Saturday, May 18, 2013
Twinkies, wheaties, and soil carbon
Before we delve further into a random array of topics in science and its transmission, my personal advisor (brother) has suggested that I explain my own research. So if I had a few minutes to try and sell my research at a middle school level (more about that in a later post), what would I say? Well it is dinner time, so there will be a bit of a food theme.
As the well-worn phrase goes, "carbon is the building block of life". Life as most of us know it starts with plants taking up carbon dioxide gas from the air and using it to grow, but this "living" carbon is only a very small fraction of the total amount on earth. In fact, there is about four times more carbon stored in soils than in land plants, and if plants were to store as much carbon as soils, tropical rainforests would need to cover six to ten times as much land as they do currently.
In most soils, this carbon predominantly comes from dead plant parts, and the organisms that live in the soil eat this. However, they obviously don't eat it all, because soil generally builds up over time. This is because, like humans, these detritivores (dead stuff eaters) have preferences for what they eat. Leaf sugars are like twinkies to them, and they gobble them up, but fallen twigs are more like Wheaties, and require a lot of digestion to get them into a form that the microbes can use. However, how much microbes prefer twinkies over Wheaties depends on a number of factors, including who they are, how many twinkies or Wheaties there are, and possibly how hot it is outside. Fungi are health freaks, and like the slow-release energy of Wheaties, while some bacteria are in it for the short-term gain and prefer twinkies. Higher temperatures make microbes grow faster, but in order to support this growth, they must eat more. In the excitement of the higher temperatures, microbes also tend to waste more food, releasing a greater proportion of what they eat as the greenhouse gas carbon dioxide rather than using it to make more copies of themselves. As a result, the amount of carbon stored in soil decreases while the level of carbon dioxide in the air increases, allowing for more warming. If further warming means the microbes continue to eat more of the soil carbon and convert it into carbon dioxide, then there could be even more climate warming.
(image courtesy of http://postcodegazette.com/venueImages/orig/WL_420524.jpg)
In my lab, we try and determine whether this exacerbated warming will actually occur. From what I said before, you might think that warming will stop when the twinkies run out, but in experiments where researchers artificially warm fields to mimic future climate change, they sometimes find that warming makes plants produce even more twinkies, because when the microbes eat the twinkies, they release nutrients which enable the plants to make more. However, in other cases, warming stresses plants, which makes them convert some of the twinkie sugars in leaves into Wheatie sugars (ick), which in addition to being yucky themselves, may also prevent the soil microbes from being able to eat the twinkies. But warming may also make Wheaties more delicious by favoring Wheatie-eaters over twinkie-eaters, or by partially converting Wheaties into something more closely representing a Twinkie, like a hot dog roll. Finally, what I look at for my project is whether microbes may "adapt" to warmer temperatures and be more frugal with their Wheaties and twinkies, keeping more of the carbon in their food for making microbe babies, and wasting less as carbon. Ultimately, it is how well microbes balance breathing and baby-making which determines how much carbon stays in the soil for the long-run.
Microbes on twinkies (courtesy of: http://piremongolia.files.wordpress.com/2011/07/soil-microbes.png)...
Microbes on Wheaties...(courtesy of http://upload.wikimedia.org/wikipedia/commons/7/7d/Trichoderma_sp_young_conidiophore.jpg)