Improved methodology for tracing a pulse of 13C-labelled tree photosynthate carbon to ectomycorrhizal roots, other soil biota and soil processes in the field

Abstract

Isotopic pulse-labelling of photosynthate allows tracing of carbon (C) from tree canopies to below-ground biota and calculations of its turnover in roots and recipient soil microorganisms. A high concentration of label is desirable but is difficult to achieve in field studies of intact ecosystem patches with trees. Moreover, root systems of trees overlap considerably in most forests, which requires a large labelled area to minimize the impact of C allocated below-ground by un-labelled trees. We describe a method which combines a high level of labelling at ambient concentrations of CO2, [CO2], with undisturbed root systems and a model to account for root C and root-derived C from un-labelled trees. We raised 5-m-tall chambers, each covering 50 m(2) of ground (volume 250 m(3)) in a young boreal Pinus sylvestris L. forest with up to 5 m tall trees. Rather than a conventional single release of (CO2)-C-13, we used five consecutive releases, each followed by a draw-down period, thus avoiding high [CO2]. Hence, we elevated successively the (CO2)-C-13 from 1.1 to 23 atom% after the first release to 61 atom% after the fifth, while maintaining [CO2] below 500 p.p.m. during 4-4.5 h of labelling. The average abundance of (CO2)-C-13 was as high as 42 atom%. We used the central 10 m(2) of the 50 m(2) area for sampling of roots and other soil biota. We modelled the dilution of labelled C across the plots by un-labelled C from roots of trees outside the area. In the central 10 m(2) area, similar to 85% of roots and root-associated biota received C from labelled trees. In summary, we elevated the labelling of roots and associated soil biota four-fold compared with previous studies and described the commonly overlooked impact of roots from un-labelled trees outside the labelled area.

Keywords

forests; mycorrhiza; soil biology; stable isotope probing; tree below-ground C flux

Published in

Tree Physiology
2025, volume: 45, number: 1, article number: tpae169
Publisher: OXFORD UNIV PRESS

SLU Authors

• Högberg, Peter

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    

• Klatt, Christian

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    

• Franklin, Oskar

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    
  • International Institute for Applied Systems Analysis (IIASA)

• Henriksson, Nils

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    

• Lim, Hyungwoo

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    

• Inselsbacher, Erich

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    
  • University of Natural Resources and Life Sciences, Vienna (BOKU)

• Hurry, Vaughan

  • Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences
    

• Näsholm, Torgny

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    

• Nordström Högberg, Mona

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    

UKÄ Subject classification

Forest Science

Publication identifier

• DOI: https://doi.org/10.1093/treephys/tpae169

Permanent link to this page (URI)

https://res.slu.se/id/publ/140654