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CROP ECOLOGY, MANAGEMENT & QUALITY

O₃ Sensitivity in a Potential C₄ Bioenergy Crop: Sugarcane in California

Dep. of Botany and Plant Sciences and Air Pollution Research Center, Univ. of California, Riverside, CA 92521, and Kearney Agric. Center, 9240 S. Riverbend Ave., Parlier, CA 93648

^* Corresponding author (david{at}uckac.edu).

The C₄ perennial grasses have many potential virtues as bioenergy crops—high productivity and water use efficiency, multiyear crop cycle that minimizes replanting costs, and wide environmental adaptation. In the productive San Joaquin Valley (SJV) of California, these species also confront high levels of ozone (O₃) air pollution. It is often assumed that C₄ species will exhibit tolerance to O₃, relative to C₃ species, based on limited crop yield-loss data and on responses to a contrasting gaseous air pollutant, sulfur dioxide (SO₂). Tolerance to O₃ of high-biomass C₄ crops such as sugarcane (Saccharum spp.) has not been demonstrated. Here we tested the hypothesis that a clone of sugarcane currently grown on a small commercial scale in the O₃–impacted SJV will exhibit tolerance to O₃. The hypothesis was disproven. Biomass production declined by over one-third and allocation to roots declined by over two-thirds, over a range of O₃ exposures (4, 58, and 114 ppb, 12-h means). These responses are comparable to responses previously reported for O₃–sensitive C₃ crop species. Greater O₃ tolerance may be required to maximize the potential viability of bioethanol production using tall tropical grasses such as sugarcane (for sucrose) or energy canes (for cellulose) in O₃–impacted western valleys. In the case of the locally successful sugarcane clone examined here, the C₄ photosynthetic pathway did not confer resistance to O₃ exposure.

Abbreviations: CSTR, continuously stirred tank reactor • PAR, photosynthetically active radiation • PST, Pacific Standard Time • RH, relative humidity • SJV, San Joaquin Valley • T, temperature