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Arbuscular mycorrhiza suppresses microbial abundance, and particularly that of ammonia oxidizing bacteria, in agricultural soils

Summary

This study examined how a beneficial fungus called arbuscular mycorrhiza affects bacteria that break down ammonia in soil. Researchers tested 50 different agricultural soils and found that the fungus suppressed ammonia-oxidizing bacteria populations. Interestingly, the presence of the fungus actually increased ammonia levels in soil while decreasing nitrate, suggesting the relationship is more complex than simple competition for nutrients.

Background

Arbuscular mycorrhizal (AM) fungi form symbiotic relationships with most terrestrial plants and play a crucial role in nutrient uptake. Ammonia-oxidizing (AO) microorganisms are important for soil nitrogen cycling. The interactions between these two microbial guilds are complex and variable across different soil types.

Objective

To investigate quantitative and compositional responses of indigenous microorganisms in 50 different agricultural field soils to the actively growing mycelium of the AM fungus Rhizophagus irregularis, particularly examining interactions with ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA), and comammox Nitrospira.

Results

AM fungus systematically suppressed the abundance of AOB and comammox Nitrospira across different soils, while AOA abundance remained unaffected. Surprisingly, AM fungal presence increased soil ammonium concentrations while decreasing nitrate levels. The suppression of AOB correlated with soil pH and was accompanied by changes in AOB community structure.

Conclusion

The interaction between AM fungi and ammonia-oxidizing microorganisms extends beyond simple competition for ammonium and may involve complex mechanisms including effects on soil nitrogen cycling pathways, differential nutrient use trajectories, or biologically-produced nitrification inhibitors.
  • Published in:Frontiers in Microbiology,
  • Study Type:Experimental Study,
  • Source: 10.3389/fmicb.2025.1671859
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