Tropospheric ozone (O3) is a harmful air pollutant that can negatively impact plant growth and development. Current O3 concentrations ([O3]) decrease forest productivity and crop yields and future [O3] will likely increase if current emission rates continue. However, the specific effects of elevated [O3] 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 O3 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 [O3] 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 [O3] compared to charcoal-filtered air. Relative to ambient air, fumigation with [O3] between 70 and 100 ppb decreased yield by 27% and individual seed weight by 18%. Reproductive development of both C3 and C4 plants was sensitive to elevated [O3], and lifecycle, flowering class and reproductive growth habit did not significantly affect a plant's response to elevated [O3] for many components of reproductive development. However, elevated [O3] 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 O3 on plants with different growth habits, reproductive strategies and photosynthetic types, the evidence strongly suggests that detrimental effects of O3 on reproductive growth and development are compromising current crop yields and the fitness of native plant species.
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