Boreal and temperate trees show strong acclimation of respiration to warming

Acclimation of leaf respiration to a 3–5-year period of warming by 3.4 °C for 10 North American tree species in forest conditions eliminated 80% of the increase in leaf respiration expected of non-acclimated trees; this suggests that the increase in respiration rates of terrestrial plants from climate warming, and the associated increase in atmospheric CO 2 levels, may be less than anticipated. How tree acclimation limits CO 2 output Increasing plant respiration in a warming world might be expected to further accelerate warming by releasing additional CO 2 into the atmosphere, but the extent to which plants acclimate to high temperatures in the long-term is poorly quantified. Peter Reich et al . have measured acclimation of leaf respiration to a three- to five-year period of warming (by 3.4 °C) for ten North American tree species in forest conditions. They find that acclimation eliminated 80% of the increase in leaf respiration expected of non-acclimated trees. This result suggests that the increase in respiration rates of terrestrial plants resulting from climate warming — and the associated increase in atmospheric CO 2 concentration — may be less than anticipated. Plant respiration results in an annual flux of carbon dioxide (CO 2 ) 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 CO 2 release, and hence further atmospheric warming 1 , 2 . Plant respiration can acclimate to altered temperatures, however, weakening the positive feedback of plant respiration to rising global air temperature 3 , 4 , 5 , 6 , 7 , but a lack of evidence on long-term (weeks to years) acclimation to climate warming in field settings currently hinders realistic predictions of respiratory release of CO 2 under future climatic conditions. Here we demonstrate strong acclimation of leaf respiration to both experimental warming and seasonal temperature variation for juveniles of ten North American tree species growing for several years in forest conditions. Plants grown and measured at 3.4 °C above ambient temperature increased leaf respiration by an average of 5% compared to plants grown and measured at ambient temperature; without acclimation, these increases would have been 23%. Thus, acclimation eliminated 80% of the expected increase in leaf respiration of non-acclimated pl