Nitrogen Use Efficiency Variability And Physiological Responses Of Different Sorghum Genotypes Influenced By Nitrogen Deficiency

Cultivation of low-N tolerant sorghum cultivars is of great importance in improving the grain yield of sorghum on barren fields or low fertility soils and in the promotion of nitrogen use efficiency of sorghum.Genotypic variability in nitrogen use efficiency was found in different genotypes of sorghum,but the mechanisms are still not yet clear.An indoor experiment was conducted in greenhouse by means of pot with soil medium to explore the effects of low nitrogen stress on plant growth,yield components,N use efficiency and related traits,N accumulation and translocation rate,leaf SPAD readings,leaf soluble protein contents,leaf leaf inorganic nitrogen?NO₃^--N?NO₂^--N and NH₄⁺-N?content and nitrogen assimilation enzymes in terms of nitrate reductase?NR?,nitrite reductase?NiR?,glutamine synthetase?GS?and glutamate synthetase?GOGAT?at both flag leaf and grain filling stages of two low-N susceptible genotypes?Jiya2 and TX7000B?and two low-N tolerant genotypes?SX44B and TX378?under normal N supply(NN,0.24 gN·kg^-1soil)and low N supply(LN,0.04 gN·kg^-1soil).Understanding the physiological responses of sorghum influenced by N deficiency was pratical to provide theoretical basis for further improvement in the cultivation of low-N tolerant sorghum genotypes.The main research content and research results are as follows:1.LN treatment resulted in a decrease of 13.87%and 19.25%respectively for Jiya2 and TX7000B,compared with the grain yield?GY?of NN treatment.However,LN treatment didn't decrease the GY of SX44B and TX378.2.The relative grain N accumulation,relative plant N accumulation and relative N harvest index?ratios of trait values under LN treatment to those under NN treatment?were inconsistent with the low nitrogen tolerant performance of sorghum.By contrast,the low-N tolerant genotypes had a higher relative nitrogen partial factor productivity?NPFP?and relative nitrogen utilization efficiency?NutE?than low-N susceptible genotypes.The NPFP of SX44B and TX378 under LN treatment were 6.19 and 7.49 times of that under NN treatment,while the NPFP of Jiya 2 and TX7000B were 5.17and 4.85 times,respectively.The NutE of SX44B and TX378 under LN treatment were 1.84 and 1.85 times of that under NN treatment,whereas the values of Jiya 2 and TX7000B were 1.67 and 1.35 times.LN treatment significantly increased the nitrogen remobilization rate?NRE?of the sorghum leaf and stem,and the degree of NRE was independent of the sorghum low-N tolerant characteristics.Path analysis showed that plant nitrogen accumulation and NutE contributed the same to grain yield under NN treatment,while the importance of NutE was over plant nitrogen accumulation in defining the GY under LN treatment.3.LN treatment decreased the leaf SPAD readings of low-N susceptible genotypes from emergence to anthesis,and had no effects on the low-N tolerant genotypes.At flag leaf stage,compared with NN treatment,the leaf soluble proteins?LSP?of low-N susceptible genotypes Jiya2 and TX7000B under LN treatment were decreased by 36.37%and 14.71%,respectively,while LN treatment didn't decrease the LSP of the low-N tolerant genotypes.At grain filling stage,the LN treatment significantly decreased the LSP of Jiya2,TX7000B,SX44B and TX378 by 28.41%,55.74%,38.22%and35.40%,respectively.The two treatments didn't have effect on the total number of sorghum leaves.LN treatment significantly increased the number of dead leaves,but significantly decreased the number of surviving leaves.4.Leaf inorganic N content was irrelevant to the low N tolerance of sorghum.Leaf inorganic N content at flag leaf stage was significantly lower than that at grain filling stage.LN treatment significantly decreased the leaf NR,GS and GOGAT activity of Jiya2 and TX7000B.On the contrary,leaf nitrogen assimilation enzyme activity of SX44B was not notably changed by N level and leaf GS activity of TX378 was significantly increased under LN treatment.