Ibrom, Andreas

Linderson, Maj-Lena

Lindroth, A.

Mikkelsen, Teis Nørgaard

Pilegaard, Kim

Online Research Database In Technology

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Downloaded from orbit.dtu.dk on: Dec 17, 2017Water use efficiency as a means to assess forest carbon uptake for differentmanagement strategiesLinderson, Maj-Lena; Mikkelsen, Teis Nørgaard; Ibrom, Andreas; Lindroth, A.; Pilegaard, KimPublished in:Proceedings (cd-rom)Publication date:2009Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Linderson, M-L., Mikkelsen, T. N., Ibrom, A., Lindroth, A., & Pilegaard, K. (2009). Water use efficiency as ameans to assess forest carbon uptake for different management strategies. In Proceedings (cd-rom) Max-Planck-Institute for Biogeochemistry.WATER USE EFFICIENCY AS A MEANS TO ASSESS FOREST CARBON UPTAKE FOR DIFFERENT MANAGEMENT STRATEGIES  M-L. Linderson1,2, T. N. Mikkelsen1, A. Ibrom1, A. Lindroth2, K. Pilegaard1 1Risoe DTU National Laboratory for Sustainable Energy, Roskilde, Denmark; Maj.Lena.Linderson@risoe.dk 2Dept. of Physical Geography and Ecosystems Analysis, Lund University, Sweden   ABSTRACT The possibility to use water use efficiency (WUE) as a means for up scaling leaf carbon uptake to forest stand scale is assessed. Leaf physiology observations from the Sorø beech forest, Denmark, were used to evaluate leaf WUE variability and its environmental dependencies. Whole tree carbon half-hourly and daily WUE was assessed using MAESTRA model simulations. Preliminary results indicate that both leaf and canopy WUE are dependent only on VDP and light and may thus be assessed from sap flow in combination with PAR and VPD measurements above the forest.     INTRODUCTION New tools are needed to assess forest stand carbon uptake for different forest management strategies and species composition where other methods, e.g. flux towers, fail due to large spatial integration. Water use efficiency (WUE) – the relationship between carbon uptake (Fc) and water use of the tree (Fw) – is considered to be a conservative species property only depending on the vapor pressure deficit (VPD) (Bierhuizen, J. F. and Slatyer, 1965; Baldocchi et al. 1987; Law et al. 2002):  constant=VPDFFwc   If this relationship is valid for leaves, disregarding their position in the tree, stem WUE is also constant and stem sap-flow measurements can be used to estimate carbon uptake of the whole tree and, with a representative selection of sap-flow measured trees, of the whole stand. The aim of this study is to assess the possibility to use water use efficiency (WUE) as a means for up scaling leaf carbon uptake to forest stand scale.  DATA AND METHOD The leaf flux measurements originates from the Soroe forest, a Danish 80-years old beech (Fagus sylvatica L) forest with an average tree height of 25 m and stand density of 430 stems/ha further described in Pilegaard et al. (2006). Fc and Fw were measured at four different heights during the growing seasons of 1999 and 2000, using an LCA-3 infrared gas analyzer (ADC) with a Parkinson leaf chamber, where PAR and transpiration were registered simultaneously as photosynthesis.   The leaf physiology observations were used to evaluate leaf WUE variability and its environmental dependencies. Whole tree carbon half-hourly and daily WUE was assessed applying the observed leaf WUE*VPD dependency of PAR to the MAESTRA model simulations, thus using the meteorological and physiological effects on the light distribution within the canopy. The MAESTRA model was parameterized according to physiological observations of the Soroe beech forest (e.g. leaf optical properties, vertical leaf area distribution and tree structure) (Ibrom et al. 2006).  CONCLUDING RESULTS Canopy net carbon uptake can successfully be calculated from sap flow measurements for the Soroe beech forest based on the following findings: • Observations show that WUE is dependent of incoming PAR below 500 μmol m-2 s-1 and, for the full range, dependent on VPD and independent of both different levels of the trees and for the variation in environmental parameters. • Modeled daily canopy WUE for daytime fluxes (6-18 hours) are dependent only on VDP and light and may thus be assessed from sap flow in combination with PAR and VPD measurements above the forest.  • Low morning and evening fluxes are not included in the estimations but constitute only to a small part of the fluxes and are thus negligible.  • The method, so far, require that woody respiration and night time leaf respiration is treated separately.  REFERENCES Baldocchi, D. D., Verma, S. B. and Anderson, D. E., 1987. Canopy photosynthesis and water-use efficiency in a deciduous forest. Journal of Applied Ecology 24: 251_260. Bierhuizen, J. F. and Slatyer, R. O., 1965. Effect of atmospheric concentration of water vapour fluxes over terrestrial ecosystems. Global Change Biology 2: 159-168. Ibrom, A. et al., 2006. A comparative analysis of simulated and observed photosynthetic CO2 uptake in two coniferous forest canopies. Tree Physiology, 26(7): 845 - 864. Law, B., et al. (2002), Environmental controls over carbon dioxide and water vapor exchange of terrestrial vegetation, Agricultural and Forest Meteorology, 113, 97– 120. Pilegaard, K. et al., 2003. Field measurements of atmosphere biosphere interactions in a Danish beech forest. Boreal Environment Research 8: 315-333.  

Water use efficiency as a means to assess forest carbon uptake for different management strategies

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Water use efficiency as a means to assess forest carbon uptake for different management strategies

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