Growth stage dependence of the grain yield response to ozone in spring wheat (Triticum aestivum L.)

Field grown spring wheat (Triticum aestivum L.) was exposed to three different ozone treatments in open-top chambers: nonfiltered air (NF), non-filtered air with the same ozone dose (2500 nl l(-1) h above 40 nl l(-1)) during 38 days before anthesis (NF+pre), and during 26 days after onset of anthesis (NF+post). In addition, ambient air plots (AA) were used. During the respective treatment periods in NF+pre and NF+post, the 12 h daytime (between 08:00 and 20:00 hours) long-term average of the ozone concentration was between 40 and 45 nl l(-1). The ozone concentration was around 20-25 nl l(-1) in the NF treatment, as well as in the NF+pre and NF+post treatments, during the NF+post and the NF+pre periods, respectively. The grain yield in NF+post was 11% lower than in NF and this difference was statistically significant. The difference in grain yield between the NF+pre treatment and the NF treatment was small (2%) and not statistically significant. Similar effects as for grain yield were obtained for straw yield and 1000-grain weight, with the harvest index and the water content of the grain at harvest being uninfluenced by the treatments. The protein content of the grain was 15% in the NF+post treatment, which was significantly higher than the contents in the NF treatment (13.7%) and in the NF+pre treatment (13.9%). The chlorophyll content of the flag leaves declined earlier in the NF+post treatment compared with the NF and NF+pre treatments. The difference in this parameter between NF+pre and NF was small. It is concluded that ozone exposure is much more effective in decreasing the grain yield of wheat between anthesis and end of grain filling than ozone exposure before anthesis. (C) 1998 Elsevier Science B.V. All rights reserved.