Measuring methane emissions from tree shoots: challenges and advances
Authors: Tenhovirta Salla , Kohl Lukas , Koskinen Markku , Polvinen Tatu , Haikarainen Iikka , Pihlatie Mari 
Published: February 2023

&lt;p&gt;Recent evidence shows that the shoots of Scots pine trees are a source of small emissions of methane (CH&lt;sub&gt;4&lt;/sub&gt;), but it remains unclear if these emissions significantly reduce the CH&lt;sub&gt;4&lt;/sub&gt; sink strength of boreal forests. Progress in the shoot methane research is hindered by the technical challenges of shoot-level trace-gas flux measurements requiring closed-loop, non-steady-state chamber systems, as well as the difficulties in producing sufficient measurement data from hard-to-reach canopies in remote field sites.&lt;/p&gt;
&lt;p&gt;&amp;#160;&lt;/p&gt;
&lt;p&gt;We have identified possible sources of disturbance by VOCs and water vapour in spectral, laser-based online measurement systems, and developed ways to manage them (Kohl &lt;em&gt;et al.&lt;/em&gt;, 2019; Tenhovirta &lt;em&gt;et al.&lt;/em&gt;, 2022). Extended measurement campaigns in ambient conditions were made possible by conducting the measurements on tree saplings instead of mature trees, resulting in the finding that CH&lt;sub&gt;4&lt;/sub&gt; emissions from shoots increase with solar radiation and are enhanced by temperature (Tenhovirta &lt;em&gt;et al.&lt;/em&gt;, 2022). Our automated chamber measurement system in the greenhouse (Kohl, Koskinen &lt;em&gt;et al.&lt;/em&gt;, 2021) has enabled continuous measurements and control/treatment experiments. These measurements reveal that the CH&lt;sub&gt;4&lt;/sub&gt; emissions from Scots pine shoots follow diel cycles (Kohl, Tenhovirta, &lt;em&gt;et al.&lt;/em&gt;, in prep.), and rule out soil production or photosynthesis as a source for these emissions (Tenhovirta &lt;em&gt;et al&lt;/em&gt;., in prep). In addition, developing this system has provided solutions to common issues associated to chamber measurements, including excessive heating, water vapour accumulation and leakage.&lt;/p&gt;
&lt;p&gt;&amp;#160;&lt;/p&gt;
&lt;p&gt;In this contribution we show how some of these issues are solved in manual and automatic chamber systems to achieve reliable measurements, how to choose detection limits, and what solutions we propose for the remaining challenges.&lt;/p&gt;
&lt;p&gt;&amp;#160;&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;&amp;#160;&lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;Kohl L, Koskinen M, Polvinen T, Tenhovirta SAM, Rissanen K, Patama M, Zanetti A, Pihlatie M&lt;/strong&gt;. &lt;strong&gt;2021&lt;/strong&gt;. An automated system for trace gas flux measurements from plant foliage and other plant compartments. &lt;em&gt;Atmospheric Measurement Techniques&lt;/em&gt; &lt;strong&gt;14&lt;/strong&gt;: 4445&amp;#8211;4460.&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;Kohl L, Koskinen M, Rissanen K, Haikarainen I, Polvinen T, Hell&amp;#233;n H, Pihlatie M&lt;/strong&gt;. &lt;strong&gt;2019&lt;/strong&gt;. Technical note: Interferences of volatile organic compounds (VOC) on methane concentration measurements. &lt;em&gt;Technical note: Interferences of volatile organic compounds (VOC) on methane concentration measurements&lt;/em&gt;: 1&amp;#8211;18.&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;Tenhovirta SAM, Kohl L, Koskinen M, Patama M, Lintunen A, Zanetti A, Lilja R, Pihlatie M&lt;/strong&gt;. &lt;strong&gt;2022&lt;/strong&gt;. Solar radiation drives methane emissions from the shoots of Scots pine. &lt;em&gt;New Phytologist&lt;/em&gt; &lt;strong&gt;235&lt;/strong&gt;: 66&amp;#8211;77.&lt;/p&gt;