Effect of Elevated CO_2 Concentration and Nitrogen Application on Translocation of Dry Matter and Nitrogen Restored before Anthesis in Winter Wheat

Either CO2 enrichment or nitrogen (N) application has effects to increase grain yield, as well as dry matter and N ac-cumulation in winter wheat (Triticum aestivum L.). To understand the effects and interaction of both factors on dry matter and N restored before anthesis and translocated from vegetative organs into grains, we carried out a pot experiment across two cropping seasons using wheat cultivars Xiaoyan 22 (2007–2008) and Xiaoyan 22 and Xiaoyan 6 (2008–2009). Wheat cultivars were grown in open top chambers (OTCs) under conditions of ambient CO2 concentration (AT, 375 μL L-1) and elevated CO2 concentration (ET, 680 μL L-1 in 2007–2008 and 750 μL L-1 in 2008–2009). N fertilizer was applied at levels of 0, 0.1, 0.2, and 0.3 g kg-1 soil in 2007–2008 and 0, 0.15, and 0.30 g kg-1 soil in 2008–2009. Accumulation and translation of dry matter and N in pre-anthesis vegetative organs (stem + sheath, leaf blade, and spike) and shoot in all treatments were measured. CO2 enrichment and N nutri-tion improvement increased dry matter and N accumulation in grain and pre-anthesis vegetative organs, and translocation amounts of dry matter and N from vegetative organs and shoot into grains. The reasonable N application promoted the positive effects of CO2 concentration on dry matter and N accumulation and translocation. Compared to AT, ET advanced the contribution and translocation rates of dry matter from vegetative organs and shoot into grains. The effects of CO2 enrichment on the N contribu-tion and translocation rates in vegetative organs and shoot were different among years and cultivars. Elevated CO2 increased the N contribution and translocation rates in every vegetative organ and shoot in 2007–2008 cropping season and those in stem + sheath and spike in 2008–2009 cropping season. However, in 2008–2009 cropping season, elevated CO2 reduced the N contribution rate in leaf blade and shoot of both cultivars under N levels of 0.15 and 0.30 g kg-1. The N translocation rates of leaf blade and shoot were increased in Xiaoyan 22 under all N levels and only the N translocation rate of shoot was increased in Xiaoyan 6 under N level of 0.3 g kg-1. The interaction between CO2 concentration and N nutrition positively affected the contribution and translocation rates of dry matter and N in vegetative organs and pre-anthesis shoot in most cases. This result suggested that elevated CO2 enhanced grain yield and N accumulation through promoting accumulation before anthesis and translocation after anthesis of dry matter and nitrogen in vegetative organs and shoot in some way.