Accurate predictions of plant respiratory responses to differing climates are essential in order to forecast the effects of climate change on plant performance and the global carbon cycle. Many plant species appear to be capable of respiratory acclimation, which can offset the marked acceleration of dark respiration associated with temperature increases. However, it remains unclear if acclimation is a function of temperature, leaf chemistry or a combination of these extrinsic and intrinsic factors, and, more importantly, how long-term respiratory acclimation influences plant performance. In the growing season of 2007, we assessed in situ respiratory acclimation (or lack thereof) and its consequences for average rates of leaf dark respiration in aspen (Populus tremuloides) and cottonwood (Populus deltoides) along a 9º latitudinal gradient from northern Wisconsin to southern Illinois. Across sites, there was a 13ºC range in mean night temperature during a 30-day interval in July and August.

Results/Conclusions

Contrary to previous studies, we found no short-term respiratory acclimation in any species during this interval, but did find long-term acclimation in aspen and cottonwood. Long-term acclimation was driven by a downward shift in base respiration rates and was more pronounced in warmer climates. Aspen exhibited a 35% reduction in respiration from mid to late summer when grown in a warm climate (southern Illinois), and only a ~20% reduction when grown in a cooler climate (northern Wisconsin). Similarly, cottonwood showed a 44% reduction in temperature-adjusted respiration rates when grown in a warm climate, but exhibited a 10% increase in respiration rates when grown in a cooler climate. Sweetgum and birch showed similar reductions in warm and cool climates leading to no significant short- or long-term acclimation. Our results showed that species differed in the extent of respiratory acclimation along our latitudinal gradient, but differences were not consistent between temperate and boreal species. We also found that leaf chemistry (i.e. nitrogen concentration) played a key role in respiratory acclimation.