Growth, shoot phenology and physiology of diverse seed sources of black spruce: I. Seedling responses to varied atmospheric CO2 concentrations and photoperiods

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Abstract
We conducted a greenhouse experiment to determine: (1) if diverse provenances of black spruce (Picea mariana (Mill.) B.S.P.) respond similarly in growth, phenology and physiology to an approximately 300 ppm increase in atmospheric CO2 concentration, and (2) the influence of photoperiod on both provenance and provenance × CO2 interaction effects. Seedlings from provenances that originated from the Yukon (63°34′ N, 135°55′ W), British Columbia (58°47′ N, 123°38′ W), Alberta (52°22′ N, 115°15′ W), Newfoundland (50°54′ N, 56°06′ W) and Ontario (48°59′ N, 80°38′ W and 45°10′ N, 77°10′ W) were subjected to growth analysis in greenhouse growth chambers supplied with 712 ± 93 (SD) ppm CO2 (elevated) or 394 ± 59 ppm CO2 (ambient). Seedlings from Provenances 7000 and 6901 were also subjected to an extended photoperiod treatment and periodically measured for shoot and root gas exchange. In response to a natural photoperiod, southern provenances grew more, broke and set bud later, and partitioned more biomass to shoot versus root than northern provenances. These differences among provenances were influenced by the extended photoperiod treatment but not by the elevated CO2 treatment. Averaged across all provenances, elevated CO2 increased seedling final weights by 55%; however, the elevated CO2 treatment had no effect on the provenance differences in any measured trait. We conclude that the large differences in physiology, phenology and growth among these diverse provenances of black spruce were expressed similarly in both ambient and elevated atmospheric CO2 concentrations.

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