Populus tremuloides photosynthesis and crown architecture in response to elevated CO2 and soil N availability

• Published in: Oecologia Vol. 110; no. 3; pp. 328 - 336
• Main Authors: Kubiske, M.E, Pregitzer, K.S, Mikan, C.J, Zak, D.R, Maziasz, J.L, Teeri, J.A
• Format: Journal Article
• Language: English
• Published: Berlin Springer-Verlag 01.01.1997; Springer
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Atmospherics; Autoecology; Biological and medical sciences; Carbon dioxide; carbon dioxide enrichment; Ecophysiology; Forest soils; Fundamental and applied biological sciences. Psychology; Leaf area; Leaves; nitrogen; nutrient availability; Photosynthesis; Plant roots; Plants; Plants and fungi; Tree growth; Trees; United States; North America; America; Michigan; Populus tremuloides; Resource allocation; Carbon dioxide; Increase; Plant leaf; Nitrogen; Carbon; Salicaceae; Dicotyledones; Angiospermae; Tree crown; Hardwood forest tree; Spermatophyta; Photosynthesis
• ISSN: 0029-8549; 1432-1939
• DOI: 10.1007/PL00008813

We tested the hypothesis that elevated CO₂ would stimulate proportionally higher photosynthesis in the lower crown of Populus trees due to less N retrans-location, compared to tree crowns in ambient CO₂. Such a response could increase belowground C allocation, particularly in trees with an indeterminate growth pattern such as Populus tremuloides. Rooted cuttings of P. tremuloides were grown in ambient and twice ambient (elevated) CO₂ and in low and high soil N availability (89 ± 7 and 333 ± 16 ng N g-1day-1net mineralization, respectively) for 95 days using open-top chambers and open-bottom root boxes. Elevated CO₂ resulted in significantly higher maximum leaf photosynthesis ($A_{\text{max}}$) at both soil N levels.$A_{\text{max}}$was higher at high N than at low N soil in elevated, but not ambient CO₂. Photosynthetic N use efficiency was higher at elevated than ambient CO₂ in both soil types. Elevated CO₂ resulted in proportionally higher whole leaf A in the lower three-quarters to one-half of the crown for both soil types. At elevated CO₂ and high N availability, lower crown leaves had significantly lower ratios of carboxylation capacity to electron transport capacity ($V_{\text{c}_{\text{max}}}/J_{\text{max}}$) than at ambient CO₂ and/or low N availability. From the top to the bottom of the tree crowns,$V_{c_{\text{max}}}/J_{\text{max}}$increased in ambient CO₂, but it decreased in elevated CO₂ indicating a greater relative investment of N into light harvesting for the lower crown. Only the mid-crown leaves at both N levels exhibited photosynthetic down regulation to elevated CO₂. Stem biomass segments (consisting of three nodes and internodes) were compared to the total$A_{\text{leaf}}$for each segment. This analysis indicated that increased$A_{\text{leaf}}$at elevated CO₂ did not result in a proportional increase in local stem segment mass, suggesting that C allocation to sinks other than the local stem segment increased disproportionally. Since C allocated to roots in young Populus trees is primarily assimilated by leaves in the lower crown, the results of this study suggest a mechanism by which C allocation to roots in young trees may increase in elevated CO₂.