Photosynthetic responses to understory shade and elevated carbon dioxide concentration in four northern hardwood tree species

TitlePhotosynthetic responses to understory shade and elevated carbon dioxide concentration in four northern hardwood tree species
Publication TypeJournal Article
Year of Publication2006
AuthorsSefcik LTaylor, Zak DR, Ellsworth DS
JournalTree Physiology
Volume26
Issue12
Pagination1589-1599
Date Published12/2006
KeywordsVASCULAR PLANTS
Abstract

Seedling responses to elevated atmospheric CO2 concentration ([CO2]) 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 +mol molv1)) and understory shade (deep and moderate) in open-top chambers placed in a forest understory. The elevated [CO2] 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 [CO2], long-term enhancement of photosynthesis was 10% lower than the instantaneous enhancement seen in ambient-[ CO2]-grown plants (P < 0.021). Overall, growth light environment affected long-term photosynthetic enhancement by elevated [CO2]: as the growth irradiance increased, proportional enhancement due to elevated [CO2] decreased from 97% for plants grownin deep shade to47% for plants grownin moderate shade. Results suggest that in N-limited northern temperate forests, trees grown in deep shade may display greater photosynthetic gains from a CO2-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 [CO2] translate into improved growth and survival of shade-intolerant species, it could alter the future composition and dynamics of successional forest communities.