Original Article

Trees

, Volume 15, Issue 5, pp 262-270

The effect of elevated carbon dioxide and ozone on leaf- and branch-level photosynthesis and potential plant-level carbon gain in aspen

  • Asko NoormetsAffiliated withMichigan Technological University, School of Forestry and Wood Products, Houghton, MI 49931, USA
  • , Evan P. McDonaldAffiliated withUSDA Forest Service, Forestry Sciences Laboratory, 5985 Highway K, Rhinelander, WI 54501, USA
  • , Richard E. DicksonAffiliated withUSDA Forest Service, Forestry Sciences Laboratory, 5985 Highway K, Rhinelander, WI 54501, USA
  • , Eric L. KrugerAffiliated withUniversity of Wisconsin-Madison, College of Agricultural and Life Sciences, Madison, WI 53706, USA
  • , Anu SôberAffiliated withInstitute of Ecology, Tartu Department, Riia 181, Tartu, Estonia
  • ,  J. IsebrandsAffiliated withUSDA Forest Service, Forestry Sciences Laboratory, 5985 Highway K, Rhinelander, WI 54501, USA
  • , David F. KarnoskyAffiliated withMichigan Technological University, School of Forestry and Wood Products, Houghton, MI 49931, USA

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Abstract.

Two aspen (Populus tremuloides Michx.) clones, differing in O3 tolerance, were grown in a free-air CO2 enrichment (FACE) facility near Rhinelander, Wisconsin, and exposed to ambient air, elevated CO2, elevated O3 and elevated CO<SUB>2</SUB>+O<SUB>3</SUB>. Leaf instantaneous light-saturated photosynthesis (P S) and leaf areas (A) were measured for all leaves of the current terminal, upper (current year) and the current-year increment of lower (1-year-old) lateral branches. An average, representative branch was chosen from each branch class. In addition, the average photosynthetic rate was estimated for the short-shoot leaves. A summing approach was used to estimate potential whole-plant C gain. The results of this method indicated that treatment differences were more pronounced at the plant- than at the leaf- or branch-level, because minor effects within modules accrued in scaling to plant level. The whole-plant response in C gain was determined by the counteracting changes in P S and A. For example, in the O3-sensitive clone (259), inhibition of P S in elevated O3 (at both ambient and elevated CO2) was partially ameliorated by an increase in total A. For the O3-tolerant clone (216), on the other hand, stimulation of photosynthetic rates in elevated CO2 was nullified by decreased total A.

Elevated carbon dioxide and ozone Leaf area Photosynthesis Populus tremuloides (Michx.) Potential carbon gain