Effect Of Source-sink Manipulation On Cotton Yield,Quality,and Carbon And Nitrogen Metabolism

The dynamics of source to sink ratio is closely associated with the distribution of crop assimilates among various components.Cotton nutrients are partitioned between vegetative organs like main stem,branches and leaves and reproductive forms such as bolls and squares.The modulation of source to sink ratio will affect the assimilates allocation between the vegetative and reproductive growths,and in turn the development of cotton yield.The present study aimed to examine the carbon and nitrogen metabolism as influenced by the manipulation of source or sink biomass and its relationship to lint yield.Four treatments imposed on leaves or white flowers were applied at first flowering including white flowers removal over 1 wk(WFR1),flower removal over 2 wk(WFR2),1/2 of leaf area pruned(LAP1),3/4 of leaf area pruned(LAP 2)and with no modification as the control(CK).Five samplings were taken at peak flowering,peak fruiting,early boll opening,middle boll opening and late boll opening,respectively.The main research results are as follows:WFR1 yielded similar to the control but the lint yield of the others was decreased.Bolls per plant and boll weight were reduced in two leaf pruning treatments compared to the control.Two flower removal treatments had less bolls per plant than the control.Fiber strength and elongation were decreased in LAP2.Uniformity index was significantly higher in WFR2 than in WFR1 and LAP1.In the case of LAP2,the contents of sucrose,fructose and glucose were significantly higher at peak fruiting and early boll opening stages relative to other treatments.At middle boll opening stage,sugar contents were decreased significantly.Net photosynthetic rate was increased first and thereafter decreased.The malondialdehyde content in leaves was significantly higher at early boll opening stage compared with the control treatment.The content of soluble protein was significantly lower at early boll opening stage than that of the control treatment.The chlorophyll content was slightly higher at early boll opening stage than that of the control treatment,but the opposite was true of at middle boll opening stage.Total nitrogen and free amino acid contents were significantly higher at full blooming than those of control and other treatments.It may be the result of compensatory growth due to physical hurt of leaves.The leaf area index and sink to source ratio reached the highest value at middle boll opening stage and then dropped gradually.There was no significant difference from the control in carbon and nitrogen metabolism for WFR2,but it delayed the aging of the plant.There was an increase in non-structural carbohydrate content with leaves in the early sampling resulting in a decrease in the net photosynthetic rate.Nonstructural carbohydrates was decreased in the middle and late reproductive stages and exhibited no difference from the control.The soluble protein content in leaves was higher in peak blooming and peak fruiting than that of the control,but no difference at later stage.The malondialdehyde content in leaves was significantly lower than that of the control.Leaf area index was not significantly different from that of the control.The sink to source ratio was lower than that of the control treatment.The reason is most likely that the nutrients produced by the source organs mainly flow to the vegetative growth of cotton,and thus inhibit the growth of cotton bolls.With respect of WFR1 the sucrose content was higher but starch content was lower compared to the control treatment.The net photosynthetic rate was comparable to that of the control.Nitrate reductase activity was significantly greater than or comparable to that of the control from early boll opening onwards.Leaf PEPC activity was significantly greater than or comparable to that of the control from peak blooming onwards.Ammonium and nitrate levels were at higher levels over the booming period.There were no significant differences in leaf malondialdehyde and soluble protein contents from the control throughout the entire sampling period.The total and ammonium contents of LAP1 were significantly lower than those of the control.The free amino acid content was significantly lower than that of the control.The net photosynthetic rate and chlorophyll content were significantly lower than those of the control.However,NR activity was significantly greater at peak flowering and fruiting stages than that of the control.The chlorophyll of the leaves was lower than that of the control treatment at early boll opening.The malondialdehyde content was slightly higher at late boll opening stage than that of the control treatment.Leaf pruning led to early senescence,decreased boll weight and bolls per plant and final loss of lint yield in cotton.The senescence performance was linked to the intensity of leaf pruning in cotton as indicated by decreased carbon and nitrogen metabolism.Although WFR1 had a smaller bolls per plant but a comparable yield to the control as a result of enhanced carbon nitrogen metabolism.WFR2 resulted in a delayed maturation and redirected more nutrients to vegetative growth which may produce less bolls per plants.