Yield and economic losses of winter wheat and rice due to ozone in the Yangtze River Delta during 2014-2019.

Ground-level ozone (O3) is the main phytotoxic air pollutant causing crop yield reduction in China. As the main grain producing area in China, the Yangtze River Delta (YRD) is facing serious O3 pollution. This study analyzed the hourly ground-level O3 observation data of 158 stations from 2014 to 2019 in YRD, and grain production data of 193 districts and counties. The exposure-response relationships based on AOT40 (accumulated hourly O3 concentration above 40 ppb) was used to estimate the yield loss and economic loss of two food crops (winter wheat and rice). This study used spatial interpolation and calculated the specific data values of each district and county in order to improve the assessment reliability. For years 2014-2019, averaged O3 concentration during the 75 days growing period of rice and wheat were 33.1-50.6 ppb and 32.2-48.0 ppb, AOT40 value were 5.2-12.0 ppm h and 4.6-9.4 ppm h, and the averaged relative yield losses were 4.9%-11.4% and 9.4%-19.3%, respectively. The trend of O3 in the YRD in a six-year period peaked in 2016 and 2017 for rice and winter wheat, respectively. During 2014-2017, the average estimated yield loss of rice was 2445 Mt. accounting for about 9.1% of the actual production, and the average estimated economic loss was about 1037 million USD; for winter wheat, it was 2025 Mt, 20.4% and 736 million USD, respectively. These results urge governments to provide effective policies and measures to control O3 pollution.

Yield and economic losses in maize caused by ambient ozone in the North China Plain (2014-2017).

Maize is the second most important crop per harvested area in the world. The North China Plain (NCP) is a highly populated and relevant agricultural region in China, experiencing some of the highest ozone (O3) concentrations worldwide. It produces ~24% of the total maize production of China in years 2014-2017. For these years, we used observational O3 data in combination with geostatistic methods to estimate county-level production and economic losses due to O3 in the NCP. AOT40 (accumulated ozone exposure over an hourly threshold of 40 ppb) values during the maize growing season (90 days before maturity) progressively increased in the four consecutive years: 13.7 ppm h, 15.4 ppm h, 16.9 ppm h and 22.7 ppm h. Mean relative yield losses were 8.2% in 2014, 9.2% in 2015, 10.4% in 2016 and 13.4% in 2017. These yield losses, derived from exposure-response functions, resulted in crop production losses of 530.3 × 104 t, 617.8 × 104 t, 713.8 × 104 t, and 953.4 × 104 t, as well as economic losses of 2343 million USD, 2672 million USD, 1887 million USD, and 2404 million USD from 2014 to 2017. The NCP is a key area in China for monitoring the effectiveness of the clean air action policies aiming at reducing emissions of air pollutants. Despite these measures, O3 concentrations have increased in NCP, and reduction of this pollutant are challenging. We suggest an increase in the number of rural air quality stations for better characterizing O3 trends in cropland areas, as well as the application of different mitigation measures. They may involve more stringent air quality regulations and changes in crops, breeding tolerant cultivars and a crop management taking into account O3 pollution.

Assessment of O3-induced yield and economic losses for wheat in the North China Plain from 2014 to 2017, China.

Tropospheric ozone (O3) is a pollutant of widespread concern in the world and especially in China for its negative effects on agricultural crops. For the first time, yield and economic losses of wheat between 2014 and 2017 were estimated for the North China Plain (NCP) using observational hourly O3 data from 312 monitoring stations and exposure-response functions based on AOT40 index (accumulated hourly O3 concentration above 40 ppb) from a Chinese study. AOT40 values from 2014 to 2017 during the wheat growing seasons (75-days, 44 before and 30 after mid-anthesis) ranged from 3.1 to 14.9 ppm h, 4.9-17.5 ppm h, 7.3-17.6 ppm h, and 0.5-18.6 ppm h, respectively. The highest AOT40 values were observed in the Beijing-Tianjin-Hebei region. The values of relative yield losses from 2014 to 2017 were in the ranges of 6.4-30.5%, 10.0-35.8%, 14.9-34.1%, and 21.6-38.2%, respectively. The total wheat production losses in NCP for 2014-2017 accounted for 18.5%, 22.7%, 26.2% and 30.8% in the whole production, while the economic losses amounted to 6,292 million USD, 8,524 million USD, 10,068 million USD, and 12,404 million USD, respectively. The important impact of O3 in this area, which is of global importance, should be considered when assessing wheat yield production. Our results also show an increasing trend in AOT40, relative yield loss, total crop production loss and economic loss in the four consecutive years.

A quantitative assessment of hormetic responses of plants to ozone.

Evaluations of ozone effects on vegetation across the globe over the last seven decades have mostly incorporated exposure levels that were multi-fold the preindustrial concentrations. As such, global risk assessments and derivation of critical levels for protecting plants and food supplies were based on extrapolation from high to low exposure levels. These were developed in an era when it was thought that stress biology is framed around a linear dose-response. However, it has recently emerged that stress biology commonly displays non-linear, hormetic processes. The current biological understanding highlights that the strategy of extrapolating from high to low exposure levels may lead to biased estimates. Here, we analyzed a diverse sample of published empirical data of approximately 500 stimulatory, hormetic-like dose-responses induced by ozone in plants. The median value of the maximum stimulatory responses induced by elevated ozone was 124%, and commonly <150%, of the background response (control), independently of species and response variable. The maximum stimulatory response to ozone was similar among types of response variables and major plant species. It was also similar among clades, between herbaceous and woody plants, between deciduous and evergreen trees, and between annual and perennial herbaceous plants. There were modest differences in the stimulatory response between genera and between families which may reflect different experimental designs and conditions among studies. The responses varied significantly upon type of exposure system, with open-top chambers (OTCs) underestimating the maximum stimulatory response compared to free-air ozone-concentration enrichment (FACE) systems. These findings suggest that plants show a generalized hormetic stimulation by ozone which is constrained within certain limits of biological plasticity, being highly generalizable, evolutionarily based, and maintained over ecological scales. They further highlight that non-linear responses should be taken into account when assessing the ozone effects on plants.