Effects of Future Heat Waves on Pine and Oak Tree Photosynthesis
Ameye, M., Wertin, T.M., Bauweraerts, I., McGuire, M.A., Teskey, R.O. and Steppe, K. 2012. The effect of induced heat waves on Pinus taeda and Quercus rubra seedlings in ambient and elevated CO2 atmospheres. New Phytologist 196: 448-461.
Working with the most recent fully-developed leaves of well watered and fertilized seedlings grown in 7.6-L pots out-of-doors at Athens, Georgia (USA) within polyethylene chambers maintained at ambient and elevated air temperatures (Tamb and T<amb + 3°C), as well as seven-day heat waves consisting of a biweekly +6°C heat wave or a monthly +12°C heat wave - which treatments were maintained throughout the growing season - Ameye et al. measured rates of net photosynthesis before, during and after the mid-summer heat waves they created. Under such experimental conditions, according to the six scientists who conducted the study, "an immediate and significant decline in net photosynthesis was observed in seedlings that were subjected to a +12°C heat wave, but not in seedlings subjected to a +6°C heat wave." And they remark that "after the third day of the +12°C heat wave, net photosynthesis values stabilized at positive values and did not show signs of further reduction, indicating that the photosynthetic apparatus did not accrue additional stress or damage as the heat wave continued."
In light of such responses, Ameye et al. conclude that "if soil moisture is adequate, trees will experience negative effects in photosynthetic performance only with the occurrence of extreme heat waves." And in light of the fact that "elevated CO2 diminished these negative effects," they opine that "the future climate may not be as detrimental to plant communities as previously assumed."
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