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

Abstract

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), PODY[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.