Andy McLeod, University of Edinburgh
Chris - In 2006, scientists discovered that plants produce significant amounts of the greenhouse gas, methane. The research caused quite a stir and it led to a rethink about the role of plants and forests in global warming. One of the questions that needed answering is how plants emit methane. And so, a research group at the University of Edinburgh set up the aptly named, ‘Methane Project’. Plant Earth podcast presenter Sue Nelson met with Andy McLeod at the University School of Geosciences to find out more.
Andy - The Methane Project is to investigate the mechanisms by which plant leaves can emit the greenhouse gas methane.
Sue - So how do you go about doing that because I don't see many plants here in your laboratory?
Andy - Well there are no plants here now but what we do is enclose the plant leaves inside chambers and these chambers are specially constructed to transmit ultra violet radiation which you find in sunlight and we use the chambers to determine what gasses are emitted and that includes methane.
Sue - So, although scientists know that this process is happening, you know that methane is being produced by plants, albeit relatively recently, we still don't know how this methane is produced and this is where your labs come in.
Andy - Yeah, the purpose of the project was to investigate the role that ultraviolet radiation may play in causing this methane emission and it would seem that the ultraviolet radiation, when it impacts organic molecules within the leaf can result in the release of methane into the atmosphere.
Sue - Well let's go through how you actually go about doing that - we've got two small labs off a corridor side by side, let's start with the quieter one inside, what goes on in here?
Andy - In this lab we have a very powerful xenon arc lamp which can produce very high levels of visible and ultraviolet radiation.
Sue - That's just this little black box here which produces a huge blinding white light I assume.
Andy - Yes, absolutely. We have to wear eye protection when we're using this. We filter out the infrared radiation which would heat up the leaves of the plants, we then filter out particular wavelengths of ultraviolet so that we can determine which wavelengths of ultraviolet are producing the effects we observe.
Sue - Do you use any types of plant in particular or is that irrelevant?
Andy - The purpose of the project was to evaluate a range of plant types to determine whether particular plant types produce more methane on UV radiation compared to others. Our partners in the project are the Royal Botanic Gardens in Edinburgh where they have a large range of plant types in their collection which are made available to us for this investigation.
Sue - Right, well let's go to the next lab which is a little bit noisier - here we go - there's a big fan whirring at the end. We've got a bench with what look like kitchen fluorescent tubes of lighting above it, almost like a sun bed but with all sorts of wiring and copper tubing and syringes beneath, not the sort of sun bed you would want to actually lay on.
Andy - No, it is in fact very like a sun bed but the tubes used in this system produce very high levels of ultraviolet B radiation which would actually give us a sun tan far too quickly and be quite dangerous.
Sue - So you irradiate, effectively, the plants and then you simply attach some sort of piece of equipment to the plant in order to measure the methane. We must be talking about very small amounts of methane here?
Andy - Yes, one of the problems is measuring the very small amounts of methane produced and we do this in two different ways. When we have a closed chamber where there is no air flowing through it we can transfer gas samples in a syringe to the gas chromatograph on the other side of the lab where the concentrations are measured. We also have a monitor beneath the system here which gives us continuous measurements of methane if the gas is flowing through the chamber.
Sue - And what stage are you at at the moment in terms of your project?
Andy - This is the final stages of the project where we're completing some of the measurements and we're analysing some of the chemical constituents of the leaves to see how they may be involved in the process.
Sue - And at the end of it what do you hope to gain? Obviously you want more of an insight into how the process works but do you think you're at that stage of getting it? Do you know how this process works now?
Andy - We're fairly confident that ultraviolet radiation does result in the production of methane and some other trace gases from plant leaves. In terms of quantifying how much that is it seems that it is still a very small amount making quite a small contribution to global emissions of methane into the atmosphere.
Sue - So there are still other areas to be discovered in terms of how methane is produced by plants?
Andy - There may indeed be other mechanisms and there are reports in the literature that physical damage causes the emission of methane from plant leaves and also other environmental stresses like high temperature.
Chris - Andy McLeod from the University of Edinburgh on the Methane Project. There's a longer version of that interview on the Planet Earth podcast which you can find on our website of our Planet Earth online. Incidentally, the same technique was also used by planetary scientists in meteorites recently. It has allowed them to discover that meteorites bombarding the surface of Mars contained enough carbon to generate methane when exposed to sunlight and that solve the problem of why methane has been detected on Mars too.
The default assumption is that the methan is produced by methanogenic archaea.