Estimating canopy gross primary production by combining phloem stable isotopes with canopy and mesophyll conductances

• Published in: Plant, Cell & Environment
• Main Authors: Vernay, Antoine, Tian, Xianglin, Chi, Jinshu, Linder, Sune, Mäkelä, Annikki, Oren, Ram, Peichl, Matthias, Stangl, Zsofia, Tor-ngern, Pantana, Marshall, John
• Other Authors: Department of Forest Ecology and Management, Swedish University of Agricultural Sciences (SLU), Department of Forest Sciences Helsinki, Faculty of Agriculture and Forestry Helsinki, University of Helsinki-University of Helsinki, Southern Swedish Forest Research Centre, Nicholas School of the Environment and Earth Sciences, Duke University Durham, Chulalongkorn University Bangkok, Erkko Visiting Professor Programme of the Jane and Aatos Erkko 375th Anniversary Fund, Kempestiftelserna SMK-1743, Knut & Alice Wallenberg Foundation2015.0047
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2020
• Subjects: boreal forest; stand transpiration; intrinsic water-use efficiency; mesophyll conductance; nitrogen fertilization; phloem delta C-13; PRELES; sap flux; envir; geo; Northern Sweden
• Online Access: https://doi.org/10.1111/pce.13835; https://hal.archives-ouvertes.fr/hal-02883481/file/Vernay%20et%20al,%20PrePrint_PCE_2020.pdf; https://hal.archives-ouvertes.fr/hal-02883481

International audience Gross primary production (GPP) is a key component of the forest carbon cycle. However, our knowledge of GPP at the stand scale remains uncertain because estimates derived from eddy covariance (EC) rely on semi-empirical modeling and the assumptions of the EC technique are sometimes not fully met. We propose using the sap flux/isotope method as an alternative way to estimate canopy GPP, termed GPPiso/SF, at the stand scale and at daily resolution. It is based on canopy conductance inferred from 38 sap flux and intrinsic water-use efficiency estimated from the stable carbon isotope composition of phloem contents. The GPPiso/SF estimate was further corrected for seasonal variations in photosynthetic capacity and mesophyll conductance. We compared our estimate of GPPiso/SF to the GPP derived from PRELES, a model parameterised with EC data. The comparisons were performed in a highly instrumented, boreal Scots pine forest in northern Sweden, including a nitrogen fertilised and a reference plot. The resulting annual and daily GPPiso/SF estimates agreed well with PRELES, in the fertilised plot and the reference plot. We discuss the GPPiso/SF method as an alternative which can be widely applied 46 without terrain restrictions, where the assumptions of EC are not met.