Effects of elevated CO2, nitrogen supply and tropospheric ozone on spring wheat .1. Growth and yield

Spring wheat (Triticum aestivum L. cv. Minaret) was exposed to three CO2 levels, in combination with two nitrogen fertilizer levels and two levels of tropospheric ozone, from sowing to ripening in open-top chambers. Three additional nitrogen fertilizer treatments were carried out at the lowest and the highest CO2 level, respectively. Plants were harvested at growth stages 31, 65 and 93 and separated into up to eight fractions to gain information about biomass partitioning. CO2 enrichment (263 mu l litre(-1) above ambient levels) drastically increased biomass of organs serving as long-term carbohydrate pools. Peduncle weight increased by 92%, stem weight by 73% and flag leaf sheath weight by 59% at growth stage 65. Average increase in shoot biomass due to CO2 enrichment amounted to 51% at growth stage 65 and 36% at final harvest. Average yield increase was 34%. Elevated nitrogen application was most effective on biomass of green tissues. Yield was increased by 30% when nitrogen application was increased from 150 to 270 kg N ha(-1). Significant interactions were observed between CO2 enrichment and nitrogen application. Yield increase due to CO2 ranged from 23% at 120 kg N to 47% at 330 kg N. Triticum aestivum cv. Minaret was not very responsive to ozone at 1.5 times ambient levels. 1000 grain weight was slightly decreased, which was compensated by an increased number of grains.