The Effects Of N Management On Photosynthate Distribution And Nitrogenase Activity Of Soybean

A pot experiment was conducted to study the effects of N management on photosynthate distribution and nitrogenase activity of soybean with the treatments of N 0, 30 and 60 kg/hm2 levels, and topdressing N 30 kg/hm2 at R1, R2, R3 and R4 stages on the base of N 30 kg/hm2. Soluble sugar content, starch content, ureide content, the dry weight of roots, roots volume and the N content in soybean were analyzed. The main results are as follows.Topdressing N treatments at different stages increased soluble sugar content and accumulation in all organs of soybean. Compared with N60, the soluble sugar content in soybean leaves of N30+R2 increased by 16.87% (P<0.01). The soluble sugar content in soybean stems get the highest value at R6 stage. Compared with N60, the soluble sugar content in stems of N30+R2 increased by 11.89% (P<0.05). Compared with N60, topdressing N treatments at different stages enhanced soluble sugar content in soybean roots. Topdressing N at R2 stage increased the soluble sugar content in soybean roots by 14.98% at R4 stage (P<0.05). The soluble sugar content in soybean roots increased as N application rate increase. The soluble sugar accumulation in soybean leaves and stems get the highest value at R4 and R6 stages. Compared with N60, topdressing N treatments at different stages enhanced the soluble sugar accumulation. Compared with N60, the soluble sugar accumulation in leaves, stems and roots all increased by 17.15%, 35.09% and 20.36% (P<0.05). It noted that Topdressing N at R2 stage conducived to the formation of the photosynthetic product of the accumulation and transport, enhanced transport to the roots. Increased the roots soluble sugar accumulation and enhanced the amount of nitrogen-fixing nodule.Topdressing N treatments at different stages increased starch content and accumulation. When carbohydrate has been consumpted large amount of the starch provided carbon frame. Compared with N60, topdressing N treatments enhanced starch content in soybean leaves and stems at R5 stage. Compared with N60, the starch content in soybean leaves of N30+R2 increased by 17.68%. The starch content in soybean stems get the highest value at R5 stage. Compared with N60, the starch content in stems of N30+R4 increased by 22.86% (P<0.01). Before R4 stage the leaves are in accumulation state. Then distributed to other organs at R5 stage. Topdressing N treatments maintained relatively high amount of starch accumulation. Topdressing N can delay the leaves senescence, and therefore enhance the accumulation of photosynthetic products.The available carbohydrates in soybean leaves at the state of accumulation at R1 to R4 stages. And these substances also distributed the available carbohydrates to other organs. The available carbohydrates mainly distributed to stems and pods after R4 stage. The accumulation and distribution of topdressing N treatments at different stages were higher then the treatment N60. Compared with N60, topdressing N at R2 stage plant availability of carbohydrates distributed in stems increased 33.14% at R5 to R6 stages. And the pods accumulation increased by 21.17% than N60 (P<0.05). Compared with N60, topdressing N treatments at different stages enhanced the distribution of plant availability of carbohydrates in soybean leaves at R5 to R6 stage. The export rate is higher than N60 by 8.38%.The dry weight of soybean nodules decreased as N application rate increased at R1 to R4 stages. Note the early reproductive growth of nitrogen will inhibit nodule. Compared with N60, topdressing N treatments at different stages enhanced the dry weight of nodules at the late reproductive. Compared with N60, the dry weight of nodules of N30+R2 increased by 23.64% (P>0.05). N accumulation in nudoles are decreased as N application rate increased at early reproductive. The N accumulation in roots and nudoles all increased as N application rate increased at R5 stage. Note the late topdressing nitrogen fertilizer nitrogen could be due to excessive pre-mitigation of the root system resulting from inhibition. Improve the post-root vitality, delayed nodule senescence. Ureide as a metabolic product of urease, its content and root nodule nitrogenase activity was positively correlated. Both organs contain ureide, content expressed as stems>pod>leaves. The ureide content of leaves and stems expressed as N0>N30>N60, That pre-N there is too much inhibition of nitrogen-fixing nodule. Compared with N60, topdressing N at R2 stage plant ureide content in leaves, stems and pods all increased. The dry weight of roots and roots volume of topdressing N treatments were higher than N60. Compared with N60, N30+R2 enhanced the dry weight of roots and roots volume by 13.71% and 9% (P<0.05).The yield was increased for different N application rate increased. The yield of N30+R2 was highest among all the treatments. Compared with N60, the yield increased by 11.84% (P<0.05).