Growth and yield stimulation under elevated CO₂ and drought:A meta-analysis on crops

Exposure of plants to elevated CO2 (eCO2) has a number of physiological effects, including increased photosynthetic carbon fixation and decreased stomatal conductance, resulting in greater growth and yield and also improved water use efficiency. Therefore, eCO2 is considered to ameliorate the adverse effects of drought. To test this assumption in existing literature, we undertook a meta-analysis to study the interactive effects of eCO2 and experimentally imposed drought on biomass and yield of crops and pasture grasses. We found that for crop species with C3 metabolism, eCO2 stimulates biomass accumulation and yield under both well-watered and dry conditions to a similar extent. For C4 crops, however, stimulation of biomass accumulation and yield by eCO2 occurs only under dry growing conditions. Disentangling other functional groups (annuals vs. perennials, crop species, experimental setups) also showed that plant metabolism greatly determines the overall effect of eCO2 and water availability on plant performance. Our results suggest that crops grown in areas with limited water availability will benefit from future eCO2, regardless of their metabolism. Drought leads to stomatal limitation of photosynthesis in both C3 and C4 crops, which is alleviated when the plants are grown under eCO2.