Effect of UV radiation and temperature on the emission of methane from plant biomass and structural components

The recently reported finding that plant matter and living plants produce significant amounts of the important greenhouse gas methane under aerobic conditions has led to an intense scientific and public controversy. Whereas some studies question the up-scaling method that was used to estimate the global source strength, others have suggested that experimental artifacts could have caused the reported signals, and two studies, one based on isotope labeling, have recently reported the absence of CH4 emissions from plants. Here we show - using several independent experimental analysis techniques - that dry and detached fresh plant matter, as well as several structural plant components, emit significant amounts of methane upon irradiation with UV light and/or heating. Emissions from UV irradiation are almost instantaneous, indicating a direct photochemical process. Longtime irradiation experiments demonstrate that the size of the CH4 producing reservoir is large, exceeding potential interferences from degassing or desorption processes by several orders of magnitude. A dry leaf of a pure C-13 plant produces (CH4)-C-13 at a similar rate as dry leaves of non-labeled plants produce non-labeled methane.