Photosynthesis and respiratory acclimation in Quercus rubra L. along an urban-to-rural temperature gradient


The role of the terrestrial biosphere as a carbon sink or source is a critical and still poorly understood component of predicting global climate change. In particular, the response of plant respiration (R) to temperature remains a major uncertainty in current prediction models. Using a natural nighttime temperature gradient from New York City to surrounding rural areas, we investigated R rates in common red oak (Quercus rubra L.). Oaks were grown from seed at four sites along an urban to rural gradient as well as in growth chambers. We measured rates of photosynthesis and R in five one-year-old seedlings at each site. Leaves from mature trees along the gradient were also sampled for short-term response of R to temperature. Photosynthetic rates in seedlings did not differ significantly between sites. R in seedlings was lowest in NYC and progressively higher at increasing distances from the city, indicating respiratory acclimation along the gradient. In contrast, results from growth chambers and mature trees exhibited reverse acclimation with higher rates of R in plants grown at elevated temperatures. While there is some evidence to suggest the occurrence of respiratory acclimation to temperature along the gradient, more research is required before a definitive conclusion can be made.