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An interesting relationship: soil temperature and climate change


Blog originally posted on The GLOBE Scientists' Blog: http://blog.globe.gov/sciblog/2013/01/30/an-interesting-relationship-soil-temperature-and-climate-change/

It seems common place that warmer air temperature leads to warmer soil temperature. And while this relationship seems intuitive, the effect isn’t always studied, especially with respect to the response from microorganisms. That is why researchers are investigating what happens when the soil temperature increases.

An intricate network of soil microorganisms From: Commonwealth Scientific and Industrial Research Organisation (CISRO).

An intricate network of soil microorganisms From: Commonwealth Scientific and Industrial Research Organisation (CISRO).

The study, performed by scientists from the University of New Hampshire, the University of California-Davis and the Marine Biological Laboratory, examined how microorganisms in the soil respond to temperature changes.  By learning more about that process, scientists could then improve the prediction of how much carbon dioxide is released from the soil.

Microorganisms in the soil release carbon dioxide as a byproduct of how they utilize their food source.  There are two types of food sources: glucose, a simple food source that is release from plant roots, and phenol, a complex food source that comes from decomposing organic matter such as wood and leaves.  Under normal conditions, they release at least 10 times the amount of carbon dioxide that human activities do in a year through the breakdown of these two food sources.  For a perspective on what this amount means, take a look at the graph below, taken from a study from 2010.

Time series of global carbon emissions from fossil fuels. Image from EPA.

Time series of global carbon emissions from fossil fuels. Image from EPA.

This dramatic amount of carbon dioxide is usually absorbed through the root uptake of trees.  But if the soil warms too much, then these microorganisms are not as efficient at breaking down their food, and thus release more carbon dioxide as they expend the energy.  They are then over-producing, and the trees and plants will not take up as much.  In the short term, it may lead to a positive feedback cycle – where more carbon dioxide is emitted contributing to the rising amount of carbon dioxide in the atmosphere.

However, this same research showed that these microorganisms may have the once again become efficient with their food breakdown after many years of warmer soil temperatures.  After approximately 18 years, the community once again became efficient in their ability to break down food.  This may be due to one of the following things: a change in the community of microorganisms (i.e. the type of microorganism changes), a change in the available nutrients,  and/or species adaptation.

While GLOBE doesn't have protocols to look directly at microorganisms in the soil, it does have protocols to examine soil temperature.  This is just as important, because soil temperature directly affects many things, such as the timing of Budburst, Green Up and Green Down.  The timing of the phenological processes is important because it informs farmers when to plant crops.   For these reasons, it is very valuable to collect soil temperature data and monitor its changes through the seasons and years.

Suggested activity: Have you collecting soil temperature data?  Did you participate in December's Surface Temperature Field Campaign?  Have you seen any changes?  We'd love to hear about your experience!  Leave a comment, share with us on our Facebook page, or send us an email.  And make sure you enter the data you're collecting into the GLOBE database!

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