Comparative measurements of arbuscular mycorrhizal fungal responses to agricultural management practices

Authors: Lehman, R - Michael; Osborne, Shannon; TAHERI, WENDY - Former ARS Employee; BUYER, JEFFREY - Retired ARS Employee; CHIM, BEE - Oak Ridge Institute For Science And Education (ORISE)

Submitted to: Mycorrhiza
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/15/2019
Publication Date: 3/15/2019
Citation: Lehman, R.M., Osborne, S.L., Taheri, W.I., Buyer, J.S., Chim, B. 2019. Comparative measurements of arbuscular mycorrhizal fungal responses to agricultural management practices. Mycorrhiza. 29:227-235. https://doi.org/10.1007/s00572-019-00884-4.
DOI: https://doi.org/10.1007/s00572-019-00884-4

Interpretive Summary: Arbuscular mycorrhizal (AM) fungi are considered to be a key group of soil organisms for soil health assessments and developing relationships between agricultural management practices, soil health, and ecosystem services. Thus, ensuring there is an effective and consistent measurement of AM fungi is important to developing improved agricultural practices. Unfortunately, it is not clear which measure of AM fungi is most useful for this purpose. In a three-year study of fall cover crop effects on corn production, we evaluated different measures of AM fungi, including propagule numbers, biomass (lipid biomarkers), and activity (root colonization). We found the number of AM fungi propagules capable of colonization of plant roots was an effective measure of AM fungal response to cover crop treatments. Biomass measured by the neutral lipid fraction was also responsive, while the same biomarker in the phospholipid fraction was not as useful. Neither the number of AM fungal propagules or mass of lipid biomarkers were related to measures of crop performance. Corn root colonization did not respond to cover crop treatment. Most surprisingly, high levels of corn root colonization by AM fungi were negatively related to corn grain N concentration and plant biomass at maturity. Understanding the range of responses in measures of AM fungi will advance identification and characterization of improved cropping practices.

Technical Abstract: Arbuscular mycorrhizal (AM) fungi are considered to be a key group of soil organisms for assessments of soil biological properties and developing relationships among crop production management practices, soil properties, crop performance, and ecosystem services. In a field study of cover crop treatments established during the transition from small grains to corn (Zea mays L), we assessed multiple measures of AM fungal responses to the management treatments: soil propagule numbers, biomass via lipid biomarkers, and root colonization extent. Our objectives were to determine response variables that reliably distinguished cover crop treatments and formed consistent relationships with grain yield, plant biomass, and mineral nutrient concentrations of the following corn crop. The number of soil AM fungal propagules and amount of the NLFA biomarker C16:1cis11 measured on fall-collected soils most consistently and significantly responded to fall cover crop treatments. Neither of these measures of soil inoculum potential were strongly related with measures of crop performance. The PLFA biomarker C16:1cis11 was marginally responsive to cover crop, but did not strongly relate to crop performance parameters. Corn root colonization by AM fungi was not significantly affected by cover crop treatment, but significant negative relationships were found between root colonization and grain N concentration and plant biomass at maturity. In contrast, a significant positive relationship between root colonization and plant N concentration at the 6-leaf stage was found. Understanding the relative effectiveness and limitations of AM fungal response variables will inform their application in field studies of agricultural management practices.