Effects of Long-term Ozone Exposure on the Photosynthesis Capacity of Grain Pericarp and Grain-filling of Winter-wheat

Abstract

Dry matter accumulation, photosynthetic pigments content and chlorophyll a fluorescence parameters (via IMAGIN鄄PAM, H. Walz, Effeltrich, Germany) in the pericarp were studied in developing wheat grains in response to varying ozone concentration: charcoal filtered air (CF, O 3 ranging over 4-28 nL / L) , ambient air (NF, O 3 ranging over 7-78 nL / L) , 100 nL / L O 3 (CF100, O 3 ranging over 96-108 nL / L) and 150 nL / L O 3 (CF150, O 3 ranging over 145-160nL / L) and beside, a closed Open Top Chamber(5H, O 3 ranging over 15-68 nL / L) was set up for comparison. It was observed that CF100 and CF150 treatment significantly reduced the length of winter wheat grain along with its maximum width, maximum thickness, volume, number of grain per ear, grain filling duration and the average filling rate before the end of peak compared with NF. Their 1000鄄grain weight of CF100 and CF150 was constantly lower than NF (and CF) , finally, there was 10.7% and 17. 8% decline, respectively. From 8 th to 16 th day after anthesis, CF100 and CF150 were significantly higher than other three groups, yet after 16 days, they declined rapidly to the extent that they lag the other http: / / www.ecologica.cn groups significantly after 18 th day. Under enhanced O 3 , grain yield decrease resulted mainly from the declining of volume, grain filling duration and number of grain per ear. In conclusion, high concentration of O 3 delayed the grain development process at the earlier period of grain filling but advances senescence at the later period which sharply shorted the grain filling duration. The potential electron transport rate, equivalent to the parameter ETR max , was suppressed at the beginning of grain filling stage but promoted in middle stage. And then it fell rapidly due to the grain aging in advance. In addition, under high concentration of O 3 , the green layer of pericarp played a more important role in dry matter accumulation and nutrient synthesis.