Possible Mechanisms Of Efficient Utilization Of Potassium By Rice (Oryza Sativa L.)

Numerous amount of research demonstrates that there is great genotypic difference in K uptake and utilization, which offers a possibility to tackle the K deficient problem in rice by the genetic method. However, to date, the mechanism of K efficiency in rice is, due to its complexity, not yet fully understood. It is obvious that there exists a necessity to understand the mechanism involving K absorption and utilization. In this study, in order to screen rice genotypes with high K use efficiency, solution culture was conducted in a greenhouse of Zhejiang University, Huajiachi Campus. significant differences in K absorption and use efficiency among different rice genotypes (Oryza Sativa L.) were observed. Since K absorption and utilization by rice is generally recognized to be related with a number of factors, present study is to aim at how these factors, K dynamic change in rice rhizosphere under flooded soil, N sources, and excessive Fe2~ supply, affect K use efficiency of hybrid rice. The obtained results are summarized as follows: 1. hybrid rice showed higher dry matter accumulation and more vigorous growth than its parent lines and conventional rice at the high potassium level. Furthermore, the heterosis of hybrid rice is better demonstrated with NO7N under high K supply level than either with NH4~/ NO3~or with 118 NH4~-N. Absorption and utilization of K is also related with N sources~with a more significant response to low K stress conditions. 2. Potassium has an ameliorating effect on Fe2~ toxicity which has been a constraint to lowland rice production in tropical and subtropical areas. The results from the present experiments showed that excessive Fe2~ in nutrient solution, even as low as 0.36 mmolL? greatly decreased root and shoot dry weights, root length, and shoot length of the hybrid ricerChemical analysis showed that excessive Fe2~ supply remarkably reduced concentrations of K, P, and N in the plants, indicating the effect on nutrient status of plants. High K supply ameliorated the negative effects of higher Fe2~, as indicated by increases in biomass and nutrient contents. Proper level of K supply reduced the excessive translocation of Fe2~ from roots to shoots, especially to the upper leaves. The concentration of phosphorus which is an antagonistic nutrient to Fe2~ was significantly increased by K supply. Ameliorating effects of K may be attributed to the antagonistic effect of K on Fe absorption and translocation to shoots, especially to upper leaves, the most sensitive part. 3. There was significant difference in potassium use efficiency of rice among various genotypes. The efficient genotypes had higher growth potential and use efficiency than potassium inefficient genotypes although both efficient genotypes and inefficient genotypes displayed a lower potassium content and a poorer growth(indicated by their height, root length, shoot dry matter, and root dry matter)under low potassium conditions, 4. relative whole plant dry weight (RWDW), relative potassium 119 accumulation (RWPA), and relative whole plant K use efficiency (RWKUE), in this case, were proven to be applicable parameters for screening potassium efficiency genotype. 5. Result also showed that different potassium levels affected...