No stimulation in root production in response to 4 years of in situ CO2 enrichment at the Swiss treeline

Authors

  • I. Tanya Handa,

    Corresponding author
    1. Institute of Botany, University of Basel, Schönbeinstrasse 6, CH-4056 Basel, Switzerland;
    2. Centre of Functional Ecology and Evolution (CEFE-CNRS), 1919 route de Mende, Montpellier cedex 5, France; and
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  • Frank Hagedorn,

    1. Swiss Federal Institute of Forest, Snow and Landsacape Research (WSL), Zürcherstrasse 111, CH-8903 Birmensdorf, Switzerland
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  • Stephan Hättenschwiler

    1. Institute of Botany, University of Basel, Schönbeinstrasse 6, CH-4056 Basel, Switzerland;
    2. Centre of Functional Ecology and Evolution (CEFE-CNRS), 1919 route de Mende, Montpellier cedex 5, France; and
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*Correspondence author. E-mail: tanya.handa@cefe.cnrs.fr

Summary

  • 1Plants are frequently observed to increase carbon allocation to below-ground sinks and particularly, to accelerate fine root turnover in response to rising atmospheric CO2 concentration. While these strong below-ground responses have predominantly been observed in rapidly expanding systems, late successional plant communities have rarely been studied.
  • 2In an ongoing free air CO2 enrichment (FACE) experiment, we assessed below-ground responses to elevated CO2 after 4 years, in a treeline ecosystem in the Swiss Central Alps (2180 m a.s.l.) dominated by a late successional ericaceous dwarf shrub community (Vaccinium myrtillus, V. uliginosum, Empetrum hermaphroditum), and a sparse overstorey of 30-year-old Larix decidua and Pinus uncinata trees. Measurements included quantification of fine root growth using ingrowth root cores and parallel standing crop harvests and decomposition of roots using litter bags.
  • 3Elevated CO2 did not stimulate root growth of the treated vegetation (although some significant above-ground growth responses were observed), nor did altered root decomposition occur. Root quality measurements indicated that elevated CO2 resulted in significantly higher starch concentrations, but no change in N concentration, or root dehydrogenase activity.
  • 4The use of the stable isotope δ13C permitted us to trace the new carbon entering the system through our CO2 enrichment treatment. We observed that only c. 30% of new root biomass (< 2 mm) was formed by new carbon indicating a rather slow root turnover in this system.
  • 5Our data show that fine root growth may be much less stimulated by elevated CO2 in systems with late successional elements than has been reported in ecosystems with a rapidly expanding plant community biomass.

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