Growth and physiological responses of two sugarcane cultivars exposed to elevated surface ozone

Abstract

Surface ozone (O₃) pollution is known to have a detrimental effect on agriculture whilst rising carbon dioxide (CO₂) concentrations are sometimes found to offer plants protection against O₃ effects. Considering the important role of sugarcane (Saccharum spp. hybrids) as a major food crop in South Africa and its contribution to the national economy, the tolerance of this crop to O₃ damage must be established. A pilot study using open-top chambers was conducted whereby two local commercial sugarcane cultivars (NCo376 and N31) were fumigated during the summer growth season to explore the effects of elevated O₃ as well as the interacting effects of O₃ and CO₂ on various stress and crop quality indicators. Statistical significance of differences in treatment means was analysed by hierarchical linear modelling to account for variability between chamber and pots in explaining changes across individual plants. The results revealed a significant reduction in the number of dead leaves (senescing) for the N31 cultivar exposed to elevated O₃ compared with the other treatments. There was also a statistically significant decrease in chlorophyll fluorescence (used to assess photosynthetic performance) in the O₃-treated NCo376 plants. This pilot study shows limited effects of O₃ fumigation on growth and physiology, with preliminary indications that sugarcane is less sensitive to O₃ than other crops. An increase in O₃ concentrations associated with future climate change is expected, which will have implications for cultivar selection as a possible adaptation strategy to reduce susceptibility of this crop to O₃.

Significance:

• This article adds to the existing literature on sugarcane and ozone (O₃). We present a pilot study for two cultivars of sugarcane and explore interacting effects of O₃ and carbon dioxide (CO₂) on various stress and crop quality indicators.
• We employed a mixed effects model to account for variability between chamber and pots, a challenge when working with plants.
• This is the first time African sugarcane has been investigated and, although the findings show limited statistical effect of O₃ and CO₂, future studies can vary the conditions of this experiment to produce more data points for a dose-response function.