Characteristics Of The Nitrogen And Phosphorus Absorption And Utilization In Apple Rootstocks On Different Phosphorus Level

As one of the essential mineral elements in plants, phosphorus can facilitate the differentiation of flower bud. Whereas due to the fixation of chemicals, phosphorus applied to soil were transferred to Occluded P that was unavailable to plants, which lowered the available phosphorus in soil. It is of great significance researching and excavating phosphorus efficient apple rootstocks for remission low phosphorus stress and enhance phosphorus use efficiency. Moreover, phosphorus is an indispensable element in nitrogen metabolism for its role in promoting the NO3- reduction and assimilation. Whereas excessive phosphorus tend to depress the synthesis of protein for the increase in free amino acid and amides. Thus, several kinds of apple wild rootstocks were used to study the characteristics of phosphorus absorption and utilization under the condition of low phosphorus stress, as well as the absorption and utilization of nitrogen on different P level, aiming to pick out the efficient rootstocks on nitrogen and phosphorus absorption and utilization on different P level. Thus, appropriate nitrogen and phosphorus proportion was formulated and the nutrient efficiency of fruit trees was enhanced.1.In this experiment, five kinds of one-year-old apple rootstocks [Malus hupehensis Rehd., M. micromalus Makino, M. baccata Borkh., M. prunifolia(Willd)Borkh. and M.sievesii(Ledeb.)Roemer] were used. The relative phosphorus efficiencies of five rootstocks from high to low are in order: M. prunifolia(Willd)Borkh.(93.66%)>Malus hupehensis Rehd.(87.69%)>M. baccata Borkh.(83.44%)>M. micromalus Makino.(74.54%)>M. sievesii(Ledeb.)Roemer.(74.01%). The phosphorus absorption efficiencies(PAE)of five rootstocks from high to low are in order: M. prunifolia(Willd)Borkh.>Malus hupehensis Rehd.>M.baccata Borkh.>M. sievesii(Ledeb.)Roemer.>M. micromalus Makino, while the phosphorus utilization efficiencies(PUE)are in order: Malus hupehensis Rehd.>M. prunifolia(Willd)Borkh.>M. micromalus Makino>M. sievesii(Ledeb.)Roemer>M. baccata Borkh. Considering the kinetic parameters of H2PO4-, the values of the highest Vmax of the five rootstocks are inorder: M. prunifolia( Willd) Borkh. [ 101.81μmol/(g·h) ] > Malus hupehensis Rehd.[66.40μmol/(g·h) ]> M. baccata Borkh.[45.00μmol/(g·h) ]> M. sievesii(Ledeb.)Roemer[44.32μmol/(g·h) ]> M. micromalus Makino[41.28μmol/(g·h) ]. The values of Km are in order: Malus hupehensis Rehd.(4.05μmol/L) < M. prunifolia(Willd)Borkh.(8.68μmol/L)< M. baccata Borkh.(12.29 μmol/L) < M. sievesii(Ledeb.)Roemer(8.68μmol/L)< M.micromalus Makino(13.57μmol/L). Total surface area and length of absorption root of M.prunifolia(Willd)Borkh are the highest, while those of M. micromalus Makino are the lowest.In conclusion, both the relative phosphorus efficiency and PAE of M. prunifolia(Willd)Borkh.are the highest under phosphorus stress, and with the best growth vigor and the strongest P absorption capacity, M. prunifolia(Willd)Borkh. is the rootstock that best adapted to low phosphorus stress. The relative phosphorus efficiency of Malus hupehensis Rehd. is only second to M. prunifolia( Willd) Borkh., but with the highest PUE, its capacity to low phosphorus stress ranks second to M. prunifolia(Willd)Borkh.. Further analysis show that the values of PAE of the five rootstocks are significantly positively correlated with the surface area and length of absorption root, indicating that the root absorption area of plants are enlarged to promote the acquisition of P by increasing the root surface area and length under low phosphorus stress.2.Three kinds of one-year-old apple rootstocks[Malus hupehensis Rehd.,M. micromalus Makino and M. prunifolia(Willd)Borkh.] were labeled by 15N-urea in this study. Phosphorus acquisition efficiency of the rootstocks increased with the phosphorus level in P0-P1 treatment, and then decreased with a high phosphorus application. Ndff value of M. prunifolia(Willd)Borkh. was high in P0-P2 treatment, and the nitrogen utilization efficiency was highest in P1 treatment(6.389%), while the Ndff value and nitrogen utilization efficiency was the lowest in P3 treatment. Ndff value of M. micromalus Makino varied little with P levels,and the nitrogen utilization efficiency in P3-P4 treatment, presented a high level. Ndff value of Malus hupehensis Rehd. decreased after an increasing with the phosphorus application,with a minimum in P1 and a maximum in P2, and the Ndff value of root,stem and leaf were5.212%, 4.547%, 5.793% respectively, exceeded that of M. prunifolia(Willd)Borkh.and M.micromalus Makino significantly. The nitrogen utilization efficiency of Malus hupehensisRehd. was the highest on P2 treatment(4.856%), and then followed a downtrend. As a consequence, the nitrogen utilization rate of M. prunifolia(Willd)Borkh. which is native to northern Shaanxi plateau, is high on low phosphorus condition, thus it can be a reference to the apple rootstocks applied in this region from the perspective of P utilization. M.micromalus Makino present high nitrogen utilization rate on high phosphorus level, hence it can be used in high phosphorus apple orchard in Bohai bay. Nitrogen utilization of Malus hupehensis Rehd. is high in medium phosphorus level, along with the strong resistance and graft compatibility, so it’s widely used in newly built orchard in the hills.3.In this study, we focused on the NO3--N absorption and utilization of Malus hupehensis Rehd. seedlings on different phosphorus level, aiming to excavate the key factors influencing nitrogen utilization ratio, which provide theoretical basis for scientific and efficient utilization of the fertilizer in apple orchard.The 15 N tracer technique and non-invasive micro-test technique(NMT) were used to determine the nitrogen absorption and utilization ratio of Malus hupehensis Rehd. seedlings on different phosphorus level.The root length, root surface area and quantity of root tips as well as the Ndff value were very low when the seedlings were grown in phosphorus deficiency environment(0-1.0mmol/L), and with the addition of phosphorus application(2.0-4.0 mmol/L), obvious growth of the seedlings can be seen thus the parameters determined above increased significantly. Whereas the root growth was restrained when the seedlings were in excess phosphorus application(6.0-16.0 mmol/L), and the absorption of nitrogen decreased in consequence. The utilization of nitrogen varied on different phosphorus level: the utilization ratio of phosphorus deficiency treatment was lower than that on normal phosphorus environment, while the nitrogen utilization decreased violently when the phosphorus application was overdose.The absorption and utilization capacity were restrained when the seedlings were in phosphorus deficiency environment,while the root growth and nitrogen absorption was promoted with appropriate phosphorus application, whereas with the overdose application of phosphorus, the root growth and nitrogen utilization decreased.