Effects of elevated CO2 and cyclic drought on potato under varying radiation regimes

► Cyclic drought and elevated CO2 response of major agronomic crop studied. ► Water use efficiency and harvest index enhanced by drought under two CO2 levels. ► Water use efficiency and yield were higher for plants grown under elevated CO2. ► Effects of drought vary based on potato developmental stage. ► Results suggest water management can be used to adapt production as climate changes. Climate change predictions include increased frequency of episodic drought in many potato (Solanum tuberosum L.) producing regions in the world. Quantitative data on potato response to periodic drought under elevated atmospheric carbon dioxide (CO2) conditions is lacking, but is needed to improve crop modeling tools suitable for investigating adaptation strategies. Two experiments E1 and E2 were conducted in sunlit soil-plant-atmosphere research (SPAR) chambers to evaluate effects of short-term drought cycles at ambient and twice-ambient CO2. Experiments were conducted in the same growing season, but at different planting dates in order to further examine effects of variation in solar radiation during the drought periods (daily average photosynthetically active radiation of 43.9molm−2d−1 in E1 and 24.7molm−2d−1 in E2). Drought cycles were applied at post-tuber initiation (R) or at both vegetative and post tuber-initiation (VR) stages. While total dry matter in E1 was nearly twice that of E2 as a result of the radiation differences, relative responses to drought and CO2 were consistent. Total dry matter production was reduced proportionately based on the number of drought cycles, with twice-droughted VR plants producing less biomass than non-droughted controls. Harvest index and the ratio of tuber to total dry matter growth rate increased with drought frequency, suggesting that tuber sink strength was higher for VR plants than R. Harvest index, the ratio of tuber to total plant growth rate, and tuber dry matter for VR and R treated plants were also higher at elevated versus ambient CO2. Water use efficiency for water deficient versus water sufficient plants was correlated with harvest index and also increased at the higher CO2 concentration. As there was also little influence of drought or CO2 on leaf extension characteristics, differences in dry matter production and allometric responses were assumed to predominantly be a function of assimilation rate and carbon partitioning. These results confirm potato drought sensitivity in terms of yield response is influenced by devel