No detectable aerobic methane efflux from plant material, nor from adsorption/desorption processes

In early 2006, Keppler et al. (Nature, 439: 187-191) reported a novel finding that plant leaves, and even simple organic materials, can release methane under aerobic conditions. We investigated here whether the reported methane release might simply arise from methane desorption from sample surfaces after prior exposure to higher methane concentrations. We exposed standard cellulose filter papers (i.e. organic material with a high surface area) to atmospheric methane concentration and then transferred them to a low-methane atmosphere. Our results suggest that any desorption flux was extremely small (-0.0001 +/- 0.0019 ngCH(4) kgDW(-1) s(-1)) and would play no quantitatively significant role in modifying any measured methane fluxes. We also incubated fresh detached leaves of several species and intact Zea mays seedlings under aerobic and low-light conditions. After correcting for a small measured methane influx into empty chambers, measured rates of methane emission by plant materials were zero or, at most, very small, ranging from -0.25 +/- 1.1 ngCH(4) kgDW(-1) s(-1) for Zea mays seedlings to 0.10 +/- 0.08 ngCH(4) kgDW(-1) s(-1) for a mixture of freshly detached grasses. These rates were much smaller than the rates originally reported by Keppler et al. (2006).