Phenological development, leaf emergence, tillering and leaf area index, and duration of spring wheat across Europe in response to CO2 and ozone

Phenological development, leaf emergence, tillering and leaf area index (LA I), and duration (LAD) of spring wheat cv. Minaret, grown in open-top chamb ers at different sites throughout Europe for up to 3 years at each site, we re investigated in response to elevated CO2 (ambient CO2 x2) and ozone (amb ient ozone x1.5) concentrations. Phenological development varied among experiments and was partly explained by differences in temperature among sites and years. There was a weak posit ive relationship between the thermal rate of development and the mean dayle ngth for the period from emergence to anthesis. Main stems produced on aver age 7.7 leaves with little variation among experiments. Variation was highe r for the thermal rate of leaf emergence, which was partly explained by dif ferences in the rate of change of daylength at plant emergence among season s. Phenological development, rate of leaf emergence and final leaf number w ere not affected by CO2 and ozone exposure. Responses of tillering and LAI to CO2 and ozone exposure were significant only in some experiments. Howeve r, the direction of responses was consistent for most experiments. The numb er of tillers and ears per plant, respectively, was increased as a result o f CO2 enrichment by about 13% at the beginning of stem elongation (DC31), a t anthesis and at maturity. Exposure to ozone had no effect on tillering. L AI was increased as a result of CO2 elevation by about 11% at DC31 and by a bout 14% at anthesis. Ozone exposure reduced LAI at anthesis by about 9%. N o such effect was observed at DC31. There were very few interactive effects of CO2 and ozone on tillering and LAI. Variations in tillering and LAI, an d their responses to CO2 and ozone exposure, were partly explained by singl e linear relationships considering differences in plant density, tiller den sity and the duration of developmental phases among experiments. Considerat ion of temperature and incident photosynthetically active radiation in this analysis did not reduce the unexplained variation. There was a negative ef fect of ozone exposure on leaf area duration at most sites. Direct effects of elevated CO2 concentration on leaf senescence, both positive and negativ e, were observed in some experiments. There was evidence in several experim ents that elevated CO2 concentration ameliorated the negative effect of ozo ne on leaf area duration. It was concluded from these results that an analy sis of the interactive effects of climate, CO2 and ozone on canopy developm ent requires reference to the physiological processes involved. (C) 1999 El sevier Science B.V. All rights reserved.