Estimating the AM fungal resources of wheat fields

Abstract

The arbuscular mycorrhizal (AM) fungi are a taxonomic group of microscopic soil dwellers generally promoting the growth of most plant species, including wheat, by mobilizing soil minerals, in particular soil P. Despite the importance of the AM fungi for plant nutrition, no technology exists to identify the fields in which AM fungi are doing a good job with feeding P to crops and the fields where agronomic interventions are required. We set out to fill this gap and examined 225 commercial fields in 2007, 2009 and 2010. We first found that P yields were limited by P supply rates below 3.5 μg P 10 cm-2 day-1. Fifty seven percent of the organic fields surveyed were below this threshold. A trend for higher P use efficiency in organic than conventional wheat crops at low soil P fertility levels was concurrent with higher levels of AM root colonization. The AM fungal communities of soils were simpler than expected. Some 122 phylotypes were found, but only ten of these accounted for over half of the AM fungal DNA sequences encountered. The main drivers of AM fungal diversity varied with the species of AM fungi. Among all the variables considered, soil organic matter level and soil texture were most often significantly correlated with the relative abundance of the different AM fungi. The research results suggest the possibility of using simple regression models to estimate the quality of soil AM fungal communities invisible to the naked eye. It appears that national databases on soils and climate, and soil analyses using PRS™-probe can be used to develop cost effective tools allowing the management of nutrient efficient wheat production systems based on ecological principles.