Antagonistic Effects of AMF and SOB in Soybean Rhizosphere: New Insights into Soil Microbial Interactions

Soil Microbial Interactions: AMF vs. SOB in Soybean Rhizosphere

Soil health and crop productivity often depend on complex interactions between plants and soil microorganisms. Two important microbial groups—arbuscular mycorrhizal fungi (AMF) and sulfur-oxidizing bacteria (SOB)—play key roles in nutrient cycling and soil fertility.

Traditionally, AMF and SOB are believed to act synergistically, enhancing nutrient uptake and plant growth. However, a new study investigating their combined effects in sulfur-deficient, acidified soybean soils revealed a surprising antagonistic relationship that challenges previous assumptions.

Key Findings: When Allies Turn into Adversaries

The research explored interactions between Funneliformis mosseae (AMF) and Acidithiobacillus thiooxidans (SOB) in soybean rhizosphere soils under continuous cropping.

1. Reduced Soybean Growth Under Co-Inoculation

Inoculating AMF alone improved soybean height, dry weight, and available soil sulfur.
SOB alone or combined with AMF inhibited plant growth, suggesting antagonistic interactions under acidic, sulfur-deficient conditions.

2. Decline in Sulfur Cycling Genes

AMF alone increased the abundance of sulfur-related genes (dsrA, soxY, yedZ, apsA).
SOB alone or co-inoculation reduced these genes, limiting sulfur oxidation efficiency in soils.

3. Impact of Soil pH and Microbial Secretions

High fructose and glucose levels secreted by AMF roots inhibited SOB growth.
Acidic conditions and excess carbon sources disrupted SOB’s autotrophic metabolism, lowering sulfur oxidation capacity.

Why This Matters for Agriculture

Continuous soybean cropping often leads to:

Sulfur depletion in soils
Soil acidification due to fertilizer overuse
Reduced crop yields and soil fertility

This study suggests that microbial interactions are context-dependent. While AMF can boost nutrient uptake and soil fertility, their combined use with SOB may not always be beneficial, especially in acidic, sulfur-deficient soils.

Towards Sustainable Soil Management

The findings highlight the need to:

Tailor microbial inoculant strategies to soil pH, nutrient status, and crop requirements
Study carbon exudation effects on soil microbial communities
Develop integrated soil fertility approaches for sustainable farming

Conclusion: Rethinking Microbial Fertilizers

The research provides new insights into plant-microbe-soil interactions, showing that AMF and SOB may compete rather than cooperate under certain conditions.

Future studies should explore:

How to balance microbial interactions for better nutrient cycling
The role of carbon exudates in shaping soil microbial networks
Field-scale validation of microbial inoculant performance

These findings could help farmers and soil scientists design eco-friendly, site-specific soil fertility management practices for sustainable agriculture.

Reference

Pan, L., Chen, J., Wang, L., & Cai, B. (2025). New insights into the antagonistic effect of AMF and SOB: A preliminary study on the ability of Funneliformis mosseae to inhibit sulfur oxidation by Acidithiobacillus thiooxidans. Plant and Soil. https://doi.org/10.1007/s11104-025-07885-7