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Genetic variation among pines and spruces in assimilation efficiencies and photosynthetic regulation under elevated CO2

Major, JohnE., Mosseler, Alex, Malcolm, JohnW.
Trees 2018 v.32 no.1 pp. 215-229
Picea glauca, Pinus strobus, biomass, carbon dioxide, carbon dioxide enrichment, carboxylation, electron transfer, genetic variation, phosphates, photosynthesis, seedlings, trees
KEY MESSAGE: After 3 years of elevated CO₂ treatments, spruce P ₙ 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. Assimilation to internal CO₂ (AC ᵢ) 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 (V cₘₐₓ) and maximum assimilation (A ₘₐₓ) values than spruces, and there was a significant downregulation in V cₘₐₓ and A ₘₐₓ for both genera in eCO₂, but more so for the spruces. For the maximum rate of electron transport (J ₘₐₓ) 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 (P ₙ₅₇₀) was 13.0% greater for pines and 9.0% lower for spruces under eCO₂ compared with aCO₂. Comparing responses under eCO₂ to aCO₂, P ₙ₅₇₀ was equal for WS but lower for the other spruces; however, WP declined, RP showed no difference, JP had greater P ₙ₅₇₀, and PP had substantially greater P ₙ₅₇₀. For pines, there appears to be a consistent enhanced sink effect on P ₙ across all species. Corresponding P ₙ₅₇₀ 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 P ₙ .