Methane Production Explained Largely by Water Content in the Heartwood of Living Trees in Upland Forests

Abstract

Most forests worldwide are located in upland landscapes. Previous studies have mainly focused on ground methane (CH4) flux in upland forests, and living tree stem‐based CH4 processes and fluxes are thus relatively poorly understood. This study investigated the relationship between CH4 concentration and water content in the heartwood of living trees in midtemperate, warm temperate, and subtropical upland forests and also measured seasonal changes of in situ stem CH4 flux and the CH4 concentration and water content in the heartwood of Populus davidiana Dode in a warm temperate upland forest. We found that approximately 4–13% of tree stems or approximately 8–31% of tree species had a substantial CH4 concentration of ≥10,000 μL L−1 in their heartwood across the three types of upland forests. The heartwood CH4 concentration was related to water content by a power function. A threshold of water content occurred beyond which CH4 was produced at high levels in the heartwood. The CH4 emissions from the breast height stems of P. davidiana ranged from 202.1 to 331.6 μg m−2 h−1 on a stem surface area basis during July–October 2016 and were significantly linearly correlated with the CH4 concentration or water content in the heartwood throughout the experimental period, but the linear correlation was not significant at daily and monthly scales. Temperature was not a limiting factor for CH4 production during July–October 2016, and thus, most of the CH4 production may be explained by water content in the heartwood of living trees in upland forests.

Standing Dead Trees are a Conduit for the Atmospheric Flux of CH4 and CO2 from Wetlands

“…As a result of internal barriers to diffusion in the inner bark and xylem, it is not unusual to observe high gas concentrations in trunks and stems relative to atmospheric air (Teskey et al 2008), a pattern that has been observed in both living trees (Teskey et al 2008;Covey et al 2012;Wang et al 2017) and deadwood stocks (Covey et al 2016;Warner et al 2017). Several studies, as reviewed in Teskey et al (2008) and as observed in Wang et al 2017, have noted a positive correlation between internal concentrations of stem gases and measured efflux across the plant-atmosphere interface. Therefore, chamber-based work was necessary to 1) confirm if the high internal gas concentrations observed in this study escaped the plant-atmosphere interface as a flux and 2) more finely resolve if deadwood stocks, such as snags, represent a source or a sink of carbon flux to the atmosphere.…”

“…tree stems) might also be a source of CH4 flux from wetlands, a pathway that was confirmed in 1998 by Rusch and Rennenberg. A handful of studies have expanded on this initial research, confirming live trees as a pathway for CH4 emissions in both upland and wetland systems [see review by Carmichael et al (2014) and references therein, in addition to more recent papers by Pangala et al (2015), Terazawa et al (2015), Machacova et al (2016), Wang et al (2016), Wang et al (2017), and Warner et al (2017)]. In these studies, CH4 flux occurred across all possible exchanging surfaces at the plant-atmosphere interface, including the leaf, stem, and trunk.…”

“…However, as in Pitz and Megonigal (2017), methodological limitations in our study did not allow for the determination of the source of the accumulated gases. Potential sources of gas production include chemicallydriven degradation of methoxyl groups in plant tissue (Keppler et al 2006;McLeod et al 2008;Vigano et al 2008), microbial decomposition of woody tissue in the snag (Zeikus and Ward 1974;Covey et al 2012;Lenhart et al 2012;Hietala et al 2015;Wang et al 2017), and/or plantmediated transport from the sediment (Gauci et al 2010;Pangala et al 2012;Terazawa et al 2015).…”

Are methane emissions from mangrove stems a cryptic carbon loss pathway? Insights from a catastrophic forest mortality

“…When tree mortality occurs, water is evacuated from the complex internal hydraulic channels within the trees, spanning from the roots to the atmosphere; leaving an array of empty internal cavities that facilitate upward (nonpressurized) diffusive gas transportation (Carmichael et al, 2018). It is also plausible that a portion of the CH 4 flux from dead stems originates aboveground due to the chemical degradation of plant tissue (Keppler et al, 2006), in situ methanogenesis from organic matter decomposition (Covey et al, 2012;Wang et al, 2017), or CH 4 from saprotrophic fungi (Mukhin & Voronin, 2008;Lenhart et al, 2012). However, most studies conclude that the bulk of living tree stem CH 4 emissions originate from the rhizosphere and are either transported upwards through the roots via nonpressurized (diffusion) and/or pressurized processes (xylem and sap flow) (Maier et al, 2018;Barba et al, 2019b).…”

Variation in soil lignin protection mechanisms in five successional gradients of mixed broadleaf–pine forests

“…The frost-free period lasts between 120 and 130 d and mean annual precipitation ranges from 695 to 983 mm yr −1 , most of which occurs between June and August (Lou et al, 2013;Wang et al, 2018a). The local soil is classified as darkbrown mountain forest albic soil according to the Chinese soil classification system, Alfisol according to the US soil taxonomy (Chen et al, 2017a;Shao et al, 2018), or Eutric cambisol according to the Food and Agriculture Organization of the United Nations classification (Wang et al, 2017). The parent materials of these soils originate from weathered volcanic ash and basalt.…”