Studies On Impacts Of Consecutive Cold Day On Rice And Variety Arrangement Decisions In Shenyang

Based on characteristics of climate change and pressing need to variety arrangement in rice planting, a new index quantizing the effect of low temperature to rice damage, consecutive cold day index(CCDI) was constructed in this research, its tempo-spatial patterns were studied in Northeast China. The Effects of consecutive cold day on physiecology and yield of rice with different mature periods, marked middle, middle-late, late maturity varieties with9023,9035and9036, respectively, were evaluated and the decision-making of variety arrangement were tradeoffed with proper proportions in Shenyang region. The results are as follows:1. In Northeast China, a substantial decrease in CCDI was found (p<0.01), the main variation of CCDI was that there were obvious fall in four seasons in recent45a with the largest drop in winter and smallest in summer. Negative relationships was found between annual mean temperature and seasonal CCDI (p<0.01). Sensitivities of CCDI to temperature were different in four seasons for difference in rise of mean temperature being larger than that in drop of CCDI in spring, summer, autumn and winter, descended order by winter>autumn>spring>summer. However, a slight drop in summer temperature and small rise in summer CCDI were found after2000with annual mean temperarue increased and annual CCDI decreased at the same time. The crop yield fluctuated with CCDI obviously with larger drop in crop yield in lower latitude region.2. The dependences of rice yield on consecutive cold day varied with maturity period type, key stage and low temperature intensity. Experienced consecutive cold day (CCD) at tillering stage, the rice yields of three maturity period varieties showed rising tendency and increasing magnitude changed with maturity period type with largest in9023, smallest in9036. The rice yields increased in9023,9035and9036in low temperature condition that it was3℃lower than normal temperature in jointing stage, descended order by9023>9035>9036. However, when temperature was5℃lower than normal temperature, drop yields was found in9035and9036. The yield of three maturity period rice showed dropping after experienced CCD in blooming stage with larger drop in lower temperature and decreasing order by9036>9035>9023.3. Experienced CCD in tillering stage, the tiller process was inhibited temporarily, however the ultimate stems and ripe panicles increased, it is the main reason that9023yield rosed. For in jointing stage, the increasing tillers after encountering low temperature can ripe at harvest stage, so the ultimate stems and ripe panicles increased and the yield showed the same tendency as did in tillering stage. But for meeting with CCD in blooming stage, the smaller panicles resulted in lower9023yield for the reason that the nutrient competition intensified between the new tillers being increased after blooming stage and the old tillers being at reproduction stage. The rates of empty and shriveled grain decreased obviously when9035variety rice had be exposed in low temperature at tillering or jointing stages, the final yields went up although the first and secondary branches on panicles decreased. But for meeting with CCD at blooming stage, another disadvantageous factor to yield, the rising empty grain induced by larger unpregnant spikelet caused9035yield decreasing. The final stems and panicles dropped and the spikelets on secondary branch went up if9036variety rice experienced low temperature at tillering, jointing or blooming stage, moreover, the empty grain proportion rosed when it encountered CCD at jointing or blooming stage. Considering all factors, when9036variety rice encountered low temperature at different key stages, the yield showed rising tendency at tillering stage, rising tendency in3℃and dropping tendency in5℃lower than normal temperature at jointing stage, dramatically decreasing tendency at blooming stage.4. The dependences of photosynthesis process on CCD varied with rice varieties and key stages. The maximum photosynthesis rate decreased by descended order9036>9035>9023when three maturity period rices experienced low temperature.9023apparent photosynthesis quantum efficiencies increased after being exposed to low temperature at all key stages, whereas those of9035and9036increased at early stages and decreased at late stages.9035and9036apparent photosynthesis carboxylation efficiencies decreased after being exposed to low temperature at all key stages, however, that of9023decreased at tillering stage and decreased at blooming stage. After consecutive clod day. light use efficiencies rosed in9023, dropped in9035and9036; rising stomatal conductance was found in9023, however decreasing pattern showed in9036. Low temperature had little effects on photosynthesis system Ⅰ, however it can prohibited severely carboxylation ability of photosynthesis system Ⅱ, which induced photosynthesis rate declined dramatically at high light intensity. Generally speaking, CCD had little effect on9023photosynthesis process, even moderate low temperature could enhance its photosynthesis ability, and however it could reduce photosynthesis ability of9035and9036characterized by larger dropping photosynthesis ability in lower temperature. The more rice maturity period longer, was the more uneasily to be recovered in dropping photosynthesis ability, which might be the main reason that the9036tillers of late maturity period variety wilted in large quantity and its yield decreased dramatically after it experienced low temperature at key stages.5. The probabilities of CCDI at tillering, jointing and blooming stages will decrease in Shenyang region in the future characterized by inter-and decadal-annual variations markedly, with high CCDI in2013-2018,2026,2028-2029,2032. Predicted middle maturity period variety rice yield will drop, whereas middle-late and late mature rice will have increasing yields in the next about40years. Mixing ratio of three varieties of rice with different mature stage expressed on the85%total yield guarantee rate in this study every five years during1951to2050. In the next10years, CCD will occurred frequently, so the cultivated area proportion of middle maturity period variety rice should increase to57%-69%. The proportion of middle-late maturity period variety rice should enlarge during2011-2030gradually. The appropriate proportion of late maturity period variety rice should be between8%and16%during2011-2025, and increase from11%in2031-2035to51%in the stage of2046-2050. Based on above different maturity period variety rice arrangement, the rice yield would increase, with0.96%in2011-2015,1.36%in2026-2030and9.41%in2041-2050higher than average yield in2006-2010.