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, Makela, Annikki, Oren, Ram, Peichl, Matthias, Stangl, Zsofia R., Tor-Ngern, Pantana, Marshall, John D.
• Other Authors: Department of Forest Sciences, Forest Modelling Group
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2020
• Subjects: boreal forest; intrinsic water-use efficiency; mesophyll conductance; nitrogen fertilization; phloem delta C-13; PRELES; sap flux; stand transpiration; WATER-USE EFFICIENCY; EDDY COVARIANCE TECHNIQUE; CARBON-DIOXIDE EXCHANGE; SAP FLOW MEASUREMENT; STOMATAL CONDUCTANCE; SCOTS PINE; SOIL-WATER; LEAF-AREA; PHOTOSYNTHETIC CAPACITY; TEMPERATURE RESPONSE; 11831 Plant biology; 4112 Forestry; Northern Sweden
• Online Access: http://hdl.handle.net/10138/318584

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 modelling 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 GPP(iso/SF), at the stand scale and at daily resolution. It is based on canopy conductance inferred from sap flux and intrinsic water-use efficiency estimated from the stable carbon isotope composition of phloem contents. The GPP(iso/SF)estimate was further corrected for seasonal variations in photosynthetic capacity and mesophyll conductance. We compared our estimate of GPP(iso/SF)to the GPP derived from PRELES, a model parameterized with EC data. The comparisons were performed in a highly instrumented, boreal Scots pine forest in northern Sweden, including a nitrogen fertilized and a reference plot. The resulting annual and daily GPP(iso/SF)estimates agreed well with PRELES, in the fertilized plot and the reference plot. We discuss the GPP(iso/SF)method as an alternative which can be widely applied without terrain restrictions, where the assumptions of EC are not met. Peer reviewed