A meta-analysis of responses of canopy photosynthetic conversion efficiency to environmental factors reveals major causes of yield gap

Improving plant energy conversion efficiency (ε_c) is crucial for increasing food and bioenergy crop production and yields. Using a meta-analysis, the effects of greenhouse gases, weather-related stresses projected to intensify due to climate change, and management practices including inputs, shading, and intercropping on ε_c were statistically quantified from 140 published studies to identify where improvements would have the largest impact on closing yield gaps. Variation in the response of ε_c to treatment type and dosage, plant characteristics, and growth conditions were also examined. Significant mean increases in ε_c were caused by elevated [CO₂] (20%), shade (18%), and intercropping (15%). ε_c increased curvilinearly up to 55% with nitrogen additions whereas phosphorus application was most beneficial at low levels. Significant decreases in ε_c of-8.4% due to elevated [O₃],-16.8% due to water stress, and-6.5% due to foliar damage were found. A non-significant decrease in ε_c of-17.3% was caused by temperature stress. These results identify the need to engineer greater stress tolerance and enhanced responses to positive factors such as [CO₂] and nitrogen to improve average yields and yield potential. Optimizing management strategies will also enhance the benefits possible with intercropping, shade, and pest resilience. To determine optimal practices for ε_c improvement, further studies should be conducted in the field since several responses were exaggerated by non-field experimental conditions.