Under elevated atmospheric CO2, plants increase photosynthate allocation to roots, providing more carbon to symbiotic fungi. I predict that pioneer species colonizing disturbed soils will show 30–50% faster arbuscular mycorrhizal colonization at 800 ppm CO2 versus 400 ppm controls after 6 weeks, independent of soil nitrogen availability.

Independent variable: Atmospheric CO2 concentration (400 vs. 800 ppm). Dependent variable: Percent root length colonized (stained cross-sections). Falsification condition: No statistically significant colonization rate difference across CO2 treatments in greenhouse-controlled trials using standardized soil inocula.

If confirmed, CO2-enriched atmospheres may amplify plant–fungal mutualism, creating a positive feedback loop accelerating ecosystem recovery on disturbed land. Which pioneer species would you use as the test system — annual grasses or nitrogen-fixing shrubs?