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  • From: <mdnagel@verizon.net>
  • To: Healthy soil and sustainable growing <livingontheland@lists.ibiblio.org>
  • Subject: [Livingontheland] Glomalin hiding place for a third of the world's stored soil carbon
  • Date: Mon, 07 Jul 2008 18:52:15 -0500 (CDT)

Another way/reason that petrochemical farming is going to die out...


-Mark Nagel
Everett, WA


Source:
http://findarticles.com/p/articles/mi_m3741/is_9_50/ai_92589768/print?tag=artBody;col1

Glomalin hiding place for a third of the world's stored soil carbon
Don Comis

A sticky protein seems to be the unsung hero of soil carbon storage.

Until its discovery in 1996 by ARS soil scientist Sara F. Wright, this soil
"super glue" was mistaken for an unidentifiable constituent of soil organic
matter. Rather, it permeates organic matter, binding it to silt, sand, and
clay particles. Not only does glomalin contain 30 to 40 percent carbon, but
it also forms clumps of soil granules called aggregates. These add structure
to soil and keep other stored soil carbon from escaping.

As a glycoprotein, glomalin stores carbon in both its protein and
carbohydrate (glucose or sugar) subunits. Wright, who is with the Sustainable
Agricultural Systems Laboratory in Beltsville, Maryland, thinks the glomalin
molecule is a clump of small glycoproteins with iron and other ions attached.
She found that glomalin contains from 1 to 9 percent tightly bound iron.

Glomalin is causing a complete reexamination of what makes up soil organic
matter. It is increasingly being included in studies of carbon storage and
soil quality. In fact, the U.S. Department of Energy, as part of its interest
in carbon storage as an offset to rising atmospheric carbon dioxide
(C[O.sub.2]) levels, partially funded a recent study by lab technician
Kristine A. Nichols, a colleague of Wright's. Nichols reported on the study
as part of her doctoral dissertation in soil science at the University of
Maryland.

That study showed that glomalin accounts for 27 percent of the carbon in soil
and is a major component of soil organic matter. Nichols, Wright, and E.
Kudjo Dzantor, a soil scientist at the University of Maryland-College Park,
found that glomalin weighs 2 to 24 times more than humic acid, a product of
decaying plants that up to now was thought to be the main contributor to soil
carbon. But humic acid contributes only about 8 percent of the carbon.
Another team recently used carbon dating to estimate that glomalin lasts 7 to
42 years, depending on conditions.

For the study, the scientists compared different chemical extraction
techniques using eight different soils from Colorado, Georgia, Maryland, and
Nebraska. They found that current assays greatly underestimate the amount of
glomalin present in soils. By comparing weights of extracted organic matter
fractions (glomalin, humic acid, fulvic acid, and particulate organic
matter), Nichols found four times more glomalin than humic acid. She also
found that the extraction method she and Wright use underestimates glomalin
in certain soils where it is more tightly bound than usual.

In a companion study, Nichols, Wright, and Dzantor teamed up with ARS chemist
Walter F. Schmidt to examine organic matter extracted from the same soils
under a nuclear magnetic resonance (NMR) imager. They found that glomalin's
structure differs from that of humic acid--or any other organic matter
component--and has unique structural units.

In a current study in Costa Rica, partly funded by the National Science
Foundation, Wright is using glomalin levels and root growth to measure the
amount of carbon stored in soils beneath tropical forests. She is finding
lower levels of glomalin than expected and a much shorter lifespan. "We think
it's because of the higher temperatures and moisture in tropical soils," she
explains. These factors break down glomalin.

Forests, croplands, and grasslands around the world are thought to be
valuable for offsetting carbon dioxide emissions from industry and vehicles.
In fact, some private markets have already started offering carbon credits
for sale by owners of such land. Industry could buy the credits as offsets
for their emissions. The expectation is that these credits would be traded
just as pollution credits are currently traded worldwide.

How Does Glomalin Work?

It is glomalin that gives soil its tilth--a subtle texture that enables
experienced farmers and gardeners to judge great soil by feeling the smooth
granules as they flow through their fingers.

Arbuscular mycorrhizal fungi, found living on plant roots around the world,
appear to be the only producers of glomalin. Wright named glomalin after
Glomales, the taxonomic order that arbuscular mycorrhizal fungi belong to.
The fungi use carbon from the plant to grow and make glomalin. In return, the
fungi's hairlike filaments, called hyphae, extend the reach of plant roots.
Hyphae function as pipes to funnel more water and nutrients--particularly
phosphorus--to the plants.

"We've seen glomalin on the outside of the hyphae, and we believe this is how
the hyphae seal themselves so they can carry water and nutrients. It may also
be what gives them the rigidity they need to span the air spaces between soil
particles," says Wright.

As a plant grows, the fungi move down the root and form new hyphae to
colonize the growing roots. When hyphae higher up on the roots stop
transporting nutrients, their protective glomalin sloughs off into the soil.
There it attaches to particles of minerals (sand, silt, and clay) and organic
matter, forming clumps. This type of soil structure is stable enough to
resist wind and water erosion, but porous enough to let air, water, and roots
move through it. It also harbors more beneficial microbes, holds more water,
and helps the soil surface resist crusting.

Scientists think hyphae have a lifespan of days to weeks. The much longer
lifespan of glomalin suggests that the current technique of weighing hyphae
samples to estimate fungal carbon storage grossly underestimates the amount
of soil carbon stored. In fact, Wright and colleagues found that glomalin
contributes much more nitrogen and carbon to the soil than do hyphae or other
soil microbes.

Rising C[O.sub.2] Boosts Glomalin, Too

In an earlier study, Wright and scientists from the University of California
at Riverside and Stanford University showed that higher C[O.sub.2] levels in
the atmosphere stimulate the fungi to produce more glomalin.

