Friday, August 26, 2005

A tale of two gases

As our understanding of the natural world around us grows, we often find things that are distinctly surprising to say the least. Firstly, Nature has a news item discussing a paper from a Swedish group that looked to see if trees actually take up excess CO2 (one of those gases that is important in the greenhouse effect), which as plants use CO2 to 'breathe' they figured would grow better with excess CO2. It turns out that really isn't the case,
The team artificially created sustained carbon-dioxide-rich conditions in the patch measuring 500 square metres by spraying pure carbon dioxide into the canopy of about a dozen mature deciduous trees. Each day during the six-month annual growth season, the scientists sprayed two tons of extra carbon dioxide, from industrial waste, into the canopy. This simulated an atmosphere loaded with about 530 ppm of carbon dioxide, roughly 1.5 times what exists today.

But after four years the researchers found no signs of enhanced biomass growth in stems or leaves, they report in Science1. The trees had merely pumped the extra carbon through their bodies, quickly re-releasing it through root and soil microbe respiration; there was no lasting effect on growth and photosynthesis.
Which is a bit of a bummer, although it will be good if it turns out that the excess CO2 is stored by soil microbes (possibly used up, some bacteria can use CO2 in their metabolism, much like plants). On the other hand however, a group working on methane, a gas even worse than CO2 in terms of the greenhouse effect, found that despite the large amounts of methane produced by swamps, the majority of it is actually retained rather than being a massive production house of the gas. The reason why?
A clue comes from the fact that most of the carbon in peat bogs ends up in the form of peat, an accumulation of dead sphagnum moss. The methane discrepancy could be explained if the living moss plants gobble up the gas as it's produced. But one snag in this explanation is that plants don't have the biochemical tricks needed to oxidize methane into a form they could use for energy.

Suspecting that the moss may be getting help from a microbe, a team led by Jaap Damsté and Marc Strous, microbiologists at Radboud University in Nijmegen, the Netherlands, and the Royal Netherlands Institute for Sea Research in Den Burg, respectively, gave moss plants a vigorous washing and then probed them for the presence of bacterial RNA. Sure enough, they found telltale sequences of methane-munching bacteria and also found dense clusters of the bacteria within the plant's tissue.
Once again, life manages to make use of things in equilibrium despite what may seem intuitive to us. The trees and plants from the nature news item didn't appear to get any particular benefit out of using excess carbon. This is probably because things are similar to the scenario in the peat bog. The amount of total excess carbon has been produced in an equilibrium with the amount being lost for a considerable amount of time and the natural environment has become 'used' to that scenario. Excess carbon is merely kicked out, rather than being used because the plants and trees in the ecosystem aren't really metabolically 'geared up' so to speak to be able to use that carbon. Given time and assuming that using the excess CO2 would provide an appropriate selection pressure, plants and microbes may develop means to use the excess CO2 more effectively.

This is similar to what has happened in the peat bog, over evolutionary time bacteria in that environment have had the selective pressure and time to be able to use the methane that is produced, ensuring that excess methane isn't spat out into the environment and things are pretty much in balance. The question that should be important to us, especially as we're the ones who are increasing the amounts of greenhouse gases in the environment, is how quickly can bacteria/plants adapt to make use of the excess gases (bring things back to a sort of balance) we are providing and can they do it before any damage is done?