[Effects of free-air CO2 enrichment on nitrogen uptake and utilization of wheat].

In this paper, the effects of free-air CO2 enrichment (FACE) and its interaction with nitrogen supply on the nitrogen content, uptake, allocation, and use efficiency of winter wheat variety Ningmai 9 at its different growth stages were studied in 2001-2003. The results showed that under FACE treatment, the nitrogen content in wheat plant sampled at different growth stages all decreased significantly, with an average decrement of 4.4% to 13.4% compared with the control. The nitrogen accumulation under FACE increased significantly (9.2% -32.3%), and the increasing rate was larger at middle growth stage than at early and late growth stages. Nitrogen fraction was higher in stem, but lower in leaf. As for spike, the accumulation of nitrogen depended on the growth stage. FACE resulted in a significant increase (5.5% -10.3%) of nitrogen use efficiency for biomass production at all growth stages, of nitrogen harvest index (16.3%) at maturing stage, and of nitrogen use efficiency (9.3%) for grain yield. Nitrogen application increased the nitrogen content of wheat plant and its N uptake at all growth stages, decreased the nitrogen use efficiency, but had less effect on the nitrogen allocation in different organs.

[Effects of free-air CO2 enrichment (FACE) on dry matter production and allocation in wheat].

A free-air CO2 enrichment (FACE) experiment was conducted in 2001-2003 to study the effects of predicted higher CO2 levels on the dry matter (DM) production and allocation in winter wheat variety Ningmai 9. The results showed that under FACE, the DM production had an increase of 10. 8% , 31. 6% , 40. 5% and 27. 2% during the growth periods from sowing to wintering ( Period 1 ) , wintering to jointing ( Period 2) , jointing to booting ( Period 3) , and booting to heading (Period 4) , respectively, but a decrease of 5. 5% in the period from heading to grain maturity (Period 5). As a result, the final total biomass at maturity was increased by 13. 6%. FACE had no significant effect on leaf area index (LAI) and net assimilation rate (NAR) in Period 1, but made the LAI in Period 2 increased obviously, and the NAR decreased dramatically in Period 3. Under FACE, the proportion of leaf to total above-ground DM decreased, while that of stem (including sheath) to total above-ground DM showed an opposite trend in the whole growth period. The percentage and total amount of soluble sugar and starch in the stem at grain-filling stage were also increased obviously under FACE.

[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%).