Effects Of Sustained Soild Drought During Flowering And Boll Formation On Biomass Accumulation And Photosynthetic Characteristics Of The Youngest Fully Expanded Leaf On The Main Stem From Terminal

Reduced water supply has become a major challenge to cotton(Gossypium hirsutum L.)production.Pond and pot experiments were conducted for 2 years in Nanjing(32°02'N,118°50'E),China,to investigate the responses of lint yield,fiber quality,biomass accumulation at different fruiting branches of cotton plant and photosynthetic characteristics of the youngest fully expanded leaf on the main stem from terminal to varying soil relative water content during the flowering and boll forming stages.The treatment comprises three levels of soil relative water content(SRWC(75±5)%,SRWC(60±5)%and SRWC(45±5)%).Improving cotton yield is the main purpose of cotton production,planting density is one of the regulating factors to the production and fiber quality of cotton.The study focused on:(1)Effect of Sustained Soil Drought during Flowering and Boll Formation on Lint Yield and Fiber Quality at Different Fruiting Branches;(2)Effects of Plant Density on Dry matter Accumulation and Distribution of Hybrid Cotton;(3)Effects of Plant Density on Uptake and Utilization of N,P and K of Hybrid Cotton.The main results were as follows:1 Effect of Sustained Soil Drought during Flowering and Boll Formation on Lint Yield and Fiber Quality at Different Fruiting BranchesThe bud number and boll number were reduced with duration of drought,whereas shedding rate was increased.SRWC(45±5)%had a more serious impact on reproductive growth,at the end of reproductive development,the number of bud approached zero and boll number suspended increase.SRWC(60±5)%and SRWC(45±5)%resulted in 27.8%-40.6%and 61.4%-72.2%reduction in lint yield which was mainly due to the reduction of boll number,whereas drought increased proportion of lint yield on the bottom five fruiting branches(FB1-5)by 28.4%to 33.1%and 49.5%to 74.7%under SRWC(60±5)%and SRWC(45±5)%,respectively.Drought was disadvantageous to fiber length at middle and top fruiting branches.It was concluded that the greater the drought enhanced the more the abovementioned measurements were affected.2 Effect of Sustained Soil Drought during Flowering and Boll Formation on Biomass and Nitrogen Accumulation and Distributioncotton different organ biomass and the whole plant biomass was significantly decreased with the duration of drought,while at the same time R/S ratio was increased.in SRWC(60±5)%,the proportion of vegetative organ was decreased while the proportion of reproductive organ was in increased.In SRWC(45±5)%,the proportion of vegetative and reproductive organs was all decreased.Biomass accumulation followed the function of logistic as a normal organism growth pattern,differences existed among treatments in progress of cotton plant biomass accumulation and ROB accumulation progress was affected by fruiting branches.Decreased soil relative water content enhanced N content and accumulation of per plant in different fruit branches,N content accumulation followed the function of y=ae-bx,with soil relative water content decreasing,the value of a and b increased.3 Effect of Sustained Soil Drought during Flowering and Boll Formation on Photosynthetic Characteristics of the Youngest Fully Expanded Leaf on the Main Stem From TerminalUnder SRWC(60±5)%treatment,net photosynthetic rate(Pn)and stomatal conductance(Gs)decreased sharply when drought for 0-24 days,after that it decreased slowly,meanwhile Chla,Chlb and total chlorophyll content reached a maximum at 24DD then decreased slowly.Furthermore,SRWC(60±5)%treatments resulted in significantly lower leaf RWC than controls at the 24DD(the duration of drought).The changes of palisade tissue thickness,stomatal length and width were not obvious after 24DD,under SRWC(60±5)%treatment.Under SRWC(45±5)%treatment,net photosynthetic rate(Pn)and stomatal conductance(Gs)decreased sharply when drought for 0-17 days,after that it decreased slowly,meanwhile Chla,Chlb and total chlorophyll content reached a maximum at 17DD then decreasedslowly.Furthermore,SRWC(45±5)%treatments resulted in significantly lower leaf RWC than controls at the 17DD(the duration of drought).The changes of palisade tissue thickness,stomatal length and width were not obvious after 17DD,under SRWC(45±5)%treatment.The critical stress time of Pn in current study was 24 and 17 days respectively under SRWC(65±5)%and SRWC(40±5)%treatment.Water deficit produced significantly increase palisade tissue thickness and there is a bigger change in SRWC(60±5)%.