Carbon dioxide and methane exchange of a patterned subarctic fen during two contrasting growing seasons

Heiskanen, Lauri; Tuovinen, Juha-Pekka; Räsänen, Aleksi; Virtanen, Tarmo; Juutinen, Sari; Lohila, Annalea; Penttilä, Timo; Linkosalmi, Maiju; Mikola, Juha; Laurila, Tuomas; Aurela, Mika

The patterned microtopography of subarctic mires generates a variety of environmental conditions, and carbon dioxide (COinline-formula2) and methane (CHinline-formula4) dynamics vary spatially among different plant community types (PCTs). We studied the COinline-formula2 and CHinline-formula4 exchange between a subarctic fen and the atmosphere at Kaamanen in northern Finland based on flux chamber and eddy covariance measurements in 2017–2018. We observed strong spatial variation in carbon dynamics between the four main PCTs studied, which were largely controlled by water table level and differences in vegetation composition. The ecosystem respiration (ER) and gross primary productivity (GPP) increased gradually from the wettest PCT to the drier ones, and both ER and GPP were larger for all PCTs during the warmer and drier growing season 2018. We estimated that in 2017 the growing season COinline-formula2 balances of the PCTs ranged from inline-formula−20 g C minline-formula−2 (Trichophorum tussock PCT) to 64 g C minline-formula−2 (string margin PCT), while in 2018 all PCTs were small COinline-formula2 sources (10–22 g C minline-formula−2). We observed small growing season CHinline-formula4 emissions (inline-formula< 1 g C minline-formula−2) from the driest PCT, while the other three PCTs had significantly larger emissions (mean 7.9, range 5.6–10.1 g C minline-formula−2) during the two growing seasons. Compared to the annual COinline-formula2 balance (inline-formula−8.5 inline-formula± 4.0 g C minline-formula−2) of the fen in 2017, in 2018 the annual balance (inline-formula−5.6 inline-formula± 3.7 g C minline-formula−2) was affected by an earlier onset of photosynthesis in spring, which increased the COinline-formula2 sink, and a drought event during summer, which decreased the sink. The CHinline-formula4 emissions were also affected by the drought. The annual CHinline-formula4 balance of the fen was 7.3 inline-formula± 0.2 g C minline-formula−2 in 2017 and 6.2 inline-formula± 0.1 g C minline-formula−2 in 2018. Thus, the carbon balance of the fen was close to zero in both years. The PCTs that were adapted to drier conditions provided ecosystem-level resilience to carbon loss due to water level drawdown.

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Heiskanen, Lauri / Tuovinen, Juha-Pekka / Räsänen, Aleksi / et al: Carbon dioxide and methane exchange of a patterned subarctic fen during two contrasting growing seasons. 2021. Copernicus Publications.

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