Disaggregation of canopy photosynthesis among tree species in a mixed broadleaf forest

Abstract

Carbon dioxide sequestration from the atmosphere is commonly assessed using the eddy covariance method. Its net flux signal can be decomposed into gross primary production and ecosystem respiration components, but these have seldom been tested against independent methods. In addition, eddy covariance lacks the ability to partition carbon sequestration among individual trees or species within mixed forests. Therefore, we compared gross primary production from eddy covariance versus an independent method based on sap flow and water-use efficiency, as measured by the tissue heat balance method and delta C-13 of phloem contents, respectively. The latter measurements were conducted on individual trees throughout a growing season in a mixed broadleaf forest dominated by three tree species, namely English oak, narrow-leaved ash and common hornbeam (Quercus robur L., Fraxinus angustifolia Vahl, and Carpinus betulus L., respectively). In this context, we applied an alternative ecophysiological method aimed at verifying the accuracy of a state-of-the-art eddy covariance system while also offering a solution to the partitioning problem. We observed strong agreement in the ecosystem gross primary production estimates (R-2 = 0.56; P < 0.0001), with correlation being especially high and nearly on the 1:1 line in the period before the end of July (R-2 = 0.85; P < 0.0001). After this period, the estimates of gross primary production began to diverge. Possible reasons for the divergence are discussed, focusing especially on phenology and the limitation of the isotopic data. English oak showed the highest per-tree daily photosynthetic rates among tree species, but the smaller, more abundant common hornbeam contributed most to the stand-level summation, especially early in the spring. These findings provide a rigorous test of the methods and the species-level photosynthesis offers avenues for enhancing forest management aimed at carbon sequestration.

Keywords

deciduous angiosperms; eddy covariance; gross primary production; phenology; phloem isotopes; sap flow

Published in

Tree Physiology
2024, Volume: 44, number: 7, article number: tpae064Publisher: OXFORD UNIV PRESS

SLU Authors

• Marshall, John

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    
  • Leibniz Centre for Agricultural Landscape Research (ZALF)
  • The Czech Academy of Sciences
  • University of Gothenburg

UKÄ Subject classification

Forest Science


Publication identifier

DOI: https://doi.org/10.1093/treephys/tpae064

Permanent link to this page (URI)

https://res.slu.se/id/publ/131381