4. Reducing Nitrous Oxide Emissions with Intercropping video

Trees Can Help Save the World - Chapter 4

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For more information about the Canadian Agricultural Greenhouse Gases Program, visit: http://agr.gc.ca

To contact researchers:

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Edited Transcript:

In the previous chapter, you saw Canadian researchers quantifying how much carbon trees can absorb in farm fields. By sequestering carbon, trees remove carbon dioxide from the atmosphere. You also saw how trees can co-exist with farm crops.

Funded by Canada’s Agricultural Greenhouse Gases Program, the research project focuses on tree-based intercropping systems in Ontario and Quebec. Intercropping involves planting trees in rows and planting farm crops in the alleys between the rows of trees.

The soil in farm fields is alive with microorganisms. Microorganisms are necessary for nitrogen cycling, a key process in healthy soil. But some microorganisms are responsible for the creation of nitrous oxide gas.

Nitrous oxide is one of the most potent greenhouse gases – more harmful to the ozone layer than carbon dioxide – and farm fields are a major source of nitrous oxide gas emissions.

Here at the University of Guelph intercropping site, researchers are collecting soil samples so they can study microorganisms. The goal is to determine whether certain species of trees have more or less of the microorganisms that contribute to nitrous oxide emissions.

The research is focused on four tree species: red oak, hybrid poplar, black walnut and Norway spruce.

Dr. Kari Dunfield heads up the microbiology research team at the University of Guelph.

Dr. Dunfield: We are really interested in soil microbial communities. We are involved in looking at what’s happening underground, what bacteria and fungi are involved associated with the trees we’re growing to see what kind of activity they’re doing; what kind of function they have in the soil.

But how do some microorganisms contribute to the production of nitrous oxide gas?

Microorganisms called nitrifiers facilitate nitrogen cycling, a process that benefits the soil. Denitrifiers are microorganisms that interrupt the nitrogen cycling process, resulting in harmful nitrous oxide gas emissions.

Dr. Dunfield: We are really interested in looking at the organisms and seeing is there any agricultural practice that can minimize those organisms in the soil, can we promote other organisms or is there some tree system that actually enhances the amount of denitrifiers or decreases the amount of these denitrifiers.

To identify microorganisms that facilitate the production of nitrous oxide gas, the scientists investigate their DNA.

Dr. Dunfield: It’s the same for forensics where you’re looking at a DNA sample from a person and then looking specifically at their genes and seeing who they are based upon what genes are present. It’s the exact same process that we’re following but we’re looking at the soil and seeing what organisms are present.

The process begins by filtering a soil sample to capture and clean DNA.

Dr. Dunfield: And then we end up with just a tiny tube with a clear, it looks like water really. And it has DNA in it.

Chemicals are added to break up microbial cells and protect the DNA.

Dr. Dunfield: We target the ones we’re interested in. So we’re looking at denitrifiers and nitrifiers specifically. We take the DNA in the system and we use a process called PCR or preliminary chain reaction and that multiplies it millions and millions of times so that we can actually visualize it on a gel.

After about an hour in the PCR, the duplicated DNA is injected into a gel with tiny wells. The DNA is then subjected to an electrical current that causes the DNA to move throughout the gel. Next, the DNA is placed into an ultra violet chamber. The scientists can then visualize the DNA on a computer screen.

To complete the process, the scientists use another system called quantitative preliminary chain reaction. It can actually quantify the number of microorganisms that contribute to nitrous oxide gas emissions.

The research has revealed where these harmful microorganisms are most prevalent in the University of Guelph intercropping system.

Dr. Dunfield: The community of the microorganisms tends to be higher the further out you go from the trees. So there are more of these organisms in the cropping system than there are close to the trees. So that’s something that we were curious about.

Of the four tree species in the study, red oak, black walnut, Norway spruce and hybrid poplar, poplar came out on top. The research found that soil microorganisms near poplar trees contain a specific gene in their DNA. The gene converts harmful nitrous oxide gas into harmless nitrogen gas.

The study also revealed that red oak trees show good potential for reducing nitrous oxide gas emissions.