Mycorrhizal fungi for enhanced nitrate retention and soil organic matter in agricultural soils

Overview

This research program investigates how arbuscular mycorrhizal fungi (AMF) can be leveraged to increase nitrate retention and build soil organic matter (SOM) in agricultural systems. The overarching premise is that AMF enhance nitrification and nitrogen storage by forming stable soil aggregates that harbor nitrifying bacteria, while simultaneously increasing SOM that reduces hydraulic conductivity and nitrate leaching from the mycorrhizosphere. The work specifically examines how root architecture (extensive versus tap root systems) influences AMF colonization density and aggregate formation, with effects expected to be more pronounced in sandy soils than in loams.

The findings have direct implications for sustainable agriculture, nutrient management, and environmental stewardship. By improving the soil's capacity to retain nitrogen and build organic carbon, this approach offers a biologically based pathway to reduce fertilizer losses, improve crop nutrient use efficiency, and enhance long-term soil health.

Technical specifications

Core research approach:

• Rhizotron-based experiments using two soil types (sand and loam) and two plant species with contrasting root architectures
• Controls include unplanted soil and sterilized, non-inoculated soil to isolate AMF-specific effects
• Soil analyses before and after harvest measuring soil organic matter, soil carbon fractions, total nitrogen and phosphorus, NOx concentrations, mycorrhizal spore counts, saturated hydraulic conductivity, and aggregate size distribution
• MicroCT imaging at the Danforth Center to visualize aggregate structure and distribution non-destructively
• Molecular characterization of ammonia-oxidizing bacteria (amoA) and denitrifier genes (nirK/nirS) linked to aggregate size classes
• Modeling of nitrate transport and denitrification dynamics as a function of aggregate size

Key mechanisms under investigation:

• AMF-driven formation of soil aggregates that concentrate nitrifying microorganisms
• SOM accumulation in smaller soil pores that increases water retention and reduces nitrate flux
• Differential AMF colonization and aggregate formation between extensive and tap root systems
• Amplified effects in sandy soils due to their lower baseline aggregation and organic matter

Technology readiness level

This is an active fundamental research program at the proof-of-concept stage. Prior laboratory work has demonstrated that ammonia-oxidizing bacteria, nitrate, and organic matter are enriched in mycorrhizal soils compared to non-inoculated controls in sandy soil. However, aggregate size distribution and intra-aggregate nitrate concentrations have not yet been characterized. The proposed rhizotron experiments, combined with microCT imaging and molecular analyses, will provide the mechanistic validation needed to advance the technology toward field-scale evaluation and potential commercial application in nutrient management and soil health products.