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Effects of Elevated CO2 on Fungal Infection of an Annual California Grass
Rillig, M.C., Allen, M.F., Klironomos, J.N. and Field, C.B.  1998.  Arbuscular mycorrhizal percent root infection and infection intensity of Bromus hordeaceus grown in elevated atmospheric CO2Mycologia 90: 199-205.

What was done
The authors grew Bromus hordeaceus, an annual California grass, in pots placed within open-top chambers receiving ambient or ambient plus 350 ppm atmospheric CO2 for four months to determine the effects of elevated CO2 on the arbuscular mycorrhizal fungi associated with this species.

What was learned
Elevated CO2 did not affect percent root infection by arbuscular mycorrhizal fungal hyphae, nor did it affect colonized root length, which are two parameters commonly reported by those studying the effects of atmospheric CO2 enrichment on fungi.  However, elevated CO2 did increase percent root infected by arbuscules, and arbuscular mycorrhizal infection intensity in all but the youngest roots investigated, indicating that an increase in carbon allocation to the fungal symbiont occurred with atmospheric CO2 enrichment in spite of the absence of an increase in percent hyphal infection or colonized root length.

What it means
The results of this research indicate that as the CO2 content of the air continues to rise, greater amounts of carbon will likely be allocated to the arbuscular mycorrhizal fungi associated with this grass species.  Thus, the fungi should be able to build a greater mycorrhizal network for transferring nutrients between itself and its host, thereby leading to increased plant productivity and growth.  In addition, these results suggest that many previous studies, which typically reported fungal root colonization on a percentage basis, may have, in the words of the authors, "obscured significant and subtle changes of carbon allocation to the mycobiont."  Thus, researchers should include measurements of percent infection intensity or percent infection by fungal structures other than hyphae in order to avoid underestimating the important responses of arbuscular mycorrhizal fungi to elevated CO2.

Reviewed 15 January 1999