| In recent years,due to the frequent occurrence of abnormal and extreme climate changes,the middle and late rice production is often subjected to flooding stress and resulted serious yield loss,especially frequency occurred in stagnant flooding stress.At present,a number of studies have focused on the effects of flooding stress on the growth,yield,quality,and stress resistance physiology of rice,but there are few representative variety types were used Moreover,it is still unknown about the effects of flooding stress on light interception and transformation,assimilate accumulation and transportation,fertilizer absorption and utilization efficiency,and related physiological mechanisms,as well as the changes in lodging traits.Therefore,this study selected different types of rice varieties[V1-HHZ(conventional indica rice),V2-WYJ3(conventional japonica rice),V3-YLY900(indica hybrid rice),V4-Y4949(japonica hybrid rice),and V5-IR64 Sub1(Sub1 genotype)]to explore the effects of stagnant flooding stress during the tillering stage on rice carbon and nitrogen metabolism and related physiological mechanisms under field planting conditions.The main results are as follows:(1)Effects of stagnant flooding stress on the growth trait of riceUnder stagnant flooding stress at the tillering stage,the plant height and specific leaf weight of rice varieties significantly increased,while the indicators such as tiller number,leaf area index,leaf biomass,stem biomass,total biomass,and crop growth rate significantly decreased.On average,plant height was increased by 17.0%and 14.0%respectively,in the past two years,and specific leaf weight were increased by 32.2%and 26.4%,respectively.On the contrary,the number of tillers was decreased by 62.1%and 57.8%,the leaf area index was decreased by 67.6%and 59.0%,the leaf biomass was decreased by 68.1%and 60.8%,the stem biomass was decreased by 68.6%and 62.0%,and the total biomass and crop growth rate decreased by 68.4%and 61.4%,respectively,in the past two years.(2)Effects of stagnant flooding on light energy absorption and utilization of rice The chlorophyll content,light interception,light radiation interception,and light energy utilization efficiency of rice were significantly decreased under stagnant flooding stress during the tillering stage,leading to a decrease in the accumulation and transport of assimilates.On average,over the past two years,the chlorophyll content of rice was decreased by 42.6%and 35.9%,the light interception decreased by 66.1%and 59.5%,the light radiation interception rate decreased by 46.7%and 35.2%,and the light energy utilization rate decreased by 34.1%and 33.9%,respectively.(3)Effects of stagnant flooding on accumulation and transport of assimilates in riceFlooding stress could lead to rapid depletion of non-structural carbohydrates(NSC)in rice,and it could also increase the activity of enzymes related to the accumulation and transportation of assimilates,such as sucrose phosphate synthase(SPS),alpha amylase(α-AL),and beta amylase(β-AL),On average,NSC decreased by 24.0%,SPS activity increased by 14.3%,α-AL activity increased by 16.8%,and β-AL activity increased by 20.7%under stagnant flooding stress at the tillering stage.Rice could alleviate the consumption of NSC by stem elongation under waterlogging stress by increasing the enzyme activities of SPS,α-AL,and β-AL to accelerate the accumulation and transport of assimilates.Rice promoted the accumulation and transport of assimilates by increasing the enzyme activities of SPS,α-AL and β-AL,to alleviate NSC consumption caused by stem elongation under waterlogging stress.(4)Effects of stagnant flooding on nitrogen uptake and utilization of riceThe stagnant flooding stress at the tillering stage significantly affected the nitrogen uptake and utilization of rice,with a significant decrease in total N uptake(NUP)and partial factor productivity of applied N(PFP),but a significant increase in N harvest index(NHI)and N use efficiency for grain production(NUEg).On average,during the two study years,NUP decreased by 57.3%and 45.4%,NHI decreased by 29.9%and 22.3%,NUEg decreased by 26.5%and 21.2%,and PFP decreased by 55.9%and 24.9%,respectively.The enzymes related to nitrogen absorption and utilization showed significant changes under stagnant flooding treatment at the tillering stage:NIR activity significantly decreased,whereas NR,GS,and GOGAT activities significantly increased.Overall,NR activity increased by 38.6%,NIR activity decreased by 32.2%,GS activity increased by 51.5%,and GOGAT activity increased by 49.1%.(5)Effects of stagnant flooding on the lodging trait of riceThe lodging trait of rice was significantly affected by stagnant flooding stress at the tillering stage.Overall,under flooding stress,the plant height at maturity(PHM),fresh weight at maturity(FWM),bending moment(BM),and lodging index(LI)of rice significantly decreased,whereas intemode dry weight(NDW),dry weight per unit length of intemode(DWUL),and breaking resistance(BR)significantly increased;The changes in intemode length(NL)and intemode diameter(ND)were relatively smaller and varied with rice variety.On average,the two-year average declines in PHM,FWM,BM,and LI were 5.1%,1.3%,23.2%,and 1.7%,respectively.The average growth rates of NL,ND,NDW,DWUL,and BR over the past two years were 5.9%,4.7%,24.6%,39.2%,and 4.1%,respectively.(6)Effects of stagnant flooding on rice yield and yield componentsThe stagnant flooding stress during the tillering stage could lead to a synchronous decrease in the number of panicles,grains,seed setting rate,and grain weight of rice,ultimately leading to the yield loss On average,during the two years,the number of rice panicles decreased by 48.5%and 47.7%,the number of grains decreased by 20.6%and 26.4%,the seed setting rate decreased by 12.9%and 12.7%,the grain weight decreased by 7.9%and 8.8%,and the yield decreased by 31.7%and 34.8%,respectively.The results indicated that the abnormal carbon metabolism in rice caused by semi flooding stress during the tillering stage could be one of the main reasons for the decrease in rice yield. |
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