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Key message: After 3 years of elevated CO2 treatments, spruce Pn regulation from aCO2 to eCO2 was strongly related to total dry mass change (%), whereas pines displayed the same trend, but the relationship was not statistically significant.Abstract: Assimilation to internal CO2 (ACi) response curve parameters were grown and quantified under ambient (aCO2) and elevated (eCO2) CO2 treatments for two commercially important tree genera, Pinus and Picea spp. The species include Pinus strobus (WP), P. resinosa (RP), P. banksiana (JP), P. rigida (PP), Picea glauca (WS), P. rubens (RS), P. mariana (BS), and P. abies (NS). Seedlings were 4 years old and dosed for 3 years at the time of measurements. Overall, pines had greater maximum rates of carboxylation (Vcmax) and maximum assimilation (Amax) values than spruces, and there was a significant downregulation in Vcmax and Amax for both genera in eCO2, but more so for the spruces. For the maximum rate of electron transport (Jmax) and the rate of triose phosphate utilization (TPU), there was no significant genus effect, but there was a significant downregulation in eCO2. For these four traits, all spruces downregulated, whereas each pine species responded quite differently. White pine downregulated the most, followed by RP; no change for JP, and PP traits increased under eCO2. At an intermediate CO2 level, net photosynthesis @570 ppm CO2 (Pn570) was 13.0% greater for pines and 9.0% lower for spruces under eCO2 compared with aCO2. Comparing responses under eCO2 to aCO2, Pn570 was equal for WS but lower for the other spruces; however, WP declined, RP showed no difference, JP had greater Pn570, and PP had substantially greater Pn570. For pines, there appears to be a consistent enhanced sink effect on Pn across all species. Corresponding Pn570 change from aCO2 to eCO2 across spruce species showed a strong positive and statistically significant correlation to biomass stimulation that supports the theory of sink regulation of Pn. [ABSTRACT FROM AUTHOR] |
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