Is methane released from the forest canopy?

Abstract

Laboratory experiments show that rates of CH4 emission from plant material depend exponentially on temperature and linearly on UV irradiance. The UV irradiance shall be spectrally weighted and shorter wavelengths results in higher CH4 emissions. Global upscaling models for estimating aerobic CH4, based on lab results, have be conducted with varying results, but until now field measurements based on profile and eddy covariance measurements have failed to show CH4 emissions from forest canopies. To detect CH4 production or consumption in the canopy of a beech stand we connected a CH4 analyzer to a canopy air profile system that samples air below and above the canopy from seven different heights. A profile system with many vertical sample points can detect gas concentration gradients with a high sensitivity only under conditions with no or little air movements. Under these conditions we found indications of periodic CH4 emissions in the canopy, but more data need to be analyzed before the magnitude of the canopy source of CH4 can be established

Leaf surface wax is a source of plant methane formation under UV radiation and in the presence of oxygen

“…Night‐time measurements in a temperate beech forest indicated a small CH 4 emission from canopy leaves (Mikkelsen et al . ), and it seems appropriate to scale the dark emission with mass and temperature (Bruhn et al . ).…”

A novel pathway of direct methane production and emission by eukaryotes including plants, animals and fungi: An overview

“…soil or plant water) and whether plants have their own mechanism(s) to produce CH 4 have been debated (Bruhn et al, 2012;Keppler et al, 2009;Nisbet et al, 2009). Evidence is now accumulating to indicate that plants can produce CH 4 even in the presence of oxygen (Bruggemann et al, 2009;Bruhn et al, 2009Bruhn et al, , 2014Cao et al, 2008;Fraser et al, 2015;Keppler et al, 2008;Lenhart et al, 2014;McLeod et al, 2008;Messenger et al, 2009;Mikkelsen et al, 2011;Reid, 2009, 2011;Sanhueza and Donoso, 2006;Sinha et al, 2007;Vigano et al, 2009Vigano et al, , 2008Wang et al, 2009aWang et al, , 2009bWang et al, , 2011aWatanabe et al, 2012;Wishkerman et al, 2011).…”

“…Early field work did not report enough details about the environmental conditions. We have attempted to provide explanations for potential impacts that may have occurred in some studies (Table S1); for instance, an impact from UV radiation might have occurred at experimental sites with high elevations, thereby affecting the observation of CH 4 emissions (Cao et al, 2008;Mikkelsen et al, 2011). Furthermore, results have shown that CH 4 concentrations are greater in upland forests than in lowland forests (do Carmo et al, 2006;Sinha et al, 2007).…”

Terrestrial plant methane production and emission

“…At the ecosystem scale, all studies applying chamber‐based measurements (Sanhueza and Donoso 2006, Cao et al 2008, Wang et al 2009a) could confirm CH 4 release in an anaerobic atmosphere at least during some periods. On the other hand, studies of vertical profiles of [CH 4 ] both indicate CH 4 release (Mikkelsen et al 2011) and no CH 4 release (Bowling et al 2009). Diel profiles of [CH 4 ] in both temperate and tropical forest systems indicated CH 4 release (Sinha et al 2007), whereas eddy covariance CH 4 measurements over a Californian pine plantation did not (Smeets et al 2009).…”