Interesting, though I have no idea what to make of this, from a reader:

Come on, Jonah! Plants and methane flies in the face of known science. And the guys who came up with this had no metabolic explanation for methane emissions and plants. There’s an article in this week’s Nature on this very issue with scientists finding no evidence for the claim. Methane comes from anaerobic digestion in the TCA cycle, which plants are unable to perform. http://www.nature.com/nature/journal/v447/n7140/pdf/447011a.pdf (See attached file: 447011a.pdf)

Update: It’s the manure, stupid, say many readers. For example:

The article you linked explained the situation. Keep in mind that in less developed countries, animal waste is a more likely source of fertilizer. Also, remember the fuel source in Mad Max: Thunderdome?
“It’s the bacteria that thrive in flooded paddies that produce methane, by decomposing manure used as fertilizer and other organic matter in the oxygen-free environment. The gas is emitted through the plants or directly into the atmosphere.”