| The continuous increase of atmospheric CO2 concentration is one of the most prominent and definite phenomenon in the global climate change factors.As the substrate for plant photosynthesis,high CO2 concentration increased the carbon supply for rice and resulted in yield increase and grain quality deterioration,but whether this effect relates to plant source sink levels and their interactions is unknown.This study was conducted in rice field by using FACE(Free Air CO2 Enrichment)platform.The CO2 concentration projected to occur in 2050 was simulated as high CO2 concentration compared with the ambient.Two independent sink-source manipulation experiments were conducted to study the influence of high CO2 concentration and sink-source manipulation on rice yield and grain quality traits including processing quality,appearance,nutritional quality,cooking and eating quality,and the genotypic variation was also examined.Experiment one:Super rice YLY900 and NJ9108 were grown in ambient(AMB)and elevated CO2(FACE)plots,at flowering stage five sink-source manipulation treatments were performed:intact plants(CK),cut off flag leaves(LC1),cut off all top three functional leaves(LC3),cut off one branch every three branches of a panicle(1/3SR),and cut off one branch every two branches of a panicle(1/2SR).The main results are as follows:1.Compared with AMB,FACE significantly increased grain yield of two rice varieties by 8%on average.Elevated CO2-induced yield increases at different sink-source manipulation situations of CK,LC1,LC3,1/3SR and 1/2SR were 5%,15%**,21%**,1%and-0.3%,respectively.Compared with CK,sink-source manipulation treatments of LC1,LC3,1/3SR and 1/2SR decreased grain yield of two rice varieties on average by 9%*,44%**,22%**and 43%**,respectively.The analysis of yield components revealed that FACE had no significant influence on panicle number,spikelet number per panicle and filled-grain weight,but increased grain filling percentage by 3%on average.Compared with CK,LC1 and LC3 decreased grain filling percentage by 10%**and 46%**,respectively;1/3SR and 1/2SR decreased spikelet number per panicle by 32%**and 49%*,but increased grain filling percentage by 10%**and filled-grain weight by 2%.2.FACE decreased brown rice percentage,milled rice percentage and head rice percentage,but the effects were not statistically significant.Compared with CK,all treatments of sink-source manipulation decreased milled grain percentage,cut off branches decreased brown rice percentage,although the magnitudes of the decreases were small(<2%),but in most cases the effects were statistically significant.3.FACE had no effects on grain length,grain width,the ratio of grain length to width and chalky grain percentage of head rice,but increased chalky degree by 15%on average,in the range of 3-44%for different sink-source manipulation treatments.Compared with CK,LC3 increased grain length and chalky degree by 2%**and 24%**,respectively;cut off branches increased grain width but decreased the ratio of grain length to width,although the magnitudes of the changes were small(<2%),but in most cases the effects were statistically significant.4.FACE decreased protein concentration of milled rice by 11%on average,in the range of 6～18%**for different sink-source manipulation treatments.FACE induced a trend of decrease in mineral element concentrations of milled rice,and the decreases in the concentration of S,Mg,Ca,Zn,Fe,Mn and Cu were in the range of 14～37%,all reached p<0.1.On the contrast,FACE increased rice phytate concentration by 5%on average.Compared with CK,sink-source manipulations(except for LC1)increased rice protein concentration;cut off leaves showed a trend of increase in the concentration of S,Mg,Ca,Zn,Fe and Mn,but a trend of decrease in phytate concentration;cut off branches increased the concentrations of P,S,Mg,Ca,Zn,Fe and Cu.5.The RVA profile of rice powder was measured.FACE increased breakdown by 7%*on average,but decreased set-back by 2%.Compared with CK,sink-source manipulations increased set-back(<14%**),but decreased breakdown(<17%**).FACE increased appearance,stickiness,balance and the taste of cooked rice(9～12%**),but decreased the hardness of cooked rice by 6%**.Compared with CK,sink-source manipulations(except for LC1)decreased appearance,stickiness,balance and the taste,but increased the hardness of cooked rice,and in most cases the changes were significant at p<0.05.6.FACE increased peak temperature and final temperature of DSC profile by about 