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Seasonal patterns of photosynthesis in Douglas fir seedlings during the third and fourth year of exposure to elevated CO 2 and temperature
Author(s) -
Lewis J. D.,
Lucash M.,
Olszyk D.,
Tingey D. T.
Publication year - 2001
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1046/j.1365-3040.2001.00700.x
Subject(s) - photosynthesis , zoology , douglas fir , seasonality , horticulture , botany , chemistry , biology , ecology
The interactive effects of elevated atmospheric CO 2 and temperature on seasonal patterns of photosynthesis in Douglas fir ( Psuedotsuga menziesii (Mirb.) Franco) seedlings were examined. Seedlings were grown in sunlit chambers controlled to track either ambient (~400 p.p.m.) CO 2 or ambient +200 p.p.m. CO 2 , and either ambient temperature or ambient +4 °C. Light‐saturated net photosynthetic rates were measured approximately monthly over a 21 month period. Elevated CO 2 increased net photosynthetic rates by an average of 21% across temperature treatments during both the 1996 hydrologic year, the third year of exposure, and the 1997 hydrologic year. Elevated mean annual temperature increased net photosynthetic rates by an average of 33% across CO 2 treatments during both years. Seasonal temperature changes also affected net photosynthetic rates. Across treatments, net photosynthetic rates were highest in the spring and autumn, and lowest in July, August and December–January. Seasonal increases in temperature were not correlated with increases in the relative photosynthetic response to elevated CO 2 . Seasonal shifts in the photosynthetic temperature optimum reduced temperature effects on the relative response to elevated CO 2 . These results suggest that the effects of elevated CO 2 on net photosynthetic rates in Douglas fir are largely independent of temperature.