| Potassium(K) is one of the macronutrient for plant, and cotton is very sensitive to low K environment. To get better cotton variety and improve the K efficiency of cotton, our group selected two typical cotton genotypes with very different K efficiencies from 86 cotton varieties in China since 2001, one is K efficient genotype 103 and the other is K inefficient genotype 122. Using these two genotypes studied the high K efficiency mechanisms of cotton.This study was based on previous researches and improved our kownledge about high K efficiency mechanisms of cotton on both K absorption and K utilization, including the root formate differences, the relationship between root development and phytohormone, potassium absorption patterens, relationships of chemical changes and potassium deficiency symptem on leaves, potassium and photosynthesis product recycle pattern differences, and a field experiment to study the economical and ecological difference of the two genotypes. The first three is K absorption related and the rest of the three is K utilization related. The main results of this study as follows: 1 Mechanisms of potassium absorption diference of the two cotton genotypes1.1 Under normal K environment, the two cotton genotypes had equally amount of fine root, which is mainly in charge of water and mineral nutrient absorption from environment, however, genotype 103 had a better root system, because the coarse root, which is functional in anchoring the plant to defend lodging was also well developed. Under low K environment, there was big difference between these two genotypes on root growth. Genotype 103 obviously had much better root formation than genotype 122. Fine root development was significantly improved for genotype 103, but for genotypes 122, root development was limited by K deficient environment, which might reduce its absorption ability. About the corase root, both genotypes were negatively affected by low K environment, but genotype 103 still got significantly better development. So, roots of genotype 103 had better changes to improve its K efficiency to adapt low K environment better, but genotype 122 had not.1.2 Root development was directly affected by carbonhydrate accumulation, and also regulated by mineral nutrient and phytohormones content in root. To find out why genotype 103 had better root system under K deficient environment, the three factors mentioned above were studied. Genotype 103 accumulated more protein and carbonhydrate under low K environment, even higher than it under normal K environment, which means genotype 103 had positive adaptation behavious under K deficiency circumstance, but for genotype 122, protein and carbonhydrate amount was decreased by K deficiency. Potassium concentration in roots of the two cotton genotypes did not show much difference, but magnesium, which is an important substitution ion to K in cell was significantly higher than it under normal K condition in genotype 103, and also significantly higher than genotypes 122 under low K condition. Phytohormone concentrations were more stable in the root of genotype 103 in different K environment, no matter it was positive or negative regulated plant root development, especially the concentration of auxin, which would greatly promote the root growth. To sum up, genotype 103 could have better root development under low K environment due to the positive regulation of higher protein and carbonhydrate accumulation, higher amount of magnesium to relief K deficiency condition in cell and higher contentration of auxin.1.3 Potassium uptake pattern affects its absorption efficiency and nutrient adaptivity of plant. Potassium uptake kinetic study showed genotype 103 was more adaptive to low K environment, and genotype 122 would grow normally with higher K supply. Using typical inhibitors to K+ channel and transport protein to study which K uptake system was majoring K absorption under different K condition, the results revealed cotton plant adapted low K environment by absorbing K+ via high affinity K transport system after growing in K deficiency environment for two weeks. As for the two genotypes growing in the normal K condition, genotype 103 absorbed K+ more via high affinity K transport system when transplanted them to K deficiency environment, which would help it to absorp K+ from environment efficiently, but genotype 122 did not have this adaptation strategy.2 Mechanisms of potassium usilization diference of the two cotton genotypes2.1 According to the results of Fourier transform infrared spectroscopic(FTIR) analysis, potassium affected photosynthesis transport of the two genotypes in a very different way. Genotype 103 could transport sugars efficiently even under low K environment, as for genotype 122, most its sugars accumulated in leaf. Structure of proteins, which attributed to plant cell wall was seriously affected by K deficiency in a negative way for genotype 122. Another FTIR analysis based on cell wall samples of the two genotypes showed there was an obviously accumulation of carbonhydrate on cell wall for genotype 122, which might affect cell development under low K environment and cause more serious K deficiency symptoms. 2.2 Nutrient recycle ability in plant is also important for plant to adapt nutrient deficiency environment better. Under normal K environment, K was more prefer to transporte to stem and leafstalk of cotton, which were reported as “temporary store” for K. There was no significant of difference of K transport pattern between these two genotypes under normal K condition, but under low K environment, significantly higher amount of K was translocated to root for genotype 103, and genotype 122 did not have this change at the same nutrient condition. So, more efficient photosynthesis product transportation and K recycled to root might be the reason genotype 103 has better root development thus has better low K adaptation ability. 3 Economical and ecological effects of the two cotton genotypes in field trialIn field experiment, the two genotypes grew in a very different way after bloom. With the same K fertilizer application, genotype 122 lost lots of bolls, and genotype 103 kept most of them. Although genotype 122 had havier single boll, the seed cotton yield was significantly lower than genotype 103. So genotype 103 has much higher output with the same fertilizer input, even with the lowest K fertilizer input, its yield of seed cotton still much higher than genotype 122. See cotton yields of genotype 103 increased by 9.2%, 33.8% and 25.0% compared with genotype 122 in the same fertilizing condition, and the ratio of output increased by 39.2%, 33.8% and 25.9%. Besides, genotype 103 could use soil N and P more efficiently, N efficiency increased by 40.2%, 35.3% and 24.6% than genotype 122, P efficiency increased by 39.4%, 33.9% and 25.2%. Soil nutrient concentration of genotype 103 was higher than genotype 122, which benifited in reducing the fertilizer input of following crops. This study demonstrated that even decrease the amount of fertilizer input into agriculture system, using crops with high nutrient efficiency could balance the agriculture product demand with resources limits problem and environmental protection. The physiological studies in this paper also could provide a few ways that might be helpful to breed better cotton varieties with higher K efficiency. |
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