Quantifying the effects of ozone on plant reproductive growth and development

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.