Climate warming presents significantly asymmetric trends with greatly seasonal and diurnal differences, greater temperature elevations existing in the winter-spring season than in the summer-autumn season and at the nighttime than at the daytime. To date, this is till lack of evidence about the effects of asymmetric warming on the quality of winter-wheat grain based on field experiments. Here, we performed field warming experiment under free air temperature increased (FATI) facility to investigate the impacts of asymmetric warming on the contents and components of starch and protein in winter-wheat grain during 2007-2009 in Nanjing, Jiangsu province, China. The results showed that the all-day warming (AW), daytime warming (DW), and nighttime warming (NW) treatments significantly advanced the grain-filling stage and changed the appearance time and days of high temperature above 32degreesC in grain-filling stage, consequently resulting in obvious changes of starch component, protein content and protein components. Treatments AW, DW, and NW had no significant impact on the starch content of winter-wheat grain but tended to increase the ratio of amylose content to amylopectin content. The highest values of the ratio of amylose content to amylopectin content existed in the DW plots which were 6.9% and 46.2% higher than those in the control plots in the two years, respectively. The content of grain protein was significantly decreased by warming with the content order of CK > DW > NW > AW. Warming decreased the grain protein contents by 9.1%, 5.4%, and 6.9%, respectively in the AW, DW, and NW treatments on average of the two years. The effects of warming on grain protein components were complicated. However, DW showed a regular impact on protein components. The two-year result showed that the lowest content of albumin and the greatest content of globulin occurred in the DW plot with the lowest ratio of glutelin content to gliadin content. All these results demonstrate that the effects of asymmetric climate warming on the quality of winter-wheat grain are complicated with significant differences among warming patterns and experimental years.
