Growth and Yield Responses of Potato to Mixtures of Carbon Dioxide and Ozone

Elevated carbon dioxide (CO 2 ) concentrations in the atmosphere can stimulate plant growth and yield, whereas ground‐level ozone (O 3 ) concentrations cause the opposite effect in many areas of the world. Recent experiments show that elevated CO 2 can protect some plants from O 3 stress, but this has not been tested for most crop species. Our objective was to determine if elevated CO 2 protects Irish potato ( Solanum tuberosum L.) from foliar injury and suppression of growth and yield caused by O 3 An O 3 –resistant cultivar (Superior) and an O 3 –sensitive cultivar (Dark Red Norland) were exposed from within 10 d after emergence to maturity to mixtures of three CO 2 and three O 3 treatments in open‐top field chambers. The three CO 2 treatments were ambient (370 μL L −1 ) and two treatments with CO 2 added to ambient CO 2 for 24 h d −1 (540 and 715 μL L −1 ). The O 3 treatments were charcoal‐filtered air (15 nL L −1 ), nonfiltered air (45 nL L −1 ), and nonfiltered air with O 3 added for 12 h d −1 (80 nL L −1 ). Elevated O 3 and CO 2 caused extensive foliar injury of Dark Red Norland, but caused only slight injury of Superior. Elevated CO 2 increased growth and tuber yield of both cultivars, whereas elevated O 3 generally suppressed growth and yield, mainly of Dark Red Norland. Elevated CO 2 appeared to protect Dark Red Norland from O 3 –induced suppression of shoot, root, and tuber weight as measured at midseason but did not protect either cultivar from O 3 stress at the final harvest. The results further illustrate the difficulty in predicting effects of O 3 + CO 2 mixtures based on the effects of the individual gases.