title: Photosynthetic acclimation of overstory Populus tremuloides and understory Acer saccharum to elevated atmospheric CO2 concentration: interactions with shade and soil nitrogen.
abstract: We exposed Populus tremuloides Michx. and Acer saccharum Marsh. to a factorial combination of ambient and elevated atmospheric CO2 concentrations ([CO2]) and high-nitrogen (N) and low-N soil treatments in open-top chambers for 3 years. Our objective was to compare photosynthetic acclimation to elevated [CO2] between species of contrasting shade tolerance, and to determine if soil N or shading modify the acclimation response. Sun and shade leaf responses to elevated [CO2] and soil N were compared between upper and lower canopy leaves of P. tremuloides and between A. saccharum seedlings grown with and without shading by P. tremuloides. Both species had higher leaf N concentrations and photosynthetic rates in high-N soil than in low-N soil, and these characteristics were higher for P. tremuloides than for A. saccharum. Electron transport capacity (Jmax) and carboxylation capacity (Vcmax) generally decreased with atmospheric CO2 enrichment in all 3 years of the experiment, but there was no evidence that elevated [CO2] altered the relationship between them. On a leaf area basis, both Jmax and Vcmax acclimated to elevated [CO2] more strongly in shade leaves than in sun leaves of P. tremuloides. However, the apparent [CO2] x shade interaction was largely driven by differences in specific leaf area (m2 g-1) between sun and shade leaves. In A. saccharum, photosynthesis acclimated more strongly to elevated [CO2] in sun leaves than in shade leaves on both leaf area and mass bases. We conclude that trees rooted freely in the ground can exhibit photosynthetic acclimation to elevated [CO2], and the response may be modified by light environment. The hypothesis that photosynthesis acclimates more completely to elevated [CO2] in shade-tolerant species than in shade-intolerant species was not supported.
authors.affiliation: Department of Forestry, Box 9681, Mississippi State University, Mississippi State, MS 39762, USA. mkubiske@fs.fed.us
authors.forename: Mark E
authors.initials: ME
authors.lastname: Kubiske
authors.forename: Donald R
authors.initials: DR
authors.lastname: Zak
authors.forename: Kurt S
authors.initials: KS
authors.lastname: Pregitzer
authors.forename: Yu
authors.initials: Y
authors.lastname: Takeuchi
mesh_terms: D000064:Acclimatization / Q000502:physiology; D031002:Acer / Q000502:physiology*; D002245:Carbon Dioxide / Q000502:physiology; D008027:Light; D009584:Nitrogen / Q000502:physiology; D010788:Photosynthesis / Q000502:physiology*; D018515:Plant Leaves / Q000033:anatomy & histology / Q000502:physiology; D032107:Populus / Q000502:physiology*; D012987:Soil; D014197:Trees / Q000502:physiology*
chemical_list: D012987:Soil; D002245:Carbon Dioxide; D009584:Nitrogen