Effect of different daytime and night-time temperature regimes on the foliar respiration of Pinus taeda: predicting the effect of variable temperature on acclimation

The objectives of this study were to determine the acclimation of loblolly pine (Pinus taeda L.) foliar respiration to different night-time low temper atures, daytime high temperatures, and daily mean temperatures, and then to use the responses of temperature acclimation to various temperature regime s to predict acclimation under fluctuating temperatures. Experiments were c onducted on two-year-old seedlings in growth chambers using different combi nations of day and night-time temperatures. The first experiment exposed tr ees to 22/22, 29/22, 22/15, and 29/15 degreesC day/night (d/n). When measur ed at a common temperature (15, 22 or 29 degreesC), respiration rates were lower for trees exposed to higher treatment temperatures and acclimation wa s influenced by both day and night-time temperature. However, the extent of acclimation did not relate to mean temperature, i.e. respiration rates mea sured at a common temperature ranked as follows for seedlings exposed to di fferent temperature regimes, 22/15 > 22/22 > 29/15 congruent to 29/22 degre esC d/n. Rather, acclimation of foliar respiration was linearly related to mean daily respiration rate, where mean daily respiration rate is the avera ge of the respiration rates measured at the day and night-time treatment te mperatures. The discrepancy between mean daily respiration rate and mean da ily temperature occurred because respiration increased exponentially with i ncreasing temperature. In a second experiment, the same seedlings were expo sed to 22/22, 15/15, 25.5/18.5, and 25.5/15 degreesC d/n to test the relati onship between mean daily respiration rate and acclimation. As in the first experiment, acclimation was linearly related to mean daily respiration rat e. The concept of effective acclimation temperature, which is the temperatu re at which the mean daily respiration rate occurs, was derived from these results as a means to predict the extent that foliar respiration acclimates to treatment temperature.