Preprints
https://doi.org/10.5194/bg-2021-287
https://doi.org/10.5194/bg-2021-287

  12 Nov 2021

12 Nov 2021

Review status: this preprint is currently under review for the journal BG.

Massive C loss from subalpine grassland soil with seasonal warming larger than 1.5 °C in an altitudinal transplantation experiment

Matthias Volk1, Matthias Suter2, Anne-Lena Wahl1, and Seraina Bassin1,3 Matthias Volk et al.
  • 1Climate and Agriculture, Agroscope, Reckenholzstrasse 191, 8046 Zurich, Switzerland
  • 2Forage Production and Grassland Systems, Agroscope, Reckenholzstrasse 191, 8046 Zurich, Switzerland
  • 3Pädagogische Hochschule Schaffhausen, Ebnatstrasse 80, 8200 Schaffhausen, Switzerland

Abstract. Climate change is associated with a change in soil organic carbon (SOC) stocks, implying a feedback mechanism on global warming. Grassland soils represent 28 % of the global soil C sink and are therefore important for the atmospheric greenhouse gas concentration.

In a field experiment in the Swiss Alps we recorded changes in the ecosystem organic carbon stock under climate change conditions, while quantifying the ecosystem C fluxes at the same time (ecosystem respiration, gross primary productivity, C export in plant material and leachate water). We exposed 216 grassland monoliths to six different climate scenarios (CS) in an altitudinal transplantation experiment. In addition, we applied an irrigation treatment (+12–21 % annual precipitation) and an N deposition treatment (+3 and +15 kg N ha−1 a−1) in a factorial design, simulating summer-drought mitigation and atmospheric N pollution.

In five years the ecosystem C stock, consisting of plant C and SOC, dropped dramatically by about −14 % (−1034 ± 610 g C m−2) with the CS treatment representing a +3.0 °C seasonal (Apr.–Oct.) warming. N deposition and the irrigation treatment caused no significant effects. Measurements of C fluxes revealed that ecosystem respiration increased by 10 % at the +1.5 °C warmer CS site and by 38 % at the +3 °C warmer CS site (P ≤ 0.001 each), compared to the CS reference site with no warming. However, gross primary productivity was unaffected by warming, as were the amounts of exported C in harvested plant material and leachate water (dissolved organic C). As a result, the five year C flux balance resulted in a climate scenario effect of −936 ± 138 g C m−2 at the +3.0 °C CS, similar to the C stock climate scenario effect. It is likely that this dramatic C loss of the grassland is a transient effect before a new, climate adjusted steady state is reached.

Matthias Volk et al.

Status: open (until 24 Dec 2021)

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Matthias Volk et al.

Matthias Volk et al.

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Short summary
Because soils are an important sink for greenhouse gasses, we subjected sub-alpine grassland to a six level climate change treatment. Two independent methods showed that at warming > 1.5 °C the grassland ecosystem lost ca. 14 % or ca. 1 kg C m−2 in five years. This shrinking of the terrestrial C sink implies a substantial positive feedback to the atmospheric greenhouse effect. It is likely that this dramatic C loss is a transient effect before a new, climate adjusted steady state is reached.
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