[Effects of free-air CO2 enrichment (FACE) on yield formation of wheat]

To investigate the effects of predicted higher CO2 levels on the growth duration, plant height, yield, and yield components of wheat (Triticum aestivum L.), a free-air CO2 enrichment (FACE) experiment with weak gluten variety Ningmai 9 was conducted at Anzhen of Wuxi in Jiangsu Province in 2001-2002 and 2002-2003 growth seasons. The target [CO2] in FACE plots was 200 microl x L(-1) above that in ambient air. Three levels of N were supplied, i.e., 90 kg x hm(-2) (2001-2002) and 125 kg x hm(-2)(2002-2003) (low level, LN), 180 kg x hm(-2) 2002-2003) (medium level, MN), and 250 kg x hm(-2)(high level, HN). The durations from sowing to heading and from heading to maturity and the whole growth period of wheat in FACE plots shortened 1.3 , 1.3 and 2.6 days, respectively, compared with the control. FACE increased the plant height (+4.0% significantly, due to the increases of panicle length and of the first and second internode lengths. FACE also greatly increased the grain yield by an average of 24.6%. Across the two years, there was a positive [CO2] x N interaction for grain yield, with a yield increase of 15.2%, 21.4% and 35.4% at LN, MN and HN, respectively. The ears per square meter in FACE plots was increased by an average of 17.8% mainly due to the increase of maximum tiller number per unit ground area rather than that of the percentage of productive tiller (panicle bearing). In addition, FACE increased the grain number per ear (+2.9% and the individual grain mass (+4.8%).