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Response of a Sub-Tropical Tree to Elevated CO2 and Temperature
Sheu, B.-H. and Lin, C.-K. 1999. Photosynthetic response of seedlings of the sub-tropical tree Schima superba with exposure to elevated carbon dioxide and temperature. Environmental and Experimental Botany 41: 57-65.

What was done
Fifty-day old seedlings were grown for six months in pots placed within glass chambers receiving atmospheric CO2 concentrations of 360 and 720 ppm. In addition, at each CO2 concentration half of the seedlings were grown at an optimal day/night temperature regime of 25/20C, while the other half were subjected to a higher temperature treatment of 30/25C. Thus, the authors studied the effects of elevated CO2 and temperature on photosynthesis and growth in this important native hardwood species common to Taiwan.

What was learned
Six months growth in elevated CO2 caused photosynthetic acclimation to occur, regardless of temperature treatment, as indicated by a slight reduction in the photosynthetic capacity of CO2-enriched trees. However, when photosynthetic rates were measured at growth CO2 concentrations, CO2-enriched seedlings exhibited rates that were 20 and 40% greater than those displayed by ambiently-grown trees at the optimal and elevated temperature regimes, respectively. In fact, the absolute magnitude of photosynthesis increased with atmospheric CO2 enrichment and temperature, demonstrating that the optimal growth temperature for this species increased with increasing CO2 concentration.

With the increased carbohydrate supply, resulting from enhanced photosynthetic rates, CO2-enriched trees accumulated greater biomass than did seedlings exposed to ambient CO2 concentrations, regardless of growth temperature. In addition, the positive effect of elevated CO2 on dry matter accumulation increased with temperature; and CO2-enriched trees displayed total dry weights that were 14 and 49% greater than control seedlings at optimal and elevated growth temperatures, respectively.

What it means
As the CO2 content of the air increases, this valuable tree species of Taiwan will likely exhibit both enhanced rates of photosynthesis and increased biomass production. Moreover, if temperatures in the region increase, regardless of the cause, this species will not need to migrate towards cooler climates, but should remain within its current range and grow even better than it did prior to the temperature increase, due to the positive interaction that rising atmospheric CO2 concentrations and air temperatures have on its growth.

Reviewed 15 January 2000