Comparison of biochemical and microscopic methods for quantification of arbuscular mycorrhizal fungi in soil and roots

• Arbuscular mycorrhizal fungi were quantified by microscopy and lipid analysis.
• Ester-linked biomarker analysis gave results similar to microscopic analysis.
• The neutral lipid biomarker was significantly correlated with AMF spore density.
• The phospholipid biomarker did not significantly correlate to spores or colonization.

Arbuscular mycorrhizal fungi (AMF) are well-known plant symbionts which provide enhanced phosphorus uptake as well as other benefits to their host plants. Quantification of mycorrhizal density and root colonization has traditionally been performed by root staining and microscopic examination methods, which are time-consuming, laborious, and difficult to reproduce between laboratories. A number of biochemical markers for estimating mycorrhizal hyphae and spores have been published. In this study we grew maize plants in three different soils in a replicated greenhouse experiment and compared the results from two microscopic methods, spore density and root colonization, to the results from three lipid biomarker methods: neutral lipid fatty acid, phospholipid fatty acid, and ester-linked fatty acid analysis. Ester-linked fatty acid analysis gave consistent results for both spore density and root colonization, but neutral lipid fatty acid analysis had the highest correlation to AMF spore counts. Phospholipid fatty acid analysis was not correlated to spore density and did not reproducibly correlate to root colonization.