Effects Of Asymmetric Warming On Growth,yield And Quality In Rice

Global warming is now unequivocal and is posing serious threats to productivity and grain quality related attributes of rice. Up till now, most of previous researches related to the influence of high temperature treatments on rice growth, yield and quality were based on crop model estimation, or have been conducted under controlled environments. However, limited information is available on the response and mechanism of contrasting rice genotypes under field conditions against different warming treatments. Therefore, we installed a new field warming facility which was designed and established by our research group, and grown four varieties with different sensitivity range to high temperature HHZ(Huanghuazhan), SY63(Shanyou63),YLY6(Yangliangyou6) and LYP9(Liangyoupeijiu) in this study. Our objectives were to study the effects of different temperature treatments on rice growth,grain yield, yield components and rice quality, and also to compare the responses difference between varieties against different warming treatments.The main conclusions are as follows:1. The increments of the free air temperature increase system were around 0.79-2.84℃, and were higher in the middle and later periods than that of earlier. The average increment of daytime and nighttime warming before full heading stage were 0.79℃ and 1.51-1.97℃ respectively, while the average increment of DW(daytime warming) and nighttime warming after full heading stage were 1.56-2.23℃and 2.20-2.84℃ respectively. The daytime mean temperature at the heading stage of HHZ was 32-33℃, however, the daytime mean temperature at the main grain filling stage of HHZ that from head emergency to the early 20 days of grain filling of LYP9,YLY6 and SY63,was about 30℃.2. Different warming treatments significantly affect the growth of rice. Warming treatments have a propensity to decrease the height of plant, and the AW(all-day warming) significantly diminished plant height. DW and NW(nighttime warming) significantly enhanced the leaf area index of LYP9 and YLY6 at full heading stage, respectively, and also there were increasing trends of leaf area index of SY63 under AW treatments. AW and DW significantly augmented panicle length(except YLY6), while the response of panicle length to NW were varied significantly among varieties. The declining speed of chlorophyll content in grain filling stage of HHZ and SY63 was accelerated by DW, while the changes of flag leaf chlorophyll content of HHZ and SY63 were not affected by AW and NW.3. Warming treatments significantly influence the yield of rice, all-day warming treatment showed the largest influence,while AW, DW and NW decreased the average yield(HHZ, SY63 and LYP9) by 26.0 %, 7.3 % and 7.0% respectively. AW resulted in the largest decline in LYP9 by 35%; the smallest decline observed in SY63, nevertheless the difference was not significant when compared with control. There were no significance difference recorded in grain yield between DW,NW and control under the conditions of our experiment for all varieties that we have used.The main reason leading to the decrease of yield in AW were the decrease of specific filling and grain weight,and the spikelets per panicle of HHZ and YLY6 were also significantly declined under AW. The decrease of specific filling was closely related to the decrease of pollen fertility and pollen grains on the stigma; while the reduction of grain weight were due to the decrease of grain width and length and also decrease of spikelets per panicle in HHZ and YLY6 were mainly associated to the reduction of differentiated spikelets on the secondry branches which was caused by warming treatments.4. The dry matter accumulation and translocation in varieties with different sensitivities(tolerant or susceptible)have different responses to different temperature increasing modes. LYP9 was found to be most sensitive against AW and also the DW effects on LYP9 were related to their growth period, DW promote the dry matter accumulation before full heading stage, while decreased the TAA( translocation amount of pre-anthesis assimilate) and TAR( translocation rate of pre-anthesis assimilate significantly after full heading; whereas LYP9 appeared to be more sensitive against the enhance day temperature than high night temperature.YLY6 observed to be most sensitive against AW, and was sensitive to DW,but was insensitive to NW for there were increasing trends of SSWFH,TAA and TAR under DW treatment.HZ and SY63 were more sensitive to AW and AW because of reduction in the TAA and TAR of HHZ and SY63; however the difference were not significant. While on other hand HHZ and SY63 were tolerant to DW.5. Warming treatments had different affects on rice qualities. AW and DW significantly decreased the brown rice rate, while AW and NW significantly augmented the head rice of SY63.The gel consistence of SY63 and the protein content of HHZ and LYP9 were significantly increased in DW and NW treatments. Warming treatments had no significant effects on rice chalkiness, amylose content and alkali spreading value.