| The atmospheric CO2 concentration has continued to rise since the industrial revolution.In order to accurately predict the influence of rising greenhouse gases on the food security in near future,we need to study the effects of elevated CO2 on the lodging resistance of main staple crops and the associated mechanisms,in addition to its effects on the yield and grain quality of crops.However,there are very few reports on the changes in lodging resistance and its mechanisms of major staple crops in response to elevated CO2 concentration,and to the best of my knowledge,no reports on hybrid or super rice combination were found so far.By using FACE(Free Air CO2 Enrichment)platform,I grew two super hybrid rice varieties YLY2 and YY2640,which were the latest released varieties with high yield records,in ambient(Ambient)and elevated CO2 concentration(FACE,Ambient+200 ?mol mol-0)conditions in 2014 and 2015.During the grain filling stage,the traits related to plant lodging resistance were measured to examine the effects of elevated CO2 concentration on lodging resistance of super rice,the genotypic variation between two rice varieties,and the possible causes of the effects.The traits contributed to lodging resistance of rice are pushing resistance of the whole plant in the field,lodging index of the basal internodes,bending force,bending moment,culm length,culm weight,cross-sectional area,the largest and smallest diameters of the basal internodes,the concentration of non-structural carbohydrates,mineral element concentration(P,K,Si),and the number and area of large or small vascular bundles.The main results are as follows:1.Compared with Ambient,FACE showed a trend of increase in the pushing resistance of a whole plant or of a single culm measured in the field,and the increases in 2014 were more pronounced than in 2015.For example,FACE increased the pushing resistance of a whole plant by 26.9%*and 8.6%+ in 2014 and 2015,respectively;FACE increased the pushing resistance of a single culm by 9.9%*and 4.9%in 2014 and 2015,respectively.2.FACE decreased lodging index of the basal internodes of two varieties.On average,FACE decreased lodging index of the basal internodes at 25 days after heading(DAH)by 10.6%in 2014 and 9.5%*in 2015,that at maturity by 12.6%+ in 2014 and 9.5%**in 2015,respectively.Lodging index is a function of bending force and bending moment.FACE increased the bending force of the basal internodes at maturity for two varieties,same with bending moment.Averaged over all basal internodes,FACE increased bending force of the basal internodes at 25 DAH by 11.4%in 2014 and 19.2%**in 2015,that at maturity by 27.1%**in 2014 and 15.6%**in 2015,respectively.FACE increased bending moment of the basal internodes at 25 DAH by-3.6%in 2014 and 11.2%**in 2015,increased that at maturity by 12.4%*in 2014 and 7.4%**in 2015,respectively.3.There was a trend of increase by FACE on culm length of the basal internodes at maturity,and the largest increase reached 5.6%.Same trend of increase by FACE was found on the fresh weight,dry weight,fresh weight per unit length and dry weight per unit length of the basal internodes.For example in 2015,FACE increased the dry weight of the basal internodes at 25 DAH by 22.0%*and that at maturity by 3.0%+;FACE increased the dry weight per unit length of the basal internodes at 25 DAH by 19.5%+ and that at maturity by 11.0%.4.There was a trend of increase by FACE on cross-sectional area of the basal internodes during rice grain filling period.Averaged over all basal internodes,FACE increased cross-sectional area of the basal internodes at 25 DAH by 3.8%in 2014 and 1.8%in 2015,that at maturity by 14.5%*in 2014 and 4.8%*in 2015,respectively.The cross sectional area of the internode is a function of the largest and smallest diameter of the internode.There was a trend of increase by FACE on the largest or smallest diameters of the basal internode during grain filling period,and in general the magnitude of increase at maturity was greater than that at 25 DAH.Averaged over all basal internodes in two years,FACE increased the largest and smallest diameters of the basal internodes by 0.5%?2.9%at 25 DAH,and by 1.4%?4.7%*at maturity.Similarly,FACE induced a trend of increase in culm-wall thickness of the basal internodes during grain filling stage.Averaged over all basal internodes,FACE increased culm-wall thickness of the basal internodes by-1.7%at 25 DAH and 5.7%**at maturity in 2014,by 9.8%*at 25 DAH and 5.2%**at maturity in 2015,respectively.5.There was a trend of increase by FACE on the concentrations of soluble sugar,starch and non-structural carbohydrates(NSC)during grain filling stage for both varieties.Averaged over all basal internodes in two years,FACE induced increases of the concentrations of soluble sugar,starch and non-structural carbohydrates(NSC)were in the range of 9.5%?25.8%**,2.0%?41.7%**and 4.5%?25.6%**,respectively.On the contrast,the concentrations of P,K and Si in the basal internodes showed a trend of decrease under FACE.Averaged over all basal internodes,FACE induced decreases of the concentrations of P,K and Si were in the range of 4.1%-35.3%**,6.4%?20.9%**and 11.6%+?15.6%+,respectively.6.The large and small vascular bundles of the basal internodes were decreased by FACE during the middle of grain filling stage,but the number of air cavity showed a trend of increase.Averaged over all basal internodes at 25 DAH in 2015,FACE decreased the large and small vascular bundles by 4.5%*and 4.7%+,but increased the air cavities by 8.8%.On the contrast,the areas of large vascular bundle and air cavity showed trends of increase by FACE.For example,FACE increased the areas of large vascular bundle and air cavity at 25 DAH by 12.5%+ and 27.3%*,respectively.In summary,although grain yield of super rice significantly increased under elevated CO2 concentration,plant lodging risk showed a trend of decrease.The decrease of lodging risk under FACE was attributed to increased bending forces of basal internodes,and the latter was associated with the increases in cross-sectional area and culm-wall thickness of the internodes.Significant CO2 by variety interactions were detected for most lodging traits through ANOVA analysis,which indicated there were genotypic differences between two rice varieties in response to elevated CO2 concentration. |
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