Study On Nitrogen Metabolism Echanism And Relative Enzymatic Activity Of Soybean

This work has been conducted from 2002 to 2004 by using field tests and frame tests (pot without bottom) with black soil and two cultivars, DN47 (high-oil) and SN 10 (high-yield). From 2002 to 2003, nitrogen fertilizer was applied separately at beginning bloom (R1), full bloom (R2) and full pod (R4) stages. In 2004, four treatments, non pop-up, the poo-up. dressing at beginning bloom (R1) and non-dressing at beginning bloom (R1), were set. According to the nitrogen accumulation, translocation, mechanism of nitrogen assimilation and relevant enzymatic activities of soybean of the above-treatments, results were shown as follows:Nitrogen nutrition of soybean may be divided into five stages: 1) cotyledons supply stage (VC), where the cotyledons supply the mineral nutrients and carbohydrates, this stage includes emergence stage and cotyledon stage; (2) mineral nitrogen supply stage, from the first trifoliolate stage (V1) to beginning bloom (R1), where the plant absorbs mainly NO3--N; (3) Mineral nitrogen supply and nitrogen fixation stage: from the beginning bloom (R1) to the full pod (R4), where the soil partially supply the plant with mineral nitrogen, yet the other part of nitrogen is fixed by plant itself; (4) nitrogen fixation supply stage, from full pod to full size stage (R4-R6), where the nitrogen comes mainly from the nitrogen fixation by nodules, at this stage, on one side, vegetative organs begins to translocate nitrogen to the reproductive organs, on the other side, they still accumulate nitrogen from the roots; (5) fast nitrogen translocation stage, from the beginning seed to the full maturity stage, where the nitrogen accumulated in the vegetative organs were rapidly translocated into the pods, and nitrogen from roots comes mainly from the nitrogen fixed by nodules, pods accumulate intensively nitrogen at this stage.The shape of nitrogen accumulation in the soybean plant was similar to that of dry matter. At the full bloom and the beginning seed stage, the accumulation rate was the fastest in the trifoliolates, petioles and stems of the plant. Nitrogen and dry matter accumulated mainly in the trifoliolates in the early growing stages, whereas the quantities accumulated in the petioles and stems increased progressively, but the proportion in the trifoliolates decreased a bit. Nitrogen in the vegetative organs is translocated to the pods after the beginning seed stage. The translocation rate of nitrogen from the trifoliolates was significantly higher than those from stems and from petioles. Under the frame tests conditions, the outflow rates of nitrogen from trifoliolates, stems and petioles are respectively 428.5-436.4 mg/plant, 232.8-320.7 mg/plant and 83.0-103.2mg/plant, and took up 29.6-32.6 % nitrogen in the seed. The translocation rate of nitrogen was higher in the stems than that in the trifoliolates which was similar to the translocation rate in the petioles, they were respectively 70.1-76.3%, 56.1-56.7%, 54.0-59.3%.Trend of non-water-soluble nitrogen (NWSN) in the plant was similar to that of total nitrogen, they were positively correlated (R2=0.9631). The NWSN content in trifoliolates was higher than that in stems, which was similar to the NWSN content in petioles. The NWSN /total nitrogen ratio was bigger than 90 % in trifoliolates, higher than that in stems and that in petioles, but they changed hardly with growing stages. The main components of water-soluble nitrogen (WSN) are NO3-1-N, ammonia nitrogen and ureides. The WSN content of soybean's trifoliolates is low. yet the changes were very small; WSN content in stems was higher than that of petioles comparable to that of trifoliolates. At seedling stage (V4). the WSN content was at a higher content, followed by a rapid decline until full bloom stage, then followed by another increase. The WSN content in the pods was high and remained the translocation-sink of nitrogen. The ammonia nitrogen took up-to 90 % of the WSN. yet the proportion of NO3--N and ureides was very low. For stems, at early and later stages, the ammonia nitrogen/water-soluble nitrogen was relatively higher, yet lower at the middle growing stages. The ammonia nitrogen /WSN ratios are respectively 32.4-36.5%. 43.2%~54.2%. 24.2-25.7% at V4, V2 and V6 stages. In the WSN of stems, the NO3--N content is higher at the early growing stages, and kept decreasing with growing stages until a NO3--N /WAN ratio of 54.4-62.0 %, the NO3--N /WAN ratio was extremely low at R4 and R5. The proportion of ureides in the WSN of the stem (U/WSN ratio) was low at the early growing stage, but increased with growing stages rapidly and reached to more than 73.0 % at R6. In the petiole, the ammonia nitrogen /WSN ratio was low at the early growing stages, and increased progressively with growing stages and the maximum (65 %) came at R5. The U/WSN ratio in the petiole was lower than that in the stem with similar trends. The NO3--N /WSN ratio in the petiole decreased with growing stages and reached to 77.1-83.1% at V4-R1 stages, significantly higher than that in the petiole.The ureides content in pods and in stems was higher than that in trifoliolates and that in petioles, and the upper part of stem had a higher Ureides content. In ureides. the content of allantioc acid was higher than that of allantoin; the relative abundance of ureides (URA) was 44.5%-49.0% or higher at R: stage, then increased rapidly to a level higher than that of NO3--N: the content of NO3--N in petiole was higher than that of ureides before R4 stage where the Ureides content reached 38.9%-44.0%, followed by a rapid decrease. The ureides dominated in pods where the content of NO3--N was extremely low. This showed that the effect of ureides on the reproductive organs was extremely important.Glutamine synthetase (GS), Glutamin-oxoglutamate amino-translocationase (GOGAT) and allantoinase were respectively detected in root, nodule, stem, leaf, pod shell and seed, but nitrate reductase (NR) was only detected in leaf. GS activity changed with the growing stages showing only a peak at R2; trends of GS activity in trifoliolates were different to those in stem and in root.The GS activity in various organs followed the order: nodule> stem, root>pod >shell> seed > leaf. NADH-GOGAT activity in stem changed with growing stages showing a peak at R| for cultivar DN47 and at R2 for cultivar SN10; There was no regularity in leaf; the activity in root of cultivar SN10 changed with the growing stages showing a peak at R2, no regularity was found in root of cultivar DN47. In nodules, the NADH-GOGAT activity was higher at V4. The NR activity is higher at V4, and then decreased with the following stages and fell down to a very low level at R4. The order of allantoinase activity was: pod shell >stem > seed > nodule> root> leaf; In stem, the allantoinase activity was higher at seedling stage (V4) than that in root and that in leaf, and the allantoinase activity in leaf remained constant.The effect of pop-ups and nitrogen dressing at beginning bloom stage on the total N and chlorophyll content was small, but they increased the WSN content at seedling stage and full bloom stage, and remarkably increased the NO3--N in the stem and in the petiole. Pop-ups treatment increased content of ureides at R1, and nitrogen dressing at beginning bloom increased the content of ureides of the plant, especially in the stem, but there was no regularity at R4. Nitrogen dressing significantly increased the yield, but pop-ups did not.