Betula shrubs as conduits for soil methane on peatlands

Methane (CH₄) emissions from a peatland are a balance between CH₄-producing and consuming processes in the peat.Certain graminoid and other herbaceous plant species provide a pathway for CH₄ to escape from the peat profile without becoming available to CH₄-consuming microbes (eg. Riutta et al. 2020). Whether also shrubs such as Betula nana and trees such as B. pubescens that are abundant in peatlands provide such a pathway is at least partly an open question.

We measured CH₄ fluxes of B. nana shoots both at a field site on a north boreal fen and in a climate-controlled (temperature, PAR) cabinet setup. In the field, sporadic measurements were made with manual chambers. Both chamber setups enclosed one shoot of the plant. In the climate-controlled setup, flux was measured multiple times per hour with an automated chamber system, and CH₄ concentration in the soil was monitored with gas samples. PAR and temperature were monitored by the automated setup. ¹³C-labelled CH₄ was injected into the soil in the climate-controlled setup to confirm that the source of the CH₄ in the chamber was the soil and not possible aerobic CH₄ production in the shoot, nor external contamination. Potential microbial CH₄ production within B. nana is evaluated through PCR detection and sequencing of the methanogenic mcrA gene (in progress). In the climate-controlled setup, fluxes were measured similarly also from saplings of B. pubescens and B. pendula – a related species that does not grow in peatlands. A computerized tomography (CT) scan of the plants was performed to assess the presence or absence of aerenchymatic tissues, which could act as a pathway for the CH₄ in the plant.

CH₄ emission from B. nana shoots was observed both in the field and in the climate-controlled setup. No PAR dependence of the emission was found, excluding the possibility of aerobic production of CH₄ in the shoot. Further, the labelling experiment confirmed that B. nana acted as a conduit for CH₄ originating from the soil. B. pubescens showed little flux and B. pendula no flux, even though CH₄ was present in the soil. The CT scan confirmed presence of aerenchymatic tissue in the shoots B. nana and to a lesser extent in B. pubescens but not in B. pendula.

 

 

References

Riutta, T., Korrensalo, A., Laine, A.M., Laine, J., Tuittila, E.-S., 2020. Interacting effects of vegetation components and water level on methane dynamics in a boreal fen. Biogeosciences 17, 727–740.