Abstract

Abstract. Vascular plant-dominated cushion bogs, which are exclusive to the Southern Hemisphere, are highly productive and constitute large sinks for atmospheric carbon dioxide compared to their moss-dominated counterparts around the globe. In this study, we experimentally investigated how a cushion bog plant community responded to elevated surface temperature conditions as they are predicted to occur in a future climate. We conducted the study in a cushion bog dominated by Astelia pumila on Tierra del Fuego, Argentina. We installed a year-round passive warming experiment using semicircular plastic walls that raised average near-surface air temperatures by between 0.4 and 0.7 ∘C (at the 3 of the 10 treatment plots which were equipped with temperature sensors). We focused on characterizing differences in morphological cushion plant traits and in carbon dioxide exchange dynamics using chamber gas flux measurements. We used a mechanistic modeling approach to quantify physiological plant traits and to partition the net carbon dioxide flux into its two components of photosynthesis and total ecosystem respiration. We found that A. pumila reduced its photosynthetic activity under elevated temperatures. At the same time, we observed enhanced respiration which we largely attribute, due to the limited effect of our passive warming on soil temperatures, to an increase in autotrophic respiration. Passively warmed A. pumila cushions sequestered between 55 % and 85 % less carbon dioxide than untreated control cushions over the main growing season. Our results suggest that even moderate future warming under the SSP1-2.6 scenario could decrease the carbon sink function of austral cushion bogs.

Highlights

  • Peatlands are an important component of the global carbon cycle due to the long-term accumulation of organic matter in peat soils (Gorham, 1991; Parish et al, 2008; Alexandrov et al, 2020)

  • We modeled the measured CO2 net ecosystem exchange (NEE) fluxes from the treatment and control plots separately using a combination of two deterministic functions in a single bulk model as in Runkle et al

  • The open-side chamber treatment resulted in higher nearsurface (1 cm above canopy) air temperatures at the treatment plots compared to the control plots

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Summary

Introduction

Peatlands are an important component of the global carbon cycle due to the long-term accumulation of organic matter in peat soils (Gorham, 1991; Parish et al, 2008; Alexandrov et al, 2020). Peatland CO2 dynamics are mainly controlled by radiation, temperature, soil water content, and plant community composition. Ecosystem respiration generally responds positively to increased temperatures (Gallego-Sala et al, 2018) and negatively to oxygen-depleted soil conditions (Wilson et al, 2016). Water saturation in soils typically leads to low oxygen availability and to low heterotrophic respiration. If vascular plants are present, they can transport oxygen into water-saturated soil layers and create oxic zones close to their roots, where respiration can be enhanced

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