Traits related to light-energy processing have significant ecological implications for plant fitness. We studied the effects of elevated atmospheric CO2 concentration ([CO2]) on chloroplast pigment traits of a red spruce (RS) (Picea rubens Sarg.)-black spruce (BS) (P. mariana (Mill.) B.S.P.) genetic complex in two experiments: (1) a comparative species' provenance experiment from across the near-northern part of the RS range; and (2) an intra- and interspecific controlled-cross experiment. Results from the provenance experiment showed that total chlorophyll (a + b) concentration was, on average, 15% higher in ambient [CO2] than in elevated [CO2] (P < 0.001). In ambient [CO2], BS populations averaged 11% higher total chlorophyll and carotenoid concentrations than RS populations (P < 0.001). There were significant species, CO2, and species x CO2 interaction effects, with chlorophyll concentration decreasing about 7 and 26% for BS and RS, respectively, in response to elevated [CO2]. Results from the controlled-cross experiment showed that families with a hybrid index of 25 (25% RS) had the highest total chlorophyll concentrations, and families with hybrid indices of 75 and 100 had among the lowest amounts. Initial analysis of the controlled-cross experiment supported a more additive model of inheritance; however, parental analysis showed a significant and predominant male effect for chlorophyll concentration. In ambient and elevated [CO2] environments, crosses with BS males had 10.6 and 17.6% higher total chlorophyll concentrations than crosses with hybrid and RS males, respectively. Our results show that chlorophyll concentration is under strong genetic control, and that these traits are positively correlated with productivity within and across species. A significant positive correlation between chlorophyll concentration and the ratio of total plant N to root dry mass was also found (r = 0.872). The almost fourfold decrease in chlorophyll concentration in RS suggests that it would be at a competitive disadvantage compared with BS in a high [CO2] environment.
