Effects Of Soil Progressive Drought On The Formation Of Cotton Yield And Fiber Quality During The Flowering And Boll-Forming Stage

Flowering and boll-forming stage is the key yield determinant period of upland cotton. Progressive duration drought stress occurring during this stage significantly reduced cotton final productivity and fiber quality. It can provide a theoretical basis for exploring some physiological regulatory pathways to improve cotton yield and fiber quality by studying the physiology and ecological mechanisms in the effects of progressive drought on cotton yield and fiber quality formation. Pot experiments were conducted to 50 days drought in 2011, 2012and 2013 at research filed area of Nanjing Agricultural University (118°50’E,32°02’N, and middle lower reaches of Yangtze River Valley). Three relative soil water content treatments were imposed:(75±5)%, (60±5)%, (45±5)%.The study focused on:(1) Effects of soil progressive drought on cotton yield and fiber quality during the flowering and boll-forming stage; (2) Effects of soil progressive drought during the flowering and boll-forming stage on photosynthesis and chlorophyll fluorescence characteristics of the subtending leaf to cotton boll; (3) Effects of soil progressive drought on soil fertility of cotton field during the flowering and boll-forming stage. The main results were as follows.1 Effects of soil progressive drought on cotton yield and fiber quality during the flowering and boll-forming stageIt reduced the number of bolls at prometaphase, because drought treatment decreased the developing intensity of total notes, the developing intensity of total bolls and increased the cotton abscission rate at prometaphase. Under the drought treatment, the number of the bolls in middle branches more than it’s in lower branches and the number of bolls in upper branches is very little; Soil drought restrains the number of bolls per plant, boll weight, but it affected the lint percentage insignificantly. The contribution rate of yield components to yield be changed under drought, it reduced the contribution rate of number of bolls and the lint percentage to yield, meanwhile increased the contribution rate of boll weight to yield; Soil drought affected the fiber length more significantly than fiber micronaire and strength, but effects of drought on uniformity were no significantly. Fiber quality of middle branches were affected worsen by drought.2 Effects of soil progressive drought during the flowering and boll-forming stage on photosynthesis and chlorophyll fluorescence characteristics of the subtending leaf to cotton bollNet photosynthetic rate (Pn), stomatal conductance (Gs) and leaf intercellular CO2 concentration (Ci) decreased while Ls increased under SRWC(60±5)% when drought for 0-21 days. Furthermore, there is no significant change in Chlorophyll fluorescence characteristics. This indicated that stomatal limitation was the main reason for the reduction of photosynthesis. In addition, when drought for 21-49 days under SRWC(60±5)%, Pn kept decreasing, while Ci began to increase and Ls began to decrease. Meanwhile, Potential photochemical efficiency (Fv/Fm), quantum yield of photo system Ⅱ (ΦPSⅡ) and photochemical quenching coefficient (qP) reduced significantly, but non-photochemical quenching coefficient (NPQ) first rose then decreased. Thus, non-stomatal limitation was the main reason that the photosynthesis of cotton reduced. Photosynthetic organization and photosynthetic enzyme system were destroyed, meanwhile boll setting intensity reduced and the number of boll and yield reduced significantly. Drought for 0-14 days under SRWC(45±5)% treatment leaded to sharp decrease in Pn, Gs and Ci, whereas Ls obviously increased. There is no significant change in Fv/Fm,ΦPSⅡ, qP.So stomatal limitation was the main reason that the photosynthesis of cotton reduced; Pn decreased slowly, while Ci began to rise and Ls began to decline under SRWC(45±5)% treatment for 14-49 days. Under the same treatment, Fv/Fm, ΦPSⅡ, qP decreased while NPQ rose first then decline, which indicated that non-stomatal limitation worked to reduce the cotton photosynthetic performance. Moreover 14 days boll setting intensity reduced significantly and the number of boll and yield lead to the decline in production. The critical stress time of cotton growth in current study was 21 and 14 days respectively under SRWC(60±5)% and SRWC(45±5)% treatment during the flowering and boll-forming stage.3 Effects of soil progressive drought on soil fertility of cotton field during the flowering and boll-forming stageSoil bacteria biomass C and N reduced significant under drought, and they tended to decrease with increasing drought days. Bacteria biomass C to N ratio reduced significant under SRWC(60±5)% treatment, but increased under SRWC(45±5)% treatment. Soil Urease, Phosphatase, Invertase activities reduced significant, and they showed downward trend with increasing duration of drought. Catalase activities had been raised significantly under SRWC(45±5)% treatment, but SRWC(60±5)% treatment didn’t change it in compared with control. Soil available potassium, available phosphorus and available nitrogen had a substantial reduction with progressive drought, meanwhile root activity also reduced. The biomass and nitrogen accumulation of cotton decreased. In summary, soil progressive drought affected the cycling of soil nutrient by reducing the microbe biomass and soil enzyme activity. It reduced the availability of soil nutrient and root activity, then inhibited the nutrient to be absorbed and accumulated of cotton structures. Consequently, cotton yield and fiber quality were changed.