Abstract: Climate warming presents significantly asymmetric trends with greatly diurnal differences, greater temperature elevations existing for the daily mean minimum temperature than for the daily mean maximum temperature. So far, the evidence is lacking for the effects of asymmetric warming on grain quality of single cropping rice based on field experiments. We performed field warming experiment under Free Air Temperature Increased (FATI) facility to investigate the impacts of asymmetric warming on grain quality and activities of key enzymes of single cropping rice in 2008 in Nanjing city, Jiangsu province, China. The results showed that the all-day warming (AW), daytime warming (DW) and nighttime warming (NW) treatments obviously advanced the grain filling and seed setting stage and changed the beginning date and the duration of high temperature above 35°C in the stage of grain filling, consequently resulting in obvious changes of head rice rate, chalky grain rate, chalkiness, RVA characteristics, starch content and its components, protein content and the activities of key enzymes for starch and protein syntheses. All the treatments decreased significantly head rice rate, increased significantly chalky grain rate and chalkiness of rice grain, and had no significant impact on the starch content of rice grain but tended to reduce the amylose content and increase the ratio of amylopectin to amylose. And the highest values of the amylose content and the ratio of amylopectin to amylose existed in the NW and AW plots which were 4.5% lower and 4.6% higher than those in the control plots in 2008, respectively. The activity of ADPG-PPase in grain decreased under the warmed plots during the early phase of rice grain filling,while had certain differences during the middle and late phases of rice grain filling. Warming treatments had no significant effect on the activity of SBE in grain. There were increasing trends of peak viscosity, hot viscosity, break down and pasting temperature, and decreasing trends of final viscosity, setback and consistency in rice grain under the warmed plots. The highest increase of peak viscosity and break down existed in the AW plots, and the highest decrease of final viscosity and consistency existed in the DW plots compared with those in control plots. The content of grain protein was decreased by warming treatments. Grain protein contents were significantly decreased by 5.6% and 4.0%, respectively in the AW and NW treatments. The activities of GS and GOGAT in grain were decreased under the warmed plots during the early phase of rice grain filling, while there were differences for them during the middle and late phase of rice grain filling. All these results suggest that milling and appearance qualities of rice would get worse under warming plots. The impact of ADPG-PPase activity was greater on amylose content and that of SBE on amylopectin content in rice during the early phase of grain filling. The protein synthesis was closely related to the activities of GS and GOGAT during the early phase of rice filling. Therefore, the effects of asymmetric climate warming on grain quality and activities of key enzymes for single cropping rice are complicated.

Key words: Climate warming, Free air temperature increased (FATI), Rice quality, Starch, Protein, Key enzyme