Young sugarcane plants exhibit higher photosynthetic tolerance to acute ozone exposure than energy cane

Abstract

We evaluated the impact of acute ozone (O 3 ) on photosynthesis of energy cane and sugarcane, hypothesizing that energy cane –known for its resilience to environmental disturbances– would exhibit higher tolerance to O 3 than sugarcane. Under growth chamber conditions, plants were exposed to three O 3 concentrations (0, 150, and 300 ppb) for three consecutive days. Leaf CO 2 assimilation declined in both crops after one day of exposure at 150 and 300 ppb O 3 . While sugarcane maintained similar performance at both 150 and 300 ppb O 3 , energy cane showed the lowest photosynthetic rates at 300 ppb O 3 . Such higher sensitivity of energy cane was driven by reduced photochemical efficiency (Φ PSII ) at 150 ppb O 3 and by low stomatal conductance and Φ PSII at 300 ppb O 3 . Notably, sugarcane showed significant stomatal closure after three days of exposure to 150 ppb O 3 , preventing further O 3 influx and maintaining CO 2 assimilation. However, this protective mechanism was not effective under 300 ppb O 3 . PEPCase and Rubisco carboxylation rates decreased in both crops after three days under O 3 exposure. The rates of decline in leaf CO 2 assimilation due to increasing air O 3 concentration were higher in sugarcane and in energy cane, i.e., 0.2 and 0.3 mmol m⁻ 2 s⁻ 1 per 10-ppb O 3 increase, respectively. Contrary to our initial hypothesis, energy cane was more sensitive to acute O 3 exposure. Sugarcane exhibited greater short-term photosynthetic tolerance to O 3 linked to stomatal regulation and photochemical stability.

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