Accelerated Plant Metabolism May Not Speed Up Climate Change as Much as Anticipated
Plant respiration can acclimate to altered temperatures.
A long-term study found that, over time, plants can adjust their metabolic rate to reduce the amount of carbon dioxide (CO2) returned to the atmosphere due to warming.
Climate change impacts many aspects of Earth’s ecosystems, often in ways that can either slow or accelerate climate change. In a warming world, the return of CO2 to the atmosphere, via plant respiration, was expected to increase with temperature. This study found that plants growing in warmer conditions made adjustments that kept their metabolism on a stable trajectory, eliminating 80% of the possible “extra” carbon flux that would be released by nonacclimatized plants. If such responses are general, the acceleration of climate change by heightened plant respiration in a warmer world will be much smaller than anticipated by theory or Earth system models.
Plant respiration results in an annual CO2 flux to the atmosphere that is six times as large as that due to the emissions from fossil fuel burning, so changes in either will impact future climate. As plant respiration responds positively to temperature, a warming world may result in additional respiratory CO2 releases and, hence, further atmospheric warming. Plant respiration can acclimate to altered temperatures (e.g., by downward reduction of their entire temperature-response curve in warmer conditions), weakening the positive feedback of plant respiration to rising global air temperature. However, lack of evidence on long-term (weeks to years) acclimation to climate warming in field settings currently hinders realistic predictions of respiratory release of CO2 under future climatic conditions. To address this knowledge gap, a study was conducted from 2009 to 2013 to assess the acclimation capacity of more than 1,200 individuals of 10 dominant North American boreal and temperate tree species grown in ambient and warmed (+3.4 °C) plots in a unique open-air warming experiment in both open and understory forest habitats at two sites (~150 km apart) at the boreal-temperate forest ecotone in Minnesota, USA. For 1,620 leaves of these individuals, respiration was measured from 12 °C to 37 °C. Results found strong acclimation of leaf respiration to both experimental warming and seasonal temperature variation for juveniles of all 10 species. Plants grown and measured at temperatures 3.4 °C above ambient increased leaf respiration by 5% on average compared to plants grown and measured at ambient temperatures; without acclimation, these increases would have been 23%. Thus, acclimation eliminated 80% of the increase in leaf respiration expected of nonacclimated plants. Acclimation of leaf respiration per degree temperature change was similar for experimental warming and seasonal temperature variation. Moreover, the observed increase in leaf respiration per degree increase in temperature was less than half as large as the average reported for prior studies, which were conducted largely over shorter time scales in laboratory settings. If such dampening effects of leaf thermal acclimation occur generally, the increase of terrestrial plant respiration rates in response to climate warming may be less than predicted and, thus, may not raise atmospheric CO2 concentrations as much as anticipated.
University of Minnesota
This research was supported predominantly by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research award number: DE-FG02-07ER64456. Additional support was provided by the Minnesota Agricultural Experiment Station number: MIN-42-030 and number: MIN-42-060; Minnesota Department of Natural Resources; and College of Food, Agricultural, and Natural Resources Sciences and Wilderness Research Foundation, University of Minnesota.
Reich, P. B., et al. “Boreal and temperate trees show strong acclimation of respiration to warming.” Nature 531, 633–36 (2016). DOI:10.1038/nature17142.