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A Newly-Discovered Benefit of Mycorrhizal Fungi
Rinaudo, V., Barberi, P., Giovannetti, M. and van der Heijden, M.G.A. 2010. Mycorrhizal fungi suppress aggressive agricultural weeds. Plant and Soil 333: 7-20.

The authors write that "previous work has emphasized that AMF [arbuscular mycorrhizal fungi] are important for the sustainability of agricultural ecosystems by enhancing crop nutrition (Plenchette et al., 1983; Gosling et al., 2006), by reducing nutrient leaching losses after heavy rain (van der Heijden, 2010), by providing protection against stress and disease (Auge, 2001; Sikes et al., 2009) and by improving soil structure (Rillig and Mummey, 2006). And now, in their new study, they explore another positive impact of AMF: their ability to suppress the negative consequences of aggressive agricultural weeds, which each year reduce crop yields around the world by between 10 and 30% (Oerke and Dehne, 1997).

What was done
Rinaudo et al., as they describe it, "investigated the impact of AMF and AMF diversity (three versus one AMF taxon) on weed growth in experimental microcosms where a crop (sunflower) was grown together with six widespread weed species."

What was learned
In the words of the four researchers, "the total biomass of sunflower grown alone in monocultures was 22% higher compared to microcosms where sunflower was grown in mixture together with weeds," while "the total weed biomass in microcosms with sunflower was on average 47% lower in microcosms with AMF, compared to microcosms without AMF." And when the weeds were grown alone, the effect of AMF presence was to reduce weed biomass by 25%.

What it means
Rinaudo et al. say their study shows that "AMF have the ability to suppress growth of some aggressive agricultural weeds, including Chenopodium album and Echinocloa crus-galli, which belong to the top ten of the world's most aggressive weeds." In addition, they note that the sunflower plants they grew "benefited from AMF through improved phosphorus uptake," which "points to a novel characteristic of the mycorrhizal symbiosis, namely that AMF have the ability to suppress unwanted weed species, while at the same time promoting nutrition of the target crop species," which work "supports two earlier reports by Vatovec et al. (2005) and Jordan and Huerd (2008)." And in further commenting on this aspect of their work, they say that "sunflower obtained 48% more phosphorus when AMF were present, while AMF reduced weed phosphorus content of the three mycorrhizal weeds (Digitaria sanguinalis, Echinochloa crus-galli, Setaria viridis) by 21%."

The significance of these findings with respect to the ongoing rise in the air's CO2 content is linked to the relationship that exists between atmospheric CO2 enrichment and AMF growth and development. As may be seen by perusing the materials that are identified when searching for arbuscular mycorrhizal fungi on our website's search feature (home page upper right-hand corner), as the air's CO2 content rises, it will likely impact crop-fungal interactions by increasing the percent of the crop's root system colonized by either mycorrhizal fungal hyphae or arbuscular structures, thereby promoting the positive phenomena documented by Rinaudo et al.

Auge, R.M. 2001. Water relations, drought and vesicular-arbuscular mycorrhizal symbiosis. Mycorrhiza 11: 3-42.

Gosling, P., Hodge, A., Goodlass, G. and Bending, G.C. 2006. Arbuscular mycorrhizal fungi and organic farming. Agriculture, Ecosystems and Environment 113: 17-35.

Jordan, N. and Huerd, S. 2008. Effects of soil fungi on weed communities in a corn-soybean rotation. Renewable Agriculture and Food Systems 23: 108-117.

Oerke, E.C. and Dehne, H.W. 1997. Global crop production and the efficacy of crop protection -- current situation and future trends. European Journal of Plant Pathology 103: 203-215.

Plenchette, C., Fortin, J.A. and Furlan, V. 1983. Growth responses of several plant species to mycorrhizae in a soil of moderate P-fertility. 1. Mycorrhizal dependency under field conditions. Plant and Soil 70: 199-209.

Rillig, M.C. and Mummey, D.L. 2006. Mycorrhizas and soil structure. New Phytologist 171: 41-53.

Sikes, B.A., Kottenie, K. and Klironomos, J.N. 2009. Plant and fungal identity determines pathogen protection of plant roots by arbuscular mycorrhizas. Journal of Ecology 97: 1274-1280.

van der Heijden, M.G.,A. 2010. Mycorrhizal fungi reduce nutrient loss from model grassland ecosystems. Ecology 91: 1163-1171.

Vatovec, C., Jordan, N. and Huerd, S. 2005. Responsiveness of certain agronomic weed species to arbuscular mycorrhizal fungi. Renewable Agriculture and Food Systems 20: 181-189.

Reviewed 24 November 2010