Infrared Sheds Light on Beneficial Microbes

Infrared spectroscopy can quickly spot beneficial fungi on roots in soil, according to Francisco Calderon, a soil scientist at the Agricultural Research Service Central Great Plains Resources Management Research Unit in Akron, Colorado.

This type of spectroscopy has become established practice for quick and reliable analysis of grain and forage quality, as well as other agricultural uses, thanks in part to ARS scientists. But Calderon’s idea to use it for detecting fungal-root associations in soils was never explored before. The ability to quickly analyze field soils for these beneficial fungi, called “mycorrhizae,” would allow scientists to judge which crop rotations or other farming practices increase the fungi. This is important nationwide for improving crop yields and is especially critical for semiarid areas like those found in the Central Great Plains.

Mycorrhizal fungi live in a symbiotic relationship with plants. The fungi help plants by taking up soil nutrients and water that would otherwise be difficult for plant roots to reach. In exchange, the fungi feed on the carbon sources that plants provide.

Calderon says the test could simplify, accelerate, and improve the objectivity of measurements of mycorrhizae in root samples, compared to the standard method of visual scoring through a microscope. It may also be more accurate than the newer technique of analyzing fatty acids in mycorrhizae on roots. Also, he says, “Since there is no destruction of the samples, researchers can perform other analyses on the same samples after this test is done.”

Calderon developed the technique with soil scientists Veronica Acosta-Martinez at Lubbock, Texas, and Merle Vigil at Akron. Other ARS colleagues in this study include microbiologist David Douds at Wyndmoor, Pennsylvania, and chemist James Reeves at Beltsville, Maryland.

They measured the reflectance of infrared light from dried, powdered carrot root samples. They found that the cell wall chitin and fatty acids in mycorrhizal fungi have distinct spectral signatures, absorbing infrared light at different wavelengths than standard chitin, fatty acids, and nonmycorrhizal roots. The researchers accomplished this using both mid-infrared and near-infrared spectroscopy.

Next, they plan to study the spectral properties of other crop fungal species to see whether there are universal spectral signatures for this important group of organisms.—By Don Comis, Agricultural Research Service Information Staff.

Francisco Calderon is in the USDA-ARS Central Great Plains Resources Management Research Unit, 40335 County Rd. GG, Akron, CO 80720; (970) 345-0526.

"Infrared Sheds Light on Beneficial Microbes" was published in the November/December 2010 issue of Agricultural Research magazine.