Influence Of Reduction Of Nitrogen Fertilizer Application On Root Vigor,Grain Yield And Quality In Wheat (Triticum Aestivum L.)

Field experiments and pot experiments were conducted to study the relationships between physiological characteristics,such as root vigor and key enzyme activities of NADP-dehydrogenase system,and aboveground growth,grain yield and quality under the condition of reducing nitrogen fertilization in the typical field on the Huang-Huai plain.Zhoumai 27 and Aikang 58,which were widely planted in this area,were used as materials.Six different nitrogen fertilizer levels were set: 0(N0),135(N1),157.5(N2),180(N3),202.5(N4),and 225(N5)kg�hm-2.The purpose of this study was to elucidate the key factors and regulation techniques of root vigor under different nitrogen application levels,and to provide theoretical basis for sustainable yield increase in Huang-huai plain area.Results are as follows:(1)Under appropriate nitrogen reduction(N4)conditions,photosynthetic characteristics and root physiological activities of wheat can still be maintained at high levels.Compared with N5,the changes of flag leaf SPAD value and aboveground dry matter were not obvious as reducing to N4.Reduction of nitrogen fertilizer reduces the root weight density in 0�40 cm soil layer,key enzyme activities in NADP-dehydrogenase system and root vigor.Compared with N5,the root weight density in 0�40 cm soil layer,NADP-ICDH activity and NADP-ME activity were not significantly different as reducing to N4,and decrease of root vigor was the least,with an average of 8.07%,-1.61%,while(G6PDH+6PGDH)activity slightly increased(0.61%).(2)Nitrogen fertilizer is beneficial to increase yield and improve grain quality,but moderate nitrogen reduction(N4)has less effect on grain yield and quality.Under the condition of reducing nitrogen fertilization,panicle number(per plant),grain number per spike and grain yield(per plant)all showed a downtrend.Nitrogen application(N5�N1)has significantly higher yield than the nitrogen free treatment(N0),while N4 and N5 had no significant difference.Nitrogen fertilizer reduced grain quality,but compared with N5,applying nitrogen fertilizer to N4 had less effect on soluble sugar content,starch component and branch/straight ratio of grain,and the difference between the two treatments was not significant;grain protein content only decreased by 4.25%.(3)Root vigor,NADP-dehydrogenase system key enzyme activities and yield were closely related.After re-growing stage,the activities of NADP-ICDH,NADP-ME and(G6PDH+6PGDH)were significant or extremely significant positively correlated with root vigor.Root vigor and the activities of key enzymes in root NADP-dehydrogenase system were significant or extremely significant positively correlated with grain yield.Path analysis further showed that direct effects of root vigor on yield were little,however,indirect positive effects of root vigor by means of increasing in activities of NADP-ICDH,NADP-ME and(G6PDH+6PGDH)on grain yield were significant or extremely significant.(4)The main physiological characters of root system are closely related to grain quality.During the growth and development of wheat,the content of soluble sugar and soluble protein in root were significant or extremely significant positively correlated with the content of soluble sugar,protein and starch in grain.There was a significant or extremely significant negative correlation between root vigor and NADP-dehydrogenase system key enzyme activities and grain quality traits,and a significant or extremely significant positive correlation between root vigor and grain quality traits at jointing stage and heading stage.The results indicated that reducing nitrogen application rate by 10% from N5(225 kg�hm-2)to N4(202.5 kg�hm-2)could be optimum at present in wheat field in the Huang-Huai plain,taking dynamics of aboveground photosynthesis,root physiological characteristics,grain yield and quality into account.NADP-ICDH,NADP-ME and(G6PDH+6PGDH)are closely related to the "root vigor" determined by the improved TTC method.It is concluded that wheat root vigor can be improved by high expression of NADP-ICDH,NADP-ME and(G6PDH+6PGDH)in roots,which could be achieved by means of molecular breeding and effective cultivation methods in practice,and then to achieve nitrogen reduction and no reduction of yield.The content of soluble sugar and soluble protein in wheat root is closely related to the grain quality.The grain quality can be regulated by adjusting the content of soluble sugar and soluble protein in root so as to improve the grain quality at the same time when nitrogen reduction is not reduced or slightly reduced.