Thermal acclimation of respiration but not photosynthesis in Pinus radiata

Pinus radiata L. were grown in climate-controlled cabinets under three night/day temperature treatments, and transferred between treatments to mimic changes in growth temperature. The objective was to determine the extent to which dark respiration and photosynthesis in pre-existing and new needles acclimate to changes in growth temperatures. We also assessed whether needle nitrogen influenced the potential for photosynthetic and respiratory acclimation, and further assessed if short-term ( instantaneous, measured over a few hours) respiratory responses are accurate predictors of long-term (acclimated, achieved in days-weeks) responses of respiration to changing temperature. Results show that respiration displayed considerable potential for acclimation. Cold and warm transfers resulted in some acclimation of respiration in preexisting needles, but full acclimation was displayed only in new needles formed at the new growth temperature. Short-term respiratory responses were poor predictors of the long-term response of respiration due to acclimation. There was no evidence that photosynthesis in pre-existing or new needles acclimated to changes in growth temperature. N status of leaves had little impact on the extent of acclimation. Collectively, our results indicate that there is little likelihood that respiration would be significantly stimulated in this species as night temperatures increase over the range of 10-20 degrees C, but that inclusion of temperature acclimation of respiration would in fact lead to a shift in the balance between photosynthesis and respiration in favour of carbon uptake.