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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
Links dx.doi.org/10.1007/s00442-013-2703-...
Keywords Nitrogen allocation,Carbon assimilation, Stomatal conductance, Conifer, Optimality
Subject categories Biological Sciences

Abstract

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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