Effects of elevated carbon dioxide, ozone and water availability on springwheat growth and yield

Spring wheat (Triticum aestivum L. cv. Dragon) was exposed to elevated carb on dioxide (CO2), alone (1995) or in combination with two levels of increas ed ozone (O-3) (1994) or increased irrigation (1996) during three successiv e growing seasons as part of the EU ESPACE-wheat programme and conducted in open-top chambers (OTCs) and ambient air (AA) plots at Ostad, 50 km north- east of Goteborg, Sweden. Doubling the CO2 concentration had a positive eff ect on grain yield in all 3 years (+ 21, + 7 and + 11, respectively), altho ugh only statistically significant in 1994, That year was characterised by a warm and dry summer in comparison with 1995 and 1996, in which the summer s were more humid and typical for south-west Sweden. In 1994, the CO2-induc ed increase in grain yield was associated with an increase in the duration of the green leaf area, a positive effect on straw yield and on the number of ears per square metre and a negative effect (-13%,) on grain protein con centration, Harvest index was unaffected by the elevated CO2 concentration. The only statistically significant effect of elevated CO2 in 1995 was a de crease in the grain protein concentration (-11% in both CO2 concentrations) , and in 1996 an increase (+ 21%) in the straw yield. In 1996 the soil wate r potential was less negative in elevated CO2, which is likely to reflect a lower water consumption of these plants. Addition of extra O-3 significant ly affected the grain yield (- 6 and -10%, respectively) and the 1000-grain weight negatively (- 3 and - 6%). Statistically significant interactions b etween CO2 and O-3 were obtained for the number of ears per unit area and f or the 1000-grain weight. The 1000-grain weight was negatively affected by O-3 in low CO2, but remained unaffected in the high CO2 treatment. There wa s a significant decrease (- 6%) in the grain protein concentration induced by elevated irrigation. The chambers, compared with AA plots, had a positiv e effect on plant development and on grain yield in all 3 years.