| The second general survy of soil showed that most of cultivated land in China was in heavy P-deficiency or potential P-deficiency. Heavy dressing phosphorus increased the yield of crops, but led to phosphorite resource driving to exhaustion, and too much P fertilizing has led to ecology and environment pollution. So, screening and cultivating low-P tolerant cultivars has became hot-point research field in present. Rice is the main food crop in the world, there are P-efficiency difference among different rice genotypes. This research screen more than 2000 rice cultivars in seedling stage with soil culture, and identify some of them in full-life stage with pot culture and block experiment, to achieve some typical low-P tolerant and low-P sensitive rice genotypes. Six of them including four low-P tolerant rice genotypes named 99011, 508, 580, 99112 and two low-P sensitive rice genotypes named 99012 and 99056 were selected to study their nutritional characters and physiological mechanism, and make class to them. Further research on their ecological adaptability in different pH soils were carried out. The main results are as follows:1 Though seedling screening and full-life identifying with soil culture to gain some typical low-P tolerant and low-P sensitive rice genotypes, their anastomotic ratio is 67%. This method save time, agree with practice and can achieve typical materials for further research.2 By several phosphorus level at seedling stage and full-life stage, then investigate and statistic the main biological characters. 35mg/kg additional P concentration was defined as seedling screening P concentration when available P in supplied soil is between 2 and 4mg/kg, and relative tiller ratio as the main screening index; and relative rain yield and its components especially relative effective spike and spike-formation rate were the reliable identifying indexes at full-life stage. At the same time, 2.5mg/L was regard as the feasible P concentration for study on the genotypic difference by solution culture in seedling stage.3 Different low-P tolerant mechanism was discovery by studying on the sub-factors related to P uptake efficiency, utilization efficiency and transport efficiency. As comparison to find the main contributive factors of different rice genotypes showing low P tolerant or low P sensitive, and then classify for them. The results showed that under low P stress condition, low-P tolerant rice genotypes 580, 99011 and 508 had larger biomass and less effect by changed P level than 99112. low-P tolerant rice genotype 99011 also keep higher uptake efficiency to P which owe to its long root, and strong ability of mobilizing insoluble Fe-P and Ca-P and decomposing inorganic phosphorus; it also keep higher P use efficiency, low P stress has little effect on soluble P in leaf andphloem. The maximal advantage of low-P tolerant rice genotype 508 is the large distribution coefficient of phosphorus and photoproduct to root, so it has stronger root system and large active absorption area, this make it absorb more P from low concentration P and mobilize a lot of insoluble P. Low-P tolerant rice genotype 580 has the highest P use efficiency which can be proved by the highest soluble P concentration in its phloem; in addition, this genotype has larger root active absorption area and can mobilize more Fe-P and Ca-P than others. But low-P tolerant rice genotype 99112 is a special material, it has a small biomass, and only a little P can keep its growth, Maybe it keep high relative grain yield mainly by sacrificing biomass, which was indicated by its shortening height under low P stress. Low-P sensitive rice genotype 99056 and 99012 both can mobilize or decompose very little insoluble P, their difference is 99056 has a small root system and active absorption area, so it can not uptake low concentration P; reversely, 99012 has lowest P use efficiency, and low-P stress has significant effect on shoot especially on tiller.4 Soluble protein in rice leaf and root was isolated with SDS-PAGE electrophoresis technology. The results investigated that proteins in leaf and root both expressed variantly with variable low-P stress time, and existed genotypic difference, the proteins in leaf and root have no change with low-P stress for 6 hours. One to two days later, some proteins in leaf and root of low-P tolerant rice genotypes 99011, 580 and 99112 expressed enhancedly, even several new stress proteins appeared; and there are some new proteins appeared in low-P sensitive rice genotype 99012; but for 99056, some proteins in root expressed weakenedly and two proteins disappeared. Four days later, some proteins in leaf and root of all rice genotypes expressed weakenedly or disappeared, except one or two proteins in 580 expressed enhancedly or appeared. At the same time, we screen the gel concentration with stacking gel as 3% and separation gel as 12%, which adapted to isolate proteins with molecular weight from 10.0 to 110KD. Fixation, stain and destain to gel as the sixth method in table 5.1 can take good effect.5 Results of nutrition study showed that low-P tolerant rice genotypes also keep higher uptake efficiency to N and K, this belong to synergistic-effect; and the rice cultivars with different P-efficiency had varietal uptake and use ability to Zn, Ca and Fe. Zn concentration of shoot with P200, PI00 and P50 were similar, but P35 increased Zn concentration of shoot significantly. The Zn concentration of 99112, 99056 and 99012 in shoot were higher than that of 508, 99011 and 580, especially in tillering stage and booting stage. As for total Zn in shoot, Low-P tolerant rice genotype 580 had the largest amount and followed by 99011 and 508, low-P tolerant rice genotype 99012 had the smallest amount at the three sampling stage and followed by 99056 ? Furthermore, P/Zn of 99012 in shoot was the largest, but that of 99056 was the smallest at the same P level. Rice absorb more Ca at generative phase than vegetative phase. The total Ca reducedwith decreased P level, and this showed more obvious at booting stage, but there are difference among supplied rice genotypes. The absorption of low-P sensitive rice genotypes to Ca reduced with decreased P level from seedling stage, but that of low-P tolerant rice genotypes reduced slowly after tillering stage. 508, 580 and 99011 uptake more Fe than 99112, 99056 and 99012, and their gap largened with growth process. P50 and P30 decreased the absorption of rice to Fe at vegetative stage, to generative stage, PI00 has decreased the Fe absorption significantly except 508. but low-P tolerant rice genotypes were less affected than that of low-P sensitive rice genotypes.6 Deeply study was carried out to investigate the ecological adaptability of selected rices to P-deficient soil with different pH. The results indicated the low-P tolerant ability of 99011 in alkaline soil was feeble than that in neutral and acid soils, because its relative available spike and relative grain yield in alkaline soil were less than that in neutral and acid soils for 11.1%, 9.7% and 11.8%, 8.8% respectively. But the low-P tolerant ability of 580, 508 and 99112 are similar in three soils. 99012 showed a little tolerant to low P stress in alkaline soil than in neutral and acid soils, and 99056 showed a little tolerant to low P stress in acid soil than in neutral and alkaline soils. The relative available spike and relative grain yield of 99012 in alkaline soil were more than that in neutral and acid soils for 19.6%, 19.6% and 19.6%, 22.2% respectively, and those of 99056 in acid soil were more than that in neutral and alkaline soils for 17.3%, 15.1% and 25.0%, 17.0% respectively. Furthermore, the P concentration in flag leaf and its relative value of 99011, 580, 508 and 99112 are higher than those of 99012 and 99056. |
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