Background
Gamper et al. introduce the subject of their study by noting that "arbuscular mycorrhizal fungi (AMF), an important group of obligate biotrophic symbionts at the soil-root interface, provide a crucial link for nutrient exchange between plants and soil: carbohydrates flow from the plant to the soil, and mineral nutrients in the reverse direction," remarking that "AMF are expected to modulate plant response to elevated CO2, by means of improving mineral nutrition (mainly P, Zn, Cu) and increasing resistance/tolerance of plants against an array of environmental stressors (Smith and Read, 1997)."

What was done
The authors studied the effects of elevated atmospheric CO2 (an extra 250 ppm) and N fertilization (14 vs. 56 g N m^-2) on permanent monoculture plots of two of the world's most extensively grown cool-season forage crops (Lolium perenne L. cv. Bastion and Trifolium repens L. cv. Milkanova) over a period of seven years at the Swiss FACE facility approximately 20 km northeast of Zurich.

What was learned
Gamper et al. report that "at elevated CO2 and under both N treatments, AMF root colonization of both host plant species was increased," and that "colonization levels of all three measured intraradical AMF structures (hyphae, arbuscules and vesicles) tended to be higher."  In addition, they report there was also an increase in non-AMF root colonization under elevated CO2.

What it means
Based on their findings, the authors "hypothesize that AMF provide non-P-nutritional benefits under the phosphorus-rich soil conditions of our field experiment," and that these benefits "may include improved N nutrition and increased protection against pathogens and/or herbivores."

Reference
Smith, S.E. and Read, D.J.  1997.  Mycorrhizal Symbioses.  Academic Press, London, UK.
Reviewed 12 May 2004