Elevated carbon dioxide and water stress effects on potato canopy gas exchange, water use, and productivity

Despite the agronomic importance of potato (Solanum tuberosum L.), the interaction of atmospheric carbon dioxide concentration ([CO2]) and drought has not been well studied. Two soil–plant–atmosphere research (SPAR) chamber experiments were conducted concurrently at ambient (370 μmol mol−1) and elevated (740 μmol mol−1) [CO2]. Daily irrigation for each chamber was applied according to a fixed percentage of the water uptake measured for a control chamber for each [CO2] treatment. We monitored diurnal and seasonal canopy photosynthetic (AG) and transpiration rates and organ dry weights at harvest. Plants grown under elevated [CO2] had consistently larger photosynthetic rates through most of the growth season, with the maximum AG at 1600 μmol photons m−2 s−1 14% higher at the well-watered treatments. Water stress influenced ambient [CO2] plants to a larger extent, and reduced maximum canopy AG, growth season duration, and seasonal net carbon assimilation up to 50% of the control in both [CO2] treatments. Water use efficiency increased with water stress, particularly at elevated [CO2], ranging from 4.9 to 9.3 g dry mass L−1. Larger photosynthetic rates for elevated [CO2] resulted in higher seasonal dry mass and radiation use efficiency (RUE) as compared with ambient [CO2] at the same irrigation level. This extra assimilate was partitioned to underground organs, resulting in higher harvest indices. Our findings indicate that increases in potato growth and productivity with elevated [CO2] are consistent over most levels of water stress. This work can support various climate change scenarios that evaluate different management practices with potato.