Decreasing, not increasing, leaf area will raise crop yields under global atmospheric change

Area of Science:

• Agricultural Science
• Plant Physiology
• Crop Science

Background:

• Global crop yield increases are insufficient to meet future food demand.
• Rising atmospheric carbon dioxide ([CO₂]) often increases crop leaf area, particularly in soybean.
• The impact of increased leaf area on soybean yield under current and future [CO₂] is not fully understood.

Purpose of the Study:

• To determine if increased leaf area in soybean under elevated [CO₂] is beneficial or detrimental to yield.
• To investigate the optimal leaf area for maximizing soybean seed yield.
• To assess the potential of reducing leaf area to enhance crop productivity for future food security.

Main Methods:

• Utilized a mechanistic biophysical and biochemical model (MLCan) to simulate canopy carbon exchange and microclimate.
• Parameterized the MLCan model for a modern US Midwest soybean cultivar.
• Conducted field trials under open-air conditions at the Soybean Free Air Concentration Enrichment (SoyFACE) facility, manipulating leaf area by removing a proportion of emerging leaves.

Main Results:

• Model simulations predicted that soybean crops overinvest in leaves under current and elevated [CO₂], decreasing productivity and seed yield by 8% and 10%, respectively.
• Field experiments confirmed these predictions, showing that reducing leaf area led to a statistically significant 8% increase in soybean yield.
• This demonstrates that modern soybean cultivars produce more leaf area than is optimal for yield under both current and future [CO₂] levels.

Conclusions:

• Soybean yield is negatively impacted by excessive leaf area, even under elevated atmospheric carbon dioxide.
• Reducing leaf area in soybean cultivars can significantly enhance seed yield.
• Breeding or bioengineering for reduced leaf area presents a viable strategy to substantially increase crop yields and contribute to meeting future global food demand.