Drought does not mitigate reductions in soybean photosynthesis and yield caused by elevated ozone

Area of Science:

• Agricultural Science
• Environmental Science
• Plant Physiology

Background:

• Climate change is increasing the co-occurrence of elevated tropospheric ozone and drought in agricultural regions.
• Both ozone and drought stress negatively impact plant physiology, reducing biomass and crop yield.
• The interaction between ozone and drought is complex and not well understood in field conditions.

Purpose of the Study:

• To investigate the interactive effects of elevated ozone and drought stress on soybean (Glycine max) leaf physiology and yield.
• To determine if ozone exposure alters stomatal response to drought conditions.
• To assess the impact of these combined stressors on soybean seed production.

Main Methods:

• Utilized Free Air Concentration Enrichment (FACE) to expose soybean plants to elevated ozone (100 ppb).
• Employed rainfall exclusion canopies to simulate drought conditions by intercepting approximately 40% of seasonal rainfall.
• Measured leaf-level physiological parameters, including photosynthetic capacity, stomatal conductance, and abscisic acid levels, alongside final yield components.

Main Results:

• Elevated ozone consistently reduced soybean Rubisco carboxylation capacity (-17%) and maximum electron transport capacity (-9%) over three years.
• Ozone exposure did not affect the relationship between soil moisture, abscisic acid, and stomatal conductance, indicating no prevention of drought-induced stomatal closure.
• Soybean yield was significantly reduced by elevated ozone due to fewer seeds per plot and smaller seed size; drought only impacted yield in the driest season.

Conclusions:

• The effects of elevated ozone and drought on soybean are additive rather than interactive and are dose-dependent.
• Ozone-induced damage persists even under soil moisture depletion, suggesting potential exacerbation under future climate change scenarios.
• Elevated ozone poses a significant threat to soybean yield, independent of drought, with combined impacts likely to worsen with climate change.