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 ([CO 2]) 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) [CO 2]. Daily irrigation for each chamber was applied according to a fixed percentage of the water uptake measured for a control chamber for each [CO 2] treatment. We monitored diurnal and seasonal canopy photosynthetic ( A G) and transpiration rates and organ dry weights at harvest. Plants grown under elevated [CO 2] had consistently larger photosynthetic rates through most of the growth season, with the maximum A G at 1600 μmol photons m −2 s −1 14% higher at the well-watered treatments. Water stress influenced ambient [CO 2] plants to a larger extent, and reduced maximum canopy A G, growth season duration, and seasonal net carbon assimilation up to 50% of the control in both [CO 2] treatments. Water use efficiency increased with water stress, particularly at elevated [CO 2], ranging from 4.9 to 9.3 g dry mass L −1. Larger photosynthetic rates for elevated [CO 2] resulted in higher seasonal dry mass and radiation use efficiency (RUE) as compared with ambient [CO 2] 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 [CO 2] are consistent over most levels of water stress. This work can support various climate change scenarios that evaluate different management practices with potato.