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Estimating canopy gross primary production by combining phloem stable isotopes with canopy and mesophyll conductances |
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| Authors: | Antoine Vernay Xianglin Tian Jinshu Chi Sune Linder Annikki Mäkelä Ram Oren Matthias Peichl Zsofia R. Stangl Pantana Tor-Ngern John D. Marshall |
| Affiliation: | 1. Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden;2. Department of Forest Sciences, University of Helsinki, Helsinki, Finland;3. Southern Swedish Forest Research Centre, Swedish University of Agricultural Sciences, Alnarp, Sweden;4. Department of Forest Sciences, University of Helsinki, Helsinki, Finland Division of Environmental Science & Policy, Nicholas School of the Environment, Duke University, Durham, North Carolina, USA Department of Civil & Environmental Engineering, Pratt School of Engineering, Duke University, Durham, North Carolina, USA;5. Department of Environmental Science, Faculty of Science, Chulalongkorn University, Bangkok, Thailand Environment, Health and Social Data Analytics Research Group, Chulalongkorn University, Bangkok, Thailand |
| Abstract: | 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 GPPiso/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 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 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 GPPiso/SF estimates agreed well with PRELES, in the fertilized plot and the reference plot. We discuss the GPPiso/SF method as an alternative which can be widely applied without terrain restrictions, where the assumptions of EC are not met. |
| Keywords: | boreal forest intrinsic water-use efficiency mesophyll conductance nitrogen fertilization phloem δ13C PRELES sap flux stand transpiration |