Study On The Relation Of Photorespiration To Nitrogen Use Efficiency In Different Rice Genotypes

Pot experiments were conducted to investigate the relationship between photorespiration and nitrogen use efficiency among different rice genotypes under three nitrogen levels. The nitrogen treatments were 0kgN/ha (NO),125kgN/ha (N125) and 208kgN/ha (N208). The rice genotypes of different nitrogen use efficiency were LYP9, PA64, YD6, SY63, ZS97, MH63, WYJ3, Lemont and Ceysvonic. The effects of nitrogen treatments on photorespiration, nitrogen accumulation, glycolate oxidase activity, glutamine synthetase activity, chlorophyll contents and other physiological traits among various rice genotypes were observed at different growth stages. The results showed as follows:1. Photorespiratory rate and net photosynthetic rate were significant differences among various rice genotypes at the same growth stage. Changes of photorespiratory rate were different among various rice genotypes in different growth stages. In the early growth period photorespiratory rates were relative convergence among various rice genotypes, and then, ascended differently with growth period, at last, declined in the late growth period. In this experiment, the difference between N 125 and N208 treatment was not significant.Net photosynthetic rate declined differently according to the growth period. In the early growth stage net photosynthetic rate was not significant differences between two nitrogenous treatments, but increasing nitrogen fertilizer applied rate prolonged the period of high net photosynthetic rate. So it declined differently in two nitrogen treatments in the late growth stage.The ratio of photorespiration to photosynthesis ascended increasingly according to the growing period and varied in different rice genotypes. ZS97 had higher photorespiratory rate and net photosynthetic rate; Ceysvonic had higher photorespiratory rate and the ratio of photorespiration to photosynthesis; Lemont had lower photorespiratory rate; WYJ3 had higher ratio of photorespiration to photosynthesis.2. Dry matter, Grain yield and its components were significantly different among different rice genotypes in different growth stages. Differences of the biomass and grain weight were significant among nitrogen treatments. Under this experiment condition, biomass, grain weight and number of panicles upgraded with the increase of nitrogen level. There were different performances among nine rice genotypes between two nitrogen treatments. LYP9 and SY63 had relative high dry matter accumulations and grain weight, WYJ3 had lower dry matter and accumulation, and Lemont and Ceysvonic had lower grain weight.3. Nitrogen contents in plant organ increased with the rate of the applied nitrogen fertilizer among different rice genotypes. Nitrogen contents were significant differences among various rice genotypes under the same nitrogen level. Distribution of nitrogen in organs was different among various rice genotypes. Ceysvonic had the lowest nitrogen harvest index (NHI) among the nine genotypes under three nitrogen levels, and other genotypes had different NHI under different nitrogen levels. Under N208 and N125 nitrogen condition, distribution of grain nitrogen was higher in SY63. Distribution of grain nitrogen was higher in YD6 under the NO level. Nitrogen accumulation was higher in LYP9, SY63 and ZS97; lower in WYJ3 and Lemont. The whole trend was that Indica cultivars were higher than conventional Japonica cultivars, and the lowest was widely compatible cultivars.4. Nine rice genotypes were grouped into three types by cluster analysis on the basis of the indexes, nitrogen dry matter production efficiency, nitrogen grain production efficiency, nitrogen harvest index, nitrogen agronomy efficiency, nitrogen recovery efficiency, nitrogen grain physiology efficiency, nitrogen biomass physiology efficiency, partial factor productivity of applied nitrogen. The first type had high nitrogen use efficiency, including LYP9, SY63, YD6, MH63; the second type had low nitrogen use efficiency, including PA64, Ceysvonic and ZS97; the third type was between the fist and third one, including WYJ3 and Lemont.Photorespiratory rate and the ratio of photorespiration to photosynthesis were significantly different among the three types, but net photosynthetic rate was not significantly different with the mean of the whole growth period. In the whole growth period, the genotype of high nitrogen use efficiency had low photorespiratory rate and the ratio of photorespiration to photosynthesis, while low nitrogen use efficiency had high photorespiratory rate and the ratio of photorespiration to photosynthesis.5. Contents of chlorophyll a, chlorophyll b, chlorophyll and carotenoid were significant differences among various rice genotypes. Changes of contents were similar in the whole growth period and declined with growth period. There was not significant difference between the N125 and N208 nitrogen treatments. Otherwise, the increased nitrogen fertilizer delayed the decomposing of chlorophyll.SPAD values of top three leaves varied differently with growth period. The changes were different among various rice genotypes. In the early stage, SPAD values present the change as wave. In the late growth stage, the first top leaf SPAD values declined least, the third top leaf SPAD values declined mostly, and the second top leaf SPAD values declined between the first and the third. SPAD values of the top three leaves under N208 treatment declined smaller than N125 in the late growth stage. Increasing nitrogen fertilizer maintained high SPAD values to a certain extent in the late growth stage.There were significant differences of leaf area at different growth stages among various rice genotypes, the same between the two nitrogen treatments. Nitrogen fertilizer effect on leaf area was significant. Leaf area declined less under N125 level compared with N208 level in the late growth period. Leaf area was large in MH63, SY63, LYP9 and YD6, while small and similar in ZS97 and WYJ3.6. Glycolate oxidase activity and glutamine synthestase activity were significant differences among various rice genotypes at different growth stages, but not significant differences between two nitrogenous treatments. On the whole, glycolate oxidase activity declined according to the growth stage as the same as the changes of photorespiration. The genotpye of high nitrogen use efficiency had high glutamine synthestase activity, while low nitrogen use efficiency had low glutamine synthestase activity in the late growth stage.