Respiratory alternative oxidase responds to both low- and high-temperature stress in Quercus rubra leaves along an urban-rural gradient in New York

Abstract

Summary1. Urban–rural transects can be utilized as natural gradients of temperature and also as a tool topredict how plant ecology and physiology might respond to expected global change variablessuch as elevated temperatures, CO 2 and inorganic nitrogen deposition.2. We investigated differences in respiration (R) and the balance of electron partitioning throughthe cytochrome (CP) and alternative (AP) pathways in leaves of mature Quercus rubra L. treesalong a transect from New York City to the Catskill Mountains over the course of one growingseason. In addition, we investigated the effects of elevated temperature on Q. rubra seedlings in acontrolled environment study.3. In the field study, we found that urban-grown leaves often respired at greater rates than leavesgrown at other sites and that this was likely due to higher leaf nitrogen. At each site, R at the pre-vailing growth temperature declined steadily throughout the growing season despite higher tem-peratures at the end of the summer. Differences in R were associated with changes in the relativeabundances of cytochrome and alternative oxidase proteins. Oxygen isotope discrimination (D),which reflects relative changes in AP and CP partitioning, was negatively correlated with dailyminimum temperature in trees grown at the colder rural sites, but not at the warmer urban sites.4. In the growth cabinet study, we found that R acclimated to elevated temperatures and thatthis was accompanied by a steady increase in D.5. These findings that AP partitioning increases with both high and low temperatures show thatthe AP may play an important role in plant responses to environmental conditions that elicitstress, and not simply to specific conditions such as low temperature.Key-words: acclimation, cytochrome oxidase, leaf respiration, nonstructural carbohydrates,oxygen isotope discrimination, seasonal variation, urban ecologyIntroduction