Gravenhorst, G.

Ibrom, Andreas

June, T.

Kreinlein, H.

Oltchev, A.

Panferov, O.

Rakkibu, G.

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Downloaded from orbit.dtu.dk on: Dec 20, 2017A simple alternative to the light-use efciency approach that considers canopyphotosynthesis saturation with lightIbrom, Andreas; Oltchev, A.; Panferov, O.; Kreinlein, H.; June, T.; Rakkibu, G.; Gravenhorst, G.Published in:Geophysical Research AbstractsPublication date:2008Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Ibrom, A., Oltchev, A., Panferov, O., Kreinlein, H., June, T., Rakkibu, G., & Gravenhorst, G. (2008). A simplealternative to the light-use efciency approach that considers canopy photosynthesis saturation with light.Geophysical Research Abstracts, 10, EGU2008-A-06950.Geophysical Research Abstracts,Vol. 10, EGU2008-A-06950, 2008SRef-ID: 1607-7962/gra/EGU2008-A-06950EGU General Assembly 2008© Author(s) 2008A simple alternative to the light-use efficiency approachthat considers canopy photosynthesis saturation withlightIbrom A. (1,3) Oltchev, A. (2,3), Panferov, O. (3), Kreinlein, H. (3), June, T. (4,5),Rakkibu, G. (3), Gravenhorst, G. (3)(1) Biosystems Department, Risø National Laboratory, Denmark, Technical University ofDenmark (DTU), 4000 Roskilde Denmark, (andreas.ibrom@risoe.dk/ Fax: ++45 46773160 /Phone: ++45 46774177), (2) A.N. Severtsov Institute of Ecology and Evolution of RAS,Moscow, Russia (3) Institute of Bioclimatology, Germany, Georg-August-University,Göttingen, (4) SEAMEO BIOTROP, Bogor, Indonesia, (5) Institute Pertanian Bogor (IPB),Bogor, IndonesiaAbstractWe report eddy covariance CO2 flux and meteorological observations from a trop-ical rain forest in Indonesia that clearly show saturation of canopy photosynthesis(Pg) at relatively moderate incident and absorbed photosynthetically active radiation(PAR) (Ibrom et al. 2008). CO2 fluxes were measured with and open-path fast re-sponse IRGA (LI-7500, LI-COR, NE, USA) and a 3D ultrasonic anemometer (USA1,Metek, Elmshorm, Germany). PAR absorption was calculated with a one dimensionalmodel (Oltchev et al. 2007) and complied with measured short wave albedo at the site,the Lore Lindu National Park, Central Sulawesi, Indonesia.We investigated how this saturation propagated moving from half hourly to larger timescales and found that in the tropical climate, saturation was the dominant phenomenonof the photosynthetic light response both at daily and monthly time scales. From thiswe conclude that the fundamental assumption of the very often used light-use effi-ciency approach (Monteith 1972), i.e. that light use efficiency is a constant under nonlimiting water vapour saturation deficit (D) , temperature and soil water availability,does not apply at this site. We also revisited studies from other forests and climatesand found indications for Pg saturation. These were however masked by combiningthe light-use efficiency approach with D reduction functions that are used to includecertain reduction of ε at dry (and at the same time sunny) weather situations in thesimulations.Apart from the critical evaluation of the light-use efficiency approach we also suggesta similarly simple approach that is able to include both saturation and reduction ofPg at high D levels based on a simple Blackman response approach. This approachuses the light use efficiency approach only for non saturating condition and a constantmaximum Pg (Pmax) when absorbed PAR exceeds saturating levels. As D was foundto reduce Pmax, the PAR level at which Pg saturated became a well described functionof D.We advocate replacing the current version of the light-use efficiency approach by thecombined Blackman response when simulating GPP from remote sensing products.Future research should focus to investigate biome characteristic relationships of theadditional parameter, Pmax, with climate and canopy structure.AcknowledgementsThis work was funded by the DFG and part of the collaborated research project “Sta-bility of rain forest margin areas” STORMA, SFB 552.ReferencesIbrom, A., A. Oltchev, T. June, H. Kreilein, G. Rakkibu, T. Ross, O. Panferov and G.Gravenhorst. 2008. Variation in photosynthetic light-use efficiency in a mountainoustropical rain forest in Indonesia. Tree Physiol. accepted for publicationMonteith, J.L. 1972. Solar radiation and production in tropical ecosystems. J. Appl.Ecol. 9Oltchev, A., A. Ibrom, T. Ross et al. 2007. A modelling approach for simulation ofwater and carbon dioxide exchange between multi-species tropical rain forest and theatmosphere. Ecol. Modell. doi:10.1016/j.ecolmodel.2007.10.021

A simple alternative to the light-use efﬁciency approach that considers canopy photosynthesis saturation with light

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A simple alternative to the light-use efﬁciency approach that considers canopy photosynthesis saturation with light

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