Canadian Forest Service Publications

Carbon assimilation variation and control in Picea rubens, Picea mariana, and their hybrids under ambient and elevated CO₂. 2014. Major, J.E.; Mosseler, A.; Barsi, D.C.; Campbell, M.; Malcolm, J. Trees 28: 329-344.

Year: 2014

Issued by: Atlantic Forestry Centre

Catalog ID: 35391

Language: English

Availability: PDF (request by e-mail)

Available from the Journal's Web site. †
DOI: 10.1007/s00468-013-0952-3

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Abstract

Adaptations related to gas exchange are important fitness traits in plants and have significant growth and ecological implications. Assimilation (A) and assimilation to internal CO₂ (AC_I) response curve parameters were quantified from a red spruce (RS) (Picea rubens Sarg.)–black spruce (BS) (P. mariana (Mill.) B.S.P.) controlled-cross hybrid complex grown under ambient and elevated CO₂ conditions. Under ambient conditions, maximum A (A_max), maximum rate of carboxylation by rubisco (V_cmax), maximum rate of electron transport (J_max), and carboxylation efficiency (CE) generally increased with increasing BS content; however, under elevated CO₂ conditions, hybrid index 50 (hybrid index number is the percentage of RS, balance BS) often had greater values than the other indices. There were significant hybrid index, CO₂, and hybrid index X CO₂ effects for A_growth at 360 ppm (A₃₆₀) and 729 ppm (A₇₂₀). The net A stimulation (A_stim) from ambient to elevated CO₂ treatment after 3 years was 10.8, 57.8, 74.1, 69.8, and 58.7% for hybrid indices 0 (BS), 25, 50, 75, and 100 (RS), respectively. Why does BS have the least A_stim), hybrid index 50 the most, and RS a moderate level? There was a significant relationship between A₃₆₀ and ambient total biomass among indices (P = 0.096), but none was found between A₇₂₀ and elevated CO₂ (R² = 0.931, P = 0.008), supporting the hypothesis that sink demand drives A. Traits A_max, V_cmax and J_max were correlated to total chlorophyll concentration. Moreover, A. Traits A_max, V_cmax and J_max also showed a significant underlying male effect, particularly under ambient conditions consistent with the paternal inheritance of the chloroplast genome.

Plain Language Summary

Genetic adaptations for photosynthetic response to the environment are important fitness traits in plants and have significant growth and ecological implications. We know that a short-term increase of carbon dioxide (CO₂) stimulates photosynthesis, but many questions remain: how great is the stimulation and what limits it; is there down-regulation and, if so, how much; and for all these, how do species differ? We measured photosynthetic rates and capacities in black spruce (BS), red spruce (RS), and hybrids having 25, 50, and 75% RS (balance BS) grown under ambient and elevated CO₂ conditions. Under ambient conditions, photosynthetic efficiency traits generally increased with increasing BS content; however, under elevated CO₂ conditions, the 50% hybrid generally was the most efficient. After 3 years, the stimulation in net photosynthesis from ambient to elevated CO₂ treatment was 10.8, 57.8, 74.1, 69.8, and 58.7%, for 0 to 100% RS, respectively. Why does BS have the least stimulation, the 50% hybrid the most, and RS a moderate level? We found percent stimulation in photosynthesis was strongly (R² = 0.931, P = 0.008) related to the percent change in total dry mass under elevated CO₂. This strongly suggests that demand (increased carbon sink) drives photosynthesis and the amount of down-regulation. Thus not all species or hybrids respond the same to elevated CO₂.