Background
The authors introduce their insightful review of the subject by stating that "arbuscular mycorrhizal fungi form mutualistic associations with about 70% of plant families and are abundant in all major terrestrial biomes," where they "produce the glycoprotein glomalin within their hyphal walls," which upon their senescence "is deposited within the soil, where it accumulates until it represents as much as 5% of soil carbon." The substance's significance derives from the fact that it "may reduce decomposition of organic material via the formation of aggregates, which may physically protect particulate matter from enzyme activity," thereby helping "sequester substantial amounts of C and N on a global scale."

What was done
Treseder and Turner "conducted a literature survey of glomalin concentrations from 22 ecosystems to test for relationships between standing stocks of glomalin and net primary productivity (NPP) and AM [arbuscular mycorrhizal] abundance," as well as to learn how these relationships may be influenced by changes in various environmental factors, such as atmospheric CO2 concentration.

What was learned
Focusing our attention on the latter factor, we find that the two researchers report that "elevated CO2 can enrich glomalin concentrations, as illustrated by Rillig et al. (1999) .. in serpentine and sandstone grasslands in northern California and in chaparral in southern California," and that "similar responses have been observed ... in a natural CO2 spring in New Zealand (Rillig et al., 2000) and ... in a free-air CO2 enrichment experiment in an Arizonan sorghum field (Rillig et al., 2001)." These effects of CO2 on glomalin, as they describe it, "are consistent with increases in AM abundance observed in many field manipulations of CO2 (Treseder, 2004)." In addition, they are consistent with the fact that, "globally," in Treseder and Turner's words, "glomalin stocks [are] positively correlated with NPP," which is generally always enhanced by elevated concentrations of atmospheric CO2.

What it means
As the air's CO2 content continues to rise in the years and decades ahead, we can expect to see greater ecosystem net primary productivity throughout the world, as well as an enhanced abundance of arbuscular mycorrhizal fungi associated with the roots of the ecosystems' plants. As a result, we can also expect to find greater amounts of glomalin in the ground beneath the planet's various terrestrial ecosystems and, ultimately, a greater capacity for longer-term carbon sequestration in the earth's soils.

References
Rillig, M.C., Hernandez, G.Y. and Newton, P.C.D. 2004. Arbuscular mycorrhizae respond to elevated atmospheric CO2 after long-term exposure: Evidence from a CO2 spring in New Zealand supports the resource balance model. Ecology Letters 3: 475-478.

Rillig, M.C., Wright, S.F., Allen, M.F. and Field, C.B. 1999. Rise in carbon dioxide changes soil structure. Nature 400: 628.

Rillig, M.C., Wright, S.F., Kimball, B.A., Pinter, P.J., Wall, G.W., Ottman, M.I. and Leavitt, S.W. 2001. Elevated carbon dioxide and irrigation effects on water stable aggregates in a sorghum field: A possible role for arbuscular mycorrhizal fungi. Global Change Biology 7: 333-337.

Treseder, K.K. 2004. A meta-analysis of mycorrhizal responses to nitrogen, phosphorus and atmospheric CO2 in field studies. New Phytologist 164: 347-355.