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

Improving plant energy conversion efficiency (e(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 e(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 e(c) to treatment type and dosage, plant characteristics, and growth conditions were also examined. Significant mean increases in e(c) were caused by elevated [CO2] (20%), shade (18%), and intercropping (15%). e(c) increased curvilinearly up to 55% with nitrogen additions whereas phosphorus application was most beneficial at low levels. Significant decreases in e(c) of 8.4% due to elevated [O-3], 16.8% due to water stress, and 6.5% due to foliar damage were found. A non-significant decrease in e(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 e(c) improvement, further studies should be conducted in the field since several responses were exaggerated by non-field experimental conditions.