1%,decreased the enthalpy and peak width of rice powder(4～6%),but had no effects on start temperature and peak height.Sink-source manipulation had no significant influence on the DSC traits.FACE increased starch volume,starch surface area and the percentage of large starch grains(2-4%),but decreased the percentages of small and middle-sized starch grains(3-4%).Compared with CK,sink-source manipulations of LC3,1/3SR and 1/2SR decreased starch volume,starch surface area and the percentage of large starch grains(2-5%),but increased the percentages of small and middle-sized starch grains(3～8%),all changes were significant at p<0.05.7.Significant CO2 by varieties interactions were found for most measured parameters except for yield,eating qualities and DSC traits.The interactions between CO2 and sink-source manipulations were significant at p<0.1 on yield,filled grain percentage,protein concentration,P,K,breakdown,starch volume weighted average,the percentage of small grains and the percentage of middle-sized grains.Experiment two:Japonica rice WYJ 24 was grown in ambient(AMB)and elevated CO2(FACE)plots,five sink-source manipulation treatments were performed:intact plants(CK),cut off half of leaves at jointing stage(LCH),cut off all leaves at jointing stage(LCA),cut off the first branches of a panicle at flowering stage(SRI),and cut off the second branches of a panicle at flowering stage(SR2).The main results are as follows:1.Compared with AMB,FACE increased grain yield of WYJ24 by 2%on average.Elevated CO2-induced yield increases at different sink-source manipulation situations of CK,LCH,LCA,SRI and SR2 were 5%,3%,19%+,-14%and-7%,respectively.Compared with CK,sink-source manipulation treatments of LCH,LCA,SRI and SR2 decreased grain yield of WYJ24 by 13%**,23%**,42%**and 37%**,respectively.The analysis of yield components revealed that FACE increased grain filling percentage by 2%,decreased spikelet number per panicle by 3%,but had no significant influence on panicle number per unit area and filled-grain weight.Compared with CK,LCH and LCA decreased spikelet number per panicle by 6%*and 16%**,decreased filled-grain weight in the range of 1～3%**;SR2 increased grain filling percentage and filled-grain weight by 7%*and 11%**,SRI and SR2 decreased spikelet number per panicle in the range of 45～48%**.2.FACE decreased brown rice percentage,milled rice percentage and head rice percentage(<1%).Compared with CK,cut off leaves decreased milled grain percentage and head rice percentage in the range of 1～3%;cut off branches decreased brown rice percentage(<1%),but increased milled rice percentage and head rice percentage by 5%,in most cases the effects were statistically significant.3.FACE increased chalky grain percentage and chalky degree by 30%and 36%**,decreased the ratio of grain length to width by 1%**,but had no significant influence on grain length and grain width.Compared with CK,LCH increased grain width by 1%*;cut off branches increased grain length and grain width(<3%),but decreased the ratio of grain length to width(0.5～1.2%),chalky grain percentage and chalky degree(45～85%),in most cases the effects were statistically significant.4.FACE decreased protein concentration of milled rice by 10%*on average,in the range of 8～13%**for different sink-source manipulation treatments.FACE induced a trend of decrease in mineral element concentrations of milled rice,all changes were no significant(except for S),but FACE increased rice phytate concentration by 21%**on average.Compared with CK,cut off branches increased rice protein concentration,S,Zn and B(13～48%**).5.FACE had no significant influence on RVA profile and DSC profile,but cut off branches decreased start temperature(<4%*)and peak height(7%*).FACE increased starch volume(2%+),starch surface area(2%*)and the percentage of large starch grains(4%+),but decreased the percentages of small(2%*)and middle-sized starch grains(4%+).Compared with CK,ink-source manipulations of LC3,1/3SR and 1/2SR decreased starch volume,starch surface area and the percentage of large starch grains(2～10%),but increased the percentages of small and middle-sized starch grains(1～13%),in most cases the effects were significant at p<0.1.6.The interactions between CO2 and sink-source manipulations were significant at p<0.1 on average grain weight,spikelet number per panicle,grain filling percentage,grain yield per panicle,grain width of head rice and peak temperature of DSC profile. |
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