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Trees: Another way to increase global methane?

Monday, February 1st, 2010

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Methane is a potent greenhouse gas.  Unlike CO2, which is produced by the aerobic (in the presence of oxygen) breakdown of organic matter, methane is produced by the breakdown of organic matter in anaerobic environments, such as livestock rumens, wetland soils, landfills, and rice paddies.

When we think of methane production, we don’t usually think about trees, but it looks like they may facilitate methane to the atmosphere.  How, you might ask, since most trees live in well-aerated soils?

In a forthcoming article1 in Geophysical Research Letters, Andrew Rice and colleagues show that trees in lowland, swampy areas actually conduct methane produced in soils up their stems and out their leaves, making trees an effective methane chimney.

We’ve known for years that marsh and bog plants do this, but nobody’s really looked at trees before.  The trees themselves are not making the methane (that’s done by soil bacteria), but they appear to do two things that increase the overall flux (movement) of methane to the atmosphere:  (1) tree stems provide a quick methane escape route from soils to the atmosphere and (2) trees leak root exudates (small organic molecules), which could be an organic carbon source for microbes that make methane.

In this study, they put bags around aboveground tree biomass to catch and measure methane, so it’s clear that #1 happens.  However, #2 needs further study.   You could measure it by dosing a tree with radiocarbon (14CO2) and then seeing if that gets turned into sugars by photosynthesis and eventually leaked out of roots, ultimately turning into 14C methane (14CH4) that is transported up the tree stems.

How much methane?  About 60 teragrams (1012g), or about 10% of the global production each year.  Big enough to pay attention to.

1Rice, A.L. et al. (in press) Emissions of anaerobically produced methane by trees. Geophysical Research Letters.

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Photo credit: http://www.flickr.com/photos/wirwuenscheneinbierinternationalereisegesellschaft_2008_10/ / CC BY-NC-ND 2.0

One Response to “Trees: Another way to increase global methane?”

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  1. [...] week, we also saw how trees can act as methane chimneys that release this greenhouse gas produced in swampy [...]

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