Host Plant Physiology and Mycorrhizal Functioning Shift across a Glacial through Future [CO2] Gradient

Area of Science:

• Ecology
• Plant Biology
• Mycology

Background:

• Rising atmospheric carbon dioxide ([CO2]) concentrations can alter plant nutrient and carbohydrate balance.
• Mycorrhizal associations, symbiotic relationships between fungi and plants, play a crucial role in plant nutrient uptake.
• Understanding how elevated [CO2] affects these symbioses is vital for predicting ecosystem responses to climate change.

Purpose of the Study:

• To investigate the impact of a wide [CO2] gradient on the functioning of mycorrhizal associations in two dandelion species.
• To determine if plant growth rates and vegetative plasticity mediate species-specific responses to elevated [CO2] and mycorrhizal fungi.
• To elucidate the physiological and biomass allocation mechanisms underlying these responses.

Main Methods:

• Growth of Taraxacum ceratophorum and Taraxacum officinale with and without mycorrhizal fungi across a [CO2] gradient (180–1,000 µL L−1).
• Calculation of response ratios (R_Bio) based on relative biomass of mycorrhizal and nonmycorrhizal plants.
• Structural equation modeling to assess relationships between R_Bio, host physiology, fungal growth, and biomass allocation.

Main Results:

• For Taraxacum officinale, R_Bio increased with [CO2], becoming positive at 700 µL L−1, driven by mycorrhizal effects on photosynthesis and leaf growth.
• For Taraxacum ceratophorum, R_Bio initially increased with [CO2] but then decreased, with [CO2] and fungal effects on plant growth and carbon sink strength correlating with shifts.
• Species-specific differences in growth rate and plasticity significantly influenced the magnitude and mechanisms of mycorrhizal-CO2 responses.

Conclusions:

• Rising [CO2] significantly alters mycorrhizal association functioning, generally increasing their benefit to plants.
• Nonlinear effects of elevated [CO2] may limit plant responses to mycorrhizal fungi under future climate scenarios.
• Plant growth rate and vegetative plasticity are key traits for predicting mycorrhizal responses to global change.