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


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Spring wheat (Triticum aestivum L. cv. Dragon) was exposed to elevated carbon dioxide (CO2), alone (1995) or in combination with two levels of increased ozone (O3) (1994) or increased irrigation (1996) during three successive growing seasons as part of the EU ESPACE-wheat programme and conducted in open-top chambers (OTCs) and ambient air (AA) plots at Östad, 50 km north-east of Göteborg, Sweden. Doubling the CO2 concentration had a positive effect on grain yield in all 3 years (+21, +7 and +11%, respectively), although only statistically significant in 1994. That year was characterised by a warm and dry summer in comparison with 1995 and 1996, in which the summers were more humid and typical for south-west Sweden. In 1994, the CO2-induced 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 concentration. Harvest index was unaffected by the elevated CO2 concentration. The only statistically significant effect of elevated CO2 in 1995 was a decrease in the grain protein concentration (−11% in both CO2 concentrations), and in 1996 an increase (+21%) in the straw yield. In 1996 the soil water potential was less negative in elevated CO2, which is likely to reflect a lower water consumption of these plants. Addition of extra O3 significantly affected the grain yield (−6 and −10%, respectively) and the 1 000-grain weight negatively (−3 and −6%). Statistically significant interactions between CO2 and O3 were obtained for the number of ears per unit area and for the 1 000-grain weight. The 1 000-grain weight was negatively affected by O3 in low CO2, but remained unaffected in the high CO2 treatment. There was a significant decrease (−6%) in the grain protein concentration induced by elevated irrigation. The chambers, compared with AA plots, had a positive effect on plant development and on grain yield in all 3 years.