Studies On Carbon And Nitrogen Metabolism Of N-level On Cassava Growth And Yield Formation

For the purpose to study the effect of nitrogen level(N-level)on growth,yield and physiological mechanism and provide technical guidance for north-shifting cultivation of cassava,considering that hydrology,geography,climate and soil conditions in Hunan province,We took the South China 9(SC9)as material and devised of five N-levels(0kg/667m2(N0)?6 kg/667m2(N1)?12 kg/667m2(N2)?18 kg/667m2(N3)?24 kg/667m2(N4))to investigate N-level how to influence the growth,yield and quality,photosynthetic characteristics,carbon metabolism,nitrogen metabolism.The main results include:1.Relationship between N-level and cassava growth,yield and qualityThe result showed that: 1)From N0 to N4-level,the growth potential increased successively.2)The biological yield was largest on N4-level and the economic yield was highest on N3-level.3)By analyzing fitting equation of N-level and economic produces,the amount of nitrogen fertilizer applied to the maximum yield was 15.64kg/667m2,close to N3-level.4)Under N1-level,nitrogen fertilizer application could improve dry matter content and starch content of root tuber,but exceeding N1-level,surplus nitrogen didn't play a role.5)Crude protein content on N4-level was superior to other N-levels.2.Effect of N-level on photosynthetic characteristic of cassava leavesThe result showed that: 1)From seedling stage to maturity,leaf blade SPAD value gradually decreased;In addition,more nitrogen fertilizer could increase the SPAD value of leaf blade and the SPAD value on N4-level was superior to other N-levels.2)There was no significant difference among Gs,light saturation point,CO2 saturation point and N-levels.3)These indicators(Pn,Tr,light compensation point,CO2 compensation point,AQY,CE)with the increase of N-levels showed a single-peak curve change and attained maximum value of N3-level.4)Elevated N-level inhibited Ci value.5)The utilization rate of light energy and CO2 was highest in seedling stage;The Pn value was highest in cassava formation stage.3.Effect of N-level on carbon and nitrogen metabolism key enzyme activity of cassavaUnder 0-18kg/667m2,1)N-level application could improve SS activity,and can promote the transport and decomposition of sucrose,produce more UDPG,increased starch synthesis required precursor material,more conducive to the synthesis of starch.2)N-level application could improve PEPC,PK activity,promote the formation of OAA acid and PEP,and enhanced the Calvin cycle,increasing the yield of cassava.3)N-level application could improve GS,GOT/GPT activity,enhanced the ability of cassava plants to absorb NH4+ and Glu transport,thereby promoting the synthesis of amino acids,and causing the protein content to rise.4)At the same time,the application of nitrogen fertilizer also increased the photosynthetic rate of cassava,increased the absorption and utilization of light and CO2 by cassava,and increased the photosynthetic product.5)From the whole growth period of cassava,it can be found that the carbon and nitrogen metabolism in cassava plants were the most vigorous and the photosynthetic rate was the highest at the time of root formation.Indicating that during this period,cassava plant accumulation of the fastest material.