Effects Of Nitrogen Panicle Fertilizer On Cadmium(Cd)Distribution And Transport In Shoots Of Rice

Ear stage is an important period of rice growth and development.Nitrogen application in ear stage can significantly improve rice yield and quality.At the same time,the question that whether it will affect the absorption,transport and accumulation of cadmium（Cd）in the shoot of rice is worth studying.Based on the preliminary screening in population of recombinant inbred lines to Cd accumulation of low strain 1117 and high accumulation of strain 1180 as test material,uses the soil culture experiment,under the condition of adding80 mg kg^-1Cd,set 0,40,80,160 mg kg^-1n heading levels（that is,T1、T2、T3、T4）,explore the ear for nitrogen affect cadmium accumulation in rice grain,parsing nitrogen cadmium accumulation in different parts on the ground of different periods and its contribution to the cadmium accumulation in rice grain distribution.The main research results are as follows:（1）nitrogen application at ear stage is not only beneficial to improve rice plant height,but also can increase rice yield composition,such as significantly increase the setting percentage,grain number per panicle,thousand seed weight,single spike weight,etc.Under the condition of the same Cd treatment,with spike levels increase in the amount of nitrogen fertilizer,rice in 1117 and 1180 material heading stage and filling stage and mature panicle Cd content are on the rise,the mature grain in Cd concentration in T3（normal dosage earing fertilizer nitrogen）,T4（2 times the amount of spike fertilizer nitrogen）is significantly higher than the T2（1/2 dosages earing fertilizer nitrogen）treatment,suggests that the grain Cd accumulation of two rice materials could be effectively reduced by 50%nitrogen application at ear stage,among which the grain Cd decrease of 1180 rice with high Cd accumulation rate was more significant.（2）under the treatment of cadmium,the content of cadmium in leaves,internodes,nodes and panicle of the two rice materials at ear stage could be significantly increased by nitrogen application at ear stage.Among them,Cd content in leaves at different parts increased by 37%～72%on average,108%～145%in internodes and 137%～187%in nodes,and the increase rate was gradually increased.With the advance of the growth period,the accumulation of Cd in various parts showed a continuous increasing trend.Compared with T1 treatment,T4 treatment showed the largest increase in Cd content in flag leaves of 1180materials at the mature stage,with an average increase of 1.88 times.During the grouting period,the growth rate of the first internode and the first node of 1180 materials was the largest,with an average increase of 2.84 times and 3.51 times.There are differences in the increase range of Cd content in tissues of different accumulative rice materials at different stages.Among them,the Cd concentration in nodes,internodes and panicle of 1180materials under T4（2 times of fertilizer nitrogen per panicle）treatment increased by 3.51,2.85 and 1.25 times compared with that of T1（1/2 of fertilizer nitrogen per panicle）treatment,while that of 1117 materials increased by 2.63,2.24 and 1.23 times respectively.During the grouting period,the increase rate of 1180 material leaves was 41%～86%,which was 59%～117%less than that of 1117 material leaves.（3）application of nitrogen at ear stage could significantly increase the total nitrogen,ammonia nitrogen and nitrate nitrogen content in leaves,internodes,nodes and panicle of the two rice materials at different stages after panicle heading.Among them,the total nitrogen content in leaves of each part increased by 15%～34%on average,internodes increased by 10%～26%,nodes increased by 23%～41%and panicle increased by 18%～25%.The average ammonia nitrogen content in leaves increased by 15%～33%,internode increased by 10%～25%,node increased by 24%～42%,panicle increased by 17%～25%.The average nitrate nitrogen content in leaves increased by 26%～45%,internode increased by 14%～31%,node increased by 17%～36%,spike increased by 23%～37%.2.The average increase of total nitrogen in the two rice materials was shown as>panicle>leaves>internodes,ammonia nitrogen was shown as>leaves>panicle>internodes,and nitrate nitrogen was shown as>panicle>nodes>internodes.The content of total nitrogen,ammonia nitrogen and nitrate nitrogen in the flag leaves of 1180 materials increased by37%,37%and 49%on average in the grouting period compared with T1（1/2）.The content of total nitrogen,ammonia nitrogen and nitrate nitrogen in the first internode of 1180material increased the most,with an average increase of 29%,29%and 34%respectively.The content of total nitrogen,ammonia nitrogen and nitrate nitrogen increased the most at the first node of 1180 grouting period,with an average increase of 45%,46%and 39%respectively.（3）there were differences in the increase amplitude of total nitrogen,ammonia nitrogen and nitrate nitrogen in tissues of the two materials in different periods.The increase amplitude of leaves,internodes,nodes and ears in 1180 periods was all greater than 1117.（4）from the perspective of the contribution of Cd content in different periods and different parts to Cd accumulation in rice seeds,Cd content in leaves,internodes and nodes of the two rice showed extremely significant positive correlation with Cd content in brown rice,among which Cd content in rice nodes was the most strongly correlated with that in brown rice at the filling and maturation stages,with the correlation coefficient r=0.960～0.973.The contents of nitrate,ammonium and total nitrogen in leaves,internodes and nodes of rice were significantly correlated with Cd content in grains.Among them,the nitrate,ammonium and total nitrogen contents of nodes in each period were significantly positively correlated with the Cd contents of leaves and internodes(r _leaf=0.775～0.894,r _internode=0.767～0.903).The results of correlation analysis showed that all forms of nitrogen in leaves,internodes and nodes at heading stage,filling stage and mature stage had significant and significant contributions to Cd accumulation in seeds,and nitrogen content at filling stage and mature stage was an important factor affecting Cd accumulation in seeds.To sum up,reducing the amount of nitrogen fertilizer applied at panicle can reduce the accumulation of cadmium in rice grains.That the Cd content in rice grain and the leaf blade,internode and node of Cd and total nitrogen,ammonia nitrogen,nitrate nitrogen content all have certain positive correlation,shows that the accumulation of Cd in rice grain may be related to the co-transport and redistribution of N/Cd from leaf,internode and node（source）to grain（sink）during the gradual formation of grain after heading.