Quantifying the effects of ozone on plant reproductive growth and development

Tropospheric ozone (O ₃) is a harmful air pollutant that can negatively impact plant growth and development. Current O ₃ concentrations ([O ₃]) decrease forest productivity and crop yields and future [O ₃] will likely increase if current emission rates continue. However, the specific effects of elevated [O ₃] on reproductive development, a critical stage in the plant's lifecycle, have not been quantitatively reviewed. Data from 128 peer-reviewed articles published from 1968 to 2010 describing the effects of O ₃ on reproductive growth and development were analysed using meta-analytic techniques. Studies were categorized based on experimental conditions, photosynthetic type, lifecycle, growth habit and flowering class. Current ambient [O ₃] significantly decreased seed number (-16%), fruit number (-9%) and fruit weight (-22%) compared to charcoal-filtered air. In addition, pollen germination and tube growth were decreased by elevated [O ₃] compared to charcoal-filtered air. Relative to ambient air, fumigation with [O ₃] between 70 and 100 ppb decreased yield by 27% and individual seed weight by 18%. Reproductive development of both C ₃ and C ₄ plants was sensitive to elevated [O ₃], and lifecycle, flowering class and reproductive growth habit did not significantly affect a plant's response to elevated [O ₃] for many components of reproductive development. However, elevated [O ₃] decreased fruit weight and fruit number significantly in indeterminate plants, and had no effect on these parameters in determinate plants. While gaps in knowledge remain about the effects of O ₃ on plants with different growth habits, reproductive strategies and photosynthetic types, the evidence strongly suggests that detrimental effects of O ₃ on reproductive growth and development are compromising current crop yields and the fitness of native plant species. This article is a US Government work and is in the public domain in the USA.