Herbicide residues in soil decrease microbe-mediated plant protection

Area of Science:

• Agricultural Science
• Microbiology
• Ecology

Background:

• Glyphosate residues persist longer than expected in soils, impacting rhizosphere microbes crucial for plant health.
• The effects of soil-bound glyphosate on aboveground mutualistic microbes are largely unknown.
• Epichloë species are common endophytic symbionts in cool-season grasses, providing herbivore resistance via alkaloids.

Purpose of the Study:

• To investigate the impact of soil-applied glyphosate on Epichloë endophytes.
• To assess the consequences of glyphosate exposure on plant-endophyte symbiosis and plant defense.
• To understand the broader ecological implications of herbicide residues on plant-microbe interactions.

Main Methods:

• In vitro assessment of glyphosate's effect on Epichloë endophyte growth.
• Cultivation of endophyte-symbiotic meadow fescue in soil with a glyphosate history for two years.
• Measurement of insect-toxic loline alkaloid concentrations in plants under natural herbivore infestation.

Main Results:

• Glyphosate exposure directly inhibited Epichloë endophyte growth in vitro.
• Plants grown in glyphosate-treated soil showed reduced levels of Epichloë-derived loline alkaloids.
• A correlation was observed between glyphosate presence, reduced alkaloid levels, and natural herbivore pressure.

Conclusions:

• Soil-residing glyphosate negatively affects both rhizosphere and aerial plant endophytes.
• Herbicide contamination disrupts beneficial plant-microbe symbioses, compromising plant defense mechanisms.
• Glyphosate's impact extends to plant-pest interactions, with potential cascading ecological effects.