Efects Of Plant K~+ Nutrition On Cotton Yield And Fiber Development

Since the indeterminate growth habit and the mechanism of fiber growth. cotton requires a larger amount of potassium (K) than other crops. However, China holds little K resource,which makes the soil K deficiency become a limiting factor for cotton production. Therefore,a study has been undertaken to reveal the mechanism how the soil K levels affect cotton yield and fiber properties, to establish an efficient K application strategy based on the K requirement of cotton, and to discover some approaches to enhance the low-K tolerance ability of cotton.The current research addressed the effects of soil K level on cotton yield and fiber properties, and summarized the biological basis for exhibiting low-K tolerance by comparing two tested cotton cultivars. Our study includes three experiments that (1) A screening work for low-K tolerant cotton cultivars; (2) A screening work for the critical K application rate based on plant K+-nutrient condition; (3) Two years' field test. Main results from the study are as follows.1. A low-K sensitive cotton cultivar Siza 3 and a low-K tolerant one Simian 3 were screened outTests on 12 local popular cotton cultivars have been done for defining their low-K tolerance degree. Two cotton cultivars, the low-K sensitive one Siza 3 and the low-K tolerant one Simian 3, were screened out by clustering tests from a field test on mature cottons together with a seedling test in culture solutions.2. Establishing the right K application rate in cotton field for achieving different plant K+ nutrient statusSeven levels of K rates have been applied in cotton field (0, 75, 150, 225, 300, 375, 450 kg K2O ha-1) with plants' aboveground K+ concentration have been determined for building up a model of the dynamic change of cotton plant's critical K+ concentration with days after transplant. Thereafter, a critical K application rate of Nanjing, 150 kg K2O ha-1, has been found, according to which three K application rates (0,150, 300 kg K2O ha-1) have been set for respectively achieving three types of plant K+ nutrition (K deficiency, K criticality, K sufficiency).3. Effects of plant K+ nutrition on cotton yield and fiber developmentCharacteristics of yield components,cotton boll distribution on plant and fiber dry matter accumulation have been tested, and it was found that the impact of plant K+ deficiency on lint yield was mainly achieved by decreasing the boll setting ratio of late season bolls and inhibiting fiber dry matter accumulation. The main reason causing this might be the short of supply of carbohydrate from leaves and the shortening of cellulose accumulation process in cotton fiber cells.Lengths of immature cotton fibers, main osmotically active solutes concentrations and key enzymes activities have been determined. An osmoregulation from fruiting branch K+ to fiber K+, one of the main osmotically active solutes supports fiber elongation, has been found,which could regulate fiber length by affecting the maximum velocity of fiber elongation(Vmax). Additionally, upper fruiting branches have potentials to grow longer fibers in the condition of K sufficiency. Therefore, we suggest fertilize cotton additionally when upper bolls are forming would help improve the fiber properties of upper fruiting branches.Moreover,the activities of key enzymes engaged in fiber elongation, V-ATPase?PPase?PM H+-ATPase and PEPC, were highly sensitive to plant K+ deficiency at 10-15 DPA, which would play negative roles in fiber elongation by suppressing K+ transport, cell wall acidification and malate synthesis.By determining the immature cotton fiber strength, cellulose content, water content and key enzymes activities, an accelerated maturity has been found in fiber cell, and the degree of the acceleration had a negative linear correlation with fiber strength. This premature-likely phenomenon on fiber cell was potentially caused by carbohydrate supply barrier. In addition,the activities of the key enzymes engaged in cellulose synthesis, SuSy and SPS, have been affected by low-K stress that the occurring time of their peak values were brought forward,which accordingly early terminated cellulose synthesis and finally played a negative role in fiber strength.4. Three important physiological features help cotton achieve the low-K tolerant abilityThree significant differences between two cotton cultivars have been found by comparing their appearances on coping with low-K stress. Firstly, the low-K tolerant genotype could keep the K+ concentration of fruiting branches higher, especially the upper ones. Secondly, the higher malate concentration in fiber cell could assist K+ accumulation.Thirdly, the stability of the key enzymes engaged in fiber development, V-ATPase? PPase?PM H+-ATPase and PEPC, on their activities at 10-15 DPA.