They did a 3-year study on semiarid shrub land and a 6-year study on
grasslands in San Diego County, California, using outdoor chambers with
controlled C[O.sub.2] levels. When C[O.sub.2] reached 670 parts per million
(ppm)--the level predicted by mid to late century--hyphae grew three times as
long and produced five times as much glomalin as fungi on plants growing with
today's ambient level of 370 ppm.

Longer hyphae help plants reach more water and nutrients, which could help
plants face drought in a warmer climate. The increase in glomalin production
helps soil build defenses against degradation and erosion and boosts its
productivity.

Wright says all these benefits can also come from good tillage and soil
management techniques, instead of from higher atmospheric C[O.sub.2].

"You're in the driver's seat when you use techniques proven to do the same
thing as the higher C[O.sub.2] that might be causing global warming. You can
still raise glomalin levels, improve soil structure, and increase carbon
storage without the risks of the unknowns in global climate change," she says.

Putting Glomalin to Work

Wright found that glomalin is very manageable. She is studying glomalin
levels under different farming and ranching practices. Levels were maintained
or raised by no-till, cover crops, reduced phosphorus inputs, and the sparing
use of crops that don't have arbuscular mycorrhizal fungi on their roots.
Those include members of the Brassicaceae family, like cabbage and
cauliflower, and the mustard family, like canola and crambe.

"When you grow those crops, it's like a fallow period, because glomalin
production stops," says Wright. "You need to rotate them with crops that have
glomalin-producing fungi."

In a 4-year study at the Henry A. Wallace Beltsville (Maryland) Agricultural
Research Center, Wright found that glomalin levels rose each year after
no-till was started. No-till refers to a modern conservation practice that
uses equipment to plant seeds with no prior plowing. This practice was
developed to protect soil from erosion by keeping fields covered with crop
residue.

Glomalin went from 1.3 milligrams per gram of soil (mg/g) after the first
year to 1.7 mg/g after the third. A nearby field that was plowed and planted
each year had only 0.7 mg/g. In comparison, the soil under a 15-year-old
buffer strip of grass had 2.7 mg/g.

Wright found glomalin levels up to 15 mg/g elsewhere in the Mid-Atlantic
region. But she found the highest levels--more than 100 mg/g--in Hawaiian
soils, with Japanese soils a close second. "We don't know why we found the
highest levels in Hawaii's tropical soils. We usually find lower levels in
other tropical areas, because it breaks down faster at higher temperature and
moisture levels," Wright says. "We can only guess that the Hawaiian soils
lack some organism that is breaking down glomalin in other tropical soils--or
that high soil levels of iron are protecting glomalin."

It's Persistent and It's Everywhere!

The toughness of the molecule was one of the things that struck Wright most
in her discovery of glomalin. She says it's the reason glomalin eluded
scientific detection for so long.

"It requires an unusual effort to dislodge glomalin for study: a bath in
citrate combined with heating at 250[degrees]F for at least an hour," Wright
says. "No other soil glue found to date required anything as drastic as this.

"We've learned that the sodium hydroxide used to separate out humic acid in
soil misses most of the glomalin. So, most of it was thrown away with the
insoluble humus and minerals in soil," she says. "The little bit of glomalin
left in the humic acid was thought to be nothing more than unknown foreign
substances that contaminated the experiments."

Once Wright found a way to capture glomalin, her next big surprise was how
much of it there was in some soils and how widespread it was. She tested
samples of soils from around the world and found glomalin in all.

"Anything present in these amounts has to be considered in any studies of
plant-soil interactions" Wright says. "There may be implications beyond the
carbon storage and soil quality issues--such as whether the large amounts of
iron in glomalin mean that it could be protecting plants from pathogens."

Her recent work with Nichols has shown that glomalin levels are even higher
in some soils than previously estimated.

"Glomalin is unique among soil components for its strength and stability,"
Wright says. "Other soil components that contain carbon and nitrogen, as
glomalin does, don't last very long. Microbes quickly break them down into
byproducts. And proteins from plants are degraded very quickly in soil.

"We need to learn a lot more about this molecule, though, if we are to manage
glomalin wisely. Our next step is to identify the chemical makeup of each of
its parts, including the protein core, the sugar carbohydrates, and the
attached iron and other possible ions." Nichols is starting to work on just
that.

"Once we know what sugars and proteins are there," says Nichols, "we will use
NMR and other techniques to create a three-dimensional image of the molecule.
We can then find the most likely sites to look for iron or other attached
ions.

"Researchers have studied organic matter for a long time and know its
benefits to soil. But we're just starting to learn which components of
organic matter are responsible for these benefits. That's the exciting part
of glomalin research. We've found a major component that we think definitely
has a strong role in the benefits attributed to organic matter--things like
soil stability, nutrient accessibility, and nutrient cycling."

As carbon gets assigned a dollar value in a carbon commodity market, it may
give literal meaning to the expression that good soil is black gold. And
glomalin could be viewed as its golden seal.

This research is part of Soil Resource Management, an ARS National Program
(#202) described on the World Wide Web at http://www.nps.ars.usda.gov.

Sara F. Wright and Kristine A. Nichols are with the USDA-ARS Sustainable
Agricultural Systems Laboratory, Bldg. 001, 10300 Baltimore Ave., Beltsville,
MD 20705; phone (301) 504-8156 [Wright], (301) 504-6977 [Nichols], fax (301)
504-8370, e-mail wrights@ba.ars.usda.gov, nicholsk@ba.ars.usda.gov.

COPYRIGHT 2002 U.S. Government Printing Office
COPYRIGHT 2002 Gale Group





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