Dynamics And Differences In Photosynthesis,Dry Matter Production And Storage Carbohydrates Of Stem And Roots In Cotton Lines Differing In Mature Period

Cotton is one of the important economic crops in China.The formation of cotton yield mainly comes from the photosynthetic production of leaves,but whether the remobolization of carbohydrates stored in stems and roots after flowering affects the formation of yield remains questionable.The purpose of this study was to i)observe the dynamic changes of leaves photosynthesis,dry matter accumulation and stem and root carbohydrates during cotton growth and development,ii)to compare the genotypic differences in above traits between early and mid-maturing cotton lines,and iii)to clarify the initiation timing of stem and root storage carbon mobilization and its correlation with production formation.two near-isogenic lines?4003-10,4003-6?were used as experimental materials,among which 4003-10 were an early maturing line and 4003-6 was a medium-maturing strain.They were planted in the Agricultural Science and Technology Park of Jiangxi Agricultural University in 2017-2018.The field trial was a randomized block design with three replications.Samples were taken every two weeks from cotton squaring to boll opening with a total of seven or eight times.The photosynthetic parameters of cotton main stem leaves were measured?net photosynthetic rate Pn,transpiration rate E,stomatal conductance Gs,intercellular carbon dioxide concentration IntCO₂?five times.Three plants were uprooted from each plot and decomposed into eight parts:root,main stem,branch,leaf,petiole,flower bud,seedcotton and boll shell.After being oven-dried to constant weight,dry weight data of all parts was collected and fitted by Logistic equation.The dried samples were finely shattered into powders for non-structural carbohydrates?hexose,sucrose,and starch?analysis.At cotton boll opening stage,50 cotton bolls normally opened from each plot were harvested for determining boll yield components.Twenty grams of lint from each boll sample was submitted to Supervision Inspection and Testing Center of Cotton Quality,Ministry of Agriculture,Anyang,Henan province,for determining upper half mean?UHM?fiber length,fiber bundle strength?Str?,micronaire?Mic?,length uniformity index?UI?and elongation at break?El?using a high volume instrument?HVI?900fiber testing system.Seedcotton in each plot was hand-harvested four times to determine the total yield,and then converted into lint yield per hectare throught multiplication by lint percentage.The main findings are as follows:1.The fiber length,uniformity,strength and micronaire value were numerically higher in 4003-6 than in 4003-10 with statistically significant difference for fiber bundle strength and micronaire.4003-6 had better fiber quality performance than 4003-10.Lint percentage and lint yield were higher in 4003-6 than in 4003-10.2.The leaf Pn showed a downward trend after reaching the peak at first flowering stage,and IntCO₂ was decreased earlier than P_n without significant difference between the two genotypes.Leaf area index and SPAD values were both higher in 4003-6 than in4003-10.3.The concentrations of non-structural carbohydrate?NSC?in the stem and root reached the maximum at first flowering stage,and rapidly decreased to the lowest value at peak flowering stage,and then gradually increased until cotton maturation,indicating that the decrease of NSC concentration during first flowering to peak flowering may be indicative of the massive demand of carbohydrate requested for boll development at that time.Sucrose and hexose were the predominant forms of NSCs at the early and mid-stage,and starch was the main form at the late stage,indicating that starch is accumulated as the main storage carbon at the mature stage of cotton.Cotton main stem had a higher total carbon level in 4003-6 than in 4003-10,and the reverse was true of roots..4.Logistic equation could better fit the dynamics of the reproductive mass,vegetative mass,roots and shoots dry matter in two genotypes.The rapid accumulation of dry matter in reproductive mass across two genotypes over two years was accompanied by the reductions of leaf photosynthetic rate and NSC concentration in roots and stems,suggesting that carbon remobilization in the root and stem may be triggered by the insufficient leaf photosynthetic carbon production failing to meet the requirement of carbon for boll development during peak flowering.The rapid accumulation period of4003-6 in reproductive growth,root growth and aboveground growth was longer than4003-10,which may be an important reason for the former to produce higher yield than the latter.