Greenhouse CO₂ enrichment has been widely applied in commercial production and investigated in numerous experiments worldwide, yet findings vary across dispersed studies, and its yield benefits have not been systematically quantified and interpreted at the global scale. This dissertation quantifies the greenhouse CO₂ fertilization effect, explains variation across crop functional types and harvested organs, and identifies where CO₂ enrichment is most effective under current and future climates. In Chapter 2, I compiled a global dataset of greenhouse experiments (454 observations from 147 studies) and applied meta-analysis using log response ratios (lnRR) to estimate yield gains and benchmark greenhouse CO₂ enrichment against Free-Air CO₂ Enrichment (FACE). Across comparable CO₂ increments of 115–300 ppm (ppm, parts per million by volume (μmol mol⁻¹)), greenhouse CO₂ enrichment increases yields by ~28% on average and delivers ~1.4 times larger response than FACE. Dose-response analyses suggest that yield gains peak at CO₂ concentration increment of 800–1,200 ppm. Chapter 3 identifies differences in responses among crops with harvestable organs, showing that below-ground crops (roots and tubers) exhibit roughly double the yield response of above-ground crops, which may be attributed to stronger sink capacity and carbon storage of below-ground crops. In Chapter 4, I evaluate climatic and soil controls on enrichment performance and train Random Forest models (R² around 0.7) using CMIP6 GCM ensemble to map global suitability and project changes under SSP126 and SSP585. The maps suggest a poleward shift in suitability for greenhouse CO₂ enrichment under future scenarios. Overall, this thesis integrates meta-analysis, greenhouse–FACE benchmarking, yield-CO₂ response surfaces, and machine-learning suitability mapping to provide evidence-based guidance for climate-smart greenhouse CO₂ enrichment under ongoing climate change.
Jiejie Sun (Thu,) studied this question.