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Elevated CO2 Alleviates the Negative Effects of Drought Stress in Cucumbers

Paper Reviewed
Liu, B.B., Li, M., Li, Q.M., Cui, Q.Q., Zhang, W.D., Ai, X.Z. and Bi, H.G. 2018. Combined effects of elevated CO2 concentration and drought stress on photosynthetic performance and leaf structure of cucumber (Cucumis sativus L.) seedlings. Photosynthetica 56: 942-952.

Writing as background for their work, Liu et al. (2018) say that "drought stress is one of the main environmental factors limiting plant growth and productivity of many crops," but "elevated carbon dioxide concentration can ameliorate, mitigate, or compensate for the negative impact of drought on plant growth and enable plants to remain turgid and functional for a longer period."

Desiring to learn more about these beneficial impacts, the team of seven Chinese researchers set out to investigate the combined effects of elevated CO2 and drought stress on the photosynthetic performance and leaf structure of cucumber (Cucumis sativus) seedlings. Their work was accomplished by analyzing the photosynthetic characteristics and structure of cucumber leaves of seedlings exposed to two CO2 concentrations (400 or 800 ppm) and three water (adequate water, moderate drought stress or severe drought stress) treatments for a period of seven days.

With respect to the impact of CO2 and drought on photosynthesis, Liu et al. report that drought stress decreased it significantly under both ambient and elevated CO2 levels. In contrast, elevated CO2 significantly increased net photosynthesis by 17, 26 and 31% under adequate water, moderate drought and severe drought conditions, respectively, "offset[ting] some of the impact of drought [on] net photosynthesis."

With respect to leaf structure, the authors say that elevated CO2 "increased the lengths of the palisade cells and the number of chloroplasts per palisade cell under severe drought stress, and significantly increased the grana thickness under moderate drought stress." Furthermore, it "significantly decreased stomatal density, stomatal widths and stomatal aperture on the abaxial surface of leaves under moderate drought stress." In contrast, drought stress reduced the thickness of cucumber seedling leaves, which was mainly caused by "the simultaneous decrease of palisade and spongy layers thickness."

In commenting on their many findings, Liu et al. conclude that "under drought stress conditions, elevated CO2 can change leaf tissue structures, improve photosynthetic performance, ameliorate water status and improve drought resistance of cucumber seedlings, thus alleviating the negative effects of drought stress." We could not have said it any better!

Posted 25 July 2018