Canopy development and tillering of field-grown crops of two contrasting cultivars of winter wheat (Triticum aestivum) in response to CO2 and temperature

Elevated CO2 (691 cf. 371 mu mol CO2 mol(-1) air) and warmer temperatures ( over the range 1.0 degrees C below to 1.6 degrees C above ambient) increase d light interception by crops of two contrasting cultivars (Hereward and So issons) of winter wheat (Triticum aestivum L.) during winter growth in the field. The fractional interception of light by the canopy increased more ra pidly initially in Soissons than in Hereward, but Hereward showed a much gr eater response to CO2 (35% increase in Hereward but only 7% in Soissons) at 500 degrees Cd after sowing. By terminal spikelet formation, in contrast, fractional interception was greater in Hereward than in Soissons, while the effect of CO2 was the same in both cultivars (9%). Thus, although differen ces in the relative response of canopy development to CO2 were detected bet ween cultivars initially, differences were negligible during later developm ent. The greater interception of light by the canopy in elevated CO2, at an y one temperature, resulted from increased tillering. The number of tillers plant(-1) at terminal spikelet was a linear function of main stem dry mass at this developmental stage but with a greater response in elevated CO2, v iz 2.3 and 3.8 tillers g(-1) main stem dry mass at 371 and 691 mu mol CO2 m ol(-1) air, respectively; these relations were unaffected by cultivar.