title: Photosynthetic responses to understory shade and elevated carbon dioxide concentration in four northern hardwood tree species.
abstract: Seedling responses to elevated atmospheric CO(2) concentration ([CO(2)]) and solar irradiance were measured over two growing seasons in shade-tolerant Acer saccharum Marsh. and Fagus grandifolia J.F. Ehrh. and shade-intolerant Prunus serotina, a J.F. Ehrh. and Betula papyrifera Marsh. Seedlings were exposed to a factorial combination of [CO2] (ambient and elevated (658 micromol mol-1)) and understory shade (deep and moderate) in open-top chambers placed in a forest understory. The elevated [CO(2)] treatment increased mean light-saturated net photosynthetic rate by 63% in the shade-tolerant species and 67% in the shade-intolerant species. However, when measured at the elevated [CO(2)], long-term enhancement of photosynthesis was 10% lower than the instantaneous enhancement seen in ambient-[CO(2)]-grown plants (P < 0.021). Overall, growth light environment affected long-term photosynthetic enhancement by elevated [CO(2)]: as the growth irradiance increased, proportional enhancement due to elevated [CO(2)] decreased from 97% for plants grown in deep shade to 47% for plants grown in moderate shade. Results suggest that in N-limited northern temperate forests, trees grown in deep shade may display greater photosynthetic gains from a CO(2)-enriched atmosphere than trees growing in more moderate shade, because of greater downregulation in the latter environment. If photosynthetic gains by deep-shade-grown plants in response to elevated [CO(2)] translate into improved growth and survival of shade-intolerant species, it could alter the future composition and dynamics of successional forest communities.
authors.affiliation: School of Natural Resources and Environment, 440 Church Street, University of Michigan, Ann Arbor, MI 48109-1041, USA. ltsefcik@umich.edu
authors.forename: Lesley T
authors.initials: LT
authors.lastname: Sefcik
authors.forename: Donald R
authors.initials: DR
authors.lastname: Zak
authors.forename: David S
authors.initials: DS
authors.lastname: Ellsworth
mesh_terms: D002245:Carbon Dioxide / Q000502:physiology*; D003624:Darkness; D017753:Ecosystem; D019684:Magnoliopsida / Q000502:physiology*; D009584:Nitrogen / Q000378:metabolism; D010788:Photosynthesis / Q000502:physiology*; D018515:Plant Leaves / Q000378:metabolism; D036226:Seedlings / Q000502:physiology*; D013472:Sunlight; D014197:Trees / Q000502:physiology*
chemical_list: D002245:Carbon Dioxide; D009584:Nitrogen