Effects Of Elevated CO₂ Concentration On Grain Filling Capacity And Quality Traits Of Grains At Different Positions On The Panicle Of Super Rice

Atomospheric CO2 concentration has increased from 280?mol·mol-1 in pre-industry era to the current 400?mol· mol-1,and it will reach 550?mol·mol-1 in the middle of this centrary.Rice is one of the most important staple crops,the grain filling capacity and quality traits of rice in response to atomospheric CO2 concentration have been studied intensively,but wether the effects are associated with the grain position on the panicle,and the differences between rice varieties were unclear.By using FACE(Free Air CO2 Enrichment)platform,I grew two super rice varieties YLY900 and NJ9108 in ambient(Ambient)and elevated CO2 concentration(FACE,Ambient+200?mol·mol-1)conditions to study the effects of elevated CO2 concentration on grain filling capacity and quality traits of grains at different positions on the panicle of super rice,and the genotypic variation between two rice varieties were also examined.The main results are as follows:1.Compared with Ambient,FACE increased grain yield of YLY900 and NJ9108 by 29%+and 15%,respectively.The yield increases under FACE were attributed to the increase of panicle number(NJ9108)or the increases of panicle number and filled grain percentage(YLY900).FACE increased the dry weight of culm,panicle and the above-ground biomass by 16-21%,but decreased the leaf dry weight by 5%.Accordingly,FACE decreased the ratio of leaf dry weight to the dry weight of above-ground biomass by 18%,but showed a trend of increase in the tatio of dry weight of culm or panicle to the dry weight of above-ground biomass.Significant CO2 by variety interaction was only detected for filled grain percentage.2.Compared with Ambient,FACE increased filled-grain percentage and single grain weight of YLY900 by 9.6%*and 5.3%*,but no changes were observed for NJ9108.Elevated CO2had no effects on the filled-grain percentage of the grains attached on the first branches of panicles of two rice varieties,but increased those on the second branches at the upper,middle and lower parts on a panicle of YLY900 by 9%,18%*and 31%*.Elevated CO2 increased single grain weight of the grains attached on the second branches at the upper,middle and lower part of the panicle of YLY900 by 4%+,9%+ and 15%*.When analyzing by individual grain position,the largest increases in filled-grain percentage by FACE were found for grains from the position of 2,3 or 4 on the second branches,and for single grain weight was those from the position of 3 or 4.Elevated CO2 had no effects on the filled-grain weight of YLY900,but increased that of NJ9108 by 2.0%*on average.Filled-grain weight of grains from most grain positions on the first branches showed a tendency of decrease under FACE,but those on the second branches showed an oppiste trend.3.Compared with Ambient,the high CO2 concentration prolonged the flowering period of two rice varieties,but the flowering peak was basically unchanged.From the pollen activity,the high CO2 concentration averaged 8.3%**of the two cultivars,among which YLY900 and NJ9108 increased by 13.1%and 5.3%respectively,and there was a significant interaction between CO2 treatment and variety.4.Compared with Ambient,rice grown in FACE showed a trend of decrease in brown rice percentage,milled rice percentage and head rice percentage,and head rice percentage showed the greatest reduction.Head rice percentage was decreased by 3.0%for YLY900 and 2.5%for NJ9108,respectively.The deterioration of proseeing quality by FACE was more pronounced in grains from the lower part of the panicle of two varieties.For example,head rice percentage of the grains from the first and second branches in the lower part of the panicle of YLY900 were decreased by 3.1%*and 7.1%*under FACE,but no significant changes were observed for those in the middle or upper part of the panicle.Similar trends were also found for YLY9108.5.Compared with Ambient,FACE had small effects on grain length,grain width and the ratio of grain length to width(<1%).Chalky grain percentage and chalky grain degree were decreased by 45%+ and 47%+ in YLY900 under FACE.The reduction of these two chalky parameters for grains in different positions of a panicle were in the order of upper part>middle part>lower part for both the first and second branches,and the largest reduction was 60%**.On the contrast,chalky grain percentage and chalky grain degree on average were increased by 6%and 14%in NJ9108 under FACE.The magnitudes of increases were more pronounced for grains attached on the first and second branches in the middle or lower part of the panicle.Grain chalky area of YLY900 was decreased by 4%on average under FACE,which resulted from the decreases in the second branches(7-16%)and a trend of increase in the first branches.Grain chalky area of NJ9108 was increased by 8%on average under FACE,but the responses of grains from six different positions of a panicle showed no clear trend.6.Compared with Ambient,FACE decreased the concentrations of macronutrients P,S,K,Mg and Ca in head rice of YLY900 and NJ9108 by 2-10%*and 2-17%+,respectively.The responses of macronutrient concentration in head rice to FACE varied within different grains positions on the panicle,depending on element and variety.The concentrations of micronutrients Zn,Fe,Mn,Cu and B in YLY900 were decreased by 13-16%*under FACE,and the concentrations of Fe,Cu and B in NJ9108 were decreased by 7-10%.In most cases,the responses of grain element concentrations to FACE were in the order of the second branches>the first branches or the lower part>middle or upper part.7.The amylose concentration in head rice of YLY900 showed little response to FACE;but FACE increased the amylose concentration of N9108 by 9%on average,and the most pronounced increase was found for grains from the second branches,especially in the lower part of the panicle.The RVA profile of rice powder revealed that the breakdown of YLY900 was increased by 9%+ on average under FACE,and the breakdown of grains from the upper and lower part of the panicle increased significantly,but those form the middle part showed no response to FACE.FACE had a small increase in the breakdown of NJ9108 on average(<1%),and the largest increase was found on the grains from second branches in the lower part of the panicle(30%).FACE increased the set-back of YLY900 by 2%+ on average,but the changes of grains from the first and second branches in all parts of the panicle were not significant.FACE decreased the set-back of NJ9108 by 2%+ on average,and the reductions in set-back of grains from the fiest branches weremore pronounced than those from the second branches,especially in the middle and lower part of the panicle.8.Starch DSC analysis showed that FACE had little influence on the enthalpy,start temperature,peak temperature,final temperature,peak width,peak height of rice powder for two rice varieties,grains at different branches or parts on the panicle showed the same trends.The ANOVA analysis on filled grain percentage,filled grain weight and single grain weight indicated that rice grain filling capacities among different parts of a panicle,branches and grain positions were significantly different.Two rice varieties showed similar trends,but the interactions of CO2 by these three major factors varied between two varieties.There were significant interactions for YLY900 in most cases,but no interactions for NJ9108.Grain quality traits in response to CO2 varied within different parts or different branches of the panicle,but very few traits showed significant interactions between CO2 and parts or branches of the panicle,especially for YLY900.