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Weak vertical canopy gradients of photosynthetic capacities and stomatal responses in a fertile Norway spruce stand

Journal article
Authors Lasse Tarvainen
Göran Wallin
Mats Räntfors
Johan Uddling
Published in Oecologia
Volume 173
Issue 4
Pages 1179–1189
ISSN 0029-8549
Publication year 2013
Published at Department of Biological and Environmental Sciences
Pages 1179–1189
Language en
Keywords Nitrogen allocation,Carbon assimilation, Stomatal conductance, Conifer, Optimality
Subject categories Biological Sciences


Abstract The sensitivity of carbon (C) assimilation to within-canopy nitrogen (N) allocation and of stomatal conductance (gs) to environmental variables were investigated along a vertical canopy gradient in a fertile Norway spruce [Picea abies (L.) Karst.] stand. Maximum rates of ribulose bisphosphate-saturated carboxylation (Vcmax) and electron transport (Jmax) exhibited weak relationships with needle N content. Using these relationships together with a combined stomatal-photosynthesis model, it was found that the sensitivity of C assimilation of 12 1-year old shoots to within-canopy N allocation pattern was very weak. Modelled C assimilation based on optimal compared to observed N allocation pattern increased by only 1–2 %, and altering total needle N content by ±30 % resulted in a 2–4 % change in modelled C assimilation. C assimilation was more sensitive to water use and changed by 8–12 % in response to ±30 % altered stomatal conductance. No indications of significant limitations of photosynthesis by other nutrients or non-optimal within-canopy allocation of water were detected. The sensitivity of gs to photosynthetic photon flux density (PPFD) was found to be stronger in the lower canopy, while no significant within-canopy variation was observed in light-saturated gs or stomatal sensitivity to vapour pressure deficit (VPD). The results of this study show that, at this N rich site, photosynthesis integrated for shoots at different canopy positions is only marginally affected by N allocation pattern and that increased standscale N availability would only be truly beneficial to canopy photosynthesis if it resulted in increased leaf area.

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