Acclimation of plant respiration rates (R) to climate warming is highly variable and many results appear contradictory. We tested the recently suggested hypotheses that pre-existing, long-lived leaves should exhibit a relatively limited ability for R to acclimate to climate warming, and that acclimation would occur via changes in the short-term temperature sensitivity of respiration. Seedlings of a subalpine, evergreen tree species (Eucalyptus pauciflora) were grown under naturally fluctuating conditions within its natural distribution. We used a free air temperature increase (FATI) system of infra-red ceramic lamps to raise night-time leaf temperatures by 0.3±0.1, 1.3±0.1, and 2.2±0.1 °C above ambient for 1 year. Light-saturated assimilation rates and plant growth did not change with nocturnal FATI treatments. Leaf R measured at prevailing temperatures did not differ between FATI treatments. Within each FATI treatment, nocturnal leaf R was highly sensitive to artificial temperature changes within minutes, and also correlated strongly with natural nocturnal and seasonal temperature variation. The corresponding values of Q10 of R varied according to time scale of measurements, but did not vary between FATI treatments. Instead, acclimation of R to nocturnal FATI occurred through changes in the base rate of respiration.