Interactive Effect of Elevated CO2 and Reduced Summer Precipitation on Photosynthesis is Species-Specific: The Case Study with Soil-Planted Norway Spruce and Sessile Oak in a Mountainous Forest Plot (original) (raw)
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Plant, Cell and Environment, 2001
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.
Plant, Cell & Environment, 1999
The effects of elevated atmospheric CO 2 concentration on growth of forest tree species are difficult to predict because practical limitations restrict experiments to much shorter than the average life-span of a tree. Long-term, processbased computer models must be used to extrapolate from shorter-term experiments. A key problem is to ensure a strong flow of information between experiments and models. In this study, meta-analysis techniques were used to summarize a suite of photosynthetic model parameters obtained from 15 field-based elevated [CO 2 ] experiments on European forest tree species. The parameters studied are commonly used in modelling photosynthesis, and include observed light-saturated photosynthetic rates (A max ), the potential electron transport rate (J max ), the maximum Rubisco activity (V cmax ) and leaf nitrogen concentration on mass (N m ) and area (N a ) bases. Across all experiments, light-saturated photosynthesis was strongly stimulated by growth in elevated [CO 2 ]. However, significant down-regulation of photosynthesis was also observed; when measured at the same CO 2 concentration, photosynthesis was reduced by 10-20%. The underlying biochemistry of photosynthesis was affected, as shown by a down-regulation of the parameters J max and V cmax of the order of 10%. This reduction in J max and V cmax was linked to the effects of elevated [CO 2 ] on leaf nitrogen concentration. It was concluded that the current model is adequate to model photosynthesis in elevated [CO 2 ]. Tables of model parameter values for different European forest species are given. such as those compiled by and , are therefore invaluable for improving model predictions.