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Effects of Differential Day/Night Elevated Air Temperatures on Net Photosynthesis in Cottonwood Trees
Reference
Turnbull, M.H., Murthy, R. and Griffin, K.L. 2002. The relative impacts of daytime and night-time warming on photosynthetic capacity in Populus deltoides. Plant, Cell and Environment 25: 1729-1737.

What was done
The authors manipulated day/night air temperatures around 4-m-tall cottonwood (Populus deltoides Bartr. Ex Marsh) trees growing within large experimental enclosures to study the effects of temperature on carbon relations within this tree species.

What was learned
A 6C increase in daytime air temperature enhanced rates of net photosynthesis in cottonwood saplings by 11%, while it had no impact on nocturnal rates of dark respiration. However, a 6C increase in daytime temperature, coupled with a 10C increase in nighttime temperature, enhanced rates of net photosynthesis by 64% and rates of dark respiration by 77%. Nevertheless, on an absolute scale, photosynthetic carbon gains due to the daytime temperature increase were nearly an order of magnitude greater than nocturnal carbon losses caused by the greater increase in nighttime temperature. It is believed that increases in nocturnal temperature stimulate photosynthetic carbon gains the following day because warming-induced nocturnal carbohydrate utilization reduces photosynthetic acclimation due to carbohydrate accumulation in source leaves.

What it means
If the earth continues to warm as it has in the past, carbon uptake by cottonwood trees should significantly increase. Furthermore, if it warms more at night than it does in the day, as it also has in the past, daily carbon uptake should increase to an even greater extent. Thus, any nocturnal temperature increases will likely stimulate overall carbon sequestration by cottonwood trees and probably other woody species as well.


Reviewed 29 January 2003