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JXB Advance Access published online on May 4, 2007
Journal of Experimental Botany, doi:10.1093/jxb/erm084
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© The Author [2007]. Published by Oxford University Press [on behalf of the Society for Experimental Biology]. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

RESEARCH PAPER

A complete energy balance from photons to new biomass reveals a light- and nutrient-dependent variability in the metabolic costs of carbon assimilation

Torsten Jakob*, Heiko Wagner, Katja Stehfest and Christian Wilhelm

Biology I, Plant Physiology, University Leipzig, Johannisallee 21–23, D-04103 Leipzig, Germany

* To whom correspondence should be addressed: E-mail: tjakob{at}rz.uni-leipzig.de

The energy balance of Phaeodactylum tricornutum cells from photon to biomass have been analysed under nutrient-replete and N-limiting conditions in combination with fluctuating (FL) and non-fluctuating (SL) dynamic light. For this purpose, the amount of photons absorbed has been related to electrons transported by photosystem II, to gas exchange rates, and to the newly formed biomass differentially resolved into carbohydrates, proteins, and lipids measured by means of Fourier transform infrared (FTIR) spectroscopy. Under high nutrient conditions, the quantum efficiency of carbon-related biomass production ({Phi}C) and the metabolic costs of carbon (C) production were found to be strongly controlled by the light climate. Under N-limited conditions, the light climate was less important for the efficieny of primary production. Thus, the largest range of {Phi}C dependent on the nutrient status of the cells was observed under non-fluctuating light conditions which are comparable with stratified conditions in the natural environment. It is evident that N limitation induced pronounced changes in the composition of macromolecular compounds and, thus, influenced the degree of reduction of the biomass as well as the metabolic costs of C production. However, {Phi}C and the metabolic costs are not predictable from the photosynthesis rates. In consequence, the results clearly show that bio-optical methods as well as gas exchange measurements during the light phase can severely mismatch the true energy storage in the biomass especially under high nutrient in combination with non-fluctuating light conditions.

Key words: Alternative electron pathways, diatom, dynamic light, energy balance, FTIR, global warming, nitrate, photosynthesis

Received 17 January 2007; Revised 21 March 2007 Accepted 26 March 2007


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