[Relationship Between Relative Crop Yield/Woody Plant Biomass and Ground-level Ozone Pollution in China]

Currently, ground-level ozone (O₃) pollution is increasingly serious in China, and highly threatens plant productivity. In this study, we summarized the relationship between relative crop yield or woody plant biomass and O₃ metrics, including M7 (the mean of hourly concentrations from 09:00 to 16:00), SUM06 (sum of hourly concentrations above 60 nmol·mol^-1), W126 (Sigmoidal weighted sum of the hourly concentrations during a specified period), POD[phytotoxic O₃ dose above a threshold flux of Y nmol·(m²·s)^-1], and the most commonly used AOT40 (accumulated O₃ concentrations over an hourly threshold of 40 nmol·mol^-1), and proposed their critical level to protect plants against O₃ damage. Based on the AOT40 metric, we found that the O₃ risk threshold that caused a 5% decrease in yield was 5.93 μmol·mol^-1·h for rice, 2.69 μmol·mol^-1·h for winter wheat, 8.67 μmol·mol^-1·h for maize, and 4.17 μmol·mol^-1·h for soybean, indicating that maize may be more tolerant to O₃ than the other three crops in China. The O₃ risk threshold that led to a 5% reduction in total biomass was 12.20 μmol·mol^-1·h across five poplar clones (based on experiment) and 10.87 μmol·mol^-1·h across 17 woody plants (based on integrated analysis). On the other hand, some perspectives were presented concerning the establishment of O₃ response relationships for important productivity-related parameters, and the improvement of accuracy in O₃ regional risk assessment. It is also important to consider how to couple other important factors affecting plant O₃ sensitivity (such as soil nitrogen and plant age) into the regional assessment model.