Methane emission from stems of European beech (Fagus sylvatica) offsets as much as half of methane oxidation in soil

Abstract

Summary Trees are known to be atmospheric methane (CH4) emitters. Little is known about seasonal dynamics of tree CH4 fluxes and relationships to environmental conditions. That prevents the correct estimation of net annual tree and forest CH4 exchange. We aimed to explore the contribution of stem emissions to forest CH4 exchange. We determined seasonal CH4 fluxes of mature European beech (Fagus sylvatica) stems and adjacent soil in a typical temperate beech forest of the White Carpathians with high spatial heterogeneity in soil moisture. The beech stems were net annual CH4 sources, whereas the soil was a net CH4 sink. High CH4 emitters showed clear seasonality in their stem CH4 emissions that followed stem CO2 efflux. Elevated CH4 fluxes were detected during the vegetation season. Observed high spatial variability in stem CH4 emissions was neither explicably by soil CH4 exchange nor by CH4 concentrations, water content, or temperature studied in soil profiles near each measured tree. The stem CH4 emissions offset the soil CH4 uptake by up to 46.5% and on average by 13% on stand level. In Central Europe, widely grown beech contributes markedly to seasonal dynamics of ecosystem CH4 exchange. Its contribution should be included into forest greenhouse gas flux inventories.

Large Methane Emissions From Tree Stems Complicate the Wetland Methane Budget

“…Correlations with upland forest tree stem CH 4 emissions and soil CH 4 can be complex, as trees can act as CH 4 sources, whilst the well aerated soils represent net CH 4 sinks (Barba et al., 2019b; Machacova et al., 2023; Wang et al., 2016). Within the Upper zone stand, during most of the campaigns, the drivers were also unclear, with the tree stem CH 4 fluxes often shifting between slight CH 4 sources and sinks, between various stem heights and campaigns (Figures 4 and 9, Table 1).…”

“…Two‐thirds of all tree CH 4 literature was published within the last three years. Tree stem CH 4 emissions have now been reported from various ecosystems including upland forests (Barba et al., 2019b; Machacova et al., 2016, 2023; Pitz & Megonigal, 2017; Wang et al., 2016), mangrove forests (Gao et al., 2021; Jeffrey et al., 2019b; Zhang et al., 2022), riparian forests (Flanagan et al., 2021; Gauci et al., 2022) and standing deadwood, snags or ghost forests (Carmichael & Smith, 2016; Martinez & Ardon, 2021; Warner et al., 2017). The highest tree stem CH 4 emissions, however, are exclusively attributed to forested wetland ecosystems, also known as lowland forests (Gauci et al., 2010; Jeffrey et al., 2021b; Pangala et al., 2013; Terazawa et al., 2007).…”

Methane emissions from tree stems – current knowledge and challenges: an introduction to a Virtual Issue

“…In upland forests, stem fluxes can partially offset the soil CH 4 sink capacity (e.g. 63% (Wang et al, 2016), 1-6% (Pitz & Megonigal, 2017), 100% (Flanagan et al, 2021), or 13% (Machacova et al, 2023)). Even in the only study reporting net stem CH 4 uptake, stem uptake contributed 7% of the quantity of CH 4 consumed by soils (Machacova et al, 2021a).…”

“…CH 4 produced from wood incubations under anoxic conditions provides the functional link between stem fluxes and methanogenic communities (Wang et al ., 2016). When internal production is the origin, there is usually no vertical CH 4 flux pattern observed with stem height (Wang et al ., 2016; Machacova et al ., 2023) and no correlation with soil properties or soil CH 4 fluxes and concentrations (Pitz & Megonigal, 2017; Machacova et al ., 2023), but a significant correlation with stem attributes, including wood moisture, stem diameter or wood pH (Yip et al ., 2018). However, we cannot simply conclude that soil is the origin of CH 4 emitted from tree stems in wetlands and that internal production in stems is the source in uplands.…”

CH4transport in wetland plants under controlled environmental conditions – untangling the impacts of phenology

“…Plant-mediated CH 4 transport allows soil-produced CH 4 to bypass oxidation in oxic surface peat and thus is a crucial mechanism increasing the total ecosystem CH 4 emissions both in open wetlands and woody ecosystems (Shannon et al ., 1996; Pangala et al ., 2017; Barba et al ., 2019; Ge et al ., 2023; Machacova et al ., 2023). Environmental factors such as soil water table level (WTL), temperature and porewater CH 4 concentration ([CH 4 ] pw ) have been regarded as important controls on ecosystem CH 4 emissions from wetlands (Joabsson & Christensen, 2001; Lai et al ., 2014a).…”