Acclimation of photosynthesis and respiration to increasing temperatures in trees
Nedlo, Jason Eric
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In the first of two experiments, Pinus taeda L. seedlings were grown at four locations oalong a 610 km North-South transect representing an 8.6C difference in mean growing season temperature. This allowed us to determine whether net photosynthesis and dark respiration acclimate to temperature, and if that acclimation can compensate for super- and sub-optimal growing season temperatures found within Pinus taeda’s natural range. Acclimation was evident because rates of net photosynthesis were similar among seedlings when compared to their respective mean site temperature the week before omeasurements, rates of dark respiration measured at 25C were lowest for the seedlings grown at the highest mean growing season temperature and highest for the seedlings grown at the lowest mean growing season temperature. The 44% to 50% decrease in biomass at the northernmost and southernmost sites, when compared to seedlings grown at the center of the range, indicated that temperature acclimation was not sufficient to overcome the deleterious effects that super- and sub-optimal temperatures had on biomass accretion. In the second experiment, Pinus taeda L. and Liriodendron tulipifera L. seedlings were oexposed in a controlled environment chamber to a 10C increase in temperature to investigate the rate and magnitude of temperature acclimation of net photosynthesis and dark respiration. After oten days of pre-treatment at 20C, we measured rates of net photosynthesis (Anet), dark respiration (Rd), chlorophyll fluorescence and constructed photosynthesis (A) to internal CO2 oconcentration (Ci) curves. The seedlings were then transferred to either a constant 30C or an oaverage 30C temperature treatment. Anet and Rd were measured daily. On the fifth day of treatment, we also measured chlorophyll fluorescence and constructed A/Ci curves. Complete acclimation of both species occurred within two days for Anet and within five days for Rd. Acclimation was equal in both temperature treatments indicating that acclimation responded to the mean daily temperature. The maximum electron transport rate increased 25-68%, the maximum carboxylation rate of rubisco increased 59-110%, while their ratio decreased 21-31%. Chlorophyll fluorescence ooparameters were affected in both species by the shift from a constant 20C to a constant 30C but oowere unaffected when temperatures shifted from a constant 20C to an average 30C.