Agricultural Research Service soil
scientist Sara E. Wright has discovered a unique fungal protein that may be the
primary glue that holds soils together.
She named the gooey protein "glomalin" for Glomales, the
scientific name for the group of common root-dwelling fungi that secrete the
protein through hairlike filaments called hyphae. The fungal hyphae are found
worldwide on the roots of many plants. Glomalin sloughs off of the hyphae and
finds its way into soil.
"It coats soil particles and may be what holds them together in the
stable structures we call aggregates," says Wright. "Farmers and
gardeners know them as the small grains of soil that sift through their hands
and suggest to them that the soil has good structure."
Wright knew she had something unique when it took up to 90 minutes in a
heat-sterilizing autoclave to free glomalin from the hyphae. "That's
unheard of in the soil sciences, although an hour or more of autoclaving has
been used to free proteins from some yeasts. With that level of persistence, we
knew glomalin must stay in the soil, too."
So Wright began searching soils. She started with a dozen eastern soils and
found that with the measuring technique she used, glomalin was as high as 2
percent of the total weight of a soil aggregate. When she moved on to test
soils from the West and Midwest, she found levels were dramatically lower,
although still abundant. She has also found glomalin in soil samples sent from
several cooperators throughout the world.
"It may be that the higher glomalin levels explain why eastern soils
have stronger structural stability than western soils," says Wright.
"Knowing about glomalin gives us a reason to alter farming practices to
raise or maintain glomalin levels. For example, tillage tends to lower glomalin
levels. We found that soil from no-till corn plots had more glomalin and higher
aggregate stability than soil from tilled plots." By Don
Wright is at the USDA-ARS Sustainable Agricultural Systems Laboratory,
Beltsville, MD 20705-2350; phone (301) 504-8156 ext. 335