individual growth and ecosystem production using new data collected at seven sites spanning a broad latitudinal climate gradient from Barro Colorado Island, Panama to HJ Andrews Experimental Forest, USA.
Results/Conclusions
Our prediction for E is not inconsistent with the previous estimate, but is now generalized for many taxa and is better quantified including measures of dispersion. Our prediction is supported by globally-distributed data for leaf net photosynthesis, although observed E varies widely and is strongly right-skewed. Predictions were not consistent with observed E for individuals and ecosystems, indicating higher level growth and production kinetics appear largely decoupled from ambient air temperature. We review several hypotheses that may underlie these results. Our results suggest that shifts in plant functional traits across broad climate gradients decouple plant metabolism from air temperature, and that these shifts in plant function ramify to influence higher-level growth and production. Understanding how multiple rate-limiting processes coalesce into a single E that characterizes metabolic responses to temperature, and how to best estimate E from unimodal data, remain important challenges.
