Betula shrubs as conduits for soil methane on peatlands
Authors: Koskinen Markku , Kohl Lukas , Grönholm Tiia , Polvinen Tatu , Putkinen Anuliina , Laiho Raija , Pihlatie Mari , Mäkiranta Päivi 
Published: March 2021

&lt;p&gt;&lt;span&gt;Methane (CH&lt;/span&gt;&lt;sub&gt;&lt;span&gt;4&lt;/span&gt;&lt;/sub&gt;&lt;span&gt;) emissions from a peatland are a balance between CH&lt;/span&gt;&lt;sub&gt;&lt;span&gt;4&lt;/span&gt;&lt;/sub&gt;&lt;span&gt;-producing and consuming processes in the peat.&lt;/span&gt;&lt;sub&gt;&lt;/sub&gt;&lt;span&gt;Certain graminoid and other herbaceous plant species provide a pathway for CH&lt;/span&gt;&lt;sub&gt;&lt;span&gt;4&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; to escape from the peat profile without becoming available to CH&lt;/span&gt;&lt;sub&gt;&lt;span&gt;4&lt;/span&gt;&lt;/sub&gt;&lt;span&gt;-consuming microbes (eg. Riutta et al. 2020). Whether also shrubs such as &lt;/span&gt;&lt;span&gt;&lt;em&gt;Betula nana &lt;/em&gt;&lt;/span&gt;&lt;span&gt;and trees such as &lt;/span&gt;&lt;span&gt;&lt;em&gt;B. pubescens&lt;/em&gt;&lt;/span&gt;&lt;span&gt; that are abundant in peatlands provide such a pathway is at least partly an open question.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;We measured CH&lt;/span&gt;&lt;sub&gt;&lt;span&gt;4&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; fluxes of &lt;/span&gt;&lt;span&gt;&lt;em&gt;B. nana&lt;/em&gt;&lt;/span&gt;&lt;span&gt; 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 CH&lt;/span&gt;&lt;sub&gt;&lt;span&gt;4&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; concentration in the soil was monitored with gas samples. PAR and temperature were monitored by the automated setup. &lt;/span&gt;&lt;sup&gt;&lt;span&gt;13&lt;/span&gt;&lt;/sup&gt;&lt;span&gt;C-labelled CH&lt;/span&gt;&lt;sub&gt;&lt;span&gt;4&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; was injected into the soil in the climate-controlled setup to confirm that the source of the CH&lt;/span&gt;&lt;sub&gt;&lt;span&gt;4&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; in the chamber was the soil and not possible aerobic CH&lt;/span&gt;&lt;sub&gt;&lt;span&gt;4&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; production in the shoot, nor external contamination. Potential microbial CH&lt;/span&gt;&lt;sub&gt;&lt;span&gt;4&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; production within &lt;/span&gt;&lt;span&gt;&lt;em&gt;B. nana&lt;/em&gt;&lt;/span&gt;&lt;span&gt; is evaluated through PCR detection and sequencing of the methanogenic &lt;/span&gt;&lt;span&gt;&lt;em&gt;mcrA&lt;/em&gt;&lt;/span&gt;&lt;span&gt; gene (in progress). In the climate-controlled setup, fluxes were measured similarly also from saplings of &lt;/span&gt;&lt;span&gt;&lt;em&gt;B. pubescens &lt;/em&gt;&lt;/span&gt;&lt;span&gt;and &lt;/span&gt;&lt;span&gt;&lt;em&gt;B. pendula&lt;/em&gt;&lt;/span&gt;&lt;span&gt; &amp;#8211; a related species that does not grow in peatlands&lt;/span&gt;&lt;span&gt;. 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 CH&lt;/span&gt;&lt;sub&gt;&lt;span&gt;4&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; in the plant.&lt;/span&gt;&lt;/p&gt;&lt;p&gt; &lt;span&gt;CH&lt;/span&gt;&lt;sub&gt;&lt;span&gt;4&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; emission from &lt;/span&gt;&lt;span&gt;&lt;em&gt;B. nana&lt;/em&gt;&lt;/span&gt;&lt;span&gt; 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 CH&lt;/span&gt;&lt;sub&gt;&lt;span&gt;4&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; in the shoot. Further, the labelling experiment confirmed that &lt;/span&gt;&lt;span&gt;&lt;em&gt;B. nana &lt;/em&gt;&lt;/span&gt;&lt;span&gt;acted as a conduit for CH&lt;/span&gt;&lt;sub&gt;&lt;span&gt;4&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; originating from the soil. &lt;/span&gt;&lt;span&gt;&lt;em&gt;B. pubescens &lt;/em&gt;&lt;/span&gt;&lt;span&gt;showed little flux and &lt;/span&gt;&lt;span&gt;&lt;em&gt;B. pendula &lt;/em&gt;&lt;/span&gt;&lt;span&gt;no flux, even though CH&lt;/span&gt;&lt;sub&gt;&lt;span&gt;4 &lt;/span&gt;&lt;/sub&gt;&lt;span&gt;was present in the soil. The CT scan confirmed presence of aerenchymatic tissue in the shoots &lt;/span&gt;&lt;span&gt;&lt;em&gt;B. nana &lt;/em&gt;&lt;/span&gt;&lt;span&gt;and to a lesser extent in &lt;/span&gt;&lt;span&gt;&lt;em&gt;B. pubescens &lt;/em&gt;&lt;/span&gt;&lt;span&gt;but not in &lt;/span&gt;&lt;span&gt;&lt;em&gt;B. pendula.&lt;/em&gt;&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;span&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;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&amp;#8211;740. &lt;/span&gt;&lt;/p&gt;